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Prothena Corporation plc

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FY2020 Annual Report · Prothena Corporation plc
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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

______________________________________ 
FORM 10-K
 ______________________________________

(Mark One)

☒

☐

ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the year ended December 31, 2020

TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF
1934

For the transition period from        to        

Commission file number: 001-35676
______________________________________ 
PROTHENA CORPORATION PUBLIC LIMITED COMPANY
(Exact name of registrant as specified in its charter)
______________________________________ 

Ireland
(State or other jurisdiction of 
incorporation or organization)

98-1111119
(I.R.S. Employer 
Identification No.)

77 Sir John Rogerson’s Quay, Block C        
Grand Canal Docklands
Dublin 2, D02 T804, Ireland
(Address of principal executive offices, including Zip Code)

Registrant’s telephone number, including area code: 011-353-1-236-2500

Securities registered pursuant to Section 12(b) of the Act:

Title of Each Class
Ordinary Shares, par value $0.01 per share

Trading Symbol
PRTA

Name of Each Exchange on Which Registered
The Nasdaq Global Select Market

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.

Securities registered pursuant to Section 12(g) of the Act: None
 ______________________________________

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act.

Yes ☐ No ☒

Yes  ☐  No  ☒

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the
preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the
past 90 days.

Yes  ☒ No  ☐

Indicate  by  check  mark  whether  the  registrant  has  submitted  electronically  every  Interactive  Data  File  required  to  be  submitted  pursuant  to  Rule  405  of

Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit such files).

Yes  ☒ No  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company, or an
emerging  growth  company.  See  definitions  of  “large  accelerated  filer,”  “accelerated  filer,”  “smaller  reporting  company”  and  “emerging  growth  company”  in
Rule 12b-2 of the Exchange Act.

Large accelerated filer
Non-accelerated filer

☐
☒

Accelerated filer
Smaller reporting company
Emerging growth company

☐
☒
☐

 
 
 
 
If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with

any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal
control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C 7262(b)) by the registered public accounting firm that prepared
or issued its audit report.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ☐    No  ☒

☐

☐

As of June 30, 2020, the last business day of the registrant’s most recently completed second fiscal quarter, the aggregate market value of the voting shares
held by non-affiliates of the registrant was approximately $318,748,731, based on the last reported sale of the registrant’s ordinary shares on the Nasdaq Global
Market on such date.

39,987,220 of the Registrant’s ordinary shares, par value $0.01 per share, were outstanding as of February 18, 2021.

Portions of the registrant’s Proxy Statement to be delivered to shareholders in connection with the registrant’s Annual General Meeting of Shareholders to be
held on May 18, 2021, are incorporated by reference into Part III of this Form 10-K. The registrant intends to file its Proxy Statement within 120 days after its
fiscal year ended December 31, 2020.

DOCUMENTS INCORPORATED BY REFERENCE

PROTHENA CORPORATION PLC
Annual Report on Form 10-K
For the Year Ended December 31, 2020

TABLE OF CONTENTS

PART I.

Item 1. Business
Item 1A. Risk Factors
Item 1B. Unresolved Staff Comments
Item 2. Properties
Item 3. Legal Proceedings
Item 4. Mine Safety Disclosures

PART II.

Item 5. Market for Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities
Item 6. Selected Financial Data
Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations
Item 7A. Quantitative and Qualitative Disclosures About Market Risk
Item 8. Financial Statements and Supplementary Data
Item 9. Changes in and Disagreements with Accountants on Accounting and Financial Disclosure
Item 9A. Controls and Procedures
Item 9B. Other Information

PART III.

Item 10. Directors, Executive Officers and Corporate Governance
Item 11. Executive Compensation
Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters
Item 13. Certain Relationships and Related Transactions, and Director Independence
Item 14. Principal Accounting Fees and Services

PART IV.

Item 15. Exhibits, Financial Statement Schedules

EXHIBIT INDEX

SIGNATURES

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Unless  the  context  requires  otherwise,  references  in  this  Form  10-K  to  “Prothena,”  the  “Company,”  “we,”  “our,”  or  “us”  refer  to  Prothena

Corporation plc and its subsidiaries.

Note Regarding Forward-Looking Statements

In addition to historical information, this Form 10-K contains forward-looking statements within the meaning of Section 21E of the Securities Exchange
Act of 1934, as amended. Forward-looking statements may include words such as “aim,” “anticipate,” “assume,” “believe,” “contemplate,” “continue,” “could,”
“due,”  “estimate,”  “expect,”  “goal,”  “intend,”  “may,”  “objective”  “plan,”  “predict,”  “potential,”  “positioned,”  “seek,”  “should,”  “target,”  “will,”  “would,”  and
other similar expressions that are predictions of or indicate future events and future trends, or the negative of these terms or other comparable terminology. In
addition, any statements that refer to expectations, projections, or other characterizations of future events or circumstances are forward-looking statements.

These forward-looking statements, which reflect our beliefs, objectives, and expectations as of the date hereof, are estimates based on our best judgment.
These statements relate to, among other things, our goal of building a protein dysregulation platform; the treatment potential and proposed mechanisms of action
of drug candidates; plans for future clinical studies of our drug candidates; our collaborations with Roche and Bristol-Myers Squibb and amounts we may receive
under such collaborations; the sufficiency of our cash position to fund advancement of a broad pipeline; and our anticipated need for additional capital.

Forward-looking  statements  are  subject  to risks and uncertainties,  and actual  events  or results  may differ  materially.  Factors  that  could cause  our actual
results to differ materially include, but are not limited to, the risks and uncertainties set forth in the “Summary of Risks Affecting Our Business” below, Item 1A
“Risk Factors” of this Form 10-K, and in our other filings with the U.S. Securities and Exchange Commission.

Except as required by law or by the rules and regulations of the U.S. Securities and Exchange Commission, we undertake no obligation to revise or update

any forward-looking statements to reflect any event or circumstance that arises after the date of this Form 10-K.

Summary of Risks Affecting Our Business

Our  business  subject  to  numerous  risks  and  uncertainties.  The  following  summary  highlights  some  of  the  risks  you  should  consider  with  respect  to  our
business and prospects. These risks are described more fully in Item 1A “Risk Factors” of this Form 10-K which includes a more complete discussion of the risks
summarized below as well as a discussion of other risks related to our business, our prospects, and your investment.

• We anticipate that we will incur losses for the foreseeable future and we may never sustain profitability.

• We  will  require  additional  capital  to  fund  our  operations,  and  if  we  are  unable  to  obtain  such  capital,  we  will  be  unable  to  successfully  develop  and

commercialize drug candidates.

•

•

The COVID-19 pandemic has adversely affected our business and could have a material adverse effect on our liquidity, results of operations, financial
condition, or business, including our nonclinical and clinical development programs.

Our success is largely dependent on the success of our research and development programs; our drug candidates are in various stages of development and
we may not be able to successfully discover, develop, obtain regulatory approval for, or commercialize any drug candidates.

• We have entered into collaborations with Roche and Bristol-Myers Squibb and may enter into additional collaborations in the future, and we might not

realize the anticipated benefits of such collaborations.

•

•

•

•

If clinical trials of our drug candidates are prolonged, delayed, suspended, or terminated, we may be unable to commercialize our drug candidates on a
timely basis, which would require us to incur additional costs and delay our receipt of any revenue from potential product sales.

Even if any of our drug candidates receives regulatory approval, if such approved product does not achieve broad market acceptance, the revenues that we
generate from sales of the product will be limited.

If we are unable to adequately protect or enforce the intellectual property relating to our drug candidates our ability to successfully commercialize our
drug candidates will be harmed.

Our future success depends on our ability to retain key personnel and to attract, retain, and motivate qualified personnel.

ITEM 1. BUSINESS

Overview

PART I

Prothena is a late-stage clinical company with expertise in protein dysregulation and a pipeline of investigational therapeutics with the potential to change

the course of devastating rare peripheral amyloid and neurodegenerative diseases.

Fueled by our deep scientific expertise built over decades of research, we are advancing a pipeline of therapeutic candidates for a number of indications and
novel  targets  for  which  our  ability  to  integrate  scientific  insights  around  neurological  dysfunction  and  the  biology  of  misfolded  proteins  can  be  leveraged.  Our
wholly-owned  programs  include  birtamimab  for  the  potential  treatment  of  AL  amyloidosis,  PRX004  for  the  potential  treatment  of  ATTR  amyloidosis,  and  a
portfolio  of  programs  for  the  potential  treatment  of  Alzheimer’s  disease  including  PRX012  that  targets  Aβ  (Amyloid  beta).  Our  partnered  programs  include
prasinezumab,  in  collaboration  with  Roche  for  the  potential  treatment  of  Parkinson’s  disease  and  other  related  synucleinopathies,  and  programs  that  target  tau
(PRX005), TDP-43 and an undisclosed target in collaboration with Bristol-Myers Squibb for the potential treatment of Alzheimer’s disease, amyotrophic lateral
sclerosis (ALS), or other neurodegenerative diseases.

We were formed on September 26, 2012, under the laws of Ireland and re-registered as an Irish public limited company on October 25, 2012. Our ordinary

shares began trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012, and currently trade on The Nasdaq Global Select Market.

Our Strategy

Our  goal  is  to  be  a  leading  biotechnology  company  focused  on  the  discovery  and  development  of  novel  therapies  to  treat  diseases  caused  by  protein

dysregulation.

Under  certain  pathological  conditions,  the  process  by  which  proteins  fold  into  specific  conformations  to  carry  out  their  intended  biological  activities
becomes  dysregulated.  When  this  happens,  proteins  misfold  and  propagate  many  diseases  that  are  not  adequately  addressed  by  current  therapies.  Proteins  that
misfold and aggregate to form amyloid are associated with a multitude of common and rare human diseases that can gravely damage vital organs. Amyloid can
affect any organ in the body. Our pipeline reflects our deep understanding of the contribution of these toxic proteins to the cause and progression of disease. For
example, the misfolding and aggregation of the amyloid beta (Aβ) protein leads to a build-up of amyloid in the brain, which most scientists believe is the primary
cause  of  Alzheimer’s  disease.  Parkinson’s  disease  is  characterized  by  neuronal  dysfunction  and  loss  caused  by  the  cell-to-cell  spreading  of  toxic  forms  of
aggregated alpha-synuclein protein. Transthyretin amyloidosis (ATTR amyloidosis), and AL amyloidosis are rare, progressive and fatal diseases, characterized by
deposition of aggregated misfolded transthyretin and light chain proteins, respectively, in vital organs such as the heart.

We leverage our proven protein dysregulation platform to develop novel therapeutic solutions that directly target pathogenic proteins in order to change the
course of devastating rare peripheral amyloid and neurodegenerative diseases. We are advancing a broad pipeline of therapies with novel mechanisms of action
that are uniquely suited to address unmet medical needs in targeted patient populations.

Our  plan  is  to  become  a  fully  integrated  research,  development  and  commercial  biotechnology  company.  Three  late-stage  programs  in  our  pipeline  are
initiating studies in 2021 including AFFIRM-AL, a registration-enabling Phase 3 study of birtamimab in Mayo Stage IV patients with AL amyloidosis, a Phase 2b
study of prasinezumab in patients with early Parkinson’s disease being run by Roche, and a Phase 2/3 study of PRX004 in ATTR-cardiomyopathy. In addition to
these  late-stage  programs,  we  expect  to  potentially  file  6  IND’s  over  the  next  3  years.  We  expect  to  support  this  growth  through  significant  potential  partner
payments that add to current cash position.

Key elements of our strategy to achieve our goal are to:

•

Concentrate our discovery and development efforts in areas where we have decades of scientific expertise and experience.

We  leverage  our  core  scientific  expertise  and  proven  protein  dysregulation  platform  to  develop  novel  therapeutics  for  the  potential  treatment  of  rare

peripheral amyloid and neurodegenerative diseases.

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Our pipeline is advanced by a team with scientific expertise and a track record of discovering and developing innovative, and often first-in-class programs.
Our legacy includes significant discoveries that have advanced the understanding of the biology of Alzheimer’s disease and identified and elucidated the role Aβ
plays  in  Alzheimer’s  disease  pathology.  These  findings  led  to  the  development  of  a  drug  discovery  and  development  organization  that  generated  first-in-class
clinical candidates in Alzheimer’s disease, Parkinson’s disease AL and ATTR amyloidosis.

Key elements of our scientific platform include:

• A focus on genetically-associated and biologically-validated targets implicated in disease
• An empirical and unbiased method to define key regions of a protein to target in order to optimally intervene in disease progression
• A rigorous and comprehensive approach to characterize and test molecules in preclinical models

Once  we  formulate  a  novel  hypothesis  or  approach,  we  determine  how  to  optimally  intervene  against  a  known  target.  We  employ  a  combination  of  our
understanding of normal protein structure, computational antibody design technologies and an empirical and unbiased screening process to determine the optimal
epitope to target on a pathogenic protein. Through our detailed screening process, we define critical regions of the protein involved in the pathological progression
of a particular disease to elucidate key epitopes that are hidden when a protein is normally folded but exposed when a protein misfolds and remains exposed in all
of its pathogenic aggregation states, inclusive of deposited amyloid. We engineer our molecules to interact with that epitope in a way that is most likely to intercept
or halt the underlying disease process. We do this by designing molecules with a bias toward the pathogenic forms of the protein. We then develop a multitude of
antibodies against the target, characterize specific and selective antibodies in vitro and then use them to test the initial hypothesis in vivo using animal models of
disease.  We  often  rely  on  the  use  of  preclinical  models  that  have  been  extensively  developed  to  establish  early  clinical  proof  of  concept  for  our  programs,  we
leverage our insight of disease pathology and, when possible, employ biomarker endpoints as a way to detect signals of biological activity. We may elect to start
clinical testing in indications that have well-established endpoints in order to demonstrate proof of concept as a basis for further investment in clinical trials, either
by us or potential partners.

Our  platform  produces  molecules  that  specifically  and  selectively  target  the  toxic,  or  pathogenic,  protein  species  in  order  to  alleviate  their  detrimental

effects, while - to the furthest extent possible - leaving the native, or healthy form of the protein unaffected.

We have employed our platform to optimally target key epitopes on misfolded proteins including Aβ, tau, alpha-synuclein, light chain, and transthyretin to

relevantly influence biology and achieve clinical benefit across a number of indications.

As  a  result,  decades  of  our  own  investigation  augmented  by  the  work  of  others  have  elucidated  that  targeting  the  appropriate  epitope,  with  the  optimal
binding  strength  (affinity)  in  the  context  of  the  right  clinical  design  with  appropriate  endpoints  in  the  right  patient  population  can  result  in  meaningful  clinical
benefit. Our track record of combining these elements to discover and develop novel therapeutic candidates has resulted in a robust pipeline advancing multiple
late-stage programs.

Today,  what  distinguishes  Prothena  is  that  our  pipeline  has  matured  beyond  demonstrating  target  engagement  via  downstream  biomarkers.  Instead,  our
internally discovered pipeline has generated multiple proof points that our molecules have successfully influenced biology in a manner that translates into clinical
benefit. We’ve most recently demonstrated this in AL amyloidosis, ATTR amyloidosis, and Parkinson’s disease where preclinical findings in our programs have
translated to positive clinical data.

•

Focus on diseases that lack effective therapies.

We  focus  on  the  development  of  therapies  for  serious  and/or  life-threatening  diseases  that  currently  lack  effective  therapies  or  in  areas  where  current
therapies  have  known  limitations.  Our  efforts  in  AL  amyloidosis,  ATTR  amyloidosis,  Parkinson’s  disease,  Alzheimer’s  disease,  and  other  neurological  or
peripheral amyloid diseases are examples of this.

In  Parkinson’s  disease,  currently  approved  therapies  focus  on  the  alleviation  of  early  motor  symptoms  without  addressing  the  underlying  cause  of  the
disease. We are focusing our efforts to develop a therapeutic with the potential to slow the progression of Parkinson’s disease by targeting α-synuclein protein.
Synucleins are a family of proteins, of which there are three known members: α-synuclein, β-synuclein, and γ-synuclein. The α- and β-synuclein proteins are found
primarily in brain

2

tissue. There is genetic evidence that α-synuclein plays a fundamental role in Parkinson’s disease, and an increasing body of evidence demonstrates that pathogenic
forms  of α-synuclein  can  be  propagated  and transmitted  from  cell  to  cell.  Our scientists  have  developed  prasinezumab,  an  investigational  monoclonal  antibody
targeting the pathogenic aggregated form of α-synuclein, that is designed to slow or reduce the neurodegeneration associated with α-synuclein misfolding and/or its
transmission. We are developing prasinezumab, in collaboration with Roche, for the potential treatment of Parkinson’s disease and other related synucleinopathies.

AL amyloidosis and ATTR amyloidosis are diseases caused by misfolded, pathogenic forms of light chain (AL) or transthyretin (ATTR) protein that deposit
as amyloid in vital organs such as the heart. Current therapeutic approaches seek to reduce the production of new pathogenic AL or ATTR protein in order to slow
the formation of new amyloid deposits. However, simply reducing new pathogenic protein production may not be adequate for patients who are at high risk of
early  mortality  due  to  the  substantial  existing  amyloid  deposition  in  their  vital  organs.  The  therapeutic  approaches  we  are  developing  with  birtamimab  for  AL
amyloidosis and PRX004 for ATTR amyloidosis, are investigational monoclonal antibodies designed to clear the pathogenic amyloid deposits. Birtamimab and
PRX004 are designed to target and clear amyloid deposited in organs in order to improve organ function. Current therapies do not adequately address the needs of
patients with AL and ATTR amyloidosis who have advanced stages of cardiac disease due to amyloid deposition. Improving survival for these patients is an area
of urgent need which directly aligns with birtamimab and PRX004’s differentiated depleter mechanism that targets the amyloid that causes organ dysfunction and
failure and puts patients at risk for early mortality.

Moving forward, we intend to advance new discovery-stage therapeutics for other diseases with unmet medical needs. Our discovery efforts targeting tau,

Aβ and TDP-43 for the potential treatment of Alzheimer’s disease (AD) and amyotropic lateral sclerosis (ALS) are examples of this.

•

Pursue strategic business development opportunities and collaborations and leverage external resources.

We  capitalize  on  a  foundation  of  internal  discovery  efforts  augmented  by  collaborations  with  academic  and  industry  partners  and  business  development

activities to build upon our internally generated pipeline.

Our  robust  discovery  engine  generates  new  targets  and  compounds  that  have  the  potential  to  treat  unmet  medical  needs.  For  investigational  therapeutic
programs  targeting  broad  patient  populations  that  may  require  large  clinical  trials  and  development  investment,  we  may  seek  to  collaborate  or  license  these
programs to pharmaceutical or biotechnology companies for development and/or commercialization. Our collaboration with Roche to develop prasinezumab for
the  potential  treatment  of  Parkinson’s  disease  and  other  related  synucleinopathies  and  our  global  neuroscience  R&D  collaboration  with  BMS  focused  on  three
proteins implicated in the pathogenesis of several neurodegenerative diseases are examples of this. Within these types of collaborations, we will evaluate several
strategic  options  for  designing  and  operationalizing  early  to  late-stage  development  programs.  This  includes  evaluating  the  option  of  designing  and
operationalizing clinical programs ourselves or with a partner.

We also consider opportunities to acquire or license rights or invest in differentiated product candidates or technologies to complement our existing R&D

pipeline.

We rely on, and will expand as appropriate, strong internal talent with expertise in our core areas of focus. We also rely on external resources, as needed, to
execute  efficiently  on  our  clinical  development  and  other  business  objectives.  We  engage  and  collaborate  with  consultants  and  advisors  with  certain  scientific,
clinical or other functional and/or disease area expertise to help us execute specific activities related to our programs. This may include activities such as testing
and characterizing our potential therapeutic candidates and gaining feedback and guidance on our programs through advisory boards.

•

Pursue commercialization strategies to maximize the value of our product candidates or future potential products.

As we move our drug candidates through development toward regulatory approval, we will evaluate several strategic options for commercialization. These
options include building our own internal sales force; forging partnerships with other pharmaceutical or biotechnology companies, to jointly sell and market the
product;  pursuing  regional  licensing  agreements  in  markets  where  we  do  not  have  expertise  or  infrastructure;  and  out-licensing  our  product,  whereby  another
pharmaceutical or biotechnology company sells and markets our product and pays us a royalty on sales. We evaluate options for each product based on a number
of factors including commercial synergies and expertise, capital necessary to execute on each option, size of the market to be addressed and the expertise and terms
of potential offers from other pharmaceutical and biotechnology companies. Our collaboration with Roche for the potential commercialization of prasinezumab is
an example of this strategy.

3

Our Research and Development Pipeline

Our research and development pipeline includes three therapeutic antibody programs in clinical development: Birtamimab for the potential treatment of AL
amyloidosis; prasinezumab, in collaboration with Roche, for the potential treatment of Parkinson’s disease and other related synucleinopathies; and PRX004, for
the potential treatment of ATTR amyloidosis.

In  addition  to  our  clinical  development  pipeline,  we  have  a  number  of  discovery-  and  late-preclinical-stage  programs  targeting  proteins  implicated  in
neurological diseases including tau and Aβ for the potential treatment of Alzheimer’s disease and other neurodegenerative disorders and TDP-43 for the potential
treatment of amyotrophic lateral sclerosis. Tau, TDP-43 and a third undisclosed neurodegenerative target are the focus of our collaboration with BMS.

While we are modality agnostic, we have deep expertise in antibody targeting and have developed a diverse pipeline that includes antibody as well as small
molecule  and  vaccine  approaches.  We  believe  a  diverse  portfolio  positions  us  to  make  an  impact  on  a  broad  spectrum  of  diseases  and  may  also  pursue
opportunities in other modalities such as gene and cell therapies.

The following table summarizes the status of our research and development pipeline:

Birtamimab (NEOD001) for the Potential Treatment of AL Amyloidosis

Birtamimab is an investigational humanized antibody that targets toxic misfolded light chain that causes organ dysfunction and failure in patients with AL
amyloidosis.  AL  amyloidosis  is  a  rare,  progressive,  and  fatal  disease  where  immunoglobulin  light  chain  proteins  produced  by  clonal  plasma  cells  misfold,
aggregate, and deposit as amyloid in vital organs. These toxic aggregates and amyloid deposits cause progressive damage and failure of vital organs, including the
heart.

Birtamimab  binds to both soluble and insoluble amyloid  aggregates  in multiple  organs and promotes the clearance  of amyloid deposits via phagocytosis.
This depleter mechanism of action broadly targets misfolded kappa and lambda light chain to clear deposited amyloid that causes organ dysfunction and failure in
patients with AL amyloidosis. Birtamimab has been granted Fast Track Designation by the FDA for the treatment of Mayo Stage IV patients with AL amyloidosis
to reduce the risk of mortality and has been granted Orphan Drug Designation by both the FDA and European Medicines Agency (EMA).

4

It is estimated that 200,000 to 400,000 patients globally suffer from this rare disease, with approximately 60,000 to 120,000 (or 30%) of those patients being
categorized  as  Mayo  Stage  IV.  Patients  categorized  at  diagnosis  as  Mayo  Stage  IV  have  poor  outcomes  with  current  standard-of-care  that  aims  to  reduce  the
production  of  new  protein  but  does  not  directly  target  and  clear  the  toxic  amyloid  that  deposits  in  organs.  There  are  currently  no  approved  treatments  for  AL
amyloidosis and there is an urgent unmet medical need for therapies that improve survival in patients at risk for early mortality due to amyloid deposition.

Clinical Development Program for Birtamimab

Early Development

Birtamimab was designed broadly react with a “cryptic” epitope that is exposed on misfolded kappa and lambda light chains that misfold and form amyloid.
The  epitope  is  well  defined,  highly  conserved  in  light  chains  and  exposed  from  early  stages  of  aggregation  throughout  amyloid.  Preclinical  research  has
demonstrated that birtamimab binds to both soluble and insoluble aggregated kappa and lambda immunoglobulin light chain by recognizing this epitope that is
exposed at the earliest stages of abnormal light chain misfolding and through aggregation of deposited amyloid. Our extensive preclinical findings and publications
describe  two  proposed  mechanisms  of  action  for  birtamimab:  binding  and  neutralization  of  toxic  light  chain  aggregates,  and  clearance  of  amyloid  deposits  by
phagocytosis.

In multiple clinical studies, birtamimab has been shown to be generally safe and well tolerated and has been evaluated in 302 patients receiving monthly

intravenous infusions (including 294 patients who received the recommended 24 mg/kg dose), for an average of approximately 15 months.

Phase 3 VITAL Study Results

Birtamimab  was previously  evaluated  in  the  Phase  3 VITAL  Study,  a  global  multi-center,  randomized,  double-blind,  placebo-controlled  clinical  study  of
newly diagnosed, treatment naïve patients with AL amyloidosis and cardiac involvement (N=260). Results from a post hoc analysis revealed a significant survival
benefit favoring birtamimab in a subset of patients categorized as Mayo Stage IV at baseline (n=77), with 74% of birtamimab-treated patients alive at 9 months
versus 49% of patients in the control group (hazard ratio of 0.413 (95% CI: 0.191, 0.895; p=0.0251, over 9 months).

Significant changes observed on secondary endpoints provided further evidence of clinical benefit in birtamimab-treated Mayo Stage IV patients in VITAL.
For Short Form-36 version 2 Physical Component Score (SF-36v2 PCS), an assessment of quality of life, the difference in mean change from baseline at 9 months
between  the  birtamimab  and  control  arms  of  the  study  was  +5  points  favoring  the  birtamimab  arm  (p=0.0258).  For  6  Minute  Walk  Test  (6MWT)  distance,  an
assessment of functional capacity, the difference in mean change from baseline at 9 months between the birtamimab and control arms was +27 meters favoring the
birtamimab arm (p=0.0462).

Confirmatory Phase 3 AFFIRM-AL Study Design under SPA Agreement with FDA

Based  on  further  analyses  regarding  data  from  the  VITAL  study  and  multiple  in-depth  discussions  with  the  U.S.  Food  and  Drug  Administration  (FDA),
Prothena  announced  plans  on  February  1,  2021  to  advance  birtamimab  into  the  confirmatory  Phase  3  AFFIRM-AL  study  in  Mayo  Stage  IV  patients  with  AL
amyloidosis. AFFIRM-AL is a registration-enabling Phase 3 study that will be conducted with a primary endpoint of all-cause mortality at p<0.10 under a Special
Protocol Assessment (SPA) agreement with the U.S. Food and Drug Administration (FDA).

AFFIRM-AL  will  be  a  global,  multi-center,  double-blind,  placebo-controlled,  2:1  randomized,  time-to-event  study  expected  to  enroll  approximately  150
newly diagnosed, treatment naïve patients with AL amyloidosis categorized as Mayo Stage IV. It has been designed to evaluate the primary endpoint of all-cause
mortality with a significance level of p<0.10. Secondary endpoints will assess change from baseline to month 9 in quality of life as measured by SF-36v2 PCS and
functional capacity as measured by 6MWT distance.

An  interim  analysis  will  be  conducted  when  approximately  50%  of  the  events  have  occurred,  allowing  the  independent  data  monitoring  committee  to
recommend  either  continuing  the  study  or  stopping  early  for  overwhelming  efficacy.  Patients  will  receive  24  mg/kg  of  birtamimab  or  placebo  by  intravenous
infusion every 28 days, with all patients receiving concurrent standard of care therapy consisting of a first line bortezomib-containing regimen.

5

Prasinezumab for the Potential Treatment of Parkinson’s Disease and Other Synucleinopathies

Prasinezumab is an investigational humanized monoclonal antibody that targets alpha-synuclein, a protein found in neurons that can aggregate and spread
from  cell  to  cell,  resulting  in  the  neuronal  dysfunction  and  loss  that  causes  Parkinson’s  disease  and  other  synucleinopathies.  Prasinezumab  is  the  focus  of  our
worldwide collaboration with Roche.

The  protein  α-synuclein  is  found  extensively  in  neurons  and  is  a  major  component  of  pathological  inclusions  that  characterize  several  neurodegenerative
disorders,  including  Parkinson’s  disease,  dementia  with  Lewy  bodies,  and  multiple  system  atrophy,  which  collectively  are  termed  synucleinopathies.  While  the
normal function of α-synuclein is not well understood, the protein normally occurs in a soluble form. In synucleinopathies, the α-synuclein protein can misfold and
aggregate to form soluble aggregates and insoluble fibrils that contribute to the pathology of the disease.

There is genetic evidence for a causal role of α-synuclein in Parkinson’s disease. In rare cases of familial forms of Parkinson’s disease, there are mutations in
the synuclein protein sequence, or duplication and triplications of the relevant gene leading to overproduction of α-synuclein, which may cause α-synuclein protein
to aggregate and form amyloid-like fibrils that contribute to the disease. There is also increasing evidence that this disease-causing α-synuclein can be propagated
and  transmitted  from  neuron  to  neuron,  resulting  in  a  spreading  of  neuronal  death.  Recent  studies  in  cellular  and  animal  models  suggest  that  the  spread  of  α-
synuclein-associated neurodegeneration can be disrupted by targeting aberrant forms of α-synuclein.

Parkinson’s disease is a progressive degenerative disorder of the central nervous system (CNS) that affects approximately one in 100 people over the age of
60, with incidence increasing based on an aging population. With an estimated seven to 10 million people living with Parkinson’s disease worldwide today, it is the
most  common  neurodegenerative  movement  disorder  and  fastest  growing  neurological  disorder.  The  disease  is  characterized  by  the  neuronal  accumulation  of
aggregated α-synuclein in the CNS and peripheral nervous system that results in a wide spectrum of worsening progressive motor and non-motor symptoms. While
diagnosis  currently  relies  on  motor  symptoms  classically  associated  with  Parkinson's  disease,  non-motor  symptoms  may  present  many  years  earlier.  Current
treatments  for  Parkinson’s  disease  are  symptomatic  and  only  address  a  subset  of  symptoms  such  as  motor  impairment,  dementia  or  psychosis.  Symptomatic
therapies  do  not  target  the  underlying  cause  of  the  disease  and  as  the  disease  progresses  and  dopaminergic  neurons  continue  to  be  lost,  these  drugs  lose
effectiveness, often leading to debilitating side effects as the disease progresses. There are currently no treatments available that target the underlying cause of the
disease.  Prasinezumab  is  designed  to  block  the  cell-to-cell  transmission  of  the  aggregated,  pathogenic  forms  of  alpha-synuclein  in  Parkinson's  disease,  thereby
slowing clinical decline. The goal of our approach is to slow the progressive neurodegenerative consequences of disease, a current unmet need.

Clinical Development Program for Prasinezumab

Prior to initiating clinical trials, we tested the efficacy of prasinezumab in various cellular and animal models of α-synuclein-related disease. In transgenic
mouse  models  of  Parkinson’s  disease,  passive  immunization  with  9E4,  the  murine  version  of  prasinezumab,  reduced  the  appearance  of  α-synuclein  pathology,
protected synapses and improved performance by the mice in behavioral testing.

Phase 1 Studies

During 2014, together with Roche, we advanced prasinezumab into clinical development with the initiation of two Phase 1 studies. Results of the first study,
a Phase 1 double-blind, placebo-controlled, single ascending dose trial demonstrated that prasinezumab was safe and well-tolerated in healthy volunteers, meeting
the  primary  objective  of  the  study.  Results  of  the  second  study,  a  Phase  1b  double-blind,  placebo-controlled,  multiple  ascending  dose  study  demonstrated  an
acceptable safety and tolerability profile at all dose levels tested in patients with Parkinson’s disease, meeting the primary objective of the study. CNS penetration
was demonstrated by a dose-dependent increase in prasinezumab levels in cerebrospinal fluid (CSF), and a mean concentration of prasinezumab in CSF of 0.3%
relative to serum across all dose levels, which exceeded our expectations based on our preclinical experience. Data from the study also demonstrated rapid, dose-
and time-dependent  mean  reduction  in levels  of free  serum  α-synuclein  of up to 97% after  a single  dose, which were statistically  significant  (p < 0.0001), and
maintained following two additional monthly doses.

In  June  2018,  we  published  results  from  the  Phase  1b  multiple  ascending  dose  study  of  prasinezumab  in  patients  with  Parkinson’s  disease  in  JAMA
Neurology. The  paper  is  entitled  “Safety  and  Tolerability  of  Multiple  Ascending  Doses  of  PRX002/RG7935,  an  Anti-α-Synuclein  Monoclonal  Antibody,  in
Patients With Parkinson Disease: A Randomized Clinical Trial.”

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Phase 2 PASADENA Study

The  results  from  the  Phase  1  study  further  supported  advancing  prasinezumab  into  the  Phase  2  PASADENA  Study.  PASADENA  is  a  two-part  Phase  2
clinical study in early Parkinson's disease patients that is being conducted by Roche. Part 1 is a randomized, double-blind, placebo-controlled, three-arm study and
enrolled 316 patients to evaluate the efficacy and safety of prasinezumab in patients over 52 weeks. In part 1, patients were randomized on a 1:1:1 basis to receive
one of two active doses (1500 mg or depending on body weight either 3500 mg or 4500 mg) of prasinezumab or placebo via intravenous infusion once every 4
weeks. Patients enrolled in the study must not have been on dopaminergic therapy and were not be expected to require dopaminergic therapy for at least 52 weeks.
Part 2 of the study is a 52-week blinded extension phase in which patients from the placebo arm of the study will be re-randomized onto one of two active doses on
a 1:1 basis, so that all participants will be on active treatment. Patients who were originally randomized to an active dose will continue at that dose level for the
additional  52 weeks. In part 2, patients were allowed to use concomitant dopaminergic  therapy. Any patient  who medically required  initiation of dopaminergic
therapy during part 1 had their subsequent data censored for the primary endpoint analysis.

Results from Part  1 of the PASADENA study were  presented  in a Top Abstract  oral  presentation  at the International  Parkinson and Movement  Disorder
Society’s  MDS  Virtual  Conference  2020.  While  the  study  did  not  meet  the  primary  objective,  signals  of  efficacy  on  multiple  pre-specified  secondary  and
exploratory  clinical  endpoints,  including  measures  of  motor  function  and  biomarkers,  were  demonstrated  in  both  of  the  prasinezumab  arms  when  compared  to
placebo.  In  the  PASADENA  study,  prasinezumab  significantly  reduced  decline  in  motor  function  by  35%  (pooled  dose  levels)  vs.  placebo  after  one  year  of
treatment  on  the  centrally  rated  assessment  of  Movement  Disorder  Society-Unified  Parkinson's  Disease  Rating  Scale  (MDS-UPDRS)  Part  III,  a  clinical
examination  of  motor  function.  Motor  symptoms  associated  with  Parkinson’s  disease  include  slowness  of  movement  (bradykinesia),  tremor,  rigidity,  and  gait.
Prasinezumab-treated patients also demonstrated a significant delay in time to clinically meaningful worsening of motor progression on the site rated assessment of
time to at least a 5-point progression on MDS-UPDRS Part III vs. placebo over one year, with a hazard ratio of 0.82 (pooled dose levels).

The primary endpoint of the study was the change from baseline in the MDS-UPDRS total score (Parts I, II and III) at 52 weeks in each treatment group vs.
the placebo group (pooled dose levels: –14.0%, –1.30, 80% CI=(–3.18, 0.58), p=0.38; low dose level: –21.5%, –2.02, 80% CI=(–4.21, 0.18); and high dose level: –
6.6%, –0.62, 80% CI=(–2.82, 1.58)). Signals of efficacy were observed on multiple pre-specified secondary and exploratory clinical endpoints including change
from baseline in MDS-UPDRS Part III in prasinezumab-treated patients vs. placebo at 52 weeks by central rating (pooled dose levels: –35.0%, –1.88, 80% CI=(–
3.31, –0.45), p=0.09; low dose level: –45.4%, –2.44, 80% CI=(–4.09, –0.78); and high dose level: –24.7%, –1.33, 80% CI=(–2.99, 0.34)) and by site rating (pooled
dose levels: –25.0%, –1.44, 80% CI=(–2.83, –0.06), p=0.18; low dose level: –33.8%, –1.88, 80% CI=(–3.49, –0.27); and high dose level: –18.2%, –1.02, 80% CI=
(–2.64, 0.61)). MDS-UPDRS Part III is a clinical examination of motor function that assesses motor symptoms associated with Parkinson’s disease. Prasinezumab
also delayed time to clinically meaningful worsening of motor progression in prasinezumab-treated patients vs. placebo over 52 weeks as demonstrated by site
rating of time to at least a 5-point progression in MDS-UPDRS Part III (pooled dose levels: HR=0.82, 80% CI=0.64 to 0.99, p=0.17; low dose level: HR=0.77,
80% CI=0.63 to 0.96; and high dose level: HR=0.87, CI=0.70 to 1.07).

Additional  signals  of  efficacy  on  bradykinesia  and,  separately,  a  digital  motor  score  developed  by  Roche  using  a  novel  smartphone  technology  further

extended the results shown on MDS-UPDRS Part III.

In an analysis of cerebral blood flow, assessed by changes in magnetic resonance-arterial spin labeling (MRI-ASL) in a subset of patients, prasinezumab-
treated patients showed improvement in cerebral blood flow in the putamen, an area of the brain associated with the loss of dopaminergic terminals and presence of
alpha-synuclein pathology in Parkinson’s disease, suggesting an impact on the underlying biology implicated in disease progression.

Prasinezumab was found to be generally safe and well tolerated, with the majority of adverse events reported as mild or moderate and similar across placebo

and both treatment arms.

In  October  2020,  we  announced  that  Roche  and  Prothena  will  advance  prasinezumab  into  a  late-stage  Phase  2b  study  in  patients  with  early  Parkinson’s
disease. The study will be designed to further assess the efficacy of prasinezumab by expanding upon the patient population enrolled in PASADENA to include
patients with early Parkinson’s disease on stable levodopa therapy.

Prasinezumab is the first potentially disease-modifying, anti-alpha-synuclein antibody to demonstrate signals of efficacy on multiple pre-specified secondary

and exploratory clinical endpoints in patients with early Parkinson’s disease and advance into late-stage development.

More information on the Phase 2 PASADENA study, can be found by searching NCT #03100149 on clinicaltrials.gov.

7

License, Development, and Commercialization Agreement with Roche

In December 2013, we entered into the License Agreement with Roche to develop and commercialize certain antibodies that target α-synuclein, including
prasinezumab,  which  are  referred  to  in  this  report  collectively  as  “Licensed  Products.”  The  License  Agreement  became  effective  on  January  17,  2014,  which
triggered an upfront payment to us of $30.0 million from Roche, which we received in February 2014. In July 2017, we announced that the first patient has been
enrolled in PASADENA, a global Phase 2 study of prasinezumab in patients with early Parkinson’s disease. The start of the Phase 2 PASADENA study triggered a
$30 million milestone payment from Roche to Prothena, which was earned in the second quarter of 2017.

Pursuant to the License Agreement, we are collaborating with Roche to research and develop antibody products targeting α-synuclein. Roche is providing
funding for this research, which is focused on optimizing early stage antibodies targeting α-synuclein, potentially including incorporation of Roche’s proprietary
Brain Shuttle™ technology to increase delivery of therapeutic antibodies to the brain. Roche is primarily responsible for developing, obtaining and maintaining
regulatory  approval  for,  and  commercializing  Licensed  Products  under  the  collaboration,  including  prasinezumab.  Roche  is  responsible  for  the  clinical  and
commercial manufacture and supply of Licensed Products within a defined time period following the effective date of the License Agreement.

We  have  so  far  earned  $75  million  of  a  total  $600  million  in  potential  clinical,  regulatory  and  sales  milestones.  In  addition  to  the  $30.0  million  upfront
payment and clinical milestone payment of $15.0 million (both in 2014) and the clinical milestone payment of $30.0 million in 2017, Roche is also obligated to
pay:

•

•

•

up to $350.0 million upon the achievement of additional development, regulatory and various first commercial sales milestones;

up to an additional $175.0 million in ex-U.S. commercial sales milestones; and

tiered, high single-digit to high double-digit royalties in the teens on ex-U.S. annual net sales, subject to certain adjustments.

In the U.S., Prothena and Roche share all development and commercialization costs, as well as profits, all of which will be allocated 70% to Roche and 30%
to us, for prasinezumab in the Parkinson’s disease indication, as well as any other licensed products and/or indications for which we opt in to co-develop and co-
fund.  We  may  opt  out  of  the  co-development  and  cost  and  profit  sharing  on  any  co-developed  licensed  products  and  instead  receive  U.S.  commercial  sales
milestones  totaling  up  to  $155.0  million  and  tiered,  single-digit  to  high  double-digit  royalties  in  the  teens  based  on  U.S.  annual  net  sales,  subject  to  certain
adjustments, with respect to the applicable licensed product. In addition, we have an option under the License Agreement to co-promote prasinezumab in the U.S.
in the Parkinson’s disease indication. If we exercise such option, we may also elect to co-promote additional licensed products in the U.S. approved for Parkinson’s
disease or other indications calling on the same prescriber. Outside the U.S., Roche has responsibility for developing and commercializing the licensed products.

Under the License Agreement with Roche, we granted to Roche an exclusive, worldwide license to develop, make, have made, use, sell, offer to sell, import
and export the Licensed Products. The License Agreement continues on a country-by-country basis until the expiration of all payment obligations thereunder. The
License Agreement may also be terminated (i) by Roche at will after the first anniversary of the effective date of the License Agreement, either in its entirety or on
a Licensed Product-by-Licensed Product basis, upon 90 days’ prior written notice to us prior to first commercial sale and 180 days’ prior written notice to us after
first  commercial  sale,  (ii)  by  either  party,  either  in  its  entirety  or  on  a  Licensed  Product-by-Licensed  Product  or  region-by-region  basis,  upon  written  notice  in
connection  with  a  material  breach  uncured  90  days  after  initial  written  notice,  and  (iii)  by  either  party,  in  its  entirety,  upon  insolvency  of  the  other  party.  The
License Agreement may be terminated by either party on a patent-by-patent and country-by-country basis if the other party challenges a given patent in a given
country. Our rights to co-develop licensed products under the License Agreement will terminate if we commence certain studies for certain types of competitive
products. Our rights to co-promote licensed products under the License Agreement will terminate if we commence a Phase 3 study for such competitive products.

PRX004 for the Potential Treatment of ATTR Amyloidosis

PRX004  is  an  investigational  antibody  designed  to  deplete  amyloid  associated  with  disease  pathology  in  hereditary  and  wild  type  ATTR  amyloidosis,

without affecting the native, normal tetrameric form of the protein.

ATTR amyloidosis is a rare, progressive and fatal disease characterized by deposition abnormal, non-native forms of TTR protein (amyloid) in vital organs.
ATTR amyloidosis can be hereditary (hATTR) when caused by a mutation in the TTR gene, or wild-type (wtATTR) when it occurs sporadically. In both forms of
the disease, patients can experience a spectrum of clinical manifestations due to deposition of amyloid that can affect multiple organs, most commonly the heart
and/or nervous

8

system.  The  TTR  protein  is  produced  primarily  in  the  liver  and  in  its  normal  tetrameric  form  serves  as  a  carrier  for  thyroxin  and  retinol  binding  protein  (a
transporter for vitamin A) and is also implicated in neuroprotective functions.

Wild-type ATTR (wtATTR) occurs sporadically and primarily involves cardiomyopathy. It is estimated that between 400,000 to 1.4 million patients suffer
from ATTR-cardiomyopathy (ATTR-CM). Within this population, between 130,000 to 490,000 patients are estimated to be moderate-to-advanced and categorized
as New York Heart Association Class III and IV.

In  hereditary  ATTR  amyloidosis,  mutations  in  the  TTR  gene  causes  non-native  TTR  to  accumulate  and  damage  body  organs  and  tissue,  such  as  the
peripheral  nerves  and  heart.  This  results  in  predominant  symptoms  of  neuropathy  (hATTR-PN)  and/or  cardiomyopathy  (hATTR-CM),  as  well  as  other  disease
manifestations. It is estimated that there are approximately 50,000 patients with hATTR worldwide, with approximately 10,000 characterized as hATTR-PN and
40,000 characterized as hATTR-CM.

It  is  generally  accepted  that,  at  the  time  of  diagnosis,  affected  organs  in  ATTR  patients  (both  hATTR  and  wtATTR  amyloidosis)  contain  extracellular

amyloid deposits. These deposits, together with prefibrillar species, are believed to cause organ dysfunction and failure.

Current therapeutic approaches for ATTR amyloidosis have demonstrated benefit to patients by impacting the biological pathway leading to the formation of
amyloid deposits. These approaches are designed to either reduce production of native forms of the TTR protein or bind to TTR and prevent tetramer dissociation
but do not target the non-native, pathogenic form of TTR directly.

PRX004’s  proposed  mechanism  of  action  is  to  deplete  both  circulating  non-native  TTR  to  prevent  further  deposition  and  deposited  amyloid  to  improve
organ  function.  PRX004  has  been  shown  in  preclinical  studies  to  inhibit  amyloid  fibril  formation,  neutralize  soluble  aggregate  forms  of  non-native  TTR,  and
promote clearance of insoluble amyloid fibrils through antibody-mediated phagocytosis. This differentiated depleter mechanism of action could be developed as a
monotherapy approach to ATTR amyloidosis and might also complement existing therapeutic approaches which either stabilize or reduce production of the native
TTR tetramer.

Clinical Development Program for PRX004

We generated monoclonal antibodies that selectively bind to non-native TTR and do not recognize the native, tetrameric form of TTR protein. Preclinical
data published in March 2016 in the journal Amyloid suggested that our antibodies have unique biological activity that may lead to the prevention of deposition,
and enhancement of clearance, of ATTR in patients with ATTR amyloidosis.

In  March  2018,  we  presented  new  research  related  to  PRX004  for  the  potential  treatment  of  ATTR  amyloidosis  at  the  16  International  Symposium  on
Amyloidosis (ISA) including data on our proprietary assay that specifically detects circulating non-native TTR in plasma across multiple hereditary TTR mutations
using a TTR antibody that binds to an epitope uniquely exposed on misfolded TTR but hidden in the native tetramer. Additional preclinical research was presented
at ISA showing that conformation-specific antibodies target non-native TTR and induce immune mediated clearance through phagocytosis.

th

In  May  2018,  we  announced  the  initiation  of  first-in-human  dosing  in  a  Phase  1  open-label,  multicenter  clinical  study  (NCT03336580)  of  PRX004  in
patients  with  hATTR  amyloidosis  with  peripheral  neuropathy  with  or  without  cardiomyopathy.  The  Phase  1  study  was  designed  to  determine  the  safety,
tolerability, pharmacokinetic, pharmacodynamic and maximum tolerated dose of PRX004 in patients with hATTR amyloidosis to inform future studies.

In the escalation phase of the Phase 1 study, patients received PRX004 intravenously once every 28 days for up to 3 infusions. Six dose levels (0.1, 0.3, 1.0,
3.0, 10.0, and 30.0 mg/kg) were evaluated. Eligible patients who completed the escalation or expansion phase could enroll in the long-term extension (LTE) phase
of the study and receive up to 15 additional infusions of PRX004 every 28 days.

In  December  2020,  we  reported  results  from  the  Phase  1  study  of  PRX004.  In  the  first  report  of  clinical  results  with  this  depleter  mechanism  of  action,
PRX004  showed  favorable  results  as  demonstrated  by  slowing  of  neuropathy  progression  for  all  7  evaluable  patients  at  9  months,  including  improvement  in
neuropathy in 3 of the 7 patients, and improved cardiac systolic function for all 7 patients. In this Phase 1 study, PRX004 was found to be generally safe and well
tolerated across all dose levels.

The long-term  extension portion of the Phase 1 study was disrupted by the COVID-19 pandemic.  As a result, 7 patients  received  all infusions through 9

months and were considered evaluable for efficacy. For all of the evaluable patients, slowing of

9

neuropathy progression was demonstrated by a mean change from baseline in Neuropathy Impairment Score (NIS) of +1.29 points at 9 months. This compares
favorably to a calculated mean change in NIS of +9.2 points at 9 months in untreated and placebo-treated patients with hereditary ATTR peripheral neuropathy
(hATTR-PN)  based  on  analysis  of  published  historical  data.  In  addition,  the  change  in  NIS  for  each  of  these  evaluable  patients  was  more  favorable  than  the
published historical data. In this highly progressive disease, it was encouraging to see 3 of 7 patients demonstrate improvement in neuropathy with a mean change
in  NIS  of  –3.33  points  at  9  months.  These  positive  results  were  observed  in  patients  with  or  without  concomitant  use  of  stabilizer  therapy.  PRX004  also
demonstrated improvement in cardiac systolic function in each of the 7 evaluable patients, with a mean change in GLS of –1.21% at 9 months (centrally read). For
the 3 patients who improved on NIS, GLS improvement was more pronounced, with a mean change of –1.51% at 9 months. Taken together, these positive clinical
findings suggest PRX004’s depleter mechanism of action can result in benefits in both neuropathy and cardiac function.

Monthly intravenous  (IV)  infusions  of  PRX004 were generally  safe  and well  tolerated  at all  dose levels  tested,  with 233 separate  infusions  and up to 17
infusions  per patient  in  the study. No drug-related  serious  adverse  events  (SAEs), drug-related  ≥grade  3 adverse  events,  deaths  or dose-limiting  toxicities  were
reported. The most frequent treatment-emergent AEs (≥10%) were fall, anemia, upper respiratory tract infection, back pain, constipation, diarrhea and insomnia.
No  clinically  relevant  anti-drug  antibodies  were  observed.  Consistent  with  the  proposed  mechanism  of  action,  PRX004  administration  did  not  impact  levels  of
native, normal tetrameric TTR.

Based  on  the  results  of  the  Phase  1  study,  we  are  planning  to  advance  PRX004  into  a  late-stage  study  in  moderate-to-advanced  ATTR-cardiomyopathy
patients. This is an area of urgent need which directly aligns with PRX004’s differentiated depleter mechanism that targets the amyloid that puts patients at risk of
early mortality due to organ dysfunction and failure.

Our Discovery and Preclinical Programs

We are also advancing several discovery and preclinical-stage programs for neurological diseases with significant unmet medical needs such as Alzheimer's
disease (AD) and amyotrophic lateral sclerosis (ALS). Our discovery and pre-clinical pipeline includes our proprietary Aβ programs as well as three programs (tau,
TDP-43 and an undisclosed program) that are the focus of our collaboration with BMS.

If  promising,  we  expect  to  advance  our  discovery  programs  into  preclinical  development.  New  target  discovery  will  focus  on  areas  where  we  can  bring
potential new therapies to patients expeditiously through our internal expertise and resources. Existing late discovery-stage or preclinical-stage programs may be
partnered or out-licensed.

Our  preclinical  pipeline  includes  PRX005  and  PRX012  for  the  potential  treatment  of  Alzheimer’s  disease.  These  two  programs  are  part  of  Prothena’s

Alzheimer’s disease portfolio that includes antibody, vaccine and small molecule approaches.

PRX012 for the Potential Treatment of Alzheimer’s Disease

PRX012 is an investigational antibody that targets Aβ, or Amyloid Beta, a protein implicated in Alzheimer’s disease (AD). Our scientists have advanced the

understanding of the biology of AD and made particularly impactful and fundamental discoveries that elucidated the role amyloid plays in the disease.

Monoclonal antibodies targeting key epitopes within the N-terminus of Aβ have demonstrated that reducing amyloid plaque burden is associated with the
slowing of clinical decline in Alzheimer’s disease. To address the growing prevalence of Alzheimer’s disease with a therapeutic that can be made widely accessible
to  patients,  we  have  developed  highly  potent  anti-Aβ  antibodies  that  retain  or  improve  key  attributes  that  are  thought  to  underlie  the  observed  efficacy  of  N-
terminally directed therapeutics such as aducanumab, with the aim of offering similar or improved efficacy with convenient subcutaneous dosing regimens. Our
antibodies  demonstrated  a  higher  binding  strength  to  amyloid  than  aducanumab;  specifically,  antibodies  with  as  much  as  an  11-fold  greater  affinity/avidity  for
fibrillar  Aβ than aducanumab  that  also neutralized  soluble,  toxic (i.e., oligomeric)  Aβ species.  Our antibodies  were also shown to recognize  Aβ pathology  to a
greater extent than aducanumab, demonstrating more extensive plaque area binding at lower antibody concentrations, which are estimated to be clinically relevant
exposures in the central nervous system following systemic dosing.

We  are  advancing  our  lead  candidate,  PRX012,  as  a  next-generation  approach  for  subcutaneous  administration  to  improve  access  for  patients  with

Alzheimer’s disease.

PRX005 for the Potential Treatment of Alzheimer’s Disease

PRX005 is an investigational antibody that targets tau, a protein implicated in diseases including AD, FTD, progressive supranuclear palsy (PSP), chronic

traumatic encephalopathy (CTE) and other tauopathies. Cell-to-cell transmission of

10

pathogenic  tau  in  the  extracellular  space  is  thought  to  be  the  primary  mechanism  for  the  spread  of  tau  pathology  in  Alzheimer’s  disease  and  has  been  well
established  in  vitro  and  in  vivo.  The  cell-to-cell  transmission  and  accumulation  of  pathogenic  tau  correlates  with  progression  of  symptomatology  and  clinical
decline in Alzheimer’s disease. Several antibodies targeting various tau epitopes are currently being investigated for their ability to intervene in this pathogenic
pathway and treat Alzheimer’s disease, but antibodies that target mid-domain regions of tau may demonstrate superior attributes.

We employed our empirical and unbiased epitope discovery and selection strategy to define critical regions of the tau protein involved in the pathological
spread in Alzheimer’s  disease.  Antibodies targeting  epitopes along the tau protein were developed and tested in a variety  of in vitro models. Among these, the
murine precursor of PRX005, an antibody targeting the MTBR region of tau, was shown in preclinical models to be more efficacious in blocking tau transmission
and downstream toxic functional effects than antibodies targeting other regions of tau. In these preclinical models, PRX005 demonstrated significant inhibition of
cell-to-cell transmission and neuronal internalization in vitro and in vivo, and slowed pathological progression in a tau transgenic mouse model.

Master Collaboration Agreement with Bristol-Myers Squibb

In  March  2018,  we  entered  into  the  Master  Collaboration  Agreement  (the  “Collaboration  Agreement”)  with  Celgene  (which  was  acquired  by  BMS  in
November 2019), under which Celgene (now BMS) may elect in its sole discretion to exclusively license rights to develop and commercialize antibodies targeting
Tau, TDP-43 and an undisclosed target. The Collaboration Agreement became effective on March 20, 2018, which triggered an upfront payment to us of $100
million, as well as a further payment of approximately $50 million to subscribe for 1,174,536 of the Company’s ordinary shares at a price of $42.57 per share,
pursuant to a Share Subscription Agreement (the “SSA”) as described further below.

On a program-by-program basis, following Prothena’s filing of an investigational new drug (IND) application for any of our three collaboration programs to
BMS, BMS may elect in its sole discretion to exercise its right to receive an exclusive license to develop and commercialize antibodies targeting the applicable
Collaboration Target in the U.S. (the “US Rights”). If BMS exercises the US Rights for a collaboration program, it is obligated to pay Prothena an exercise fee of
approximately $80 million per program. Thereafter, BMS would have decision making authority over development activities, and all regulatory, manufacturing
and commercialization activities, for antibody products targeting the relevant Collaboration Target (the “Collaboration Products”) in the U.S.

On a program-by-program basis, following completion of a Phase 1 clinical trial for a collaboration program for which BMS has previously exercised its US
Rights, BMS may elect in its sole discretion to exercise its right with respect to such collaboration program to receive a worldwide, exclusive license to develop
and commercialize antibodies targeting the applicable Collaboration Target (the “Global Rights”). If BMS exercises its Global Rights, BMS would be obligated to
pay Prothena an additional exercise fee of $55 million for such collaboration program. The Global Rights would then replace the US Rights for that collaboration
program, and BMS would have decision making authority over developing, obtaining and maintaining regulatory approval for, manufacturing and commercializing
the Collaboration Products worldwide.

After exercise of Global Rights for a collaboration program, Prothena is eligible to receive up to $562.5 million in regulatory and commercial milestones per
program. For obtaining either US Rights or Global Rights for such collaboration program, Prothena will also be eligible to receive tiered royalties on net sales of
Collaboration  Products  ranging  from  high  single  digit  to  high  teen  percentages,  on  a  weighted  average  basis  depending  on  the  achieving  of  certain  net  sales
thresholds. Such exercise fees, milestones and royalty payments are subject to certain reductions as specified in the Collaboration Agreement, the agreement for
US Rights and the agreement for Global Rights.

BMS will continue to pay royalties on a Collaboration Product-by-Collaboration Product and country-by-country basis, until the latest of (i) expiration of
certain patents covering the Collaboration Product, (ii) expiration of all regulatory exclusivity for the Collaboration Product, and (iii) an agreed period of time after
the first commercial sale of the Collaboration Product in the applicable country (the “Royalty Term”).

The research term under the Collaboration Agreement continues for a period of six (6) years, which BMS may extend for up to two additional 12-month
periods by paying an extension fee of $10 million per extension period. The term of Collaboration Agreement continues until the last to occur of the following: (i)
expiration of the research term, (ii) expiration of all US Rights terms, and (iii) expiration of all Global Rights terms.

The term of any agreement for US Rights or Global Rights would continue on a Collaboration Product-by-Collaboration Product and country-by-country

basis until the expiration of all Royalty Terms under such agreement.

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The  Collaboration  Agreement  may  be  terminated  (i)  by  either  party  on  a  program-by-program  basis  if  the  other  party  remains  in  material  breach  of  the
Collaboration Agreement following a cure period to remedy the material breach, (ii) by BMS at will on a program-by-program basis or in its entirety, (iii) by either
party, in its entirety, upon insolvency of the other party, or (iv) by Prothena, in its entirety, if BMS challenges a patent licensed by Prothena to BMS under the
Collaboration Agreement.

Under the SSA, BMS is subject to certain transfer and standstill restrictions, including a restriction on acquiring more than 9.9% of the Company’s share
capital for a specified period of time following the closing of the subscription of the Shares, or earlier upon announcement of the intent to consummate a change of
control of the Company by the Company or a third party, or expiration or termination of the Collaboration Agreement. In addition, BMS will be entitled to request
the  registration  of the Shares  on Form S-3ASR or Form S-3 following  termination  of  the transfer  restrictions  if the Shares  cannot  be resold  without  restriction
pursuant to Rule 144 promulgated under the Securities Act of 1933, as amended (the “Securities Act”).

Regulation

We  anticipate  that  if  we  commercialize  any  products,  the  U.S.  market  will  ultimately  be  our  most  important  market.  For  this  reason,  the  laws  and

regulations discussed below focus on the requirements applicable to biologic products in the U.S.

Government Regulation

Governmental authorities, including the FDA, the EMA and comparable regulatory authorities in other countries, regulate the development, testing, use,
labeling, manufacturing, storage, record-keeping, reporting, marketing, advertising, and promotion of pharmaceutical products. The FDA does so under the U.S.
Federal Food, Drug, and Cosmetic Act and its implementing regulations and guidance for industry, and the U.S. Public Health Service Act and its implementing
regulations.  Non-compliance  with  applicable  requirements  can  result  in  fines  and  other  judicially  imposed  sanctions,  including  product  seizures,  import
restrictions, injunctive actions and criminal prosecutions of both companies and individuals. In addition, administrative remedies can involve requests to recall
violative  products;  the  refusal  of  the  government  to  enter  into  supply  contracts;  or  the  refusal  to  approve  pending  applications  for  product  approval  until
manufacturing or other alleged deficiencies are brought into compliance. The FDA and other comparable regulatory authorities also have the authority to cause
the withdrawal of approval of a marketed product or to impose additional labeling restrictions.

The pricing of pharmaceutical products is regulated in many countries and the mechanism of price regulation varies. In the U.S., while there are limited
indirect federal government price controls over private sector purchases of drugs, it is not possible to predict future regulatory action or private sector initiatives
on the pricing of pharmaceutical products.

Product Approval

United States. In the U.S., our current drug candidates are regulated as biologic pharmaceuticals, or biologics. The FDA regulates biologics under the U.S.
Food,  Drug,  and  Cosmetics  Act,  U.S.  Public  Health  Service  Act  and  its  implementing  regulations.  Biologics  are  also  subject  to  other  federal,  state  and  local
statutes and regulations. The process required by the FDA before biologic product candidates may be marketed in the U.S. generally involves, and is not limited
to, the following:

•

•

•

•

•

•

submission to the FDA of an Investigational New Drug Application (“IND”), which must become effective before human clinical trials may begin and
must be updated annually;

completion  of extensive  nonclinical  laboratory  tests  and animal  studies,  performed  in accordance  with the FDA’s Good Laboratory  Practice  (“GLP”)
regulations;

performance of adequate and well-controlled human clinical trials to establish the efficacy and safety of the product for each proposed indication, all
performed in accordance with FDA’s current good clinical practices (“cGCP”) requirements;

completion of chemistry, manufacturing and control (“CMC”) processes and procedures to establish the safety and quality of the pharmaceutical product
in accordance with FDA’s current good manufacturing practices (“cGMP”) regulations;

submission to the FDA of a BLA for a new biologic, after completion of all required clinical trials;

satisfactory  completion  of  an  FDA  pre-approval  inspection  of  the  manufacturing  facilities  at  which  the  product  is  produced  and  tested  to  assess
compliance with regulatory requirements, including cGMP regulations; and

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• FDA review and approval of a BLA for a new biologic, prior to any commercial marketing or sale of the product in the U.S.

Nonclinical tests assess the potential safety and pharmacologic effects of a product candidate in in vitro and/or in vivo studies. The results of these studies
must be submitted to the FDA as part of an IND before human testing may proceed. An IND is a request for authorization from the FDA to manufacture and
administer  an  investigational  drug  or  biologic  product  to  humans.  The  IND  includes  the  general  investigational  plan  and  the  proposed  protocol(s)  for  human
studies. The IND also includes results of nonclinical studies and other human studies, as appropriate, as well as manufacturing information, analytical data and
any  other  available  data  or  literature  to  support  the  use  of  the  investigational  new  drug.  An  IND  must  become  effective  before  human  clinical  trials  may  be
initiated. An IND will automatically become effective 30 days after receipt by the FDA, unless before that time the FDA raises concerns or questions related to
initiation of the proposed clinical trial(s). In such a case, the IND may be placed on clinical hold and the IND sponsor and the FDA must resolve any outstanding
concerns or questions before the clinical trial(s) may begin. Accordingly, submission of an IND may or may not result in the FDA allowing a clinical trial(s) to
commence.

Clinical  trials  involve  the  administration  of  the  investigational  product  to  human  subjects  under  the  supervision  of  qualified  investigators  in  accordance
with cGCPs, which include the requirement that all research subjects provide their informed consent for their participation in any clinical trial. Clinical trials are
conducted under protocols detailing, among other things, the objectives of the study, the parameters to be used in monitoring safety, and the efficacy criteria to be
evaluated. A protocol for each clinical trial and any subsequent protocol amendments must be submitted to the FDA as part of the IND. Additionally, approval
must also be obtained from each clinical trial site’s Institutional Review Board (“IRB”) before the trials may be initiated, and the IRB must provide oversight of
the trials until completed. There are also requirements governing the reporting of ongoing clinical trials and clinical trial results to public registries.

The  clinical  investigation  of  a  pharmaceutical,  including  a  biologic,  is  generally  divided  into  three  phases.  Although  the  phases  are  usually  conducted

sequentially, they may overlap or be combined. The three phases of an investigation are as follows:

• Phase 1. Phase 1 includes the initial introduction of an investigational product into humans. Phase 1 clinical trials are typically closely monitored and
may be conducted in patients with the target disease or condition or in healthy volunteers. These studies are designed to evaluate the safety, appropriate
dosage,  metabolism  and  pharmacologic  actions  of  the  investigational  product  in  humans,  the  side  effects  associated  with  increasing  doses,  and  if
possible,  to  gain  early  evidence  on  effectiveness.  During  Phase  1  clinical  trials,  sufficient  information  about  the  investigational  product’s
pharmacokinetics  and  pharmacological  effects  may  be  obtained  to  permit  the  design  of  well-controlled  Phase  2  clinical  trials.  The  total  number  of
participants included in Phase 1 clinical trials varies, but is generally in the range of 20 to 80;

• Phase 2. Phase 2 includes controlled clinical trials conducted to preliminarily or further evaluate the efficacy and safety of the investigational product for
a specific indication(s) in patients with the disease or condition under study, to determine dosage(s) for further studies, and to identify possible adverse
side  effects  and  safety  risks  associated  with  the  product.  Phase  2  clinical  trials  are  typically  well-controlled,  closely  monitored,  and  conducted  in  a
limited patient population, usually involving no more than several hundred participants; and

• Phase  3.  Phase  3  clinical  trials  are  generally  well  controlled  clinical  trials  conducted  in  an  expanded  patient  population  generally  at  geographically
dispersed clinical trial sites. They are performed after preliminary evidence suggesting effectiveness and safety of the product has been obtained, and are
intended  to  further  evaluate  efficacy  and  safety,  to  establish  the  overall  benefit-risk  relationship  of  the  investigational  product,  and  to  provide  an
adequate basis for product approval. Phase 3 clinical trials usually involve several hundred to several thousand participants.

The clinical trial process can take many years to complete, and there can be no assurance that the data collected will support FDA approval of the product.
The  FDA  may  place  clinical  trials  on  hold  at  any  point  in  this  process  if,  among  other  reasons,  it  concludes  that  clinical  subjects  are  being  exposed  to  an
unacceptable health risk. Trials may also be terminated by IRBs, which must review and approve all research involving human subjects. Side effects or adverse
events that are reported during clinical trials can delay, impede or prevent further clinical testing and/or marketing authorization.

Information including the results of the nonclinical and clinical testing, and the chemistry, manufacturing and controls of the product are evaluated and, if
determined to be adequate, submitted to the FDA to support the proposed product labeling through a BLA. The application includes all relevant data available
from nonclinical and clinical trials, together with detailed information relating to the product’s chemistry, manufacturing, controls and proposed labeling, among
other required

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information. Data from company-sponsored clinical trials intended to test the efficacy and safety of a proposed use of a product, and/or from alternative sources,
including studies initiated by investigators may be included in a BLA.

Once the BLA submission has been accepted for filing, the FDA’s goal is to review applications within ten months from the 60 day filing date for Standard
Review (for a total of twelve months) or, in the case of Priority Review, six months from the 60 day-filing date (for a total of eight months). The review process
may be often significantly extended by FDA requests for additional information or clarification. The FDA reviews the BLA to determine, among other things,
whether the proposed product is safe and effective, which includes determining whether it is safe and effective for its intended use, and whether the product is
being  manufactured  in  accordance  with  cGMP  to  assure  and  preserve  the  product’s  identity,  strength,  quality,  potency  and  purity.  The  FDA  may  refer  the
application  to  an  advisory  committee  for  evaluation  and  recommendation  as  to  whether  the  application  should  be  approved.  The  FDA  is  not  bound  by  the
recommendation of an advisory committee, but it typically follows such recommendations.

In  certain  cases,  the  FDA  may  issue  a  Special  Protocol  Assessment  (SPA),  which  is  a  written  agreement  between  a  sponsor  and  the  FDA  that  indicates
concurrence between the parties regarding the adequacy and acceptability of specific design elements and planned analysis for a clinical trial intended to form the
basis of a licensing application. An SPA does not indicate FDA concurrence on every detail in a particular trial protocol, and final marketing approval depends
upon factors including the efficacy and safety results from the trial, the overall safety profile and an evaluation of the risk/benefit ratio for the product candidate as
demonstrated across clinical trials.

The FDA has four expedited program designations for serious conditions - Fast Track, Breakthrough Therapy, Accelerated Approval and Priority Review -
to facilitate and expedite development and review of new drugs to address unmet medical needs or provide substantial improvements in the treatment of serious or
life-threatening conditions. The Fast Track designation provides pharmaceutical manufacturers with opportunities for frequent interactions with FDA during the
product’s development and for a rolling review of the BLA. A rolling review allows for completed portions of the application to be submitted and reviewed by the
FDA prior to submission of the complete application. The Breakthrough Therapy designation provides sponsors with all of the features of Fast Track designation
as well as intensive guidance on implementing an efficient development program for the product and a commitment by the FDA to involve senior managers and
experienced  review  staff  in  the  review.  The  Accelerated  Approval  designation  allows  the  FDA  to  approve  a  product  based  on  an  effect  on  a  surrogate  or
intermediate  endpoint  that  is  reasonably  likely  to  predict  a  product’s  clinical  benefit  and  generally  requires  the  sponsor  to  conduct  required  post-approval
confirmatory trials to verify the clinical benefit. The Priority Review designation signifies that the FDA review clock for the BLA is six months, compared to ten
months following the accepted-for-filing date under standard review.

After  the  FDA  evaluates  the  BLA  and  conducts  pre-approval  inspections  of  manufacturing  facilities  where  the  candidate  product  and/or  its  active
pharmaceutical  ingredient  will  be produced,  of clinical  sites  and of the  sponsor, if deemed  necessary,  it may  issue an approval  letter  or a  Complete  Response
Letter. An approval letter authorizes commercial marketing of the biologic with specific prescribing information for specific indications. A Complete Response
Letter  indicates  that  the  review  cycle  of  the  application  is  complete  and  the  application  is  not  ready  for  approval.  A  Complete  Response  Letter  may  require
additional clinical data and/or an additional Phase 3 clinical trial(s), and/or other significant, expensive and time-consuming requirements related to clinical trials,
nonclinical studies or manufacturing. Even if such additional information is submitted, the FDA may ultimately decide that the BLA does not satisfy the criteria
for approval. The FDA could approve the BLA with a Risk Evaluation and Mitigation Strategy (“REMS”) plan to mitigate risks, which could include medication
guides, physician communication plans, or elements to assure safe use, such as restricted distribution methods, patient registries and other risk minimization tools.
The  FDA  also  may  impose  conditions  for  approval  including  but  not  limited  to,  changes  to  proposed  labeling,  changes  to  manufacturing  controls  and
specifications, or a commitment or requirement to conduct one or more post-marketing studies or additional clinical trials. Such post-marketing commitments or
requirements may include Phase 4 clinical trials and surveillance to further assess and monitor the product’s safety and effectiveness after commercialization.

European Union. In the EU, there are several pathways for marketing approval, depending on the type of product for which approval is sought. Under the
centralized procedure, a sponsor submits a single application to the EMA. The marketing application is similar to the BLA submitted to FDA in the U.S. and is
evaluated by the Committee for Medicinal Products for Human Use (the “CHMP”), the expert scientific committee of the EMA. If the CHMP determines that the
marketing application fulfills the requirements for efficacy, safety and quality (equivalent to chemistry, manufacturing and controls in the US), it will submit a
favorable  opinion  to  the  European  Commission  (the  “EC”).  The  CHMP  opinion  is  not  binding,  but  is  typically  adopted  by  the  EC.  A  marketing  application
approved by the EC is valid in all EU member states.

In  addition  to  the  centralized  procedure,  the  EC  also  has:  (i)  national  authorization  procedures,  which  requires  a  separate  application  in  and  approval

determination by each country; (ii) a decentralized procedure, whereby applicants submit identical

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applications  to  several  countries  and  receive  simultaneous  approval;  and  (iii)  a  mutual  recognition  procedure,  where  applicants  submit  an  application  to  one
country for review and approval, and other countries may accept or reject the decision in the initial country. Regardless of the approval process employed, various
regulatory authorities share responsibilities for the monitoring, detection, and evaluation of adverse events post-approval, including national authorities, the EMA,
the EC, and the marketing authorization holder.

Post-Approval Requirements

Any products manufactured or distributed by us or on our behalf pursuant to FDA approvals are subject to continuing regulation by the FDA, including
requirements for record-keeping, reporting of adverse events, and submitting biological product deviation reports to notify the FDA of unanticipated changes in
distributed products. Additionally, any significant change in the approved product or in how it is manufactured, including changes in formulation or the site of
manufacture, generally require prior FDA approval. The packaging and labeling of all products developed by us are also subject to FDA approval and ongoing
regulation.

Sponsors are required to register their facilities with the FDA and certain state agencies, and are subject to periodic unannounced inspections by the FDA
and certain state agencies for compliance with cGMP standards, which impose certain quality processes, manufacturing controls and documentation requirements
upon  us  and  our  third-party  manufacturers  in  order  to  ensure  that  the  product  is  safe,  has  the  identity  and  strength,  and  meets  the  quality,  purity  and  potency
characteristics that it purports to have. Certain states also impose requirements on manufacturers and distributors to establish the pedigree of product in the chain
of distribution, including some states that require manufacturers and others to adopt new technology capable of tracking and tracing product as it moves through
the  distribution  chain.  Noncompliance  with  cGMP  or  other  requirements  can  result  in  issuance  of  warning  letters,  civil  and  criminal  penalties,  seizures,  and
injunctive action.

FDA  regulations  also  require  investigation  and  correction  of  any  deviations  from  cGMP  requirements  and  impose  reporting  and  documentation
requirements  upon  us  and  any  third-party  manufacturers  that  we  may  decide  to  use.  Accordingly,  manufacturers  and  sponsors  must  continue  to  expend  time,
money and effort in the area of production and quality control to maintain compliance with cGMP and other aspects of regulatory compliance.

The  FDA  and  other  federal  and  state  agencies  closely  regulate  the  labeling,  marketing  and  promotion  of  drugs.  While  doctors  are  free  to  prescribe  any
product approved by the FDA for any use, a company can only make claims relating to safety and efficacy of a product that are consistent with FDA approval,
and the company is allowed to market a drug only for the particular use(s) approved by the FDA. In addition, any claims we make for our products in advertising
or  promotion  must  be  appropriately  balanced  with  important  safety  information  and  otherwise  be  adequately  substantiated.  Failure  to  comply  with  these
requirements can result in adverse publicity, warning letters, corrective advertising, injunctions, potential civil and criminal penalties, criminal prosecution, and
agreements with governmental agencies that materially restrict the manner in which a company promotes or distributes drug products. Government regulators,
including the Department of Justice and the Office of the Inspector General of the Department of Health and Human Services, as well as state authorities, have
increased their scrutiny of the promotion and marketing of drugs.

The  FDA  also  enforces  the  requirements  of  the  U.S.  Prescription  Drug  Marketing  Act,  which,  among  other  things,  imposes  various  requirements  in
connection with the distribution of product samples to physicians. Sales, marketing and scientific/educational grant programs must comply with the U.S. Anti-
Kickback Statute, the U.S. False Claims Act, and similar state laws. Pricing and rebate programs must comply with the Medicaid rebate requirements of the U.S.
Omnibus Budget Reconciliation Act. We may also be subject to the U.S. Physician Payment Sunshine Act (the “Sunshine Act”) which regulates disclosure of
payments to healthcare professionals and providers.

The U.S. Foreign Corrupt Practices Act (the “FCPA”), the Irish Criminal Justice (Corruption Offences) Act 2018 (the “Irish Corruption Act”) and the U.K.
Bribery Act prohibit companies and their representatives from offering, promising, authorizing or making payments to governmental officials (and certain private
individuals under the Irish Corruption Act and the U.K. Bribery Act) for the purpose of obtaining or retaining business abroad. In many countries, the healthcare
professionals we interact with may meet the definition of a government official for purposes of the FCPA. Failure to comply with domestic or non-domestic laws
could result in various adverse consequences, including possible delay in approval or refusal to approve a product, recalls, seizures, withdrawal of an approved
product from the market, the imposition of civil or criminal sanctions and the prosecution of executives overseeing our international operations.

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Orphan Drugs

Under the U.S. Orphan Drug Act, the FDA may grant orphan drug designation to drugs intended to treat a rare disease or condition, which is generally
defined as a disease or condition that affects fewer than 200,000 individuals in the U.S. Orphan drug designation must be requested before submitting a BLA. In
the U.S., orphan drug designation entitles a party to financial incentives such as opportunities for grant funding towards clinical trial costs, tax advantages, and
user-fee waivers. After the FDA grants orphan drug designation, the generic identity of the drug and its potential orphan use are disclosed publicly by the FDA.
Orphan drug designation does not convey any advantage in, or shorten the duration of, the regulatory review and approval process. The first BLA applicant to
receive  FDA  approval  for  a  particular  active  ingredient  to  treat  a  particular  disease  with  FDA  orphan  drug  designation  is  entitled  to  a  seven-year  exclusive
marketing period in the U.S. for that product, for that indication. During the seven-year exclusivity period, the FDA may not approve any other applications to
market the same drug for the same orphan indication, except in limited circumstances, such as demonstration of clinical superiority to the product with orphan
exclusivity or if FDA finds that the holder of the orphan drug exclusivity has not shown that it can assure the availability of sufficient quantities of the orphan
drug to meet the needs of patients with the disease or condition for which the drug was designated. As a result, even if one of our drug candidates receives orphan
exclusivity, the FDA can still approve other drugs that have a different active ingredient for use in treating the same indication or disease. Furthermore, the FDA
can waive orphan exclusivity if we are unable to manufacture sufficient supply of our product.

Pharmaceutical Coverage, Pricing and Reimbursement

Sales  of  our  products  will  depend,  in  part,  on  the  extent  to  which  our  products  will  be  covered  by  third-party  payors,  such  as  federal,  state  and  other
government  health  care  programs,  commercial  insurance  and  managed  healthcare  organizations.  These  third-party  payors  are  increasingly  reducing
reimbursements  for  medical  products,  drugs  and  services.  In  addition,  the  U.S.  government,  state  legislatures  and  other  governments  have  continued
implementing cost containment programs, including price controls, restrictions on reimbursement and requirements for substitution of generic products. Adoption
of price controls and cost- containment measures, and adoption of more restrictive policies in jurisdictions with existing controls and measures, could further limit
our net revenue and results. Decreases in third-party reimbursement for our drug candidates or a decision by a third-party payor to not cover our drug candidates
could reduce physician usage of our products once approved and have a material adverse effect on our sales, results of operations and financial condition.

Other Healthcare Laws

Although we currently do not have any products on the market, if our drug candidates are approved and we begin commercialization, we may be subject to
additional  healthcare  regulation  and  enforcement  by  the  federal  government  and  by  authorities  in  the  states  and  other  jurisdictions  in  which  we  conduct  our
business. Such laws include, without limitation, anti-kickback, fraud and abuse, false claims, privacy and security and physician sunshine laws and regulations. If
our operations are found to be in violation of any of such laws or any other governmental regulations that apply to us, we may be subject to penalties, including,
without limitation, civil and criminal penalties, damages, fines, the curtailment or restructuring of our operations, exclusion from participation in federal and state
healthcare programs and imprisonment, any of which could adversely affect our ability to operate our business and our financial results.

Intellectual Property

We seek to protect our proprietary technology and other intellectual property that we believe is important to our business, including by seeking, maintaining
and defending patents. We also rely on trade secrets and know-how to protect our business. We may may seek licenses from others as appropriate to enhance or
maintain our competitive position.

Our intellectual property is primarily directed to immunological approaches to the treatment of diseases that involve protein dysregulation, amyloidosis, or

neurodegeneration, and other proprietary technologies and processes related to our lead product development candidates.

We own or hold exclusive licenses to a number of issued U.S. patents and pending U.S. patent applications, as well as issued non-U.S. patents and pending
non-U.S. patent applications including Patent Cooperation Treaty applications. As of December 31, 2020, our patent portfolio included the following families of
patents or patent applications that we own or have exclusively licensed from other parties:

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• Approximately  6  patent  families  related  to  AL  or  AA  amyloidosis,  including  our  birtamimab  program,  including  a  composition  of  matter  patent

anticipated to expire 2029 (subject to potential adjustments in patent term as described below);

• Approximately  19  patent  families  related  to  Parkinson’s  disease  and  other  synucleinopathies,  including  our  prasinezumab  program,  including  a

composition of matter patent anticipated to expire in 2032 (subject to potential adjustments in patent term as described below);

• Approximately 9 patent families related to ATTR amyloidosis, including our PRX004 program, including a composition of matter patent anticipated to

expire in 2036 (subject to potential adjustments in patent term as described below);

• Approximately 9 patent families related to Alzheimer's disease, including our PRX005 and PRX0012 programs; and

• Approximately  16  patent  families  related  to  other  potential  targets  of  intervention  and  diseases,  including  TDP-43,  and  other  product  candidates

including vaccines.

The term of individual patents depends upon the legal term of the patents in the countries in which they are obtained. In most countries in which we file, the
patent term is 20 years from the date of filing the non-provisional application. In the U.S., a patent’s term may be lengthened by patent term adjustment, which
compensates  a  patentee  for  administrative  delays  by  the  U.S.  Patent  and  Trademark  Office  in  granting  a  patent,  or  may  be  shortened  if  a  patent  is  terminally
disclaimed over an earlier-filed patent.

The term of a patent that covers an FDA-approved drug may also be eligible for patent term extension, which permits patent term restoration of a U.S. patent
as compensation for the patent term lost during the FDA regulatory review process. The U.S. Hatch-Waxman Act permits a patent term extension of up to five
years beyond the expiration of the patent. The length of the patent term extension is related to the length of time the drug is under regulatory review. A patent term
extension cannot extend the remaining term of a patent beyond a total of 14 years from the date of product approval and only one patent can be extended for each
first regulatory review period for a product. Moreover, a patent can only be extended once, and thus, if a single patent is applicable to multiple products, it can only
be extended based on one product. Similar provisions are available in Europe and other jurisdictions to extend the term of a patent that covers an approved drug.
When possible, depending upon the length of clinical trials and other factors involved in the filing of a BLA, we expect to apply for patent term extensions for
patents covering our product candidates and their methods of use.

The patents referenced above have expiration dates ranging from 2023 through 2040 (excluding any available patent term extensions).

University  of  Tennessee  License  Agreement:  Under  a  License  Agreement  with  the  University  of  Tennessee  Research  Foundation,  we  have  exclusively
licensed  from  the  University  of  Tennessee  its  joint  ownership  interest  in  certain  patents  jointly  owned  with  us.  Those  patents  relate  to  our  program  targeting
amyloidosis (birtamimab). Under that sublicensable, worldwide license, we are required to pay to the University of Tennessee an amount equal to 1% of net sales
of any product covered by any licensed patent, plus certain additional payments in the event that all or a portion of the license is sublicensed. To date, we have not
paid or incurred any royalties to the University of Tennessee under our agreement. The agreement is effective on a country-by-country basis for the longer of (i) a
period of twenty years from the effective date of the agreement, or (ii) in each country in which a valid claim for any licensed patent or patent application exists,
expiration of such valid claim. The agreement will terminate prior to the end of its term if we become insolvent unless the University of Tennessee elects to allow
the agreement to remain in effect. The University of Tennessee may terminate the agreement prior to the end of its term upon our failure to make payment under
the agreement within 120 days of notice of such failure or upon our material breach of the agreement, which breach has not been cured within 60 days of written
notice of such breach. We may terminate the agreement prior to the end of its term if we have paid all amounts due to the University of Tennessee through the
effective  date  of  the  termination  and  provide  three  months’  written  notice  to  the  University  of  Tennessee  or  upon  material  breach  of  the  agreement  by  the
University of Tennessee, which breach has not been cured within 60 days of written notice of such breach.

University of California License Agreement: Under a License Agreement with The Regents of the University of California, we have exclusively licensed
from the University of California its joint ownership interest in certain patents jointly owned with us. Those patents relate to our program targeting Parkinson’s
disease  and  other  synucleinopathies  (prasinezumab).  Under  that  sublicensable,  worldwide  license,  we  are  required  to  pay  to  the  University  of  California  an
amount equal to 1% of net sales of any product covered by any licensed patent, plus certain additional payments for milestones achieved and sublicense revenue.
To date, we have not paid or incurred any royalties to the University of California under our agreement. The agreement is effective until the expiration date of the
last to expire licensed patent. The obligation to pay royalties

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continues on a country-by-country basis until the expiration of the last to expire patent containing a valid claim covering the applicable product. The agreement
will terminate prior to the end of its term without prior written notice if (i) we, or third parties on our behalf or at our written urging, file a claim including an
assertion that any portion of the licensed patents is invalid or unenforceable, or (ii) upon the filing of a petition for relief under the U.S. Bankruptcy Code by or
against us as a debtor or alleged debtor. The University of California may terminate the agreement prior to the end of its term upon our default, if we fail to cure
the  default  within 60 days of written  notice of such default.  We may  terminate  the  agreement  prior to the end of its term upon a 90 day written  notice to the
University of California.

University Health Network License Agreement: Under a License Agreement with the University Health Network (“UHN”), we have exclusively licensed its
joint interest in certain patents jointly owned with us, as well as its entire interest in certain patents solely owned by UHN (“UHN Background IP”). Those patents
relate to our program targeting ATTR amyloidosis (PRX004). Under that sublicensable, worldwide license, we are required to pay to UHN royalties on net sales
of any diagnostic or therapeutic product covered by a licensed patent in the U.S. and outside of the U.S., plus certain additional payments for milestones achieved
and sublicense revenue. In addition, we are required to pay to UHN a royalty on net sales of any product that is not a diagnostic or therapeutic product. To date,
we have not paid or incurred any royalties to UHN under our agreement. The agreement is effective until the expiration date of the last to expire licensed patent.
The  obligation  to  pay  royalties  continues  on  a  country-by-country  basis  until  the  expiration  of  the  last  to  expire  patent  containing  a  valid  claim  covering  the
applicable product. The agreement will terminate prior to the end of its term without prior written notice (i) upon the filing of a petition for relief under the U.S.
Bankruptcy Code by or against us as a debtor or alleged debtor, (ii) upon the filing of a claim by us challenging the validity of a patent within UHN Background
IP, or (iii) by mutual written agreement of the parties. UHN may terminate the agreement prior to the end of its term upon our default, if we fail to cure the default
within 90 days of written notice of such default. We may terminate the agreement prior to the end of its term upon a 90 day written notice to UHN.

Elan License Agreement: Under an Amended and Restated Intellectual Property License and Contribution Agreement with Elan and certain of its affiliates,
we have exclusively licensed from Elan and those affiliates certain patents and patent applications owned by them, and exclusively sublicensed from Elan and
those  affiliates  certain  patents  and  patent  applications  owned  by  Janssen  Alzheimer  Immunotherapy.  Those  licenses  are  worldwide,  fully  paid,  royalty-free,
perpetual and irrevocable, and relate to our program targeting α-synuclein. Subsequent to entering into this Agreement, Elan was acquired by Perrigo Company
plc.

Competition

The pharmaceutical  industry is highly competitive. Our principal competitors consist of major international companies, all of which are larger and have
greater financial resources, technical staff, manufacturing, R&D and marketing capabilities than we have. We also compete with smaller research companies and
generic drug and biosimilar manufacturers. The degree of competition varies for each of our programs.

A drug may be subject to competition from alternative therapies during the period of patent protection or regulatory exclusivity and thereafter it may be
subject to further competition from generic products or biosimilars. Governmental and other pressures toward the dispensing of generic products or biosimilars
may rapidly and significantly reduce, slow or reverse the growth, sales and profitability of any product not protected by patents or regulatory exclusivity, and may
adversely  affect  our  future  results  and  financial  condition.  If  we  successfully  discover,  develop  and  commercialize  any  products,  the  launch  of  competitive
products, including generic or biosimilar versions of any such products, may have a material adverse effect on our revenues and results of operations.

Our competitive position depends in part upon our ability to discover and develop innovative and cost-effective new products. If we fail to discover and

develop new products, our business, financial condition and results of operations will be materially and adversely affected.

Manufacturing

Prasinezumab  -  Boehringer  Ingelheim  Biopharmaceuticals  GmbH  (“BI”)  manufactured  clinical  supplies  of  our  drug  candidate  prasinezumab  for  our
completed  Phase  1a  single  ascending  dose  and  Phase  1b  multiple  ascending  dose  clinical  trials.  Roche,  with  whom  we  are  collaborating  on  development  of
prasinezumab,  is  manufacturing  clinical  supplies  for  the  ongoing  Phase  2  and  any  subsequent  clinical  trials  for  prasinezumab.  We  are  dependent  on  Roche  to
manufacture these clinical supplies.

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PRX004 - Rentschler Biopharma SE (“Rentschler”) is our third-party manufacturer of clinical supplies of our drug candidate PRX004. We were dependent
on Rentschler to manufacture these drug substance and drug product clinical supplies for our planned Phase 2/3 clinical trial and drug substance for any subsequent
clinical trials for PRX004. We are currently in the process of selecting a manufacturer for drug product manufacture for PRX004 and once selected we will be
dependent on this manufacturer for ongoing clinical supplies.

Birtamimab (NEOD001) -  BI  manufactured  clinical  supplies  of  our  drug  candidate  birtamimab  for  our  prior  Phase  1,  Phase  2  (PRONTO)  and  Phase  3
(VITAL) clinical trials. Rentschler is our third-party manufacturer of drug substance for our planned Phase 3 clinical trial. Such drug substance manufactured by
Rentschler  has been demonstrated  to be comparable  to the drug substance  manufactured  by BI. Catalent  Pharma  Solutions, LLC (“Catalent”)  is our third-party
manufacturer of drug product for our planned Phase 3 clinical trial, and this drug product has been demonstrated to be comparable to the drug product produced by
BI. We are dependent on Rentschler and Catalent to manufacture clinical supplies for our planned Phase 3 clinical trial.

PRX005 (Tau) - Catalent is our is our third-party manufacturer of drug substance and Berkshire Sterile Manufacturing, LLC is our third-party manufacturer
for  drug  product.  We  are  dependent  on  Catalent  and  Berkshire  (“Berkshire”)  to  manufacture  clinical  supplies  for  our  planned  Phase  1  clinical  trial  and  any
subsequent clinical trials for PRX005.

PRX012 (Aβ) - Catalent is our is our third-party manufacturer of both drug substance and drug product. We will be dependent on Catalent to manufacture

clinical supplies for our planned Phase 1 clinical trial and any subsequent clinical trial for PRX012.

Research and Development

Our  research  and  development  expenses  totaled  $74.9  million,  $50.8  million  and  $101.2  million  in  2020,  2019  and  2018,  respectively.  For  more

information, see “Management’s Discussion and Analysis of Financial Condition and Results of Operations.”

Employees

As of December 31, 2020, we had 66 employees, of whom 40 were engaged in research and development activities and the remainder were working in

general and administrative areas. The vast majority of these employees are in the U.S.

Information about Segment and Geographic Revenue

Information about segment and geographic revenue is set forth in Note 2 to the Consolidated Financial Statements included in this report.

Available information

Our  principal  executive  office  is  at  77  Sir  John  Rogerson’s  Quay,  Block  C,  Grand  Canal  Docklands,  Dublin  2,  D02  T804,  Ireland,  and  our  telephone
number at that address is 011-353-1-236-2500. We are subject to the information and periodic reporting requirements of the Securities Exchange Act of 1934, as
amended,  and,  in  accordance  therewith,  file  periodic  reports,  proxy  statements  and  other  information  with  the  U.S.  Securities  and  Exchange  Commission  (the
“SEC”). Such periodic reports, proxy statements and other information  are available for inspection and copying at the SECs Public Reference Room at 100 F
Street, NE., Washington, DC 20549 or may be obtained by calling the SEC at 1-800-SEC-0330. In addition, the SEC maintains a website at www.sec.gov that
contains reports, proxy statements and other information regarding issuers that file electronically with the SEC. We also post on the Investors page of our website,
www.prothena.com, a link to our filings with the SEC, our Corporate Governance Guidelines and Code of Conduct, which applies to all directors and employees,
and the charters  of the Audit, Compensation  and Nominating  and Corporate  Governance Committees  of our Board of Directors.  Our filings with the SEC are
posted on our website and are available free of charge as soon as reasonably practical after they are filed electronically with the SEC. Please note that information
contained on our website is not incorporated  by reference  in, or considered to be a part of, this report. You can also obtain copies of these documents free of
charge by writing or telephoning us at: Prothena Corporation plc, 77 Sir John Rogerson’s Quay, Block C, Grand Canal Docklands, Dublin 2, D02 T804, Ireland,
011-353-1-236-2500, or through the Investors page of our website.

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ITEM 1A. RISK FACTORS

You should carefully consider the risks described below, together with all of the other information included in this Form 10-K, in considering our business
and prospects. Set forth below and elsewhere in this Form 10-K and in other documents we file with the SEC are descriptions of certain risks, uncertainties, and
other factors that could cause our actual results to differ materially from those anticipated. If any of the following risks, other unknown risks, or risks that we think
are immaterial occur, our business, financial condition, results of operations, cash flows, or growth prospects could be adversely impacted, which could result in a
complete loss on your investment.

We anticipate that we will incur losses for the foreseeable future and we may never sustain profitability.

Risks Relating to Our Financial Position, Our Need for Additional Capital, and Our Business

We may not generate the cash that is necessary to finance our operations in the foreseeable future. We incurred net losses of $111.1 million, $77.7 million
and $155.6 million for the years ended December 31, 2020, 2019, and 2018, respectively. We expect to continue to incur substantial losses for the foreseeable
future as we:

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•

support the Phase 3 AFFIRM-AL clinical trial for birtamimab expected to commence in 2021, the Phase 2 PASADENA clinical trial for prasinezumab
(PRX002/RG7935) being conducted by Roche, the Phase 2b clinical trial for prasinezumab expected to commence in 2021, the Phase 2/3 clinical trial for
PRX004  expected  to  commence  in  2021,  the  Phase  1  clinical  trial  for  PRX005  expected  to  commence  in  2021,  the  Phase  1  clinical  trial  for  PRX012
expected to commence in 2022, and possibly initiate additional clinical trials for these and other programs;

develop and possibly commercialize our drug candidates, including birtamimab, prasinezumab, PRX004, PRX005, and PRX012;

undertake nonclinical development of other drug candidates and initiate clinical trials, if supported by nonclinical data;

pursue our early stage research and seek to identify additional drug candidates; and

potentially acquire rights from third parties to drug candidates or technologies through licenses, acquisitions, or other means.

We  must  generate  significant  revenue  to  achieve  and  maintain  profitability.  Even  if  we  succeed  in  discovering,  developing,  and  commercializing  one  or

more drug candidates, we may not be able to generate sufficient revenue and we may never be able to achieve or sustain profitability.

We  will  require  additional  capital  to  fund  our  operations,  and  if  we  are  unable  to  obtain  such  capital,  we  will  be  unable  to  successfully  develop  and
commercialize drug candidates.

As of December 31, 2020, we had cash and cash equivalents of $295.4 million. Although we believe, based on our current business plans, that our existing
cash and cash equivalents will be sufficient to meet our obligations for at least the next twelve months, we anticipate that we will require additional capital in order
to continue the research and development, and eventual commercialization, of our drug candidates. Our future capital requirements will depend on many factors
that are currently unknown to us, including, without limitation:

•

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•

the timing of progress, results and costs of our clinical trials, including the Phase 3 clinical trial for birtamimab expected to commence in 2021, the Phase
2  clinical  trial  for  prasinezumab,  the  Phase  2b  clinical  trial  for  prasinezumab  expected  to  commence  in  2021,  the  Phase  2/3  clinical  trial  for  PRX004
expected to commence in 2021, the Phase 1 clinical trial for PRX005 expected to commence in 2021, and the Phase 1 clinical trial for PRX012 expected
to commence in 2022;

the timing, initiation, progress, results, and costs of these and our other research, development, and possible commercialization activities;

the results of our research and nonclinical and clinical studies;

the costs of manufacturing our drug candidates for clinical development as well as for future commercialization needs;

if and when appropriate, the costs of preparing for commercialization of our drug candidates;

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•

•

•

the costs of preparing, filing, and prosecuting patent applications, and maintaining, enforcing, and defending intellectual property-related claims;

our ability to establish strategic collaborations, licensing, or other arrangements;

the timing, receipt, and amount of any capital investments, cost-sharing contributions or reimbursements, milestone payments, or royalties that we might
receive under current or potential future collaborations;

the costs to satisfy our obligations under current and potential future collaborations; and

the timing, receipt, and amount of revenues or royalties, if any, from any approved drug candidates.

We have based our expectations relating to liquidity and capital resources on assumptions that may prove to be wrong, and we could use our available capital
resources sooner than we currently expect. Because of the numerous risks and uncertainties associated with the development and commercialization of our drug
candidates,  we  are  unable  to  estimate  the  amounts  of  increased  capital  outlays  and  operating  expenses  associated  with  completing  the  development  and
commercialization of our current drug candidates.

In  the  pharmaceutical  industry,  the  research  and  development  process  is  lengthy  and  involves  a  high  degree  of  risk  and  uncertainty.  This  process  is
conducted  in  various  stages  and,  during  each  stage,  there  is  substantial  risk  that  product  candidates  in  our  research  and  development  pipeline  will  experience
difficulties, delays or failures. This makes it difficult to estimate the total costs to complete our clinical trials and to estimate anticipated completion dates with any
degree  of  accuracy,  which  raises  concerns  that  attempts  to  quantify  costs  and  provide  estimates  of  timing  may  be  misleading  by  implying  a  greater  degree  of
certainty than actually exists.

In order to develop and obtain regulatory approval for our drug candidates we will need to raise substantial additional funds. We expect to raise any such
additional funds through public or private equity or debt financings, collaborative agreements with corporate partners, or other arrangements. We cannot assure that
additional funds will be available when we need them on terms that are acceptable to us or at all. General market conditions may make it very difficult for us to
seek  or  obtain  financing  from  the  capital  markets.  If  we  raise  additional  funds  by  issuing  equity  securities,  substantial  dilution  to  existing  shareholders  would
result. If we raise additional funds by incurring debt financing, the terms of the debt may involve significant cash payment obligations as well as covenants and
specific financial ratios that may restrict our ability to operate our business. We may be required to relinquish rights to our technologies or drug candidates or grant
licenses on terms that are not favorable to us in order to raise additional funds through strategic alliances, joint ventures, or licensing arrangements.

If adequate funds are not available on a timely basis, we may be required to:

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•

•

•

terminate or delay clinical trials or other development activities for one or more of our drug candidates;

delay arrangements for activities that may be necessary to commercialize our drug candidates;

curtail or eliminate our drug research and development programs that are designed to identify new drug candidates; or

cease operations.

In addition, if we do not meet our payment obligations to third parties as they come due, we may be subject to litigation claims. Even if we are successful in
defending against these claims, litigation could result in substantial costs and distract management and may have unfavorable results that could further adversely
impact our financial condition.

The COVID-19 pandemic has adversely affected our business and could have a material adverse effect on our liquidity, results of operations, financial
condition or business, including our nonclinical and clinical development programs.

The outbreak of the novel strain of coronavirus SARS-CoV-2, which causes coronavirus disease (“COVID-19”), has evolved into a global pandemic. While
it is not possible at this time to estimate the overall impact that COVID-19 could have on our business, the continued rapid spread of COVID-19, and the measures
taken by the governments and local authorities of affected  countries and local jurisdictions, has disrupted our Phase 2 clinical trial for prasinezumab and could
disrupt and delay our planned clinical trials, our research and nonclinical studies, the manufacture or shipment of both drug substance and finished drug product for
our drug candidates for preclinical testing and clinical trials and materially adversely impact our liquidity, results of operations, financial condition, or business,
including the following:

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•

our Phase 2 clinical trial for prasinezumab has been disrupted and this and other clinical trials pursued by us and our collaboration  partners may be
further delayed or interrupted, including as a result of (i) interruptions of supply to clinical trial sites of drug candidate or other equipment or materials,
(ii) inability or unwillingness of site investigators or other study personnel to travel to study sites, dispense drug product, or otherwise treat or monitor
study participants or follow study protocols, or conduct necessary data collection or verification, (iii) inability or unwillingness of study participants to
travel  to  clinical  trial  sites,  receive  infusions,  or  otherwise  continue  to  participate  in  the  study,  (iv)  diversion  of  healthcare  resources  away  from  the
conduct of clinical trials, including the diversion of hospitals serving as our clinical trial sites and hospital staff supporting the conduct of our clinical
trials, or (v) interruptions in contracting with essential third-party vendors;

we, or our collaboration partners, may be delayed in or prevented from initiating new clinical trials of current or prospective drug candidates because of
(i) delays or difficulties in manufacturing drug product, (ii) delays or difficulties preparing regulatory submissions, (iii) delays or difficulties contracting
with essential third-party  vendors (such as contract research organizations),  (iv) delays or difficulties  enlisting  site investigators  or initiating clinical
trial sites, (v) delays or difficulties recruiting or enrolling study participants, or (vi) delays or difficulties supplying drug product or other equipment or
materials to clinical trial sites or other locations;

we may experience  delays  or interruptions  in our business operations  due to our key personnel,  or a significant  number  of our personnel,  becoming
infected with COVID-19 and therefore being unable to work, even remotely, for an extended period of time;

interruption or delays in the operations of the U.S. Food and Drug Administration (the “FDA”) and comparable foreign regulatory agencies may impact
review, inspection, and approval timelines for any of our development programs;

the  pandemic  may  adversely  affect  our  collaboration  partners,  Roche  and/or  Bristol-Myers  Squibb  (“BMS”),  in  way  that  adversely  impacts  our
collaborations with them;

business development opportunities may become more limited or difficult to undertake;

our costs may significantly increase to manage impacts to our business to complete our planned operations within our projected timelines;

changes in local regulations as part of a response to COVID-19 may require us to change the ways in which our clinical trials are conducted, which may
result in unexpected costs, or discontinuation of the clinical trials altogether;

we  may  experience  delays  in  necessary  interactions  with  local  regulators,  ethics  committees,  and  other  important  agencies  and  contractors  due  to
limitations in employee resources or forced furlough of government employees; or

our liquidity needs may be adversely impacted by the economic effects of the pandemic on financial markets.

Any one  or more  of  these  risks could  have  a material  adverse  effect  on  our liquidity,  results  of operations,  financial  condition  or business,  including  the

progress of, and timelines for, our nonclinical and clinical development programs.

In addition, the spread of COVID-19 has caused a broad impact globally, and may materially affect us economically. For example, if the subtenant to the
office  space  that  we  subleased  in  South  San  Francisco,  California  defaults  on  its  payment  obligations,  we  will  not  receive  sublease  income  to  offset  our  lease
payments to the landlord of the South San Francisco office space until such time as we are able to secure a new subtenant and enter into a new sublease agreement.
The spread of COVID-19 has had a negative impact on the commercial real estate market and there can be no assurance that we would be able to re-sublet the
space for the same rent that the current subtenant is obligated to pay us or at all.

While the potential economic impact brought by, and the duration of, COVID-19 may be difficult to assess or predict, a widespread pandemic could result in
significant  disruption  of  global  financial  markets,  reducing  our  ability  to access  capital,  which  could in  the  future  negatively  affect  our  liquidity.  In addition,  a
recession or market correction resulting from the spread of COVID-19 could materially affect our business and the market price of our ordinary shares.

The United Kingdom’s withdrawal from the European Union could have a negative effect on global economic conditions and financial markets, European
Union regulatory procedures and our business.

Following a national referendum and enactment of legislation by the government of the United Kingdom, the United Kingdom formally withdrew from the

European Union (“EU”) on January 31, 2020, commonly referred to as Brexit. The

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United Kingdom remained in the EU customs union and the single market for a transition period which expired on December 31, 2020. On December 24, 2020, the
United Kingdom and the EU reached agreement in principle on their future trading relationship and entered into the EU-UK Trade and Cooperation Agreement
which applies provisionally until February 28, 2021, by which stage it is expected to be formally ratified by the parties and fully in force. However, because the
agreement merely sets forth a framework in many respects and will require complex additional bilateral negotiations between the United Kingdom and the EU as
both  parties  continue  to  work  on  the  rules  for  implementation,  significant  political  and  economic  uncertainty  remains  as  to  aspects  of  the  future  relationship
between the United Kingdom and the EU. The uncertainty  surrounding Brexit has had and may continue to have a material  adverse effect  on global economic
conditions and the stability of global financial markets, and may significantly reduce global market liquidity and restrict the ability of key market participants to
operate in certain financial markets. Any of these factors could depress economic activity and restrict access to capital, which could have a material adverse effect
on our business, financial condition, results of operations, and/or growth prospects.

Our future success depends on our ability to retain key personnel and to attract, retain, and motivate qualified personnel.

We are highly dependent on key personnel, including Dr. Gene G. Kinney, our President and Chief Executive Officer. There can be no assurance that we
will be able to retain Dr. Kinney or any of our key personnel. The loss of the services of Dr. Kinney or any other person on whom we are highly dependent might
impede the achievement of our research, development, and commercial objectives.

Recruiting  and  retaining  qualified  scientific  and  other  personnel  are  critical  to  our  growth  and  future  success.  Competition  for  qualified  personnel  in  our
industry  is  intense.  We  may  not  be  able  to  attract  and  retain  these  personnel  on  acceptable  terms  given  that  competition.  Failure  to  recruit  and  retain  qualified
personnel could have a material adverse effect on our business, financial condition, results of operations, and/or growth prospects.

Our collaborators, prospective collaborators, and suppliers may need assurances that our financial resources and stability on a stand-alone basis are sufficient
to satisfy their requirements for doing or continuing to do business with us.

Some of our collaborators, prospective collaborators, and suppliers may need assurances that our financial resources and stability on a stand-alone basis are
sufficient to satisfy their requirements for doing or continuing to do business with us. If our collaborators, prospective collaborators or suppliers are not satisfied
with  our  financial  resources  and  stability,  it  could  have  a  material  adverse  effect  on  our  ability  to  develop  our  drug  candidates,  enter  into  licenses  or  other
agreements and on our business, financial condition or results of operations.

The agreements we entered into with Elan involve conflicts of interest and therefore may have materially disadvantageous terms to us.

We entered into certain agreements with Elan in connection with our separation from Elan, which set forth the main terms of the separation and provided a
framework for our initial relationship with Elan. These agreements may have terms that are materially disadvantageous to us or are otherwise not as favorable as
those that might be negotiated between unaffiliated third parties. In December 2013, Elan was acquired by Perrigo Company plc (“Perrigo”), and in February 2014
Perrigo caused Elan to sell all of its shares of Prothena in an underwritten offering. As a result of the acquisition of Elan by Perrigo and the subsequent sale of all of
its shares of Prothena, Perrigo may be less willing to collaborate with us in connection with the agreements to which we and Elan are a party and other matters.

We may be adversely affected by earthquakes or other natural disasters.

Our  key  facility  and  almost  all  of  our  operations  are  in  the  San  Francisco  Bay  Area  of  Northern  California,  which  in  the  past  has  experienced  severe
earthquakes. If an earthquake, other natural disaster, or similar event were to occur and prevent us from using all or a significant portion of those operations or
local critical infrastructure, or that otherwise disrupts our operations, it could be difficult or impossible for us to continue our business for a substantial period of
time. We have disaster recovery and business continuity plans, but they may prove to be inadequate in the event of a natural disaster or similar event. We may
incur substantial expenses if our disaster recovery and business continuity plans prove to be inadequate. We do not carry earthquake insurance. Furthermore, third
parties upon which we are materially dependent upon may be vulnerable to natural disasters or similar events.  Accordingly, such a natural disaster or similar event
could have an adverse effect on our business, financial condition, or results of operations.

We may experience breaches or similar disruptions of our information technology systems or data.

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Our business is increasingly dependent on critical,  complex, and interdependent information  technology systems to support business processes as well as
internal and external communications. Despite the implementation of security measures, our internal computer systems, and those of our current and any future
CROs  and  other  contractors,  consultants,  and  collaborators,  are  vulnerable  to  damage  from  cyberattacks,  “phishing”  attacks,  computer  viruses,  unauthorized
access,  natural  disasters,  terrorism,  war,  and  telecommunication  or  electrical  failures.  Attacks  upon  information  technology  systems  are  increasing  in  their
frequency, levels of persistence, sophistication, and intensity, and are being conducted by sophisticated and organized groups and individuals with a wide range of
motives and expertise. As a result of the COVID-19 pandemic, we may also face increased cybersecurity risks due to our reliance on internet technology and the
number of our employees who are working remotely, which may create additional opportunities for cybercriminals to exploit vulnerabilities. Furthermore, because
the techniques used to obtain unauthorized access to or to sabotage systems change frequently and often are not recognized until launched against a target, we may
be unable to anticipate these techniques or implement adequate preventative measures. We may also experience security breaches that may remain undetected for
an extended period. Any breakdown, malicious intrusion, or computer virus could result in the impairment of key business processes or breach of data security,
which could result in a material  disruption  of our development  programs and cause interruptions  in our business operations, whether due to a loss of our trade
secrets or other intellectual property or lead to unauthorized disclosure of personal data of our employees, third parties with which we do business, clinical trial
participants, or others. For example, the loss of clinical trial data from completed or future clinical trials could result in delays in our regulatory approval efforts
and significantly increase our costs to recover or reproduce the data. In addition, such a breach may require notification to governmental agencies, the media, or
individuals pursuant to applicable data privacy and security law and regulations. Such an event could have an adverse effect on our business, financial condition, or
results of operations. Such an event could have an adverse effect on our business, financial condition, or results of operations.

Changes in and failures to comply with U.S. and foreign privacy and data protection laws, regulations and standards may adversely affect our business,
operations, and financial performance.

We and our partners may be subject to federal, state, and foreign data privacy and security laws and regulations. The legislative and regulatory landscape for
privacy and data protection continues to evolve, and there has been an increasing focus on privacy and data protection issues, which may affect our business and
may increase our compliance costs and exposure to liability. In the United States, numerous federal and state laws and regulations, including state security breach
notification  laws,  federal  and  state  health  information  privacy  laws  (including  HIPAA,  as  amended  by  the  Health  Information  Technology  for  Economic  and
Clinical Health Act, and regulations promulgated thereunder), and federal and state consumer protection laws, govern the collection, use, disclosure, and protection
of  personal  information.  Each  of  these  laws  is  subject  to  varying  interpretations  by  courts  and  government  agencies,  creating  complex  compliance  issues.  For
example,  the  California  Consumer  Privacy  Act  (the  “CCPA”)  went  into  effect  January  1,  2020.  The  CCPA,  among  other  things,  imposes  new  data  privacy
obligations  on  covered  companies  and  provides  expanded  privacy  rights  to  California  residents,  including  the  right  to  access,  delete,  and  opt  out  of  certain
disclosures of their information. The CCPA provides for civil penalties for violations, as well as a private right of action with statutory damages for certain data
breaches, which may increase the frequency and likelihood of data breach litigation. Although the law includes limited exceptions for health-related information,
including  clinical  trial  data,  such  exceptions  may  not  apply  to  all  of  our  operations  and  processing  activities.  Further,  the  California  Privacy  Rights  Act  (the
“CPRA”), recently passed in California. The CPRA will impose additional data protection obligations on covered businesses, including additional consumer rights
processes, limitations on data uses, new audit requirements for higher risk data, and opt outs for certain uses of sensitive data. It will also create a new California
data protection agency authorized to issue substantive regulations and could result in increased privacy and information security enforcement. The majority of the
provisions will go into effect on January 1, 2023, and additional compliance investment and potential business process changes may be required. In addition, the
CCPA  has  prompted  a  number  of  proposals  for  new  federal  and  state  privacy  legislation  that,  if  passed,  could  increase  our  potential  liability,  increase  our
compliance  costs  and  adversely  affect  our  business.  If  we  fail  to  comply  with  applicable  laws  and  regulations  we  could  be  subject  to  penalties  or  sanctions,
including criminal penalties if we knowingly obtain or disclose individually identifiable health information from a covered entity in a manner that is not authorized
or permitted by HIPAA or applicable state laws.

We are also or may become subject to rapidly evolving data protection laws, rules, and regulations in foreign jurisdictions. For example, the European Union
General  Data  Protection  Regulation  (the  “GDPR”)  governs  certain  collection  and  other  processing  activities  involving  personal  data  about  individuals  in  the
European Economic Area. Among other things, the GDPR imposes requirements regarding the security of personal data, the rights of data subjects to access and
delete  personal  data,  requires  having  lawful  bases  on  which  personal  data  can  be  processed  and  transferred  outside  of  the  European  Economic  Area,  requires
changes to informed consent practices, and requires more detailed notices for clinical trial participants and investigators. In addition, the GDPR imposes substantial
fines for breaches and violations (up to the greater of €20 million or 4% of our annual global revenue). The GDPR also confers a private right of action on data
subjects and consumer associations to lodge complaints with supervisory authorities, seek judicial remedies, and obtain compensation for damages resulting from

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violations of the GDPR. Relatedly, following the United Kingdom’s withdrawal from the European Economic Area and the EU, and the expiry of the transition
period,  companies  have  to  comply  with  the  GDPR  and  the  GDPR  as  incorporated  into  United  Kingdom  national  law,  the  latter  regime  having  the  ability  to
separately fine up to the greater of £17.5 million or 4% of global turnover. The relationship between the United Kingdom and the EU in relation to certain aspects
of  data  protection  law  remains  unclear,  for  example,  around  how  data  can  lawfully  be  transferred  between  each  jurisdiction,  which  exposes  us  to  further
compliance risk. Pursuant to the EU-UK Trade and Cooperation Agreement of December 24, 2020, transfers of personal data from the EU to the United Kingdom
may continue to take place without a need for additional safeguards during a further transition period, to expire on (i) the date on which an adequacy decision with
respect to the United Kingdom is adopted by the EU Commission; or (ii) the expiry of four months, which shall be extended by a further two months unless either
the EU or the United Kingdom objects. It remains unclear whether the EU Commission will adopt an adequacy decision with respect to the United Kingdom. In the
absence of such decision after the expiry of the additional transition period, companies may need to put in place additional safeguards for transfers of personal data
from the EU to the United Kingdom, such as standard contractual clauses approved by the EU Commission.

Compliance  with  U.S.  and  foreign  data  privacy  and  security  laws,  rules,  and  regulations  could  require  us  to  take  on  more  onerous  obligations  in  our
contracts, require us to engage in costly compliance exercises, restrict our ability to collect, use and disclose data, or in some cases, impact our or our partners’ or
suppliers’ ability to operate in certain jurisdictions. Each of these constantly evolving laws can be subject to varying interpretations. If we fail to comply with any
such laws, rules, or regulations, we may face government investigations and/or enforcement actions, fines, civil or criminal penalties, private litigation, or adverse
publicity that could adversely affect our business, financial condition, and results of operations.

Risks Related to the Discovery, Development, and Regulatory Approval of Drug Candidates

Our success is largely dependent on the success of our research and development programs. Our drug candidates are in various stages of development and we
may not be able to successfully discover, develop, obtain regulatory approval for, or commercialize any drug candidates.

The  success  of  our  business  depends  substantially  upon  our  ability  to  discover,  develop,  obtain  regulatory  approval  for  and  commercialize  our  drug
candidates successfully. Our research and development programs are prone to the significant and likely risks of failure inherent in drug development, which can
result from the failure of the drug candidate to be sufficiently effective, the safety profile of the drug candidate, a clinical trial that is not sufficiently enrolled or
powered or adequately designed to detect a drug effect, or other reasons. We intend to continue to invest most of our time and financial resources in our research
and development programs.

There is no assurance that the results of the Phase 3 clinical trial for birtamimab expected to commence in 2021, the Phase 2 clinical trial for prasinezumab,

the Phase 2b clinical trial for prasinezumab expected to commence in 2021, the Phase 2/3 clinical trial for PRX004 expected to commence in 2021, the Phase 1
clinical trial for PRX005 expected to commence in 2021, and the Phase 1 clinical trial for PRX012 expected to commence in 2022 will support further
development of these drug candidates. In addition, we currently do not, and may never, have any other drug candidates in clinical trials, and we have not identified
drug candidates for many of our research programs.

Before obtaining regulatory approvals for the commercial sale of any drug candidate for a target indication, we must demonstrate with substantial evidence
gathered in adequate and well-controlled clinical trials that the drug candidate is safe and effective for use for that target indication. In the U.S., this must be done
to the satisfaction of the FDA; in the EU, this must be done to the satisfaction of the European Medicines Agency (the “EMA”); and in other countries this must be
done to the satisfaction of comparable regulatory authorities.

Satisfaction  of these  and other  regulatory  requirements  is  costly,  time  consuming,  uncertain,  and  subject  to  unanticipated  delays.  Despite  our efforts,  our

drug candidates may not:

•

•

offer improvement over existing treatment options;

be proven safe and effective in clinical trials; or

• meet applicable regulatory standards.

Positive results in nonclinical studies of a drug candidate may not be predictive of similar results in humans during clinical trials, and promising results from
early  clinical  trials  of  a  drug  candidate  may  not  be  replicated  in  later  clinical  trials.  Interim  results  of  a  clinical  trial  do  not  necessarily  predict  final  results.  A
number  of  companies  in  the  pharmaceutical  and  biotechnology  industries  have  suffered  significant  setbacks  in  late-stage  clinical  trials  even  after  achieving
promising results in

25

early-stage development. Accordingly, the results from completed nonclinical studies and early clinical trials for our drug candidates may not be predictive of the
results we may obtain in later stage studies or trials. Our nonclinical studies or clinical trials may produce negative or inconclusive results, and we may decide, or
regulators may require us, to conduct additional nonclinical studies or clinical trials, or to discontinue clinical trials altogether.

Furthermore, we have not marketed, distributed, or sold any products. Our success will, in addition to the factors discussed above, depend on the successful

commercialization of any drug candidates that obtain regulatory approval. Successful commercialization may require:

•

•

•

obtaining and maintaining commercial manufacturing arrangements with third-party manufacturers;

developing the marketing and sales capabilities, internal and/or in collaboration with pharmaceutical companies or contract sales organizations, to market
and sell any approved drug; and

acceptance of any approved drug in the medical community and by patients and third-party payers.

Many of these factors are beyond our control. We do not expect any of our drug candidates to be commercially available for several years and some or all

may never become commercially available. Accordingly, we may never generate revenues through the sale of products.

We have entered into collaborations with Roche and BMS and may enter into additional collaborations in the future, and we might not realize the anticipated
benefits of such collaborations.

Research, development, commercialization and/or strategic collaborations, including those that we have with Roche and BMS, are subject to numerous risks,

which include the following:

•

collaborators  may  have  significant  control  or  discretion  in  determining  the  efforts  and  resources  that  they  will  apply  to  a  collaboration,  and  might  not
commit sufficient efforts and resources or might misapply those efforts and resources;

• we may have limited influence or control over the approaches to research, development, and/or commercialization of products candidates in the territories

in which our collaboration partners lead research, development, and/or commercialization;

•

•

•

•

•

•

•

•

•

collaborators might not pursue research, development, and/or commercialization of collaboration drug candidates or might elect not to continue or renew
research, development, and/or commercialization programs based on nonclinical and/or clinical trial results, changes in their strategic focus due to the
acquisition of competing products, availability of funding, or other factors, such as a business combination that diverts resources or creates competing
priorities;

collaborators  might  delay,  provide  insufficient  resources  to,  or  modify  or  stop  research  or  clinical  development  for  collaboration  drug  candidates  or
require a new formulation of a drug candidate for clinical testing;

collaborators could develop or acquire products outside of the collaboration that compete directly or indirectly with our drug candidates or require a new
formulation of a drug candidate for nonclinical and/or clinical testing;

collaborators with sales, marketing, and distribution rights to one or more drug candidates might not commit sufficient resources to sales, marketing, and
distribution or might otherwise fail to successfully commercialize those drug candidates;

collaborators  might  not  properly  maintain  or  defend  our  intellectual  property  rights  or  might  use  our  intellectual  property  improperly  or  in  a  way  that
jeopardizes our intellectual property or exposes us to potential liability;

collaboration activities might result in the collaborator having intellectual property covering our activities or drug candidates, which could limit our rights
or ability to research, develop, and/or commercialize our drug candidates;

collaborators might not be in compliance with laws applicable to their activities under the collaboration, which could impact the collaboration or us;

disputes might arise between us and a collaborator that could cause a delay or termination of the collaboration or result in costly litigation that diverts
management attention and resources; and

collaborations might be terminated, which could result in a need for additional capital to pursue further research, development, and/or commercialization
of our drug candidates.

26

In  addition,  funding  provided  by  a  collaborator  might  not  be  sufficient  to  advance  drug  candidates  under  the  collaboration.  For  example,  although  BMS
(formerly Celgene) made a $100 million upfront payment to us and made a $50 million equity investment in us upon entering into the Collaboration Agreement,
we might need additional funding to advance drug candidates prior to when BMS decides whether to exercise its license rights to those drug candidates. We also
note that, on November 20, 2019, BMS acquired Celgene. BMS might take a different approach to our collaboration or determine not to continue that collaboration
whether for reasons related to that collaboration or otherwise.

If  a  collaborator  terminates  a  collaboration  or  a  program  under  a  collaboration,  including  by  failing  to  exercise  a  license  or  other  option  under  the
collaboration, whether because we fail to meet a milestone or otherwise, any potential revenue from the collaboration would be significantly reduced or eliminated.
For  example,  under  our  License  Agreement  with  Roche,  a  $60  million  clinical  milestone  payment  would  be  payable  upon  first  patient  dosed  in  the  Phase  2b
clinical trial for prasinezumab, which is expected to start in 2021. However, prior to the first patient dosed in such clinical trial, Roche may, at its sole discretion,
terminate  the  collaboration  and  not  dose  the  first  patient  in  such  clinical  trial  and  as  a  result,  would  not  owe  to  us  the  applicable  clinical  milestone  payment.
Another example, under our under our Collaboration Agreement with BMS, an $80 million option payment would be payable upon BMS’s exercise of U.S. rights
for  PRX005.  However,  BMS  may,  at  its  sole  discretion,  choose  not  to  exercise  its  option  to  such  U.S.  rights  for  PRX005  and  thus  would  not  owe  to  us  the
applicable  option  payment.  In  addition,  we  will  likely  need  to  either  secure  other  funding  to  advance  research,  development,  and/or  commercialization  of  the
relevant drug candidate or abandon that program, the development of the relevant drug candidate could be significantly delayed, and our cash expenditures could
increase significantly if we are to continue research, development, and/or commercialization of the relevant drug candidates.

Any  one  or  more  of  these  risks,  if  realized,  could  reduce  or  eliminate  future  revenue  from  drug  candidates  under  our  collaborations,  and  could  have  a

material adverse effect on our business, financial condition, results of operations, and/or growth prospects.

If clinical trials of our drug candidates are prolonged, delayed, suspended, or terminated, we may be unable to commercialize our drug candidates on a timely
basis, if at all, which would require us to incur additional costs and delay or prevent our receipt of any revenue from potential product sales.

We cannot predict whether we will encounter problems with the Phase 3 clinical trial for birtamimab expected to commence in 2021, the Phase 2 clinical
trial for prasinezumab, the Phase 2b clinical trial for prasinezumab expected to commence in 2021, the Phase 2/3 clinical trial for PRX004 expected to commence
in 2021, the Phase 1 clinical trial for PRX005 expected to commence in 2021, the Phase 1 clinical trial for PRX012 expected to commence in 2022, or any other
future clinical trials that will cause us or any regulatory authority to delay, suspend or terminate those clinical trials or delay the analysis of data derived from them.
A number of events, including any of the following, could delay the completion of our ongoing or planned clinical trials and negatively impact our ability to obtain
regulatory approval for, and to market and sell, a particular drug candidate:

•

•

•

•

•

•

•

•

conditions imposed on us by the FDA, the EMA, or other comparable regulatory authorities regarding the scope or design of our clinical trials;

delays  in obtaining,  or  our inability  to obtain,  required  approvals  from  institutional  review  boards (“IRBs”)  or other  reviewing  entities  at clinical  sites
selected for participation in our clinical trials;

insufficient supply or deficient quality of our drug candidates or other materials necessary to conduct our clinical trials;

delays in obtaining regulatory authority authorization for the conduct of our clinical trials;

lower than anticipated enrollment and/or retention rate of subjects in our clinical trials, which can be impacted by a number of factors, including size of
patient population, design of trial protocol, trial length, eligibility criteria, perceived risks and benefits of the drug candidate, patient proximity to trial
sites, patient referral practices of physicians, availability of other treatments for the relevant disease, and competition from other clinical trials;

slower than expected rates of events in trials with a composite primary endpoint that is event-based;

serious and unexpected drug-related side effects experienced by subjects in clinical trials; or

failure of our third-party contractors and collaborators to meet their contractual obligations to us or otherwise meet their development or other objectives
in a timely manner.

We are dependent upon Roche with respect to further development of prasinezumab. Under the terms of our collaboration with Roche, Roche is responsible

for that further development, including the conduct of the ongoing Phase 2 clinical trial and any future clinical trial of that drug candidate.

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Clinical trials may also be delayed or terminated as a result of ambiguous or negative data or results. In addition, a clinical trial may be delayed, suspended
or  terminated  by  us,  the  FDA,  the  EMA  or  other  comparable  regulatory  authorities,  the  IRBs  at  the  sites  where  the  IRBs  are  overseeing  a  trial,  or  the  safety
oversight committee overseeing the clinical trial at issue due to a number of factors, including:

•

•

•

•

•

•

•

failure to conduct the clinical trial in accordance with regulatory requirements or our clinical protocols;

inspection of the clinical trial operations or trial sites by the FDA, the EMA, or other regulatory authorities resulting in the imposition of a clinical hold on
or imposition of additional conditions for the conduct of the trial;

interpretation of data by the FDA, the EMA, or other regulatory authorities;

requirement by the FDA, the EMA, or other regulatory authorities to perform additional studies;

failure to achieve primary or secondary endpoints or other failure to demonstrate efficacy or adequate safety;

unforeseen safety issues; or

lack of adequate funding to continue the clinical trial.

Additionally, changes in regulatory requirements and guidance may occur and we may need to amend clinical trial protocols to reflect these changes.
Amendments may require us to resubmit our clinical trial protocols to regulatory authorities and IRBs for reexamination, which may impact the cost, timing, or
successful completion of a clinical trial.

We do not know whether our clinical trials will be conducted as planned, will need to be restructured, or will be completed on schedule, if at all. Delays in
our clinical trials will result in increased development costs for our drug candidates. In addition, if we experience delays in the completion of, or if we terminate,
any of our clinical trials, the commercial prospects for our drug candidates may be delayed or harmed and our ability to generate product revenues will be delayed
or jeopardized. Furthermore, many of the factors that cause, or lead to, a delay in the commencement or completion of clinical trials may also ultimately lead to the
denial of regulatory approval of a drug candidate.

The  regulatory  approval  processes  of  the  FDA,  the  EMA,  and  other  comparable  regulatory  authorities  are  lengthy,  time  consuming,  and  inherently
unpredictable, and if we are ultimately unable to obtain regulatory approval for our drug candidates, our business will be substantially harmed.

The time required to obtain approval by the FDA, the EMA, and other comparable regulatory authorities is inherently unpredictable but typically takes many
years  following  the  commencement  of  clinical  trials  and  depends  upon  numerous  factors,  including  the  substantial  discretion  of  the  regulatory  authorities.  In
addition, approval policies, regulations, or the type and amount of clinical data necessary to gain approval may change during the course of a drug candidate’s
clinical  development  and  may  vary  among  jurisdictions.  We  have  not  obtained  regulatory  approval  for  any  drug  candidate,  and  it  is  possible  that  none  of  our
existing drug candidates or any drug candidates we may seek to develop in the future will ever obtain regulatory approval.

Our drug candidates could fail to receive regulatory approval for many reasons, including the following:

•

the FDA, the EMA, or comparable regulatory authorities may disagree with the design, implementation, or conduct of our clinical trials;

• we may be unable to demonstrate to the satisfaction of the FDA, the EMA, or comparable regulatory authorities that a drug candidate is safe and effective

for its proposed indication;

•

the  results  of  clinical  trials  may  not  meet  the  level  of  statistical  significance  required  by  the  FDA,  the  EMA,  or  comparable  regulatory  authorities  for
approval;

• we may be unable to demonstrate that a drug candidate’s clinical and other benefits outweigh its safety risks;

•

•

•

the FDA, the EMA, or comparable regulatory authorities may disagree with our interpretation of data from nonclinical studies or clinical trials;

the data collected from clinical trials of our drug candidates may not be sufficient to support the submission of a Biologic License Application (“BLA”) to
the FDA, a Marketing Authorization Application (“MAA”) to the EMA, or similar applications to comparable regulatory authorities;

the FDA, the EMA, or comparable regulatory authorities may fail to approve the manufacturing processes or facilities of third-party manufacturers with
which we contract for clinical and commercial supplies; or

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•

the  approval  policies  or  regulations  of  the  FDA,  the  EMA,  or  comparable  regulatory  authorities  may  significantly  change  in  a  manner  rendering  our
clinical data insufficient for approval.

This lengthy approval process as well as the unpredictability of future clinical trial results may result in our failing to obtain regulatory approval to market

our drug candidates, which would significantly harm our business, results of operations and, growth prospects.

Separately, in response to the COVID-19 global pandemic, on March 10, 2020, the FDA announced its intention to postpone most inspections of foreign
manufacturing facilities and products through April 2020, and on March 18, 2020, the FDA temporarily postponed routine surveillance inspections of domestic
manufacturing  facilities.  Subsequently,  on  July  10,  2020,  the  FDA  announced  its  intention  to  resume  certain  on-site  inspections  of  domestic  manufacturing
facilities subject to a risk-based prioritization system. The FDA intends to use this risk-based assessment system to identify the categories of regulatory activity
that can occur within a given geographic area, ranging from mission critical inspections to resumption of all regulatory activities. Regulatory authorities outside the
United States may adopt similar restrictions or other policy measures in response to the COVID-19 pandemic, including providing guidance regarding the conduct
of clinical trials. If global health concerns continue to prevent the FDA or other regulatory authorities from conducting their regular inspections, or impact reviews
or  other  regulatory  activities,  it  could  significantly  impact  the  ability  of  the  FDA  or  other  regulatory  authorities  to  timely  review  and  process  our  regulatory
submissions, which could have a material adverse effect on our business.

In addition, even if we were to obtain approval, regulatory authorities may approve any of our drug candidates for fewer or more limited indications than we
request,  may  grant  approval  contingent  on  the  performance  of  costly  post-marketing  clinical  trials,  or  may  approve  a  drug  candidate  with  a  label  that  does  not
include the labeling claims necessary or desirable for the successful commercialization of that drug candidate. Any of the foregoing scenarios could materially
harm the commercial prospects for our drug candidates.

Even if our drug candidates receive regulatory approval in one country or jurisdiction, we may never receive approval or commercialize our products in other
countries or jurisdictions.

In order to market drug candidates in a particular country or jurisdiction, we must establish and comply with numerous and varying regulatory requirements
of that country or jurisdiction, including with respect to safety and efficacy. Approval procedures vary among countries and can involve additional product testing
and additional administrative review periods. The time required to obtain approval in other countries might differ from that required to obtain, for example, FDA
approval in the U.S. or EMA approval in the EU. The regulatory approval process in other countries may include all of the risks detailed above regarding FDA
approval in the U.S. and EMA approval in the EU as well as other risks. Regulatory approval in one country or jurisdiction does not ensure regulatory approval in
another country or jurisdiction, but a failure or delay in obtaining regulatory approval in one country may have a negative effect on the regulatory process in others.
Failure to obtain regulatory approval in one country or jurisdiction or any delay or setback in obtaining such approval would impair our ability to develop other
markets for that drug candidate.

Although we have obtained agreement with the FDA on a special protocol assessment (“SPA”), for our Phase 3 AFFIRM-AL trial of birtamimab, a SPA does
not guarantee approval of birtamimab or any other particular outcome from regulatory review.

On January 27, 2021, the FDA agreed to an SPA for our Phase 3 AFFIRM-AL clinical trial of birtamimab. The FDA’s SPA process is designed to facilitate
the FDA’s review and approval of drugs by allowing the FDA to evaluate proposed critical design features of certain clinical trials that are intended to form the
primary basis for determining a drug candidate’s efficacy and safety. Upon specific request by a clinical trial sponsor, the FDA will evaluate the study protocol and
statistical  analysis plan and respond to a sponsor’s questions regarding protocol design and scientific  and regulatory  requirements.  FDA aims to complete  SPA
reviews within 45 days of receipt of the request. The FDA ultimately assesses whether specific elements of the protocol design for the trial, such as entry criteria,
endpoints,  size,  duration,  and  planned  analyses,  are  acceptable  to  support  an  application  for  regulatory  approval  of  the  drug  candidate  with  respect  to  the
effectiveness  of  and  safety  for  the  indication  studied.  All  agreements  and  disagreements  between  the  FDA  and  the  sponsor  regarding  a  SPA  must  be  clearly
documented in an SPA letter or the minutes of a meeting between the sponsor and the FDA.

Although the FDA has agreed to the SPA for our Phase 3 AFFIRM-AL clinical trial, a SPA agreement does not guarantee approval of a drug candidate.
Even if the FDA agrees to the design, execution, and analysis proposed in a protocol reviewed under the SPA process, the FDA may revoke or alter its agreement
in certain circumstances. In particular, a SPA agreement is not binding on the FDA if public health concerns emerge that were unrecognized at the time of the SPA
agreement, other new scientific concerns regarding product safety or efficacy arise, the sponsor fails to comply with the agreed upon study protocol, or the relevant
data, assumptions, or information provided by the sponsor in a request for the SPA change or are found to be

29

false or to omit relevant facts. In addition, even after a SPA agreement is finalized, the SPA agreement may be modified, and such modification will be deemed
binding on the FDA review division, except under the circumstances described above, if the FDA and the sponsor agree in writing to the modification of the study
protocol  and/or  statistical  analysis  plan.  Generally,  such  modification  is  intended  to  improve  the  study.  The  FDA  retains  significant  latitude  and  discretion  in
interpreting the terms of the SPA agreement and the data and results from any study that is the subject of the SPA agreement.

Moreover, if the FDA revokes or alters its agreement under the SPA, or interprets the data collected from the clinical trial differently than the sponsor, the

FDA may not deem the data sufficient to support an application for regulatory approval.

Both before and after marketing approval, our drug candidates are subject to ongoing regulatory requirements and continued regulatory review, and if we fail
to comply with these continuing requirements, we could be subject to a variety of sanctions and the sale of any approved products could be suspended.

Both  before  and  after  regulatory  approval  to  market  a  particular  drug  candidate,  adverse  event  reporting,  manufacturing,  labeling,  packaging,  storage,
distribution,  advertising,  promotion,  record  keeping,  and  reporting  related  to  the  product  are  subject  to  extensive,  ongoing  regulatory  requirements.  These
requirements include submissions of safety and other post-marketing information and reports, as well as continued compliance with current good manufacturing
practice (“cGMP”) requirements and current good clinical practice (“cGCP”) requirements for any clinical trials that we conduct. Any regulatory approvals that we
receive for our drug candidates may also be subject to limitations on the approved indicated uses for which the product may be marketed or to the conditions of
approval, or contain requirements for potentially costly post-marketing testing, including Phase 4 clinical trials, and surveillance to monitor the safety and efficacy
of the drug candidate. Later discovery  of previously unknown problems with a product, including adverse events of unanticipated  severity or frequency,  or not
previously  observed  in  clinical  trials,  or  problems  with  our  third-party  manufacturers  or  manufacturing  processes,  or  failure  to  comply  with  the  regulatory
requirements of the FDA, the EMA, or other comparable regulatory authorities could subject us to administrative or judicially imposed sanctions, including:

•

restrictions on the marketing of our products or their manufacturing processes;

• warning letters;

•

•

•

•

•

•

•

•

•

civil or criminal penalties;

fines;

injunctions;

product seizures or detentions;

import or export bans;

voluntary or mandatory product recalls and related publicity requirements;

suspension or withdrawal of regulatory approvals;

total or partial suspension of production; and

refusal to approve pending applications for marketing approval of new products or supplements to approved applications.

The policies of the FDA, the EMA, or other comparable regulatory authority may change and additional government regulations may be enacted that could
prevent, limit or delay regulatory approval of our drug candidates. If we are slow or unable to adapt to changes in existing requirements or the adoption of new
requirements or policies, or if we are not able to maintain regulatory compliance, we may lose any marketing approval that we may have obtained, which would
adversely affect our business, prospects and ability to achieve or sustain profitability.

If side effects are identified during the time our drug candidates are in development, or, if they are approved by applicable regulatory authorities, after they are
on the market, we may choose to or be required to perform lengthy additional clinical trials, discontinue development of the affected drug candidate, change
the labeling of any such products, or withdraw any such products from the market, any of which would hinder or preclude our ability to generate revenues.

Undesirable side effects caused by our drug candidates could cause us or regulatory authorities to interrupt, delay or halt clinical trials and could result in a
more restrictive  label or the delay or denial of regulatory approval by the FDA, the EMA, or other comparable regulatory authorities. Drug-related side effects
could affect patient recruitment or the ability of enrolled patients to complete a trial or result in potential product liability claims. Any of these occurrences may
harm our business, financial condition and prospects significantly. Even if any of our drug candidates receives marketing approval, as greater

30

numbers of patients use a drug following its approval, an increase in the incidence or severity of side effects or the incidence of other post-approval problems that
were not seen or anticipated during pre-approval clinical trials could result in a number of potentially significant negative consequences, including:

•

•

regulatory authorities may withdraw their approval of the product;

regulatory  authorities  may  require  the  addition  of  labeling  statements,  such  as  contraindications,  warnings,  or  precautions;  or  impose  additional  safety
monitoring or reporting requirements;

• we may be required to change the way the product is administered, or to conduct additional clinical trials;

• we could be sued and held liable for harm caused to patients; and

•

our reputation may suffer.

Any of these events could substantially increase the costs and expenses of developing, commercializing and marketing any such drug candidates or could

harm or prevent sales of any approved products.

We deal with hazardous materials and must comply with environmental laws and regulations which can be expensive and restrict how we do business.

Some of our research and development activities involve the controlled storage, use, and disposal of hazardous materials. We are subject to U.S. federal,
state,  local,  and  other  countries’  and  jurisdictions’  laws  and  regulations  governing  the  use,  manufacture,  storage,  handling,  and  disposal  of  these  hazardous
materials. Although we believe that our safety procedures for the handling and disposing of these materials comply with the standards prescribed by these laws and
regulations, we cannot eliminate the risk of accidental contamination or injury from these materials. In the event of an accident, state or federal authorities may
curtail our use of these materials, and we could be liable for any civil damages that result, which may exceed our financial resources and may seriously harm our
business. Because we believe that our laboratory and materials handling policies and practices sufficiently mitigate the likelihood of materials liability or third-
party claims, we currently carry no insurance covering such claims. An accident could damage, or force us to shut down, our operations.

Risks Related to the Commercialization of Our Drug Candidates

Even if any of our drug candidates receives regulatory approval, if such approved product does not achieve broad market acceptance, the revenues that we
generate from sales of the product will be limited.

Even  if  any  drug  candidates  we  may  develop  or  acquire  in  the  future  obtain  regulatory  approval,  they  may  not  gain  broad  market  acceptance  among
physicians, healthcare payers, patients and the medical community. The degree of market acceptance for any approved drug candidate will depend on a number of
factors, including:

•

•

•

•

•

•

•

•

the indication and label for the product and the timing of introduction of competitive products;

demonstration of clinical safety and efficacy compared to other products;

prevalence, frequency, and severity of adverse side effects;

availability of coverage and adequate reimbursement from managed care plans and other third-party payers;

convenience and ease of administration; 

cost-effectiveness;

other potential advantages of alternative treatment methods; and

the effectiveness of marketing and distribution support of the product.

Consequently, even if we discover, develop, and commercialize a product, the product may fail to achieve broad market acceptance and we may not be able

to generate significant revenue from the product.

The success of prasinezumab in the United States, if approved, will be dependent upon the strength and performance of our collaboration with Roche. If we
fail  to  maintain  our  existing  collaboration  with  Roche,  such  termination  would  likely  have  a  material  adverse  effect  on  our  ability  to  develop  and
commercialize  prasinezumab  and  our business.  Furthermore,  if  we opt  out of  profit  and loss  sharing with Roche, our revenues  from  prasinezumab  will  be
reduced.

31

The success of sales of prasinezumab in the U.S. will be dependent on the ability of Roche to successfully develop in collaboration with us, and launch and
commercialize prasinezumab, if approved by the FDA, pursuant to the License Agreement we entered into in December 2013. Our collaboration with Roche is
complex,  particularly  with  respect  to  future  U.S.  commercialization  of  prasinezumab,  with  respect  to  financial  provisions,  allocations  of  responsibilities,  cost
estimates, and the respective rights of the parties in decision making. Accordingly, significant aspects of the development and commercialization of prasinezumab
require  Roche  to  execute  its  responsibilities  under  the  arrangement,  or  require  Roche’s  agreement  or  approval,  prior  to  implementation,  which  could  cause
significant delays that may materially impact the potential success of prasinezumab in the U.S. In addition, Roche may under some circumstances independently
develop products that compete with prasinezumab, or Roche may decide to not commit sufficient resources to the development, commercialization, marketing and
distribution  of  prasinezumab.  If  we  are  not  able  to  collaborate  effectively  with  Roche  on  plans  and  efforts  to  develop  and  commercialize  prasinezumab,  our
business could be materially adversely affected.

Furthermore, the terms of the License Agreement provide that Roche has the ability to terminate such arrangement for any reason after the first anniversary
of the License Agreement at any time upon 90 days’ notice (if prior to first commercial sale) or 180 days’ notice (if after first commercial sale). For example, even
if prasinezumab was approved by the FDA, Roche may determine that the outcomes of clinical trials made prasinezumab a less attractive commercial product and
terminate  our  collaboration.  If  the  License  Agreement  is  terminated,  our  business  and  our  ability  to  generate  revenue  from  sales  of  prasinezumab  could  be
substantially  harmed  as  we  will  be  required  to  develop,  commercialize,  and  build  our  own  sales  and  marketing  organization,  or  enter  into  another  strategic
collaboration in order to develop and commercialize prasinezumab in the U.S. Such efforts may not be successful and, even if successful, would require substantial
time and resources to carry out.

The manner in which Roche launches prasinezumab, if approved by the FDA, including the timing of launch and potential pricing, will have a significant
impact on the ultimate success of prasinezumab in the U.S, and the success of the overall commercial arrangement with Roche. If launch of commercial sales of
prasinezumab in the U.S. by Roche is delayed or prevented, our revenue will suffer and our stock price may decline. Further, if launch and resulting sales by Roche
are not deemed successful, our business would be harmed and our stock price may decline. Any lesser effort by Roche in its prasinezumab sales and marketing
efforts may result in lower revenue and thus lower profits with respect to the U.S. The outcome of Roche’s commercialization efforts in the U.S. could also have a
negative effect on investors’ perception of potential sales of prasinezumab outside of the U.S., which could also cause a decline in our stock price.

Furthermore,  pursuant  to  the  License  Agreement,  we  are  responsible  for  30%  of  all  development  and  commercialization  costs  for  prasinezumab  for  the
treatment of Parkinson’s disease in the U.S., and for any future Licensed Products and/or indications that we opt to co-develop, in each case unless we elect to opt
out of profit and loss sharing. If we elect to opt out of profit and loss sharing, we will instead receive sales milestones and royalties, and our revenue, if any, from
prasinezumab will be reduced.

Our  right  to  co-develop  prasinezumab  and  other  Licensed  Products  under  the  License  Agreement  will  terminate  if  we  commence  certain  studies  for  a
competitive product that treats Parkinson’s disease or other indications that we opted to co-develop. In addition, our right to co-promote prasinezumab and other
Licensed Products will terminate if we commence a Phase 3 study for a competitive product that treats Parkinson’s disease.

Moreover,  under  the  terms  of  the  License  Agreement,  we  rely  on  Roche  to  provide  us  estimates  of  their  costs,  revenue,  and  revenue  adjustments  and
royalties, which estimates we use in preparing our quarterly and annual financial reports. If the underlying assumptions on which Roche’s estimates were based
prove to be incorrect, actual results or revised estimates supplied by Roche that are materially different from the original estimates could require us to adjust the
estimates included in our reported financial results. If material, these adjustments could require us to restate previously reported financial results, which could have
a negative effect on our stock price.

Our ability to receive any significant revenue from prasinezumab will be dependent on Roche’s efforts and our participation in profit and loss sharing, and
may result in lower levels of income than if we marketed or developed our drug candidates entirely on our own. Roche may not fulfill its obligations or carry out
marketing activities for prasinezumab as diligently as we would like. We could also become involved in disputes with Roche, which could lead to delays in or
termination  of  development  or  commercialization  activities  and  time-consuming  and  expensive  litigation  or  arbitration.  If  Roche  terminates  or  breaches  the
License  Agreement,  or  otherwise  decides  not  to  complete  its  obligations  in  a  timely  manner,  the  chances  of  successfully  developing,  commercializing,  or
marketing prasinezumab would be materially and adversely affected.

Outside of the United States, we are solely dependent on the efforts and commitments of Roche, either directly or through third parties, to further develop and,
if prasinezumab is approved by applicable regulatory authorities, commercialize

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prasinezumab.  If  Roche’s  efforts  are  unsuccessful,  our  ability  to  generate  future  product  sales  from  prasinezumab  outside  the  United  States  would  be
significantly reduced.

Under  our  License  Agreement,  outside  of  the  U.S.,  Roche  has  responsibility  for  developing  and  commercializing  prasinezumab  and  any  future  Licensed
Products  targeting  α-synuclein.  As  a  consequence,  any  progress  and  commercial  success  outside  of  the  U.S.  is  dependent  solely  on  Roche’s  efforts  and
commitment to the program. For example, Roche may delay, reduce, or terminate development efforts relating to prasinezumab outside of the U.S., or under some
circumstances independently develop products that compete with prasinezumab, or decide not to commit sufficient resources to the commercialization, marketing,
and distribution of prasinezumab.

In the event that Roche does not diligently develop and commercialize prasinezumab, the License Agreement provides us the right to terminate the License
Agreement in connection with a material breach uncured for 90 days after notice thereof. However, our ability to enforce the provisions of the License Agreement
so as to obtain meaningful recourse within a reasonable timeframe is uncertain. Further, any decision to pursue available remedies including termination would
impact the potential success of prasinezumab, including inside the U.S., and we may choose not to terminate as we may not be able to find another partner and any
new collaboration likely will not provide comparable financial terms to those in our arrangement with Roche. In the event of our termination, this may require us to
develop and commercialize prasinezumab on our own, which is likely to result in significant additional expense and delay. Significant changes in Roche’s business
strategy,  resource  commitment  and  the  willingness  or  ability  of  Roche  to  complete  its  obligations  under  our  arrangement  could  materially  affect  the  potential
success of the drug candidate. Furthermore, if Roche does not successfully develop and commercialize prasinezumab outside of the U.S., our potential to generate
future revenue outside of the U.S. would be significantly reduced.

If  we  are  unable  to  establish  sales  and  marketing  capabilities  or  enter  into  agreements  with  third  parties  to  market  and  sell  approved  products,  we  may  be
unable to generate product revenue.

We do not currently have a fully-scaled organization for the sales, marketing, and distribution of pharmaceutical products. In order to market any products
that may be approved by the FDA, the EMA, or other comparable regulatory authorities, we must build our sales, marketing, managerial, and other non-technical
capabilities or make arrangements with third parties to perform these services.

We  have  entered  into  the  License  Agreement  with  Roche  for  the  development  of  prasinezumab  and  may  develop  our  own  sales  force  and  marketing
infrastructure to co-promote prasinezumab in the U.S. for the treatment of Parkinson’s disease and any future Licensed Products approved for Parkinson’s disease
in  the  U.S.  If  we  exercise  our  co-promotion  option  and  are  unable  to  develop  our  own  sales  force  and  marketing  infrastructure  to  effectively  commercialize
prasinezumab  or  other  Licensed  Products,  our  ability  to  generate  additional  revenue  from  potential  sales  of  prasinezumab  or  such  products  in  the  U.S.  may  be
harmed. In addition, our right to co-promote prasinezumab and other Licensed Products will terminate if we commence a Phase 3 study for a competitive product
that treats Parkinson’s disease.

For any other products that may be approved, if we are unable to establish adequate sales, marketing, and distribution capabilities, whether independently or

with third parties, we may not be able to generate product revenue and may not become profitable.

If  government  and  third-party  payers  fail  to  provide  coverage  and  adequate  reimbursement  rates  for  any  of  our  drug  candidates  that  receive  regulatory
approval, our revenue and prospects for profitability will be harmed.

In both U.S. and non-U.S. markets, our sales of any future products will depend in part upon the availability of reimbursement from third-party payers. Such
third-party  payers  include  government  health  programs  such  as  Medicare,  managed  care  providers,  private  health  insurers,  and  other  organizations.  There  is
significant uncertainty related to the third-party coverage and reimbursement of newly approved drugs. Coverage and reimbursement may not be available for any
drug that we or our collaborators commercialize and, even if these are available, the level of reimbursement may not be satisfactory. Third-party payers often rely
upon Medicare coverage policy and payment limitations in setting their own reimbursement policies. Third-party payers are also increasingly attempting to contain
healthcare costs by demanding price discounts or rebates limiting both coverage and the amounts that they will pay for new drugs, and, as a result, they may not
cover or provide adequate payment for our drug candidates. We might need to conduct post-marketing studies in order to demonstrate the cost-effectiveness of any
future products to such payers’ satisfaction. Such studies might require us to commit a significant amount of management time and financial and other resources.
Our future products might not ultimately be considered cost-effective. Adequate third-party reimbursement might not be available to enable us to maintain price
levels  sufficient  to  realize  an  appropriate  return  on  investment  in  product  development.  If  coverage  and  adequate  reimbursement  are  not  available  or
reimbursement is available only to limited levels, we or our collaborators may not be able to successfully commercialize any drug candidates for which marketing
approval is obtained.

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The  regulations  that  govern  marketing  approvals,  pricing,  coverage,  and reimbursement  for  new drugs  vary widely  from  country  to  country.  Current  and
future legislation may significantly change the approval requirements in ways that could involve additional costs and cause delays in obtaining approvals. Some
countries require approval of the sale price of a drug before it can be marketed. In many countries, the pricing review period begins after marketing or licensing
approval  is  granted.  In  some  countries,  prescription  pharmaceutical  pricing  remains  subject  to  continuing  governmental  control  even  after  initial  approval  is
granted. As a result, we or our collaborators might obtain marketing approval for a drug in a particular country, but then be subject to price regulations that delay
commercial launch of the drug, possibly for lengthy time periods, and negatively impact our ability to generate revenue from the sale of the drug in that country.
Adverse pricing limitations may hinder our ability to recoup our investment in one or more drug candidates, even if our drug candidates obtain marketing approval.

U.S. and other governments continue to propose and pass legislation designed to reduce the cost of healthcare. In the U.S., we expect that there will continue
to be federal  and state  proposals to implement  similar  governmental  controls.  In addition, recent  changes  in the Medicare  program  and increasing  emphasis  on
managed care in the U.S. will continue to put pressure on pharmaceutical product pricing. For example, in 2010, the U.S. Patient Protection and Affordable Care
Act,  as  amended  by  the  U.S.  Health  Care  and  Education  Reconciliation  Act  (collectively,  the  “ACA”),  was  enacted.  The  ACA  substantially  changed  the  way
healthcare  is  financed  by  both  governmental  and  private  insurers  and  significantly  affects  the  pharmaceutical  industry.  Among  the  provisions  of  the  ACA  of
importance to the pharmaceutical industry are the following:

•

•

•

•

•

•

•

•

•

•

•

an annual, nondeductible fee on any entity that manufactures or imports certain branded prescription drugs and biologic agents, apportioned among these
entities according to their market share in certain government healthcare programs;

an  increase  in  the  minimum  rebates  a  manufacturer  must  pay  under  the  U.S.  Medicaid  Drug  Rebate  Program  to  23.1%  and  13.0%  of  the  average
manufacturer price for branded and generic drugs, respectively;

expansion of healthcare fraud and abuse laws, including the U.S. False Claims Act and the U.S. Anti-Kickback Statute, new government investigative
powers and enhanced penalties for non-compliance;

a  new  Medicare  Part  D  coverage  gap  discount  program,  under  which  manufacturers  must  now  agree  to  offer  70  percent  point-of-sale  discounts  off
negotiated  prices  of  applicable  brand  drugs  to  eligible  beneficiaries  during  their  coverage  gap  period,  as  a  condition  for  the  manufacturer’s  outpatient
drugs to be covered under Medicare Part D;

extension of manufacturers’ Medicaid rebate liability to covered drugs dispensed to individuals who are enrolled in Medicaid managed care organizations;

expansion of eligibility criteria for Medicaid programs by, among other things, allowing states to offer Medicaid coverage to additional individuals and by
adding  new  mandatory  eligibility  categories  for  certain  individuals  with  income  at  or  below  133%  of  the  federal  poverty  level,  thereby  potentially
increasing a manufacturer’s Medicaid rebate liability;

a licensure framework for follow-on biologic products;

expansion of the entities eligible for discounts under the Public Health Service pharmaceutical pricing program;

new requirements under the federal Open Payments program and its implementing regulations;

a new requirement to annually report drug samples that manufacturers and distributors provide to physicians; and

a new Patient-Centered Outcomes Research Institute to oversee, identify priorities in, and conduct comparative clinical effectiveness research, along with
funding for such research.

In addition, other legislative changes have been proposed and adopted since the ACA was enacted. These changes include aggregate reductions to Medicare
payments  to  providers  of  up  to  2%  per  fiscal  year,  which  went  into  effect  in  2013  and  will  stay  in  effect  through  2030,  with  the  exception  of  a  temporary
suspension from May 1, 2020, through March 31, 2021, unless additional congressional action is taken. In 2013, the U.S. American Taxpayer Relief Act of 2012,
among other things, further reduced Medicare payments to several types of providers and increased the statute of limitations period for the government to recover
overpayments to providers from three to five years. These new laws may result in additional reductions in Medicare and other healthcare funding, which could
have a material adverse effect on customers for our drugs, if approved, and, accordingly, our financial operations.

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Since its enactment, the U.S. federal government has delayed or suspended implementation of certain provisions of the ACA. In addition, there have been
judicial and Congressional challenges to certain aspects of the ACA, and we expect there will be additional challenges and amendments to the ACA in the future. It
is  unclear  how  other  efforts  to  challenge,  repeal,  or  replace  the  ACA  will  impact  the  law.  The  ultimate  content,  timing,  or  effect  of  any  healthcare  reform
legislation on the U.S. healthcare industry is unclear.

We expect that other healthcare reform measures that may be adopted in the future may result in more rigorous coverage criteria and in additional downward
pressure on the price that we receive for any approved drug. Legislation and regulations affecting the pricing of pharmaceuticals might change before our drug
candidates are approved for marketing. Any reduction in reimbursement from Medicare or other government healthcare programs may result in a similar reduction
in  payments  from  private  payers.  The  implementation  of  cost  containment  measures  or  other  healthcare  reforms  may  prevent  us  from  being  able  to  generate
revenue, attain profitability or commercialize our drugs.

There can be no assurance that our drug candidates, if they are approved for sale in the U.S. or in other countries, will be considered medically reasonable
and necessary for a specific indication, that they will be considered cost-effective by third-party payers, that coverage or an adequate level of reimbursement will
be available, or that third-party payers’ reimbursement policies will not adversely affect our ability to sell our drug candidates profitably if they are approved for
sale.

The  markets  for  our  drug  candidates  are  subject  to  intense  competition.  If  we  are  unable  to  compete  effectively,  our  drug  candidates  may  be  rendered
noncompetitive or obsolete.

The research, development, and commercialization of new drugs is highly competitive. We will face competition with respect to all drug candidates we may
develop  or  commercialize  in  the  future  from  pharmaceutical  and  biotechnology  companies  worldwide.  The  key  factors  affecting  the  success  of  any  approved
product  will  be  its  indication,  label,  efficacy,  safety  profile,  drug  interactions,  method  of  administration,  pricing,  coverage,  reimbursement,  and  level  of
promotional activity relative to those of competing drugs.

Furthermore, many large pharmaceutical and biotechnology companies, academic institutions, governmental agencies, and other public and private research
organizations are pursuing the development of novel drugs that target the same indications we are targeting with our research and development program. We face,
and expect to continue to face, intense and increasing competition as new products enter the market and advanced technologies become available. Many of our
competitors have:

•

significantly  greater  financial,  technical  and  human  resources  than  we  have  and  may  be  better  equipped  to  discover,  develop,  manufacture,  and
commercialize drug candidates;

• more  extensive  experience  in  nonclinical  testing  and  clinical  trials,  obtaining  regulatory  approvals,  and  manufacturing  and  marketing  pharmaceutical

products;

•

•

drug candidates that have been approved or are in late-stage clinical development; and/or

collaborative arrangements in our target markets with leading companies and research institutions.

Competitive products may render our research and development program obsolete or noncompetitive before we can recover the expenses of developing and
commercializing  our  drug  candidates.  Furthermore,  the  development  of  new  treatment  methods  and/or  the  widespread  adoption  or  increased  utilization  of  any
vaccine  or  development  of  other  products  or  treatments  for  the  diseases  we  are  targeting  could  render  any  of  our  drug  candidates  noncompetitive,  obsolete  or
uneconomical. If we successfully develop and obtain approval for a drug candidate, we will face competition based on the safety and effectiveness of the approved
product,  the  timing  of  its  entry  into  the  market  in  relation  to  competitive  products  in  development,  the  availability  and  cost  of  supply,  marketing  and  sales
capabilities, coverage, reimbursement, price, patent position and other factors. Even if we successfully develop drug candidates but those drug candidates do not
achieve and maintain market acceptance, our business will not be successful.

Our drug candidates for which we intend to seek approval as biologic products may face competition sooner than anticipated.

Our current drug candidates are regulated by the FDA as biologic products and we intend to seek approval for these products pursuant to the BLA pathway.
The  U.S.  Biologics  Price  Competition  and  Innovation  Act  of  2009  (the  “BPCIA”)  created  an  abbreviated  pathway  for  the  approval  of  biosimilar  and
interchangeable  biologic  products.  The  abbreviated  regulatory  pathway  establishes  legal  authority  for  the  FDA  to  review  and  approve  biosimilar  biologics,
including the possible designation of a biosimilar as “interchangeable” based on its similarity to an existing brand product. Under the BPCIA, an application for a
biosimilar product cannot be approved by the FDA until 12 years after the original branded product was

35

approved under a BLA. The law is complex and is still being interpreted and implemented by the FDA. Any processes adopted by the FDA to implement BPCIA
could have a material adverse effect on the future commercial prospects for our biologic products.

We believe that any of our drug candidates approved as a biologic product under a BLA should qualify for the 12-year period of exclusivity. However, there
is a risk that this exclusivity could be shortened due to congressional action or otherwise, or that the FDA will not consider our drug candidates to be reference
products for competing products, potentially creating the opportunity for generic competition sooner than anticipated. Moreover, the extent to which a biosimilar,
once approved, will be substituted for any one of our reference products in a way that is similar to traditional generic substitution for non-biologic products is not
yet clear, and will depend on a number of marketplace and regulatory factors that are still developing.

We  are  subject  to  healthcare  and  other  laws  and  regulations,  including  anti-bribery,  anti-kickback,  fraud  and  abuse,  false  claims,  and  physician  payment
transparency  laws  and  regulations,  which  could  expose  us  to  criminal,  civil  and/or  administrative  sanctions  and  penalties;  exclusion  from  governmental
healthcare programs or reimbursements; contractual damages; and reputational harm.

Our operations and activities are directly, or indirectly through our service providers and collaborators, subject to numerous healthcare and other laws and
regulations, including, without limitation, those relating to anti-bribery, anti-kickback, fraud and abuse, false claims, physician payment transparency, and health
information privacy and security, in the U.S., the EU, and other countries and jurisdictions in which we conduct our business. These laws include:

•

the  U.S.  Anti-Kickback  Statute,  which  prohibits,  among  other  things,  persons  from  knowingly  and  willfully  soliciting,  receiving,  offering  or  paying
remuneration, directly or indirectly, in cash or in kind, to induce or reward, or in return for, either the referral of an individual for, or the purchase or
recommendation of an item or service reimbursable under a federal healthcare program, such as the Medicare and Medicaid programs. A person or entity
does not need to have actual knowledge of the statute or specific intent to violate it in order to have committed a violation;

• U.S. federal and state false claims laws, including the False Claims Act, which impose criminal and civil penalties, including civil whistleblower or qui
tam actions, against individuals or entities for knowingly presenting, or causing to be presented, claims for payment from Medicare, Medicaid, or other
third-party  payers  that  are  false  or  fraudulent  or  making  a  false  statement  to  avoid,  decrease  or  conceal  an  obligation  to  pay  money  to  the  federal
government. In addition, the government may assert that a claim including items and services resulting from a violation of the U.S. federal Anti-Kickback
Statute constitutes a false or fraudulent claim for purposes of the False Claims Act;

•

•

•

the U.S. Health Insurance Portability and Accountability Act of 1996 (“HIPAA”), which imposes criminal and civil liability for executing a scheme to
defraud  any  healthcare  benefit  program  and  making  false  statements  in  connection  with  the  delivery  of  or  payment  for  healthcare  benefits,  items  or
services. Similar to the U.S. federal Anti-Kickback Statute, a person or entity does not need to have actual knowledge of the statute or specific intent to
violate it in order to have committed a violation;

the U.S. Physician Payment Sunshine Act, which requires applicable manufacturers of drugs, devices, biologics and medical supplies for which payment
is  available  under  Medicare,  Medicaid  or  the  Children’s  Health  Insurance  Program,  with  specific  exceptions,  to  report  annually  to  the  Centers  for
Medicare & Medicaid Services (“CMS”) information related to “payments or other transfers of value” made to physicians (defined to include doctors,
dentists, optometrists, podiatrists and chiropractors) and teaching hospitals and applicable manufacturers and applicable group purchasing organizations to
report annually to CMS ownership and investment interests held by the physicians (as defined by statute) and their immediate family members. Effective
January  1,  2022,  these  reporting  obligations  will  extend  to  include  transfers  of  value  made  during  the  previous  year  to  physician  assistants,  nurse
practitioners, clinical nurse specialists, anesthesiologist assistants, certified registered nurse anesthetists, and certified nurse midwives;

laws  and  regulations  that  apply  to  sales  or  marketing  arrangements;  apply  to  healthcare  items  or  services  reimbursed  by non-governmental  third-party
payers, including private insurers; require pharmaceutical companies to comply with the pharmaceutical industry’s voluntary compliance guidelines; that
restrict payments that may be made to healthcare providers; require drug manufacturers to report information related to payments and other transfers of
value to physicians and other healthcare providers or marketing expenditures; and

•

similar and other laws and regulations in the U.S. (federal, state and local), in the EU (including member countries), and other countries and jurisdictions.

Ensuring our compliance with applicable healthcare and other laws and regulations involves substantial costs, and it is possible that governmental authorities
or third parties will assert that our business practices fail to comply with these laws and regulations. If our operations are found to be in violation of any of such
laws  and  regulations,  we may  be  subject  to  significant  civil,  criminal,  and  administrative  damages,  penalties,  and  fines,  as  well  exclusion  from  participation  in
government healthcare

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programs,  curtailment  or  restructuring  of  our  operations  and  reputational  harm,  any  of  which  could  have  a  material  adverse  effect  on  our  business,  financial
condition, or results of operations.

If a successful product liability or clinical trial claim or series of claims is brought against us for uninsured liabilities or in excess of insured liabilities, we
could incur substantial liability.

The use of our drug candidates in clinical trials and the sale of any products for which we obtain marketing approval will expose us to the risk of product
liability and clinical trial liability claims. Product liability claims might be brought against us by consumers, healthcare providers, or others selling or otherwise
coming into contact with our products. Clinical trial liability claims may be filed against us for damages suffered by clinical trial subjects or their families. If we
cannot successfully defend ourselves against product liability claims, we could incur substantial liabilities. In addition, regardless of merit or eventual outcome,
product liability claims may result in:

•

•

decreased demand for any approved drug candidates;

impairment of our business reputation;

• withdrawal of clinical trial participants;

•

•

•

•

•

costs of related litigation;

distraction of management’s attention;

substantial monetary awards to patients or other claimants;

loss of revenues; and

the inability to successfully commercialize any approved drug candidates.

We currently have clinical trial liability insurance coverage for all of our clinical trials. However, our insurance coverage may not be sufficient to reimburse
us for any expenses or losses we may suffer. Moreover, insurance coverage is becoming increasingly expensive, and, in the future, we may not be able to maintain
insurance coverage at a reasonable cost or in sufficient amounts to protect us against losses due to liability. If and when we obtain marketing approval for any of
our drug candidates, we intend to expand our insurance coverage to include the sale of commercial products; however, we may be unable to obtain this product
liability  insurance  on  commercially  reasonable  terms.  On  occasion,  large  judgments  have  been  awarded  in  class  action  lawsuits  based  on  drugs  that  had
unanticipated  side  effects.  A  successful  product  liability  claim  or  series  of  claims  brought  against  us  could  cause  our  ordinary  share  price  to  decline  and,  if
judgments exceed our insurance coverage, could decrease our cash and adversely affect our business.

Risks Related to Our Dependence on Third Parties

We rely on third parties to conduct our clinical trials, and those third parties may not perform satisfactorily, including failing to meet established deadlines for
the completion of any such clinical trials.

We do not have the ability to independently conduct clinical trials for our drug candidates, and we rely on third parties, such as consultants, contract research
organizations, medical institutions, and clinical investigators to assist us with these activities. Our reliance on these third parties for clinical development activities
results  in  reduced  control  over  these  activities.  Furthermore,  these  third  parties  may  also  have  relationships  with  other  entities,  some  of  which  may  be  our
competitors. Although we have and will enter into agreements with these third parties, we will be responsible for confirming that our clinical trials are conducted in
accordance with their general investigational plans and protocols. Moreover, the FDA, the EMA, and other comparable regulatory authorities require us to comply
with  regulations  and  standards,  commonly  referred  to  as  cGCPs,  for  conducting,  recording,  and  reporting  the  results  of  clinical  trials  to  assure  that  data  and
reported  results  are  credible  and  accurate  and  that  the  trial  participants  are  adequately  protected.  Our  reliance  on  third  parties  does  not  relieve  us  of  these
responsibilities and requirements. If we or any of our third-party contractors fail to comply with applicable cGCPs, the clinical data generated in our clinical trials
may be deemed unreliable and the FDA, the EMA, or other comparable regulatory authorities may require us to perform additional clinical trials before approving
our marketing applications. We cannot assure you that upon inspection by a given regulatory authority, such regulatory authority will determine that any of our
clinical trials complies with cGCP regulations. In addition, our clinical trials must be conducted with product produced under cGMPs. Our failure to comply with
these regulations may require us to repeat clinical trials, which would delay the regulatory approval process.

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To date, we believe our consultants, contract research organizations, and other third parties with which we are working have performed well; however, if
these third parties do not successfully carry out their contractual duties, meet expected deadlines, or comply with applicable regulations, we may be required to
replace them. Although we believe that there are a number of other third-party contractors we could engage to continue these activities, we may not be able to enter
into arrangements with alternative third-party contractors or to do so on commercially reasonable terms, which may result in a delay of our planned clinical trials.
Accordingly,  we may be delayed  in obtaining  regulatory  approvals for our drug candidates  and may be delayed in our efforts  to successfully  develop our drug
candidates.

In  addition,  our  third-party  contractors  are  not  our  employees,  and  except  for  remedies  available  to  us  under  our  agreements  with  such  third-party
contractors, we cannot control whether or not they devote sufficient time and resources to our ongoing clinical and nonclinical programs. If third-party contractors
do  not  successfully  carry  out  their  contractual  duties  or  obligations  or  meet  expected  deadlines,  if  they  need  to  be  replaced  or  if  the  quality  or  accuracy  of  the
clinical data they obtain is compromised due to the failure to adhere to our clinical protocols, regulatory requirements or for other reasons, our clinical trials may
be extended, delayed or terminated and we may not be able to obtain regulatory approval for or successfully commercialize our drug candidates. As a result, our
results of operations and the commercial prospects for our drug candidates would be harmed, our costs could increase and our ability to generate revenues could be
delayed.

If we do not establish additional strategic collaborations, we may have to alter our research, development, and/or commercialization plans.

Research,  development,  and  potential  commercialization  of  our  drug  candidates  will  require  substantial  additional  cash  to  fund  expenses.  Our  strategy
includes  potentially  collaborating  with  additional  leading  pharmaceutical  and  biotechnology  companies  to  assist  us  in  furthering  research,  development,  and/or
potential commercialization of some of our drug candidates in some or all geographies. It may be difficult to enter into one or more of such collaborations in the
future. We face significant competition in seeking appropriate collaborators and these collaborations are complex and time-consuming to negotiate and document.
We may not be able to negotiate collaborations on acceptable terms, or at all, in which case we may have to curtail the development of a particular drug candidate,
reduce or delay its development program or one or more of our other development programs, delay its potential commercialization or increase our expenditures and
undertake development or commercialization activities at our own expense. If we elect to increase our expenditures to fund development or commercialization
activities on our own, we will need to obtain additional capital, which may not be available to us on acceptable terms, or at all. If we do not have sufficient funds,
we will not be able to bring our drug candidates to market and generate product revenue.

We  have  no  manufacturing  capacity  and  depend  on  third-party  manufacturers  to  supply  us  with  nonclinical  and  clinical  trial  supplies  of  all  of  our  drug
candidates, and we will depend on third-party manufacturers to supply us with any drug product for commercial sale if we obtain marketing approval from the
FDA, the EMA, or any other comparable regulatory authority for any of our drug candidates.

We do not own or operate facilities for the manufacture, packaging, labeling, storage, testing, or distribution of nonclinical or clinical supplies of any of our
drug candidates. We instead contract with and rely on third parties to manufacture, package, label, store, test, and distribute nonclinical and clinical supplies of our
drug candidates, and we plan to continue to do so for the foreseeable future. We also rely on third-party consultants to assist us with managing these third-parties
and with our manufacturing strategy. If any of these third-parties fail to perform these activities for us, nonclinical or clinical development of our drug candidates
could be delayed, which could have an adverse effect on our business, financial condition, results of operations, and/or growth prospects.

If the FDA, the EMA, or any other comparable regulatory authority approves any of our drug candidates for commercial sale, we expect to continue to rely,
at least initially, on third-parties to manufacture, package, label, store, test, and distribute commercial supplies of such approved drug product. Significant scale-up
of manufacturing may require additional comparability validation studies, which the FDA, the EMA, or other comparable regulatory authorities must review and
approve.  Our  third-party  manufacturers  might  not  be  able  to  successfully  establish  such  comparability  or  increase  their  manufacturing  capacity  in  a  timely  or
economic  manner, or at all. If our third-party  manufacturers  are unable to successfully  establish  comparability  or increase  their manufacturing  capacity for any
drug product, and we are unable to timely establish our own manufacturing capabilities, the commercial launch of that drug candidate could be delayed or there
could be a shortage in supply, which could have an adverse effect on our business, financial condition, results of operations, and/or growth prospects.

Our third-party manufacturers’ facilities could be damaged by fire, power interruption, information system failure, natural disaster or other similar event,
which  could  cause  a  delay  or  shortage  in  supplies  of  our  drug  candidates,  which  could  have  an  adverse  effect  on  our  business,  financial  condition,  results  of
operations, and/or growth prospects.

38

Our drug candidates require, and any future drug product will require, precise, high quality manufacturing, packaging, labeling, storage, and testing that meet
stringent cGMP, other regulatory requirements and other standards. Our third-party manufacturers are subject to ongoing periodic and unannounced inspections by
the FDA, the EMA, and other comparable regulatory authorities to ensure compliance with these cGMPs, other regulatory requirements and other standards. We do
not have control over, and are dependent upon, our third-party manufacturers’ compliance with these cGMPs, regulations and standards. Any failure by a third-
party manufacturer to comply with these cGMPs, regulations or standards or that compromises the safety of any of our drug candidates or any drug product could
cause  a  delay  or  suspension  of  production  of  nonclinical  or  clinical  supplies  of  our  drug  candidates  or  commercial  supplies  of  drug  product,  cause  a  delay  or
suspension of nonclinical or clinical development, product approval and/or commercialization of our drug candidates or drug product, result in seizure or recall of
clinical or commercial supplies, result in fines and civil penalties, result in liability for any patient injury or death or otherwise increase our costs, any of which
could have an adverse effect on our business, financial condition, results of operations, and/or growth prospects. If a third-party manufacturer cannot or fails to
perform  its  contractual  commitments,  does  not  have  sufficient  capacity  to  meet  our  nonclinical,  clinical  or  eventual  commercial  requirements  or  fails  to  meet
cGMPs, regulations or other standards, we may be required to replace it or qualify an additional third-party manufacturer. Although we believe there are a number
of  potential  alternative  manufacturers,  the  number  of  manufacturers  with  the  necessary  manufacturing  and  regulatory  expertise  and  facilities  to  manufacture
biologics  like  our  antibodies  is  limited.  In  addition,  we  could  incur  significant  additional  costs  and  delays  in  identifying  and  qualifying  any  new  third-party
manufacturer, due to the technology transfer to such new manufacturer and because the FDA, the EMA, and other comparable regulatory authorities must approve
any new manufacturer prior to manufacturing our drug candidates. Such approval would require successful technology transfer, comparability and other testing and
compliance inspections. Transferring manufacturing to a new manufacturer could therefore interrupt supply, delay our clinical trials and any commercial launch,
and/or  increase  our  costs  for  our  drug  candidates,  any  of  which  could  have  an  adverse  effect  on  our  business,  financial  condition,  results  of  operations,  and/or
growth prospects.

Rentschler Biopharma SE (“Rentschler”) and Catalent Pharma Solutions, LLC (“Catalent”) are our third-party manufacturers of clinical supplies of our drug

candidate birtamimab. We are dependent on Rentschler and Catalent to manufacture these clinical supplies.

Roche, with whom we are collaborating on development of prasinezumab, manufactured clinical supplies for the Phase 2 clinical trial for prasinezumab and

is expected to do so for any subsequent clinical trials of prasinezumab. We are dependent on Roche to continue to manufacture these clinical supplies.

Rentschler is our third-party manufacturer of clinical supplies of our drug candidate PRX004. We are dependent on Rentschler to manufacture these clinical

supplies in order to initiate any subsequent clinical trials for PRX004.

Catalent and Berkshire Sterile Manufacturing, LLC (“Berkshire”) are our third-party manufacturers of clinical supplies of our drug candidate PRX005. We

are dependent on Catalent and Berkshire to manufacture these clinical supplies in order to initiate any clinical trial for PRX005.

Catalent  is  our  third-party  manufacturer  of  clinical  supplies  of  our  drug  candidate  PRX012.  We  are  dependent  on  Catalent  to  manufacture  these  clinical

supplies in order to initiate any clinical trial for PRX012.

We depend on third-party suppliers for key raw materials used in our manufacturing processes, and the loss of these third-party suppliers or their inability to
supply us with adequate raw materials could harm our business.

We rely on third-party suppliers for the raw materials required for the production of our drug candidates. Our dependence on these third-party suppliers and
the challenges we may face in obtaining adequate supplies of raw materials involve several risks, including limited control over pricing, availability, quality, and
delivery schedules. We cannot be certain that our suppliers will continue to provide us with the quantities  of these raw materials  that we require or satisfy our
anticipated  specifications  and  quality  requirements.  Any  supply  interruption  in  limited  or  sole  sourced  raw  materials  could  materially  harm  our  ability  to
manufacture our products until a new source of supply, if any, could be identified and qualified. Although we believe there are currently several other suppliers of
these raw materials, we may be unable to find a sufficient alternative supply channel in a reasonable time or on commercially reasonable terms. Any performance
failure on the part of our suppliers could delay the development and potential commercialization of our drug candidates, including limiting supplies necessary for
clinical trials and regulatory approvals, which would have a material adverse effect on our business.

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Risks Related to Our Intellectual Property

If we are unable to adequately protect or enforce the intellectual property relating to our drug candidates our ability to successfully commercialize our drug
candidates will be harmed.

Our success depends in part on our ability to obtain patent protection both in the U.S. and in other countries for our drug candidates. Our ability to protect
our drug candidates from unauthorized or infringing use by third parties depends in substantial part on our ability to obtain and maintain valid and enforceable
patents. Due to evolving legal standards relating to the patentability, validity and enforceability  of patents covering pharmaceutical  inventions and the scope of
claims  made  under  these  patents,  our  ability  to  obtain,  maintain  and  enforce  patents  is  uncertain  and  involves  complex  legal,  factual  and  scientific  questions.
Accordingly, rights under any issued patents may not provide us with sufficient protection for our drug candidates or provide sufficient protection to afford us a
commercial advantage against competitive products or processes. Additionally, our ability to obtain patent protection for our drug candidates also depends on our
collaborators, partners, contractors, and employees involved in the generation of intellectual property to carry out their contractual duties, including those to assign
or license relevant intellectual property rights developed on our behalf to us.

In  addition,  the  strength  of  patents  in  the  biotechnology  and  pharmaceutical  field  can  be  uncertain,  and  evaluating  the  scope  of  such  patents  involves
complex legal, factual, and scientific analyses and has in recent years been the subject of much litigation, resulting in court decisions, including Supreme Court
decisions,  which  have  increased  uncertainties  as  to  the  ability  to  enforce  patent  rights  in  the  future.  We  cannot  guarantee  that  any  patents  will  issue  from  any
pending or future patent applications owned by or licensed to us or our affiliates. Even if patents have issued or will issue, we cannot guarantee that the claims of
these  patents  are  or  will  be  valid  or  enforceable  or  will  provide  us  with  any  significant  protection  against  competitive  products  or  otherwise  be  commercially
valuable  to  us.  Patent  applications  in  the  U.S.  are  maintained  in  confidence  for  up  to  18  months  after  their  filing.  In  some  cases,  however,  patent  applications
remain  confidential  in  the  U.S.  Patent  and  Trademark  Office  (the  “USPTO”)  for  the  entire  time  prior  to  issuance  as  a  U.S.  patent.  Similarly,  publication  of
discoveries in the scientific or patent literature often lags behind actual discoveries. Consequently, we cannot be certain that we or our licensors or co-owners were
the first to invent, or the first to file patent applications on, our drug candidates or their use as drugs. In the event that a third party has also filed a U.S. patent
application relating to our drug candidates or a similar invention, we may have to participate in interference or derivation proceedings declared by the USPTO to
determine priority of invention in the U.S. The costs of these proceedings could be substantial and it is possible that our efforts would be unsuccessful, resulting in
a loss of our U.S. patent position. Furthermore, we may not have identified all U.S. and non-U.S. patents or published applications that affect our business either by
blocking  our  ability  to  commercialize  our  drugs  or  by  covering  similar  technologies.  Composition-of-matter  patents  on  the  biological  or  chemical  active
pharmaceutical ingredient are generally considered to be the strongest form of intellectual property protection for pharmaceutical products, as such patents provide
protection  without  regard  to  any  method  of  use.  We  cannot  be  certain  that  the  claims  in  our  patent  applications  covering  composition-of-matter  of  our  drug
candidates will be considered patentable by the USPTO and courts in the U.S. or by the patent offices and courts in other countries, nor can we be certain that the
claims in our issued composition-of-matter patents will not be found invalid or unenforceable if challenged. Method-of-use patents protect the use of a product for
the specified method. This type of patent does not prevent a competitor from making and marketing a product that is identical to our product for an indication that
is  outside  the  scope  of  the  patented  method.  Moreover,  even  if  competitors  do  not  actively  promote  their  product  for  our  targeted  indications,  physicians  may
prescribe  these  products  “off-label.”  Although  off-label  prescriptions  may  infringe  or  contribute  to  the  infringement  of  method-of-use  patents,  the  practice  is
common and such infringement is difficult to prevent or prosecute.

We cannot guarantee that any of our patent searches or analyses, including the identification of relevant patents, the scope of patent claims or the expiration
of relevant patents, are complete or thorough, nor can we be certain that we have identified each and every third-party patent and pending application in the United
States and abroad that is relevant to or necessary for the commercialization of our drug candidates in any jurisdiction. The scope of a patent claim is determined by
an interpretation of the law, the written disclosure in a patent and the patent’s prosecution history. Our interpretation of the relevance or the scope of a patent or a
pending application may be incorrect, which may negatively impact our ability to market our products. We may incorrectly determine that our products are not
covered by a third-party patent or may incorrectly predict whether a third-party’s pending application will issue with claims of relevant scope. Our determination of
the expiration date of any patent in the United States or abroad that we consider relevant may be incorrect, which may negatively impact our ability to develop and
market our drug candidates. Our failure to identify and correctly interpret relevant patents may negatively impact our ability to develop and market our products.

We  may  be  subject  to  a  third-party  preissuance  submission  of  prior  art  to  the  USPTO  and  foreign  patent  agencies,  or  become  involved  in  opposition,
derivation, reexamination, inter partes review, post-grant review, or other patent office proceedings or litigation, in the U.S. or elsewhere, challenging our patent
rights or the patent rights of others. An adverse determination in any such submission, proceeding or litigation could result in loss of exclusivity or in patent claims
being

40

narrowed, invalidated, or held unenforceable, in whole or in part, which could limit our ability to stop others from using or commercializing similar or identical
technology  and  products,  or  limit  the  duration  of  the  patent  protection  of  our  technology  and  products.  In  addition,  given  the  amount  of  time  required  for  the
development,  testing  and regulatory  review  of new drug candidates,  patents  protecting  such candidates  might  expire  before  or shortly  after  such candidates  are
commercialized.  Any  failure  to  obtain  or  maintain  patent  protection  with  respect  to  our  drug  candidates  could  have  a  material  adverse  effect  on  our  business,
financial condition, results of operations, and/or growth prospects.

Changes in U.S. patent law could diminish the value of patents in general, thereby impairing our ability to protect our products.

As  is  the  case  with  other  biopharmaceutical  companies,  our  success  is  heavily  dependent  on  intellectual  property,  particularly  patents.  Obtaining  and
enforcing  patents  in  the  biopharmaceutical  industry  involves  both  technological  and  legal  complexity  and  is  costly,  time-consuming,  and  inherently  uncertain.
Changes in either the patent laws or interpretation of the patent laws in the United States could increase the uncertainties and costs, and may diminish our ability to
protect  our  inventions,  obtain,  maintain,  and  enforce  our  intellectual  property  rights  and,  more  generally,  could  affect  the  value  of  our  intellectual  property  or
narrow the scope of our owned and licensed patents. Recent patent reform legislation in the United States and other countries, including the Leahy-Smith America
Invents Act, or the Leahy-Smith Act, signed into law on September 16, 2011, could increase those uncertainties and costs surrounding the prosecution of our patent
applications and the enforcement or defense of our issued patents. The Leahy-Smith Act includes a number of significant changes to U.S. patent law. These include
provisions  that  affect  the  way  patent  applications  are  prosecuted,  redefine  prior  art  and  provide  more  efficient  and  cost-effective  avenues  for  competitors  to
challenge the validity of patents. These include allowing third-party submission of prior art to the USPTO during patent prosecution and additional procedures to
attack the validity of a patent by USPTO administered post-grant proceedings, including post-grant review, inter partes review, and derivation proceedings. After
March 2013, under the Leahy-Smith Act, the United States transitioned to a first inventor to file system in which, assuming that the other statutory requirements
are met, the first inventor to file a patent application will be entitled to the patent on an invention regardless of whether a third-party was the first to invent the
claimed invention. A third party that files a patent application in the USPTO after March 2013, but before we file an application covering the same invention, could
therefore be awarded a patent covering an invention of ours even if we had made the invention before it was made by such third party. This will require us to be
cognizant going forward of the time from invention to filing of a patent application. Since patent applications in the United States and most other countries are
confidential for a period of time after filing or until issuance, we cannot be certain that we or our licensors were the first to either (i) file any patent application
related to our drug candidates and other proprietary technologies we may develop or (ii) invent any of the inventions claimed in our or our licensor’s patents or
patent applications. Even where we have a valid and enforceable patent, we may not be able to exclude others from practicing the claimed invention where the
other party can show that they used the invention in commerce before our filing date or the other party benefits from a compulsory license. However, the Leahy-
Smith Act and its implementation could increase the uncertainties and costs surrounding the prosecution of our patent applications and the enforcement or defense
of our issued patents, all of which could have a material adverse effect on our business, financial condition, results of operations, and/or growth prospects.

Recent  U.S.  Supreme  Court  rulings  have  narrowed  the  scope  of  patent  protection  available  in  certain  circumstances  and  weakened  the  rights  of  patent
owners in certain situations. In addition to increasing uncertainty with regard to our ability to obtain patents in the future, this combination of events has created
uncertainty with respect to the value of patents once obtained. Depending on decisions by Congress, the federal courts, the USPTO and the relevant law-making
bodies in other countries, the laws and regulations governing patents could change in unpredictable ways that would weaken our ability to obtain new patents or to
enforce our existing patents and patents that we might obtain in the future. We cannot predict how future decisions by Congress, the federal courts or the USPTO
may impact the value of our patents.

Obtaining and maintaining our patent protection depends on compliance with various procedural, document submission, fee payment, and other requirements
imposed by governmental patent agencies, and our patent protection could be reduced or eliminated for non-compliance with these requirements.

Periodic maintenance fees on any issued patent are due to be paid to the USPTO and foreign patent agencies in several stages over the lifetime of the patent.
The  USPTO  and  various  foreign  governmental  patent  agencies  require  compliance  with  a  number  of  procedural,  documentary,  fee  payment,  and  other  similar
provisions  during  the  patent  application  process.  Although  an  inadvertent  lapse,  including  due  to  the  effect  of  the  COVID-19  pandemic  on  us  or  our  patent
maintenance vendors, can in many cases be cured by payment of a late fee or by other means in accordance with the applicable rules, there are situations in which
noncompliance  can  result  in  abandonment  or  lapse  of  the  patent  or  patent  application,  resulting  in  partial  or  complete  loss  of  patent  rights  in  the  relevant
jurisdiction. Noncompliance events that could result in abandonment or lapse of a patent or patent application or invalidity of an issued patent include failure to
respond to official actions within prescribed time limits,

41

non-payment of fees, failure to properly legalize and submit formal documents, and failure to submit certain prior art. In any such event, our competitors might be
able to enter the market, which would have a material adverse effect on our business.

The lives of our patents may not be sufficient to effectively protect our products and business.

Patents have a limited lifespan. In the United States, if all maintenance fees are paid timely, the natural expiration of a patent is generally 20 years after its
first effective  filing date. Although various extensions may be available,  the life  of a patent, and the protection it affords, is limited. Given the amount of time
required for the development, testing, and regulatory review of new drug candidates, patents protecting such candidates might expire before or shortly after such
drug candidates are commercialized. Even if patents covering our drug candidates are obtained, once a patent covering a drug candidate has expired, we may be
open to competition, including biosimilar or generic medications. As a result, our patent portfolio may not provide us with sufficient rights to exclude others from
commercializing drug candidates similar or identical to ours. Our patents issued as of December 31, 2020, are anticipated to expire on dates ranging from 2023 to
2040, subject to any patent extensions that may be available for such patents. If patents are issued on our patent applications pending as of December 31, 2020, the
resulting  patents  are  projected  to  expire  on  dates  ranging  from  2025  to  2041.  In  addition,  although  upon  issuance  in  the  United  States  a  patent’s  life  can  be
increased based on certain delays caused by the USPTO, this increase can be reduced or eliminated based on certain delays caused by the patent applicant during
patent prosecution. A patent term extension based on regulatory delay may be available in the United States. However, only a single patent can be extended for
each first regulatory review period for a product, and any patent can be extended only once, for a single product. Moreover, the scope of protection during the
period  of  the  patent  term  extension  does  not  extend  to  the  full  scope  of  the  claim,  but  instead  only  to  the  scope  of  the  product  as  approved.  Laws  governing
analogous  patent  term  extensions  in  foreign  jurisdictions  vary  widely,  as  do  laws  governing  the  ability  to  obtain  multiple  patents  from  a  single  patent  family.
Additionally, we may not receive an extension if we fail to exercise due diligence during the testing phase or regulatory review process, apply within applicable
deadlines, fail to apply prior to expiration of relevant patents or otherwise fail to satisfy applicable requirements. If we are unable to obtain patent term extension or
restoration, or the term of any such extension is less than we request, the period during which we will have the right to exclusively market our product will be
shortened  and  our  competitors  may  obtain  approval  of  competing  products  following  our  patent  expiration  and  may  take  advantage  of  our  investment  in
development and clinical trials by referencing our clinical and preclinical data to launch their product earlier than might otherwise be the case, and our revenue
could  be  reduced,  possibly  materially.  If  we  do  not  have  sufficient  patent  life  to  protect  our  products,  our  business  and  results  of  operations  will  be  adversely
affected.

We may be subject to claims challenging the inventorship or ownership of our patents and other intellectual property.

We may be subject to claims that former employees, collaborators, or other third parties have an interest in our patents or other intellectual property as an
inventor or co-inventor. The failure to name the proper inventors on a patent application can result in the patents issuing thereon being unenforceable. Inventorship
disputes  may  arise  from  conflicting  views  regarding  the  contributions  of  different  individuals  named  as  inventors,  the  effects  of  foreign  laws  where  foreign
nationals are involved in the development of the subject matter of the patent, conflicting obligations of third parties involved in developing our drug candidates or
as a result of questions regarding co-ownership of potential joint inventions. For example, we may have inventorship disputes arise from conflicting obligations of
consultants or others who are involved in developing our drug candidates. Alternatively, or additionally, we may enter into agreements to clarify the scope of our
rights in such intellectual property. Litigation may be necessary to defend against these and other claims challenging inventorship. If we fail in defending any such
claims,  in  addition  to  paying  monetary  damages,  we  may  lose  valuable  intellectual  property  rights,  such  as  exclusive  ownership  of,  or  right  to  use,  valuable
intellectual property. Such an outcome could have a material adverse effect on our business. Even if we are successful in defending against such claims, litigation
could result in substantial costs and be a distraction to management and other employees.

We or our licensors may have relied on third-party consultants or collaborators or on funds from third parties, such as the U.S. government, such that we or
our licensors are not the sole and exclusive owners of the patents we in-licensed. If other third parties have ownership rights or other rights to our patents, including
in-licensed patents, they may be able to license such patents to our competitors, and our competitors could market competing products and technology. This could
have a material adverse effect on our competitive position, business, financial conditions, results of operations, and prospects.

In addition, while it is our policy to require our employees and contractors who may be involved in the conception or development of intellectual property to
execute agreements assigning such intellectual property to us, we may be unsuccessful in executing such an agreement with each party who, in fact, conceives or
develops intellectual property that we regard as our own. The assignment of intellectual property rights may not be self-executing, or the assignment agreements
may be breached, and we may be forced to bring claims against third parties, or defend claims that they may bring against us, to determine the ownership of what
we regard as our intellectual property. Such claims could have a material adverse effect on our business, financial condition, results of operations, and/or growth
prospects.

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We may not be able to protect our intellectual property rights throughout the world.

Patents are of national or regional effect, and filing, prosecuting, maintaining, and defending patents on drug candidates in all countries throughout the world
would be prohibitively expensive, and our intellectual property rights in some countries outside the United States can have a different scope and strength than do
those in the United States. In addition, the laws of some foreign countries, particularly certain developing countries, do not protect intellectual property rights to the
same extent as federal and state laws in the United States. Consequently, we may not be able to prevent third parties from practicing our inventions in all countries
outside the United States, or from selling or importing products made using our inventions in and into the United States or other jurisdictions. Competitors may use
our technologies in jurisdictions where we have not obtained patent protection to develop their own products and further, may export otherwise infringing products
to  territories  where  we  have  patent  protection,  but  enforcement  rights  are  not  as  strong  as  those  in  the  United  States.  These  products  may  compete  with  our
products and our patents or other intellectual property rights may not be effective or adequate to prevent them from competing.

We license patent rights from third-party owners. Such licenses may be subject to early termination if we fail to comply with our obligations in our licenses
with third parties, which could result in the loss of rights or technology that are material to our business.

We are a party to licenses that give us rights to third-party intellectual property or technology that is necessary or useful for our business, and we may enter
into additional licenses in the future. Under these license agreements we are obligated to pay the licensor fees, which may include annual license fees, milestone
payments, royalties, a percentage of revenues associated with the licensed technology and a percentage of sublicensing revenue. In addition, under certain of such
agreements, we are required to diligently pursue the development of products using the licensed technology. If we fail to comply with these obligations, including
due to the impact of the COVID-19 pandemic on our business operations or our use of the intellectual property licensed to us in an unauthorized manner, and fail
to cure our breach within a specified period of time, the licensor may have the right to terminate the applicable license, in which event we could lose valuable
rights and technology that are material to our business, harming our ability to develop, manufacture, and/or commercialize our platform or drug candidates.

In addition, the agreements under which we license intellectual property or technology to or from third parties are complex, and certain provisions in such
agreements may be susceptible to multiple interpretations. The resolution of any contract interpretation disagreement that may arise could narrow what we believe
to  be  the  scope  of  our  rights  to  the  relevant  intellectual  property  or  technology  or  increase  what  we  believe  to  be  our  financial  or  other  obligations  under  the
relevant  agreement,  either  of  which  could  have  a  material  adverse  effect  on  our  business,  financial  condition,  results  of  operations,  and/or  growth  prospects.
Moreover, if disputes over intellectual property that we have licensed prevent or impair our ability to maintain our current licensing arrangements on commercially
acceptable  terms,  we  may  be  unable  to  successfully  develop  and  commercialize  the  affected  drug  candidates.  Our  business  also  would  suffer  if  any  current  or
future licensors fail to abide by the terms of the license, if the licensors fail to enforce licensed patents against infringing third parties, if the licensed patents or
other rights are found to be invalid or unenforceable, or if we are unable to enter into necessary licenses on acceptable terms. Moreover, our licensors may own or
control  intellectual  property  that  has  not  been  licensed  to  us  and,  as  a  result,  we  may  be  subject  to  claims,  regardless  of  their  merit,  that  we  are  infringing  or
otherwise violating the licensor’s rights.

In addition, while we cannot currently determine the amount of the royalty obligations we would be required to pay on sales of future products, if any, the
amounts  may  be  significant.  The  amount  of  our  future  royalty  obligations  will  depend  on  the  technology  and  intellectual  property  we  use  in  products  that  we
successfully develop and commercialize, if any. Therefore, even if we successfully develop and commercialize products, we may be unable to achieve or maintain
profitability.

If we are unable to successfully obtain rights to required third-party intellectual property rights or maintain the existing intellectual property rights we have,
we  may  have  to  abandon  development  of  the  relevant  research  programs  or  drug  candidates  and  our  business,  financial  condition,  results  of  operations,  and/or
growth prospects could suffer.

Licensing of intellectual property is of critical importance to our business and involves complex legal, business and scientific issues and is complicated by
the  rapid  pace  of  scientific  discovery  in  our  industry.  Disputes  may  also  arise  between  us  and  our  licensors  regarding  intellectual  property  subject  to  a  license
agreement, including those relating to:

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the scope of rights granted under the license agreement and other interpretation-related issues;

whether and the extent to which our technology and processes infringe on intellectual property of the licensor that is not subject to the license agreement;

our right to sublicense patent and other rights to third parties under collaborative development relationships;

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whether  we  are  complying  with  our  diligence  obligations  with  respect  to  the  use  of  the  licensed  technology  in  relation  to  our  development  and
commercialization of our drug candidates, and what activities satisfy those diligence obligations;

the priority of invention of patented technology;

the amount and timing of payments owed under license agreements; and

the allocation of ownership of inventions and know-how resulting from the joint creation or use of intellectual property by our licensors and by us and our
partners.

If disputes over intellectual property that we have licensed prevent or impair our ability to maintain our current licensing arrangements on acceptable terms,
we may be unable to successfully develop and commercialize the affected drug candidates. We are generally also subject to all of the same risks with respect to
protection  of  intellectual  property  that  we  license  as  we  are  for  intellectual  property  that  we  own,  which  are  described  below.  If  we  or  our  licensors  fail  to
adequately protect this intellectual property, our ability to commercialize our products could suffer.

We depend, in part, on our licensors to file, prosecute, maintain, defend, and enforce patents and patent applications that are material to our business.

If  the licensor  retains  control  of prosecution  of the patents and patent applications  licensed  to us, we may have limited  or no control over the manner  in
which the licensor chooses to prosecute or maintain its patents and patent applications and have limited or no right to continue to prosecute any patents or patent
applications that the licensor elects to abandon. If our licensors or any future licensees having rights to file, prosecute, maintain, and defend our patent rights fail to
conduct  these  activities  for  patents  or  patent  applications  covering  any  of  our  drug  candidates,  including  due  to  the  impact  of  the  COVID-19  pandemic  on  our
licensors’  business  operations,  our  ability  to  develop  and  commercialize  those  drug  candidates  may  be  adversely  affected  and  we  may  not  be  able  to  prevent
competitors  from  making,  using,  or  selling  competing  products.  We  cannot  be  certain  that  such  activities  by  our  licensors  have  been  or  will  be  conducted  in
compliance with applicable laws and regulations or will result in valid and enforceable patents or other intellectual property rights. Pursuant to the terms of the
license agreements with some of our licensors, the licensors may have the right to control enforcement of our licensed patents or defense of any claims asserting
the invalidity of these patents and, even if we are permitted to pursue such enforcement or defense, we cannot ensure the cooperation of our licensors. We cannot
be certain that our licensors will allocate sufficient resources or prioritize their or our enforcement of such patents or defense of such claims to protect our interests
in the licensed patents. Even if we are not a party to these legal actions, an adverse outcome could harm our business because it might prevent us from continuing
to license intellectual property that we may need to operate our business. In addition, even when we have the right to control patent prosecution of licensed patents
and  patent  applications,  enforcement  of  licensed  patents,  or  defense  of  claims  asserting  the  invalidity  of  those  patents,  we  may  still  be  adversely  affected  or
prejudiced  by  actions  or  inactions  of  our  licensors  and  their  counsel  that  took  place  prior  to  or  after  our  assuming  control.  In  the  event  we  breach  any  of  our
obligations related to such prosecution, we may incur significant liability to our licensing partners.

We may wish to form collaborations in the future with respect to our drug candidates, but may not be able to do so or to realize the potential benefits of such
transactions, which may cause us to alter or delay our development and commercialization plans.

Our drug candidates may also require specific components to work effectively and efficiently, and rights to those components may be held by others. We
may be unable to in-license any compositions, methods of use, processes or other third party intellectual property rights from third parties that we identify. We may
fail to obtain any of these licenses at a reasonable cost or on reasonable terms, which would harm our business. If we fail to obtain licenses to necessary third-party
intellectual property rights, we may need to cease use of the compositions or methods covered by such third-party intellectual property rights and may need to seek
to develop alternative approaches that do not infringe on such intellectual property rights which may entail additional costs and development delays, even if we
were able to develop such alternatives, which may not be feasible. Even if we are able to obtain a license, it may be non-exclusive, thereby giving our competitors
access  to  the  same  technologies  licensed  to  us.  In  that  event,  we  may  be  required  to  expend  significant  time  and  resources  to  develop  or  license  replacement
technology. Any delays in entering  into new collaborations  or strategic  partnership  agreements related  to our drug candidates  could delay the development  and
commercialization of our drug candidates in certain geographies, which could harm our business prospects, financial condition, and results of operations.

The  licensing  and  acquisition  of  third-party  intellectual  property  rights  is  a  competitive  practice,  and  companies  that  may  be  more  established,  or  have
greater  resources  than  we  do,  may  also  be  pursuing  strategies  to  license  or  acquire  third-party  intellectual  property  rights  that  we  may  consider  necessary  or
attractive in order to commercialize our drug candidates. More established companies may have a competitive advantage over us due to their larger size and cash
resources or greater clinical

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development and commercialization capabilities. There can be no assurance that we will be able to successfully complete such negotiations and ultimately acquire
the rights to the intellectual property surrounding the additional drug candidates that we may seek to acquire.

Moreover, some of our owned and in-licensed patents or patent applications or future patents are or may be co-owned with third parties. If we are unable to
obtain an exclusive license to any such third-party co-owners’ interest in such patents or patent applications, such co-owners may be able to license their rights to
other third parties, including our competitors, and our competitors could market competing products and technology. In addition, we may need the cooperation of
any such co-owners of our patents in order to enforce such patents against third parties, and such cooperation may not be provided to us. Furthermore, our owned
and in-licensed patents may be subject to a reservation of rights by one or more third parties. Any of the foregoing could have a material adverse effect on our
competitive position, business, financial conditions, results of operations and prospects.

Litigation regarding patents, patent applications, and other proprietary rights may be expensive and time consuming. If we are involved in such litigation, it
could cause delays in bringing drug candidates to market and harm our ability to operate.

Our success will depend in part on our ability to operate without infringing the proprietary rights of third parties. Although we are not currently aware of any
litigation  or  other  proceedings  or  third-party  claims  of  intellectual  property  infringement  related  to  our  drug  candidates,  the  pharmaceutical  industry  is
characterized  by  extensive  litigation  regarding  patents  and  other  intellectual  property  rights,  as  well  as  administrative  proceedings  for  challenging  patents,
including interference, derivation, inter partes review, post-grant review, and reexamination proceedings before the USPTO, or oppositions and other comparable
proceedings in foreign jurisdictions , as well as administrative  proceedings for challenging patents, including interference,  derivation, inter partes review, post-
grant review, and reexamination proceedings before the USPTO, or oppositions and other comparable proceedings in foreign jurisdictions. Other parties may hold
or  obtain  patents  in  the  future  and  allege  that  the  use  of  our  technologies  infringes  these  patent  claims  or  that  we  are  employing  their  proprietary  technology
without authorization. Furthermore, patent reform and changes to patent laws add uncertainty to the possibility of challenge to our patents in the future. We cannot
assure you that our drug candidates and other proprietary technologies we may develop will not infringe existing or future patents owned by third parties.

In  addition,  third  parties  may  challenge  our  existing  or  future  patents.  Competitors  may  also  infringe  our  patents  or  other  intellectual  property  or  the
intellectual  property  of  our  licensors.  To  cease  such  infringement  or  unauthorized  use,  we  may  be  required  to  file  patent  infringement  claims,  which  can  be
expensive  and  time-consuming  and  divert  the  time  and  attention  of  our  management  and  scientific  personnel.  Proceedings  involving  our  patents  or  patent
applications or those of others could result in adverse decisions regarding:

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the patentability of our inventions relating to our drug candidates; and/or

the enforceability, validity or scope of protection offered by our patents relating to our drug candidates; and/or

findings that our drug candidates, products, or activities infringe third party patents or other intellectual property rights.

Litigation  or  other  legal  proceedings  relating  to  intellectual  property  claims,  with  or  without  merit,  is  unpredictable  and  generally  expensive  and  time
consuming and, even if resolved in our favor, is likely to divert significant resources from our core business including distracting our technical and management
personnel from their normal responsibilities. Such litigation or proceedings could substantially increase our operating losses and reduce the resources available for
development activities or any future sales, marketing or distribution activities. We may not have sufficient financial or other resources to adequately conduct such
litigation or proceedings. Some of our competitors may be able to sustain the costs of such litigation or proceedings more effectively than we can because of their
greater financial resources and more mature and developed intellectual property portfolios. Uncertainties resulting from the initiation and continuation of patent
litigation or other proceedings could have a material adverse effect on our ability to compete in the marketplace.

Third  parties  asserting  their  patent  or  other  intellectual  property  rights  against  us  may  seek  and  obtain  injunctive  or  other  equitable  relief,  which  could
effectively  block  our  ability  to  further  develop  and  commercialize  our  drug  candidates  or  force  us  to  cease  some  of  our  business  operations.  Defense  of  these
claims, regardless of their merit, would involve substantial litigation expense and would be a substantial diversion of management and other employee resources
from our business, cause development delays, and may impact our reputation. Claims that we have misappropriated the confidential information or trade secrets of
third parties could have a similar negative impact on our business.

In the event we are able to establish third-party infringement of our patents, the court may decide not to grant an injunction against further infringing activity
and instead award only monetary damages, which may or may not be an adequate remedy. Furthermore, because of the substantial amount of discovery required in
connection with intellectual property

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litigation, there is a risk that some of our confidential information could be compromised by disclosure during this type of litigation. In addition, there could be
public announcements of the results of hearings, motions or other interim proceedings or developments. If securities analysts or investors perceive these results to
be negative, it could have a substantial adverse effect on the price of our common stock.

If we are unable to avoid infringing the patent rights of others, we may be required to seek a license, defend an infringement action, or challenge the validity
of the patents in court. Patent litigation is costly and time consuming. We may not have sufficient resources to bring these actions to a successful conclusion. In
addition, if we do not obtain a license, develop or obtain non-infringing technology, fail to defend an infringement action successfully, or have infringed patents
declared invalid, we may:

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incur substantial monetary damages, including treble damages and attorneys’ fees for willful infringement;

obtain one or more licenses from third parties and potentially pay royalties;

redesign our infringing products, which may be impossible on a cost-effective basis or require substantial time and monetary expenditure;obtain one or
more licenses from third parties and potentially pay royalties;

redesign our infringing products, which may be impossible on a cost-effective basis or require substantial time and monetary expenditure;

encounter significant delays in bringing our drug candidates to market; and/or

be precluded from participating in the manufacture, use, or sale of our drug candidates or methods of treatment requiring licenses.

In that event, we would be unable to further develop and commercialize our drug candidates, which could harm our business significantly.

If our trademarks and trade names are not adequately protected, then we may not be able to build name recognition in our markets of interest and our business
may be adversely affected.

Our current or future trademarks or trade names may be challenged, infringed, circumvented, declared generic or descriptive, or determined to be infringing
on other marks. We may not be able to protect our rights to these trademarks and trade names or may be forced to stop using these names, which we need for name
recognition by potential partners or customers in our markets of interest. During trademark registration proceedings, we may receive rejections of our applications
by the USPTO or in other foreign jurisdictions. Although we would be given an opportunity to respond to those rejections, we may be unable to overcome such
rejections. In addition, in the USPTO and in comparable agencies in many foreign jurisdictions, third parties are given an opportunity to oppose pending trademark
applications and to seek to cancel registered trademarks. Opposition or cancellation proceedings may be filed against our trademarks, and our trademarks may not
survive such proceedings. If we are unable to establish name recognition based on our trademarks and trade names, we may not be able to compete effectively and
our business may be adversely affected. We may license our trademarks and trade names to third parties, such as distributors. Though these license agreements
may provide guidelines for how our trademarks and trade names may be used, a breach of these agreements or misuse of our trademarks and tradenames by our
licensees may jeopardize our rights in or diminish the goodwill associated with our trademarks and trade names.

Moreover, any name we have proposed to use with our drug candidate in the United States must be approved by the FDA, regardless of whether we have
registered  it,  or  applied  to  register  it,  as  a  trademark.  Similar  requirements  exist  in  Europe.  The  FDA  typically  conducts  a  review  of  proposed  product  names,
including an evaluation of potential for confusion with other product names. If the FDA (or an equivalent administrative body in a foreign jurisdiction) objects to
any of our proposed proprietary product names, it may be required to expend significant additional resources in an effort to identify a suitable substitute name that
would  qualify  under  applicable  trademark  laws,  not  infringe  the  existing  rights  of  third  parties  and  be  acceptable  to  the  FDA.  Furthermore,  in  many  countries,
owning and maintaining a trademark registration may not provide an adequate defense against a subsequent infringement claim asserted by the owner of a senior
trademark. At times, competitors or other third parties may adopt trade names or trademarks similar to ours, thereby impeding our ability to build brand identity
and possibly leading to market confusion. In addition, there could be potential trade name or trademark infringement claims brought by owners of other registered
trademarks or trademarks that incorporate variations of our registered or unregistered trademarks or trade names. If we assert trademark infringement claims, a
court may determine that the marks we have asserted are invalid or unenforceable, or that the party against whom we have asserted trademark infringement has
superior rights to the marks in question. In this case, we could ultimately be forced to cease use of such trademarks.

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We may be unable to adequately prevent disclosure of trade secrets and other proprietary information.

We rely on trade secrets to protect our proprietary technologies, especially where we do not believe patent protection is appropriate or obtainable; however,
trade  secrets  are  difficult  to  protect.  We  rely  in  part  on  confidentiality  agreements  with  our  employees,  consultants,  outside  scientific  collaborators,  sponsored
researchers,  and  other  advisors  to  protect  our  trade  secrets  and  other  proprietary  information.  These  agreements  may  not  effectively  prevent  disclosure  of
confidential  information  and  may  not  provide  an  adequate  remedy  in  the  event  of  unauthorized  disclosure  of  confidential  information.  Any  disclosure,  either
intentional or unintentional,  by our employees, the employees of third parties with whom we share our facilities  or third-party consultants and vendors that we
engage to perform research, clinical trials or manufacturing activities, or misappropriation by third parties (such as through a cybersecurity breach) of our trade
secrets or proprietary information could enable competitors to duplicate or surpass our technological achievements, thus eroding our competitive position in our
market. In addition, others may independently discover our trade secrets and proprietary information, and we would have no right to prevent them from using that
technology  or  information  to  compete  with  us. Costly  and  time-consuming  litigation  could  be  necessary  to  enforce  and  determine  the  scope  of  our  proprietary
rights, and failure to obtain or maintain trade secret protection could adversely affect our competitive business position. Furthermore, the laws of some foreign
countries do not protect proprietary rights to the same extent or in the same manner as the laws of the United States. As a result, we may encounter significant
problems in protecting and defending our intellectual property both in the United States and abroad. If we are unable to prevent unauthorized material disclosure of
our intellectual property to third parties, or misappropriation of our intellectual property by third parties, we will not be able to establish or maintain a competitive
advantage in our market, which could materially adversely affect our business, operating results, and financial condition.

We may be subject to claims that our employees, collaborators, partners, contractors, or advisors, collaborators, partners, contractors, or advisors have
wrongfully used or disclosed alleged trade secrets of third parties.

Many of our employees were previously employed at universities, Elan or Elan subsidiaries, or other biotechnology or pharmaceutical companies, including
our competitors or potential competitors. Likewise, our collaborators, partners, contractors, and advisors may have in the past, or may currently, work with or for
universities,  or  other  biotechnology  or  pharmaceutical  companies,  including  our  competitors  or  potential  competitors.  Although  we  try  to  ensure  that  our
employees do not use the proprietary information or know-how of third parties is not disclosed to us or used in their work for us, we may be subject to claims that
we  or  our  employees,  collaborators,  partners,  contractors,  or  advisors  have  used  or  disclosed  intellectual  property,  including  trade  secrets  or  other  proprietary
information, of third parties. Litigation may be necessary to defend against these claims. Even if we are successful in defending against these claims, litigation
could  result  in  substantial  cost  and  be  a  distraction  to  our  management  and  employees. If  our  defenses  to  these  claims  fail,  in  addition  to  requiring  us  to  pay
monetary damages, a court could prohibit us from using technologies or features that are essential to our drug candidates, if such technologies or features are found
to incorporate, be derived from, or benefited from the knowledge of the trade secrets or other proprietary information of third parties. Moreover, any such litigation
or  the  threat  thereof  may  adversely  affect  our  reputation,  our  ability  to  form  strategic  alliances  or  sublicense  our  rights  to  collaborators,  engage  with  scientific
advisors or hire employees or consultants, each of which would have an adverse effect on our business, results of operations and financial condition. Even if we are
successful in defending against such claims, litigation could result in substantial costs and be a distraction to management.

Intellectual property rights do not necessarily address all potential threats to our competitive advantage.

The  degree  of  future  protection  afforded  by  our  intellectual  property  rights  is  uncertain  because  intellectual  property  rights  have  limitations  and  may  not

adequately protect our business or permit us to maintain our competitive advantage. For example:

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others may be able to make drug candidates that are similar to ours but that are not covered by the claims of the patents that we own or have exclusively
licensed;

we or our licensors or future collaborators might not have been the first to make the inventions covered by the issued patent or pending patent application
that we own or have exclusively licensed;

we or our licensors or future collaborators might not have been the first to file patent applications covering certain of our inventions;

others  may  independently  develop  similar  or  alternative  technologies  or  duplicate  any  of  our  technologies  without  infringing  our  intellectual  property
rights;

it is possible that our pending patent applications will not lead to issued patents;

issued patents that we own or have exclusively licensed may be held invalid or unenforceable, as a result of legal challenges by our competitors;

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our competitors might conduct research and development activities in countries where we do not have patent rights and then use the information learned
from such activities to develop competitive products for sale in our major commercial markets;

we may not develop additional proprietary technologies that are patentable;

we cannot predict the scope of protection of any patent issuing based on our patent applications, including whether the patent applications that we own or
in-license will result in issued patents with claims that cover our drug candidates or uses thereof in the United States or in other foreign countries;

the claims of any patent issuing based on our patent applications may not provide protection against competitors or any competitive advantages, or may be
challenged by third parties;

if enforced, a court may not hold that our patents are valid, enforceable and infringed;

we may need to initiate litigation or administrative proceedings to enforce and/or defend our patent rights which will be costly whether we win or lose;

we may choose not to file a patent in order to maintain certain trade secrets or know-how, and a third party may subsequently file a patent covering such
intellectual property;

we may fail to adequately protect and police our trademarks and trade secrets; and

the patents of others may have an adverse effect on our business, including if others obtain patents claiming subject matter similar to or improving that
covered by our patents and patent applications.

Should any of these events occur, they could significantly harm our business, results of operations, and prospects.

Risks Related to Our Ordinary Shares

The market price of our ordinary shares may fluctuate widely.

Our ordinary shares commenced trading on the Nasdaq Global Market on December 21, 2012 and currently trade on the Nasdaq Global Select Market. We
cannot predict the prices at which our ordinary shares may trade. The market price of our ordinary shares may fluctuate widely, depending upon many factors,
some of which may be beyond our control, including:

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our ability to obtain financing as needed;

progress in and results from our ongoing or future nonclinical research and clinical trials;

our collaborations with third parties, including with Roche and BMS;

failure or delays in advancing our nonclinical drug candidates or other drug candidates we may develop in the future into clinical trials;

results of clinical trials conducted by others, including on drugs that would compete with our drug candidates;

issues in manufacturing our drug candidates;

regulatory developments or enforcement in the U.S. and other countries;

developments or disputes concerning patents or other proprietary rights;

introduction of technological innovations or new commercial products by our competitors;

changes in estimates or recommendations by securities analysts, if any, who cover our company;

public concern over our drug candidates;

litigation;

future sales of our ordinary shares by us or by existing shareholders;

general market conditions;

changes in the structure of healthcare payment systems;

failure of any of our drug candidates, if approved, to achieve commercial success;

economic and other external factors or other disasters or crises;

period-to-period fluctuations in our financial results;

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overall fluctuations in U.S. equity markets;

our quarterly or annual results, or those of other companies in our industry;

announcements by us or our competitors of significant acquisitions or dispositions;

the operating and ordinary share price performance of other comparable companies;

investor perception of our company and the drug development industry;

natural or environmental disasters that investors believe may affect us;

changes in tax laws or regulations applicable to our business or the interpretations of those tax laws and regulations by taxing authorities; or

fluctuations in the budgets of federal, state and local governmental entities around the world.

These  and  other  external  factors  may  cause  the  market  price  and  demand  for  our  ordinary  shares  to  fluctuate  substantially,  which  may  limit  or  prevent
investors from readily selling their ordinary shares and may otherwise negatively affect the liquidity of our ordinary shares. In particular, stock markets in general
have experienced volatility that has often been unrelated to the operating performance of a particular company. These broad market fluctuations may adversely
affect the trading price of our ordinary shares. Some companies that experienced volatility in the trading price of their stock have been the subject of securities
class action litigation. If any of our shareholders brought a lawsuit against us, we could incur substantial costs defending the lawsuit. Such a lawsuit could also
divert the time and attention of our management.

Your percentage ownership in Prothena may be diluted in the future.

As with any publicly traded  company, your percentage  ownership in us may be diluted in the  future because of equity issuances for acquisitions,  capital
raising transactions or otherwise. We may need to raise additional capital in the future. If we are able to raise additional capital, we may issue equity or convertible
debt instruments, which may severely dilute your ownership interest in us. In addition, we intend to continue to grant option awards to our directors, officers and
employees, which would dilute your ownership stake in us. As of December 31, 2020, the number of ordinary shares available for issuance pursuant to outstanding
and future equity awards under our equity plan was 10,414,384.

If we are unable to maintain effective internal controls, our business could be adversely affected.

We are subject to the reporting and other obligations under the U.S. Securities Exchange Act of 1934, as amended, including the requirements of Section 404
of the U.S. Sarbanes-Oxley Act, which require annual management assessments of the effectiveness of our internal control over financial reporting. In addition,
under  Section  404(b)  of  the  U.S.  Sarbanes-Oxley  Act,  if  we  are  either  an  “accelerated  filer”  or  “large  accelerated  filer,”  our  independent  registered  public
accounting firm must attest to the effectiveness of our internal control over financial reporting. The rules governing the standards that must be met for management
to  assess  our  internal  control  over  financial  reporting  are  complex  and  require  significant  documentation,  testing  and  possible  remediation  to  meet  the  detailed
standards under the rules. During the course of its testing, our management may identify material weaknesses or deficiencies which may not be remedied in time to
meet the deadline imposed by the Sarbanes-Oxley Act. These reporting and other obligations place significant demands on our management and administrative and
operational resources, including accounting resources.

Our  management  is  responsible  for  establishing  and  maintaining  adequate  internal  control  over  financial  reporting.  Our  internal  control  over  financial
reporting is a process designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of our financial statements for
external purposes in accordance with accounting principles generally accepted in the U.S. During the course of our review and testing of our internal controls, we
may  identify  deficiencies  and  be  unable  to  remediate  them  before  we  must  provide  the  required  reports.  Furthermore,  if  we  have  a  material  weakness  in  our
internal controls over financial reporting, we may not detect errors on a timely basis and our consolidated financial statements may be materially misstated. We, or
our  independent  registered  public  accounting  firm  (if  required),  may  not  be  able  to  conclude  on  an  ongoing  basis  that  we  have  effective  internal  control  over
financial reporting, which could harm our operating results, cause investors to lose confidence in our reported financial information and cause the trading price of
our stock to fall.

        We cannot provide assurance that a material weakness will not occur in the future, or that we will be able to conclude on an ongoing basis that we have
effective  internal  controls  over  financial  reporting  in  accordance  with  Section  404  and  the  related  rules  and  regulations  of  the  SEC  when  required.  A  material
weakness in internal control over financial reporting is a deficiency, or a combination of deficiencies, in internal control over financial reporting, such that there is
a reasonable possibility that a material misstatement of a company’s annual or interim consolidated financial statements will not be prevented or detected on a

49

timely basis by the company’s internal controls. If we cannot in the future favorably assess, or our independent registered public accounting firm (if required), is
unable to provide an unqualified attestation report on, the effectiveness of our internal controls over financial reporting, investor confidence in the reliability of our
financial reports may be adversely affected, which could have a material adverse effect on our share price. In addition, any failure to report our financial results on
an accurate and timely basis could result in sanctions, lawsuits, delisting of our shares from the Nasdaq Global Select Market or other adverse consequences that
would have an adverse effect on our business, financial position and results of operations.

If  we  were  treated  as  a  passive  foreign  investment  company  for  U.S.  federal  income  tax  purposes,  it  could  result  in  adverse  U.S.  federal  income  tax
consequences to United States holders of our ordinary shares.

Significant potential adverse U.S. federal income tax implications generally apply to U.S. investors owning shares of a passive foreign investment company
(“PFIC”), directly or indirectly. In general, we would be a PFIC for a taxable year if either (i) 75% or more of our income constitutes passive income (the “income
test”), or (ii) 50% or more of our assets produce passive income (the “asset test”). Changes in the composition of our active or passive income, passive assets or
changes in our fair market value may cause us to become a PFIC. A separate determination must be made each taxable year as to whether we are a PFIC (after the
close of each taxable year).

We do not believe we were a PFIC for U.S. federal income tax purposes for our taxable year ended December 31, 2020. However, the application of the PFIC
rules is subject to uncertainties in a number of respects, and we cannot assure that the U.S. Internal Revenue Service (the “IRS”) will not take a contrary position.
We also cannot assure that we will not be a PFIC for U.S. federal income tax purposes for the current taxable year or any future taxable year.

We may not be able to successfully maintain our tax rates, which could adversely affect our business and financial condition, results of operations and growth
prospects.

We  are  incorporated  in  Ireland  and  maintain  subsidiaries  or  offices  in  Ireland  and  the  U.S.  We  are  able  to  achieve  a  low  average  tax  rate  through  the
performance of certain functions and ownership of certain assets in tax-efficient jurisdictions, together with intra-group service agreements. However, changes in
tax laws or interpretations thereof in any of these jurisdictions could adversely affect our ability to do so in the future. Taxing authorities, such as the IRS and the
Irish Revenue Commissioners (“Irish Revenue”), actively audit and otherwise challenge these types of arrangements, and have done so in our industry. We are
subject to reviews and audits by the IRS, Irish Revenue and other taxing authorities from time to time, and the IRS, Irish Revenue or other taxing authority may
challenge  our  structure  and  inter-group  arrangements.  Responding  to  or  defending  against  challenges  from  taxing  authorities  could  be  expensive  and  time
consuming, and could divert management’s time and focus away from operating our business. We cannot predict whether and when taxing authorities will conduct
an audit, challenge our tax structure or the cost involved in responding to any such audit or challenge. If we are unsuccessful, we may be required to pay taxes for
prior  periods,  interest,  fines  or penalties,  and may  be obligated  to pay  increased  taxes  in the  future,  all  of which  could have  an adverse  effect  on our business,
financial condition, results of operations, and/or growth prospects.

Future changes to the tax laws relating to multinational corporations could adversely affect us.

Under current law, we are treated as a foreign corporation for U.S. federal tax purposes. However, changes to the U.S. Internal Revenue Code, U.S. Treasury
Regulations or other IRS guidance thereunder could adversely affect our status as a foreign corporation or otherwise affect our effective tax rate. For example, in
2017  the  United  States  enacted  tax  reform  that  contained  significant  changes  to  corporate  taxation,  including  a  provision  that  would  require  capitalization  and
amortization of research and development costs over five years for tax years beginning after December 31, 2021. In addition, the Irish Government, Irish Revenue,
U.S. Congress, the IRS, the Organization  for Economic  Co-operation  and Development,  and other  governments  and agencies  in jurisdictions  where may in the
future we do business have recently focused on issues related to the taxation of multinational corporations, and specifically in the area of “base erosion and profit
shifting,” such as where payments are made between affiliates from a jurisdiction with high tax rates to a jurisdiction with lower tax rates. As a result, the tax laws
in Ireland, the U.S., and other countries in which we may do business could change on a prospective or retroactive  basis, and any such changes could have an
adverse effect on our business, financial condition, results of operations, and/or growth prospects.

Irish law differs from the laws in effect in the United States and may afford less protection to holders of our ordinary shares.

It may not be possible to enforce court judgments obtained in the U.S. against us in Ireland based on the civil liability provisions of the U.S. federal or state
securities laws. In addition, there is uncertainty as to whether the courts of Ireland would recognize or enforce judgments of U.S. courts obtained against us or our
directors or officers based on the civil liabilities provisions of the U.S. federal or state securities laws or hear actions against us or those persons based on those
laws. We have been advised that the U.S. currently does not have a treaty with Ireland providing for the reciprocal recognition and

50

enforcement of judgments in civil and commercial matters. Therefore, a final judgment for the payment of money rendered by any U.S. federal or state court based
on civil liability, whether or not based solely on federal or state securities laws, would not automatically be enforceable in Ireland.

As an Irish incorporated company, we are governed by the Irish Companies Act 2014, as amended (the “Companies Act”), which differs in some material
respects  from  laws  generally  applicable  to  U.S.  corporations  and  shareholders,  including,  among  others,  differences  relating  to  interested  director  and  officer
transactions and shareholder lawsuits. Likewise, the duties of directors and officers of an Irish company generally are owed to the company only. Shareholders of
Irish companies generally do not have a personal right of action against directors or officers of the company and may exercise such rights of action on behalf of the
company  only  in  limited  circumstances.  Accordingly,  holders  of  our  ordinary  shares  may  have  more  difficulty  protecting  their  interests  than  would  holders  of
securities of a corporation incorporated in a jurisdiction of the U.S.

The operation of the Irish Takeover Rules may affect the ability of certain parties to acquire our ordinary shares.

Under the Irish Takeover Rules, if an acquisition of ordinary shares were to increase the aggregate holding of the acquirer and its concert parties to ordinary
shares that represent 30% or more of the voting rights of the company, the acquirer and, in certain circumstances, its concert parties would be required (except with
the consent of the Irish Takeover Panel) to make an offer for the outstanding ordinary shares at a price not less than the highest price paid for the ordinary shares by
the acquirer or its concert parties during the previous 12 months. This requirement would also be triggered by an acquisition of ordinary shares by a person holding
(together with its concert parties) ordinary shares that represent between 30% and 50% of the voting rights in the company if the effect of such acquisition were to
increase  that  person’s  percentage  of  the  voting  rights  by  0.05%  within  a  12  month  period.  Under  the  Irish  Takeover  Rules,  certain  separate  concert  parties  are
presumed to be acting in concert. Our board of directors and their relevant family members, related trusts and “controlled companies” are presumed to be acting in
concert with any corporate shareholder who holds 20% or more of our shares. The application of these presumptions may result in restrictions upon the ability of
any  of  the  concert  parties  and/or  members  of  our  board  of  directors  to  acquire  more  of  our  securities,  including  under  the  terms  of  any  executive  incentive
arrangements. In the future, we may consult with the Irish Takeover Panel with respect to the application of this presumption and the restrictions on the ability to
acquire further securities, although we are unable to provide any assurance as to whether the Irish Takeover Panel will overrule this presumption. Accordingly, the
application of the Irish Takeover Rules may restrict the ability of certain of our shareholders and directors to acquire our ordinary shares.

Irish law differs from the laws in effect in the United States with respect to defending unwanted takeover proposals and may give our board of directors less
ability to control negotiations with hostile offerors.

We are subject to the Irish Takeover Panel Act, 1997, Takeover Rules, 2013. Under those Irish Takeover Rules, our Board is not permitted to take any action
that might frustrate an offer for our ordinary shares once our Board has received an approach that may lead to an offer or has reason to believe that such an offer is
or  may  be  imminent,  subject  to  certain  exceptions.  Potentially  frustrating  actions  such  as  (i)  the  issue  of  ordinary  shares,  options  or  convertible  securities,
(ii) material acquisitions or disposals, (iii) entering into contracts other than in the ordinary course of business, or (iv) any action, other than seeking alternative
offers, which may result in frustration of an offer, are prohibited during the course of an offer or at any earlier time during which our Board has reason to believe
an offer is or may be imminent. These provisions may give our Board less ability to control negotiations with hostile offerors and protect the interests of holders of
ordinary shares than would be the case for a corporation incorporated in a jurisdiction of the U.S.

Irish law requires that our shareholders renew every five years the authority of our Board of Directors to issue shares and to do so for cash without applying
the statutory pre-emption right, and if our shareholders do not renew these authorizations by May 17, 2022 (or any renewal is subject to limitations), our ability
to raise additional capital to fund our operations would be limited.

As an Irish incorporated company, we are governed by the Companies Act. The Companies Act requires that every five years our shareholders renew the
separate authorities of our Board to (a) allot and issue shares, and (b) opt out of the statutory pre-emption right that otherwise applies to share issuances for cash
(which pre-emption right would require that shares issued for cash be offered to our existing shareholders on a pro rata basis before the shares may be issued to
new shareholders). At our shareholders' annual general meeting held on May 17, 2017, our shareholders authorized our Board to issue ordinary shares up to the
amount of our authorized share capital, and to opt out of the statutory pre-emption right for such issuances. Under Irish law, these authorizations will expire on
May 17, 2022, five years after our shareholders last renewed these authorizations. Irish law requires that our shareholders renew the authority for our Board to
issue  ordinary  shares  by  a  resolution  approved  by  not  less  than  50%  of  the  votes  cast  at  a  general  meeting  of  our  shareholders.  Irish  law  requires  that  our
shareholders renew the authority of our Board to opt out of the statutory pre-emption right in share issuances for cash by a resolution approved by not less than
75% of the votes cast at a general meeting of our shareholders. If these authorizations are not renewed before May 17,

51

2022, or are renewed with limitations, our Board would be limited in its ability to issue shares, which would limit our ability to raise additional capital to fund our
operations, including the research, development and potential commercialization of our drug candidates.

Transfers of our ordinary shares may be subject to Irish stamp duty.

Irish stamp duty may be payable in respect of transfers of our ordinary shares (currently at the rate of 1% of the price paid or the market value of the shares

acquired, if greater).

Under the Irish Stamp Duties Consolidation Act, 1999 (the “Stamp Duties Act”), a transfer of our ordinary shares from a seller who holds shares through
The Depository Trust Company (“DTC”) to a buyer who holds the acquired shares through DTC should not be subject to Irish stamp duty. Shareholders may also
transfer their shares into or out of DTC without giving rise to Irish stamp duty provided that there is no change in the beneficial ownership of such shares and the
transfer into or out of DTC is not effected in contemplation of a subsequent sale of such shares to a third party; in order to benefit from this exemption from Irish
stamp  duty,  the  seller  must  confirm  to  us  that  there  is  no  change  in  the  ultimate  beneficial  ownership  of  the  shares  as  a  result  of  the  transfer  and  there  is  no
agreement for the sale of the shares by the beneficial owner to a third party being contemplated.

A transfer of our ordinary shares (i) by a seller who holds shares outside of DTC to any buyer, or (ii) by a seller who holds the shares through DTC to a
buyer who holds the acquired shares outside of DTC, may be subject to Irish stamp duty. Payment of any Irish stamp duty is generally a legal obligation of the
transferee.

Any Irish stamp duty payable on transfers of our ordinary shares could adversely affect the price of those shares.

We do not anticipate paying cash dividends, and accordingly, shareholders must rely on ordinary share appreciation for any return on their investment.

We anticipate losing money for the foreseeable future and, even if we do ever turn a profit, we intend to retain future earnings, if any, for the development,
operation and expansion of our business. Thus, we do not anticipate declaring or paying any cash dividends for the foreseeable future. Therefore, the success of an
investment in our ordinary shares will depend upon appreciation in their value and in order to receive any income or realize a return on your investment, you will
need to sell your Prothena ordinary shares. There can be no assurance that our ordinary shares will maintain their price or appreciate in value.

Dividends paid by us may be subject to Irish dividend withholding tax.

Although we do not currently anticipate paying cash dividends, if we were to do so in the future, a dividend withholding tax (currently at a rate of 25%) may
arise. A number of exemptions from dividend withholding tax exist such that shareholders resident in the U.S. and shareholders resident in other countries that
have entered into a double taxation treaty with Ireland may be entitled to exemptions from dividend withholding tax subject to the completion of certain dividend
withholding tax declaration forms.

Shareholders  entitled  to  an  exemption  from  Irish  dividend  withholding  tax  on  any  dividends  received  from  us  will  not  be  subject  to  Irish  income  tax  in
respect  of  those  dividends,  unless  they  have  some  connection  with  Ireland  other  than  their  shareholding  (for  example,  they  are  resident  in  Ireland).  Non-Irish
resident shareholders who receive dividends subject to Irish dividend withholding tax will generally have no further liability to Irish income tax on those dividends.

Prothena ordinary shares received by means of a gift or inheritance could be subject to Irish capital acquisitions tax.

Irish capital acquisitions tax (“CAT”) could apply to a gift or inheritance of our ordinary shares irrespective of the place of residence, ordinary residence or
domicile of the parties. This is because our ordinary shares will be regarded as property situated in Ireland. The person who receives the gift or inheritance has
primary liability for CAT. Gifts and inheritances passing between spouses are exempt from CAT. It is recommended that each shareholder consult his or her own
tax advisor as to the tax consequences of holding our ordinary shares or receiving dividends from us.

ITEM 1B. UNRESOLVED STAFF COMMENTS.

None.

52

ITEM 2. PROPERTIES

Our corporate registered address and office is in Dublin, Ireland and our U.S. operations are in South San Francisco, California.

In Dublin, Ireland, we occupy approximately 133 square feet of office under a lease which expires on November 30, 2021.

In South San Francisco, California, we occupy approximately 82,000 square feet of office and laboratory space under a lease which expires in December

2023.

We believe that our facilities are sufficient to meet our current needs.

ITEM 3. LEGAL PROCEEDINGS

We  are  not  currently  a  party  to  any  material  legal  proceedings.  We  may  at  times  be  party  to  ordinary  routine  litigation  incidental  to  our  business.  When

appropriate in management’s estimation, we may record reserves in our financial statements for pending legal proceedings.

ITEM 4. MINE SAFETY DISCLOSURES

Not Applicable.

53

ITEM 5. MARKET FOR REGISTRANT'S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY

PART II

SECURITIES.

Market Information for Ordinary Shares

Our ordinary shares commenced trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012 and currently trade on The Nasdaq

Global Select Market.

Holders

There were approximately 5,355 shareholders of record of our ordinary shares as of February 18, 2021. Because many of our shares are held by brokers and

other institutions on behalf of shareholders, we are unable to estimate the total number of shareholders represented by these record holders.

Dividend Policy

We have not paid dividends in the past and do not anticipate paying dividends in the foreseeable future. Any future determination to pay dividends will be at
the discretion of our Board of Directors and will be dependent upon our financial condition, results of operations, capital requirements, and such other factors as
the Board of Directors deems relevant.

Under  Irish  law,  dividends  and  distributions  may  only  be  made  from  distributable  reserves.  Distributable  reserves  generally  means  accumulated  realized
profits, to the extent not previously utilized by distribution or capitalization, less accumulated realized losses, to the extent not previously written off in a reduction
or re-organization of capital. In addition, no distribution or dividend may be made unless the net assets of Prothena are equal to, or in excess of, the aggregate of
our called up share capital plus undistributable reserves and the distribution does not reduce our net assets below such aggregate. Undistributable reserves include
undenominated capital, the share premium account, the capital redemption reserve fund and the amount by which Prothena’s accumulated unrealized profits, so far
as not previously utilized by any capitalization, exceed our accumulated unrealized losses, so far as not previously written off in a reduction or reorganization of
capital.

The determination  as to whether or not we have sufficient  distributable  reserves  to fund a dividend must be made by reference  to the “relevant  financial
statements”  of  Prothena.  The  “relevant  financial  statements”  are  either  the  last  set  of  unconsolidated  annual  audited  financial  statements  or  other  financial
statements properly prepared in accordance  with the Irish Companies Act 2014, which give a “true and fair view” of our unconsolidated financial position and
accord  with  accepted  accounting  practice.  The  relevant  financial  statements  must  be  filed  in  the  Companies  Registration  Office  (the  official  public  registry  for
companies in Ireland).

Securities Authorized for Issuance Under Equity Compensation Plans

See Item 12 of Part III of this Form 10-K regarding information about securities authorized for issuance under our equity compensation plans.

Performance Graph

(1)

The  following  graph  shows  a  comparison  from  December  31,  2015,  through  December  31,  2020,  of  cumulative  total  return  on  assumed  investment  of
$100.00 in cash in our ordinary shares, the Nasdaq Composite Index and the Nasdaq Biotechnology Index. Such returns are based on historical results and are not
intended to suggest future performance. Points on the graph represent the performance as of end of each business day.

54

COMPARISON OF 5-YEAR CUMULATIVE TOTAL RETURN
Among Prothena Corporation plc, the Nasdaq Composite Index, and the Nasdaq Biotechnology Index

Cumulative Total Return as of
Prothena Corporation plc
Nasdaq Composite Index
Nasdaq Biotechnology Index

12/31/2015
$100
$100
$100

$
$
$

12/31/2016

12/31/2017

12/31/2018

12/31/2019

12/31/2020

72 
$
108  $
$
78 

55 
$
138  $
$
95 

15 
133 
86 

$
$
$

23  $
179  $
107  $

18 
257 
134 

(1) 

The  information  under  the  heading  “Performance  Graph”  shall  not  be  deemed  “soliciting  material”  or  to  be  “filed”  with  the  SEC  for  purposes  of
Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities under that Section, and shall not be deemed incorporated by
reference into any filing of Prothena Corporation plc under the Securities Act of 1933, as amended.

Recent Sales of Unregistered Securities

None.

Use of Proceeds

None.

Purchases of Equity Securities by the Issuer and Affiliated Purchasers

None.

Irish Law Matters

As we are an Irish public limited company, the following matters of Irish law are relevant to the holders of our ordinary shares.

Irish Restrictions on Import and Export of Capital

Except as indicated below, there are no restrictions on non-residents of Ireland dealing in Irish domestic securities, which includes ordinary shares of Irish
companies. Dividends and redemption proceeds also continue to be freely transferable to non-resident holders of such securities. The Irish Financial Transfers Act,
1992  (the  “Transfers  Act”)  gives  power  to  the  Minister  for  Finance  of  Ireland  to  restrict  financial  transfers  between  Ireland  and  other  countries  and  persons.
Financial transfers are broadly defined and include all transfers that would be movements of capital or payments within the meaning of the treaties governing the
member states of the European Union. The acquisition or disposal of interests in shares issued by an Irish incorporated company and associated payments falls
within this definition. In addition, dividends or payments on redemption or purchase of

55

shares and payments on a liquidation of an Irish incorporated company would fall within this definition. At present, the Transfers Act prohibits financial transfers
involving the late Slobodan Milosevic and associated persons, Burma (Myanmar), Belarus, certain persons indicted by the International Criminal Tribunal for the
former  Yugoslavia,  the  late  Osama  bin  Laden,  Al-Qaida,  the  Taliban  of  Afghanistan,  Democratic  Republic  of  Congo,  Democratic  People’s  Republic  of  Korea
(North Korea), Iran, Iraq, Côte d’Ivoire, Lebanon, Liberia, Zimbabwe, Sudan, Somalia, Republic of Guinea, Afghanistan, Egypt, Eritrea, Libya, Syria, Tunisia,
Ukraine, certain known terrorists and terrorist groups, and countries that harbor certain terrorist groups, without the prior permission of the Central Bank of Ireland.

Irish Taxes Applicable to U.S. Holders

Withholding Tax on Dividends

While we have no current plans to pay dividends, dividends on our ordinary shares would generally be subject to Irish Dividend Withholding Tax (“DWT”)

at 25%, unless an exemption applies.

Dividends on our ordinary shares that are owned by residents of the U.S. and held beneficially through the Depositary Trust Company (“DTC”) will not be

subject to DWT provided that the address of the beneficial owner of the ordinary shares in the records of the broker is in the U.S.

Dividends on our ordinary shares that are owned by residents of the U.S. and held directly (outside of DTC) will not be subject to DWT provided that the
shareholder has completed the appropriate Irish DWT form and this form remains valid. Such shareholders must provide the appropriate Irish DWT form to our
transfer agent at least seven business days before the record date for the first dividend payment to which they are entitled.

If any shareholder who is resident in the U.S. receives a dividend subject to DWT, he or she should generally be able to make an application for a refund

from the Irish Revenue Commissioners on the prescribed form.

While the U.S./Ireland Double Tax Treaty contains provisions regarding withholding, due to the wide scope of the exemptions from DWT available under

Irish domestic law, it would generally be unnecessary for a U.S. resident shareholder to rely on the treaty provisions.

Income Tax on Dividends

A shareholder who is neither resident nor ordinarily resident in Ireland and who is entitled to an exemption from DWT generally has no additional liability to
Irish income tax or to the universal social charge on a dividend from us unless that shareholder holds their ordinary shares in connection with a trade or business
carried on by such shareholder in Ireland through a branch or agency.

A  shareholder  who  is  neither  resident  nor  ordinarily  resident  in  Ireland  and  who  is  not  entitled  to  an  exemption  from  DWT  generally  has  no  additional
liability to Irish income tax or to the universal social charge on a dividend from us. The DWT deducted by us discharges the liability to Irish income tax and to the
universal social charge. This however is not the case where the shareholder holds their ordinary shares in connection with a trade or business carried on by such
shareholder in Ireland through a branch or agency.

Irish Tax on Capital Gains

A shareholder who is neither resident nor ordinarily resident in Ireland and does not hold their shares in connection with a trade or business carried on by

such shareholder in Ireland through a branch or agency should not be within the charge to Irish tax on capital on a disposal of our shares.

Capital Acquisitions Tax

Irish  Capital  Acquisitions  Tax  (“CAT”)  is  comprised  principally  of  gift  tax  and  inheritance  tax.  CAT  could  apply  to  a  gift  or  inheritance  of  our  ordinary
shares irrespective of the place of residence, ordinary residence or domicile of the parties. This is because our ordinary shares are regarded as property situated in
Ireland as our share register must be held in Ireland. The person who receives the gift or inheritance has primary liability for CAT.

CAT is currently levied at a rate of 33% above certain tax-free thresholds. The appropriate tax-free threshold is dependent upon (i) the relationship between
the donor and the donee and (ii) the aggregation of the values of previous gifts and inheritances received by the donee from persons within the same category of
relationship for CAT purposes. Gifts and

56

inheritances passing between spouses are exempt from CAT. Our shareholders should consult their own tax advisers as to whether CAT is creditable or deductible
in computing any domestic tax liabilities.

Stamp Duty

Irish stamp duty may be payable in respect of transfers of our ordinary shares (currently at the rate of 1% of the price paid or the market value of the shares

acquired, if greater). Payment of any Irish stamp duty is generally a legal obligation of the transferee.

A transfer of our ordinary shares from a seller who holds shares through DTC to a buyer who holds the acquired shares through DTC should not be subject to
Irish stamp duty. A transfer of our ordinary shares (i) by a seller who holds shares outside of DTC to any buyer, or (ii) by a seller who holds the shares through
DTC to a buyer who holds the acquired shares outside of DTC, may be subject to Irish stamp duty. Shareholders wishing to transfer their shares into or out of DTC
may do so without giving rise to Irish stamp duty provided that there is no change in the beneficial ownership of such shares and the transfer into or out of DTC is
not effected in contemplation of a subsequent sale of such shares to a third party. In order to benefit from this exemption from Irish stamp duty, the seller must
confirm to us that there is no change in the ultimate beneficial ownership of the shares as a result of the transfer and there is no agreement for the sale of the shares
by the beneficial owner to a third party being contemplated.

ITEM 6. SELECTED FINANCIAL DATA

The following  selected  consolidated  financial  information  has been derived  from  our audited  consolidated  financial  statements.  The information  set  forth
below is not necessarily indicative of results of future operations and should not be relied upon as an indicator of our future performance. The selected consolidated
financial  data  should  be  read  in  conjunction  with  Item  7,  “Management’s  Discussion  and  Analysis  of  Financial  Condition  and  Results  of  Operations”  and  the
Consolidated Financial Statements and notes thereto included in Item 8 of this Form 10-K in order to fully understand factors that may affect the comparability of
the information presented below.

The following tables set forth our selected consolidated financial data for the periods indicated below (amounts in thousands except for per share amounts).

57

Consolidated Statement of Operations Data:
Collaboration revenue
License revenue

Total revenue

Operating expenses:

Research and development
General and administrative
Restructuring and related impairment charges (credits)

Total operating expenses

Loss from operations
Other income (expense):

Interest income (expense), net
Other income (expense), net

Total other income (expense), net

Loss before income taxes
Provision for (benefit from) income taxes

Net loss

Basic and diluted net loss per share
Shares used to compute basic and diluted net loss per share

Consolidated Balance Sheet Data:

Cash and cash equivalents and restricted cash
Total assets
Other non-current liabilities
Total liabilities
Shareholders’ equity

2020

Year Ended December 31,
2018

2019

2017

2016

564 
289 
853 

74,884 
38,703 
— 
113,587 
(112,734)

814 
— 
814 

50,836 
35,736 
(61)
86,511 
(85,697)

955 
— 
955 

101,183 
42,482 
16,145 
159,810 
(158,855)

27,519 
— 
27,519 

134,547 
48,226 
— 
182,773 
(155,254)

1,369 
(62)
1,307 
(111,427)
(283)
(111,144) $

8,203 
196 
8,399 
(77,298)
379 
(77,677) $

2,692 
48 
2,740 
(156,115)
(470)
(155,645) $

(2.78) $

(1.95) $

(3.93) $

39,915 

39,882 

39,559 

(142)
(2,207)
(2,349)
(157,603)
(4,366)
(153,237) $

(4.07) $

37,654 

1,055 
— 
1,055 

119,534 
41,056 
— 
160,590 
(159,535)

556 
15 
571 
(158,964)
1,144 
(160,108)

(4.66)
34,351 

2020

Year Ended December 31,
2018

2019

2017

2016

298,084  $
332,975 
123,121 
148,969 
184,006 

378,427  $
419,268 
128,633 
146,347 
272,921 

431,715  $
498,796 
160,872 
175,798 
322,998 

421,676  $
496,329 
51,769 
89,140 
407,189 

390,979 
459,976 
53,498 
94,573 
365,403 

$

$

$

58

ITEM 7. MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

In  addition  to  historical  information,  this  Form  10-K  contains  forward-looking  statements  which  may  cause  our  actual  results  to  differ  materially  from
expectations, plans and anticipated results discussed in forward-looking statements. Factors that could cause our actual results to differ materially include, but are
not limited to, the risks and uncertainties set forth in the “Summary of Risks Affecting Our Business” at the beginning of this Form 10-K, Item 1A “Risk Factors”
of this Form 10-K, and in our other filings with the U.S. Securities and Exchange Commission.

This discussion should be read in conjunction with the Consolidated Financial Statements and Notes presented in Item 8 of this Form 10-K.

Overview

Prothena is a late-stage  clinical  company with expertise  in protein dysregulation  and a pipeline  of novel investigational  therapeutics  with the potential  to

change the course of devastating neurodegenerative and rare peripheral amyloid diseases.

Fueled by our deep scientific expertise built over decades of research, we are advancing a pipeline of therapeutic candidates for a number of indications and
novel  targets  for  which  our  ability  to  integrate  scientific  insights  around  neurological  dysfunction  and  the  biology  of  misfolded  proteins  can  be  leveraged.  Our
partnered  programs  include  prasinezumab  (PRX002/RG7935),  in  collaboration  with  Roche  for  the  potential  treatment  of  Parkinson’s  disease  and  other  related
synucleinopathies, and programs that target tau (PRX005), TDP-43 and an undisclosed target in collaboration with Bristol-Myers Squibb for the potential treatment
of  Alzheimer’s  disease,  amyotrophic  lateral  sclerosis  (ALS),  frontotemporal  dementia  (FTD)  or  other  neurodegenerative  diseases.  Our  wholly-owned  programs
include birtamimab for the potential treatment of AL amyloidosis, PRX004 for the potential treatment of ATTR amyloidosis, and a portfolio of programs for the
potential treatment of Alzheimer’s disease including PRX012 that targets Aβ (Amyloid beta).

We were formed on September 26, 2012, under the laws of Ireland and re-registered as an Irish public limited company on October 25, 2012. Our ordinary

shares began trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012, and currently trade on The Nasdaq Global Select Market.

Critical Accounting Policies and Estimates

Management’s discussion and analysis of our financial condition and results of operations is based on our consolidated financial statements, which have
been prepared in accordance with the accounting principles generally accepted in the U.S. (“GAAP”). The preparation of these consolidated financial statements
requires us to make estimates and assumptions for the reported amounts of assets, liabilities, revenues, expenses and related disclosures. We believe the following
policies to be critical to the judgments and estimates used in the preparation of our financial statements.

Revenue Recognition

Revenue is recognized only when we satisfy an identified performance obligation by transferring a promised good or service to a customer.

Contracts with Multiple Performance Obligations

Our License Agreement with Roche contains multiple performance obligations. We account for the individual performance obligations separately if they are
distinct.  Factors  considered  in  the  determination  of  whether  the  license  performance  obligations  are  distinct  included,  among  other  things,  the  research  and
development capabilities of Roche and Roche’s sublicense rights, and for the remaining performance obligations the fact that they are not proprietary and can be
and have been provided by other vendors. The transaction price is allocated to the separate performance obligation on a relative standalone selling price basis.

We do not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less and (ii) contracts for

which we recognize revenue at the amount to which we have the right to invoice for services performed.

59

Collaboration Revenue

Upon adoption of Financial Accounting Standards Board (the “FASB”) Accounting Standards Codification (“ASC”) 606 on January 1, 2018, we recognize
research  and  development  (“R&D”)  reimbursements  as  collaboration  revenue  earned  over  time  as  services  are  performed.  Prior  to  adoption  of  ASC  606,  we
recorded research reimbursement as collaboration revenue and development reimbursement as an offset to R&D expense once the license revenue cap was met.

Milestone Revenue

We  generally  classify  each  of  its  milestones  into  one  of  three  categories:  (i)  clinical  milestones;  (ii)  regulatory  and  development  milestones;  and  (iii)
commercial milestones. Clinical milestones are typically achieved when a product candidate advances into or completes a defined phase of clinical research. For
example, a milestone payment may be due to us upon the initiation of a clinical trial for a new indication. Regulatory and development milestones are typically
achieved upon acceptance of the submission for marketing approval of a product candidate or upon approval to market the product candidate by the U.S. Food and
Drug Administration (the “FDA”) or other regulatory authorities. For example, a milestone payment may be due to us upon submission for marketing approval of a
product candidate by the FDA. Commercial milestones are typically achieved when an approved product reaches certain defined levels of net royalty sales by the
licensee of a specified amount within a specified period.

In  general,  we  consider  such  milestone  payments  as  variable  consideration  with  constraint  and  therefore  we  recognize  the  revenue  from  such  milestone

payments as collaboration revenue at point in time when we can conclude it is probable that a significant revenue reversal will not occur in future periods.

Research and Development

We expense R&D costs as incurred. R&D expenses include, but are not limited to, salary and benefits, share-based compensation, clinical trial activities,
drug  development  and  manufacturing  prior  to  FDA  approval  and  third-party  service  fees,  including  clinical  research  organizations  and  investigative  sites.  We
recognize costs for certain development activities, such as clinical trials, based on an evaluation of the progress to completion of specific tasks using data such as
patient enrollment, clinical site activations, or information provided to us by our vendors on their actual costs incurred. The objective of our accrual policy is to
match  the  recording  of  the  expenses  in  our  Consolidated  Financial  Statements  to  the  actual  services  we  have  received  and  efforts  we  have  expended.  As  such,
expense accruals related to clinical trials are recognized based on our estimate of the degree of completion of the events specified in the specific clinical study or
trial  contract. Payments for these activities  are based on the terms of the individual  arrangements,  which may differ from the pattern of costs incurred, and are
reflected  in  our  Consolidated  Financial  Statements  as  prepaid  or  accrued  research  and  development.  Amounts  due  may  be  fixed  fee,  fee  for  service,  and  may
include upfront payments, monthly payments, and payments upon the completion of milestones or receipt of deliverables.

The  information  contained  in  Note  2  to  the  Consolidated  Financial  Statements  under  the  heading  “Recent  Accounting  Pronouncements”  is  hereby

incorporated by reference into this Part II, Item 7.

Results of Operations

Comparison of Years Ended December 31, 2020, 2019 and 2018

Revenue

Collaboration revenue

License revenue

Total revenue

_________________________

nm = not meaningful

2020

$

$

Percentage Change

2018

2020/2019

2019/2018

955 

— 
955 

(31)%

n/m

5 %

(15)%

n/m

(15)%

Year Ended  
December 31,
2019
(Dollars in thousands)
$

814 

$

564 

289 
853 

$

— 
814 

$

60

Total revenue was $0.9 million, $0.8 million, and $1.0 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Collaboration  revenue  includes  reimbursements  under  our  License  Agreement  with  Roche.  See  Note  7,  “Significant  Agreements”  to  the  Consolidated

Financial Statements regarding the Roche License Agreement for more information.

License revenue includes fees paid under that certain License Agreement entered into on March 1, 2020, between the Company's wholly owned subsidiary,
Prothena Biosciences Limited, and F. Hoffmann-La Roche Ltd and fees paid under an agreement for an option to obtain an exclusive license under certain rights in
intellectual property and materials held by the Company.

Operating Expenses

2020

Research and development

General and administrative

Restructuring and related impairment charges
(credits)

Total operating expenses

$

$

_________________________

nm = not meaningful

Year Ended  
December 31,
2019
(Dollars in thousands)
$

50,836 

$

Percentage Change

2018

2020/2019

2019/2018

74,884 

38,703 

35,736 

101,183 

42,482 

— 
113,587 

$

(61)
86,511 

$

16,145 
159,810 

47 %

8 %

(100)%

31 %

(50)%

(16)%

(100)%

(46)%

Total  operating  expenses  consist  of  R&D  expenses,  general  and  administrative  (“G&A”)  expenses  and  restructuring  and  related  impairment  charges

(credits). Our operating expenses were $113.6 million, $86.5 million and $159.8 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Our  R&D  expenses  primarily  consist  of  personnel  costs  and  related  expenses,  including  share-based  compensation  and  external  costs  associated  with
nonclinical activities and drug development related to our drug programs, including birtamimab (formerly NEOD001), prasinezumab, PRX004 and our discovery
programs. Pursuant to our License Agreement with Roche, we make payments to Roche for our share of the development expenses incurred by Roche related to
the prasinezumab program, which is included in our R&D expense.

Our G&A expenses primarily consist of professional service expenses and personnel costs and related expenses, including share-based compensation.

Research and Development Expenses

Our R&D expense increased by $24.0 million,  or 47%, for  the  year  ended  December  31,  2020,  compared  to  the  prior  year.  The  increase  for  year  ended
December 31, 2020, was primarily due to higher manufacturing costs primarily related to our PRX005, birtamimab and PRX012 programs and to a lesser extent
PRX004, higher collaboration expense with Roche related to the prasinezumab program and higher R&D consulting expense.

For the year ended December 31, 2019, our R&D expenses decreased by $50.3 million, or 50%, compared to the prior year. The decrease for the year ended
December 31, 2019, was primarily due to lower clinical costs (primarily associated with the discontinuation of the NEOD001 program partially offset by higher
costs  for  the  PRX004  program),  lower  personnel  costs  (including  share-based  compensation  expense),  lower  consulting  costs  and  lower  manufacturing  costs
(primarily associated with the discontinuation of the NEOD001 program and to a lesser extent to declines from the PRX004 program, offset in part by increase in
costs for the PRX005 program).

Our  research  activities  are  aimed  at  developing  new  drug  products.  Our  development  activities  involve  the  translation  of  our  research  into  potential  new
drugs. R&D expenses include personnel costs and related expenses, external expenses associated with nonclinical and drug development and materials, equipment
and facilities costs that are allocated to clearly related R&D activities.

The following table sets forth the R&D expenses for our major programs (specifically, any program with successful first dosing in a Phase 1 clinical trial,
which were birtamimab, prasinezumab, PRX003, PRX004 and other R&D expenses for the years ended December 31, 2020, 2019 and 2018, and the cumulative
amounts to date (in thousands):

61

(1)

Birtamimab (NEOD001) 
Prasinezumab (PRX002/RG7935)
PRX003 
PRX004 
Other R&D 

(3)

(5)

(4)

(2)

Year Ended December 31,
2019

2018

2020

Cumulative to
Date

$

$

13,113  $
18,937 
(209)
11,354 
31,689 
74,884  $

1,632  $
13,872 
157 
16,928 
18,247 
50,836  $

56,436  $
14,782 
336 
16,515 
13,114 
101,183 

323,389 
98,339 
58,958 
74,962 

(1)

(2)

(3)

(4)

(5)

Cumulative R&D costs to date for birtamimab (NEOD001) include the costs incurred from the date when the program was separately tracked in preclinical
development. Expenditures in the early discovery stage are not tracked by program and accordingly have been excluded from this cumulative amount.

Cumulative R&D costs to date for prasinezumab and related antibodies include the costs incurred from the date when the program was separately tracked in
nonclinical  development.  Expenditures  in  the  early  discovery  stage  are  not  tracked  by  program  and  accordingly  have  been  excluded  from  this  cumulative
amount. Prasinezumab costs include payments to Roche for our share of the development expenses incurred by Roche related to prasinezumab programs. For
the years ended December 31, 2020, 2019 and 2018, respectively, $0.6 million, $0.8 million and $1.0 million of reimbursements from Roche for development
services were recorded as part of collaboration revenue.

Cumulative R&D costs to date for PRX003 include the costs incurred from the date when the program was separately tracked in nonclinical development.
Expenditures in the early discovery stage are not tracked by program and accordingly have been excluded from this cumulative amount. Based on the Phase
1b multiple ascending dose study results announced in September 2017, we announced that we will not advance PRX003 into mid-stage clinical development
for psoriasis or psoriatic arthritis as previously planned.

Cumulative R&D costs to date for PRX004 include the costs incurred from the date when the program was separately tracked in nonclinical development.
Expenditures in the early discovery stage are not tracked by program and accordingly have been excluded from this cumulative amount.

Other R&D is comprised of preclinical development and discovery programs that have not progressed to first patient dosing in a Phase 1 clinical trial.

We  expect  our  R&D  expenses  to  increase  in  2021  over  the  prior  year,  primarily  due  to  increased  spending  for  our  late  stage  programs,  birtamimab  and

PRX004 .

General and Administrative Expenses

Our G&A expenses increased by $3.0 million, or 8%, for the year ended December 31, 2020, compared to the prior year. The increase for the year ended

December 31, 2020, compared to the prior year, was primarily due to higher costs for our director and officer insurance premiums.

For the year ended December 31, 2019, our G&A expenses decreased by $6.7 million, or 16%, compared to the prior year. The decrease for the year ended
December  31,  2019,  was  primarily  due  to  lower  personnel  costs  (including  share-based  compensation  expense),  receipt  of  sublease  rental  income  from  Sub-
Sublease  of  Current  SSF  Facility,  lower  legal  and  accounting  fees,  and  lower  depreciation  and  other  expenses,  which  was  offset  in  part  by  higher  lease  costs
recorded as operating expenses due to the adoption of ASC 842.

We expect our G&A expenses to increase slightly in 2021 compared to the prior year, primarily related to increases in our director and officer insurance

premiums.

Restructuring and Impairment Related Charges

In May 2018, we commenced a reorganization plan to reduce our operating costs and better align our workforce with the needs of our business following
our decision in April 2018 to discontinue further development of NEOD001. We have completed all of our restructuring activities in fiscal year 2019 and do not
expect  to  incur  additional  costs  associated  with  the  restructuring.  The  cumulative  amount  incurred  to  date  was  $16.1  million,  including  a  restructuring  credit
recorded for the year ended December 31, 2019 of approximately $61,000 primarily due to an adjustment in previously recorded employee termination benefits.
See Note 11, “Restructuring” to the Consolidated Financial Statements for more information.

62

 
Restructuring  charges  incurred  under  this  plan  primarily  consisted  of  employee  termination  benefit  and  contract  termination  costs  (including  costs
associated  with  the  termination  of  our  Commercial  Supply  Contract  with  Rentschler  Biopharma  SE).  Employee  termination  benefits  include  severance  costs,
employee-related  benefits,  supplemental  one-time  termination  payments  and  non-cash  share-based  compensation  expense  related  to  the  acceleration  of  stock
options. All of the cash payments were paid out by the end of the first quarter of 2019.

Impairment charges in 2018 were related to the write off of approximately $0.5 million of long-lived assets surrendered to the landlord as part of the full and
final settlement of our office lease in Dún Laoghaire, Ireland. We entered into a surrender agreement for our office space in Dún Laoghaire, Ireland in October
2018.

Other Income (Expense)

Interest income

Interest expense

Interest income, net

Other income (expense), net
Total other income, net

$

$

2020

Year Ended December 31,
2019
(Dollars in thousands)
$

8,203 

$

1,369 

2018

6,389 

— 

1,369 

(62)
1,307 

$

— 

8,203 

196 
8,399 

$

(3,697)

2,692 

48 
2,740 

Percentage Change

2020/2019

2019/2018

(83)%

nm

(83)%

(132)%

(84)%

28 %

(100)%

205 %

308 %

207 %

Interest income, net decreased by $6.8 million, or 83%, for the year ended December 31, 2020, compared to the prior year, primarily due to lower interest
income from our cash and money market accounts resulting from lower interest rates and lower cash and money market balances. Other income (expense), net for
the year ended December 31, 2020, was primarily foreign exchange losses from transactions with vendors denominated in Euros.

Interest income, net increased by $5.5 million, or 205%, for the year ended December 31, 2019, compared to the prior year, primarily due to higher interest
income in our cash and money market accounts associated with higher interest rates and no recorded interest expense associated with the build-to-suit accounting
upon  the  adoption  of  ASC  842  in  2019.  Other  income  (expense),  net  for  the  year  ended  December  31,  2019,  was  primarily  foreign  exchange  gains  from
transactions with vendors denominated in Euros.

Provision for (benefit from) Income Taxes

2020

Provision for (benefit from) income taxes

$

Year Ended December 31,
2019
(Dollars in thousands)
$

379 

$

(283)

Percentage Change

2018

2020/2019

2019/2018

(470)

(175)%

(181)%

The provision for (benefit from) income taxes were $(0.3) million, $0.4 million and $(0.5) million for the years ended December 31, 2020, 2019 and 2018,
respectively. The benefit from income taxes increased by $0.7 million for the year ended December 31, 2020 as compared to the same period in the prior year,
primarily due to a decrease in tax shortfall related to higher stock option cancellations in the prior year.

The provision for income taxes increased by $0.8 million for the year ended December 31, 2019, compared to the same period of the prior year, primarily
due to an increase in stock option cancellations for which we wrote off the associated deferred tax assets and an increase in the amount disallowed as tax deduction
related to compensation of certain executives during the year.

The tax provisions for all periods presented primarily reflect U.S. federal taxes associated with recurring profits attributable to intercompany services that
our U.S. subsidiary performs for the Company, and to a lesser extent, 2018 also include Swiss taxes associated with intercompany services that our former Swiss
subsidiary performed for the Company. No tax benefit has been recorded related to tax losses recognized in Ireland and any deferred tax assets for those losses are
offset by a valuation allowance.

63

Liquidity and Capital Resources

Overview

Working capital

Cash and cash equivalents

Total assets

Total liabilities

Total shareholders’ equity

December 31,

2020

2019

$

273,436 

$

295,380 

332,975 

148,969 

184,006 

360,661 

375,723 

419,268 

146,347 

272,921 

Working capital was $273.4 million as of December 31, 2020, a decrease of $87.2 million from working capital of $360.7 million as of December 31, 2019.
This decrease in working capital during the year ended December 31, 2020, was primarily due to cash use of $113.6 million for operating expenses (adjusted to
exclude non-cash charges).

As of December 31, 2020, we had $295.4 million in cash and cash equivalents. Although we believe, based on our current business plans, that our existing
cash and cash equivalents will be sufficient to meet our obligations for at least the next twelve months, we anticipate that we will require additional capital in the
future  in  order  to  continue  the  research  and  development  of  our  drug  candidates.  As  of  December  31,  2020,  $153.6  million  of  our  outstanding  cash  and  cash
equivalents related to U.S. operations are considered permanently reinvested. We do not intend to repatriate these funds. However, if these funds were repatriated
back to Ireland, we would incur a withholding tax from the dividend distribution.

We have based this estimate on assumptions that may prove to be wrong, and we could use our available capital resources sooner than we currently expect.
Because of the numerous risks and uncertainties associated with the development and commercialization of our product candidates, we are unable to estimate the
amounts  of  increased  capital  outlays  and  operating  expenses  associated  with  completing  the  development  of  our  product  candidates.  Our  future  capital
requirements will depend on numerous factors, including, without limitation, the timing of initiation, progress, results and costs of our clinical trials; the results of
our research and nonclinical studies; the costs of clinical manufacturing and of establishing commercial manufacturing arrangements; the costs of preparing, filing
and prosecuting patent applications and maintaining, enforcing and defending intellectual property-related claims; the costs and timing of capital asset purchases;
our  ability  to  establish  research  collaborations,  strategic  collaborations,  licensing  or  other  arrangements;  the  costs  to  satisfy  our  obligations  under  current  and
potential future collaborations; the costs of any in-licensing transactions; and the timing, receipt, and amount of revenues or royalties, if any, from any approved
drug candidates. Pursuant to the License Agreement with Roche, in the U.S., we and Roche share all development and commercialization costs, as well as profits,
all of which will be allocated 70% to Roche and 30% to us, for prasinezumab, as well as any other Licensed Products and/or indications for which we opt in to co-
develop and co-fund. Pursuant to the Collaboration Agreement with BMS (formerly Celgene), the Company is eligible to receive payments for commercial and
regulatory milestones and royalties on net sales of Collaboration Products. In order to develop and obtain regulatory approval for our potential products we will
need  to  raise  substantial  additional  funds.  We  expect  to  raise  any  such  additional  funds  through  public  or  private  equity  or  debt  financings,  collaborative
agreements with corporate partners or other arrangements. We cannot assume that such additional financings will be available on acceptable terms, if at all, and
such financings may only be available on terms dilutive to our shareholders.

Cash Flows for the Year Ended December 31, 2020, 2019 and 2018

The following table summarizes, for the periods indicated, selected items in our Consolidated Statements of Cash Flows (in thousands):

Net cash used in operating activities
Net cash used in investing activities
Net cash provided by financing activities
Net increase (decrease) in cash, cash equivalents and restricted cash

2020

Year Ended December 31,
2019

2018

(80,362)
(196)
215 
(80,343)

(52,969)
(547)
228 
(53,288)

(28,276)
(1,729)
40,044 
10,039 

64

 
Cash Used in Operating Activities

Net cash used in operating activities was $80.4 million for the year ended December 31, 2020, primarily due to use of $113.6 million for operating expense

(adjusted to exclude non-cash charges of approximately $27.3 million) and an increase in accounts payable, accruals and other liabilities.

Net cash used in operating activities was $53.0 million for the year ended December 31, 2019, primarily due to use of $86.5 million for operating expense

(adjusted to exclude non-cash charges of approximately $29.2 million).

Net cash used in operating activities was $28.3 million for the year ended December 31, 2018, primarily due to use of $159.8 million for operating expense
(adjusted to exclude non-cash charges) and a decrease in accounts payable and accrued liabilities, which were partially offset by $110.2 million in deferred revenue
related largely to the upfront payment from the Celgene Collaboration Agreement and reduction in prepaid and other assets.

Cash Used in Investing Activities

Net cash used in investing activities was $0.2 million, $0.5 million and $1.7 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Net cash used in investing activities for the years ended December 31, 2020, 2019 and 2018 was primarily related to purchases of property and equipment.

Cash Provided by Financing Activities

Net cash provided by financing activities was $0.2 million and $0.2 million for the years ended December 31, 2020, and 2019, respectively,  which were

proceeds from issuances of ordinary shares upon exercises of stock options.

Net  cash  provided  by  financing  activities  was  $40.0  million  for  the  year  ended  December  31,  2018,  primarily  from  the  $39.8  million  proceeds  from
Celgene’s subscription of ordinary shares at market value and, to a lesser extent, from the $4.7 million proceeds from issuances of ordinary shares upon exercises
of stock options, which were partially offset by cash payments of $4.4 million related to a build-to-suit lease obligation.

Off-Balance Sheet Arrangements

At December 31, 2020, we were not a party to any off-balance sheet arrangements that have, or are reasonably likely to have, a current or future effect on

our financial condition, changes in financial condition, revenue or expenses, results of operations, liquidity, capital expenditures or capital resources.

Contractual Obligations

Our contractual obligations as of December 31, 2020, consisted of minimum cash payments under operating leases of $19.1 million, purchase obligations of
$10.9 million (of which $3.6 million is included in accrued current liabilities), and contractual obligations under license agreements of $0.8 million (of which $0.1
million is included in accrued current liabilities). Purchase obligations consist of non-cancelable purchase commitments to suppliers. Operating leases represent our
future minimum rental commitments under our non-cancelable operating leases.

In  March  2016,  we  entered  into  a  noncancelable  operating  sublease  to  lease  128,751  square  feet  of  office  and  laboratory  space  in  South  San  Francisco,
California.  We are  obligated  to make  lease  payments  totaling  approximately  $39.2 million  over the lease  term.  Of this  obligation,  approximately  $19.0 million
remains outstanding as of December 31, 2020.

In September 2018, we entered into an agreement to lease an office space in Dublin, Ireland. The current lease term expires on November 30, 2021. The
Dublin Lease also has an automatic renewal clause, pursuant to which the agreement will be extended automatically for successive periods equal to the current
term but no less than 3 months, unless the agreement is cancelled by us. As of December 31, 2020, we are obligated to make lease payments over the remaining
term of the lease of approximately €22,000, or $27,000 as converted using an exchange rate as of December 31, 2020.

65

The following is a summary of our contractual obligations as of December 31, 2020 (in thousands):

Operating leases

 (1)

Purchase obligations
Contractual obligations under

license agreements 

Total

(2)

$

$

2021

2022

2023

2024

2025

Total
19,077 

10,900 

$

6,192 

$

6,350 

$

6,535 

$

10,900 

— 

— 

785 
30,762 

$

180 
17,272 

$

70 
6,420 

$

70 
6,605 

$

— 

— 

60 
60 

$

$

— 

— 

60 
60 

Thereafter
— 

$

— 

345 
345 

$

(1) 

See Note 6, “Commitments and Contingencies” to our Consolidated Financial Statements.

(2) 

Excludes future obligations pursuant to the cost-sharing arrangement under our License Agreement with Roche. Amounts of such obligations, if any, cannot be
determined at this time.

ITEM 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

Foreign Currency Risk

Our  business  is  primarily  conducted  in  U.S.  dollars  except  for  our  agreements  with  contract  manufacturers  for  drug  supplies  which  are  denominated  in
Euros. For the year ended December 31, 2020 we recorded a loss on foreign currency exchange rate differences of approximately $62,000 and a gain of $196,000
during the year ended December 31, 2019. If we increase our business activities that require the use of foreign currencies, we may be exposed to losses if the Euro
and other such currencies continue to strengthen against the U.S. dollar.

Interest Rate Risk

Our exposure to interest rate risk is limited to our cash equivalents, which consist of accounts maintained in money market funds. We have assessed that
there  is  no  material  exposure  to  interest  rate  risk  given  the  nature  of  money  market  funds.  In  general,  money  market  funds  are  not  subject  to  interest  rate  risk
because the interest paid on such funds fluctuates with the prevailing interest rate. Accordingly, our interest income fluctuates with short-term market conditions.

In the future, we anticipate that our exposure to interest rate risk will primarily be related to our investment portfolio. We intend to invest any surplus funds
in  accordance  with  a  policy  approved  by  our  board  of  directors  which  will  specify  the  categories,  allocations,  and  ratings  of  securities  we  may  consider  for
investment.  The  primary  objectives  of  our  investment  policy  are  to  preserve  principal  and  maintain  proper  liquidity  to  meet  our  operating  requirements.  Our
investment  policy  also  specifies  credit  quality  standards  for  our  investments  and  limits  the  amount  of  credit  exposure  to  any  single  issue,  issuer  or  type  of
investment.

Credit Risk

Financial instruments that potentially subject us to concentration of credit risk consist of cash and cash equivalents and accounts receivable. We place our
cash and cash equivalents with high credit quality financial institutions and pursuant to our investment policy, we limit the amount of credit exposure with any one
financial institution. Deposits held with banks may exceed the amount of insurance provided on such deposits. We have not experienced any losses on our deposits
of cash and cash equivalents. The Company's credit risk exposure is up to the extent recorded on the Company's Consolidated Balance Sheets.

66

 
ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

INDEX TO CONSOLIDATED FINANCIAL STATEMENTS

Consolidated Financial Statements:

Reports of Independent Registered Public Accounting Firm
Consolidated Balance Sheets as of December 31, 2020 and 2019
Consolidated Statements of Operations for the years ended December 31, 2020, 2019 and 2018
Consolidated Statements of Cash Flows for the years ended December 31, 2020, 2019 and 2018
Consolidated Statements of Shareholders’ Equity for the years ended December 31, 2020, 2019 and 2018
Notes to the Consolidated Financial Statements

Page

68
70
71
72
74
75

67

Report of Independent Registered Public Accounting Firm

To the Shareholders and Board of Directors
Prothena Corporation plc:

Opinion on the Consolidated Financial Statements

We have audited the accompanying consolidated balance sheets of Prothena Corporation plc and subsidiaries (the Company) as of December 31, 2020 and 2019,
the related consolidated statements of operations, shareholders’ equity, and cash flows for each of the years in the three-year period ended December 31, 2020 and
the related notes (collectively, the consolidated financial statements). In our opinion, the consolidated financial statements present fairly, in all material respects,
the financial position of the Company as of December 31, 2020 and 2019, and the results of its operations and its cash flows for each of the years in the three-year
period ended December 31, 2020, in conformity with U.S. generally accepted accounting principles.

Change in Accounting Principle

As discussed in Note 6 to the consolidated financial statements, the Company has changed its method of accounting for leases as of January 1, 2019 due to the
adoption of Financial Accounting Standards Board’s Accounting Standards Codification (ASC) Topic 842, Leases.

Basis for Opinion

These consolidated financial statements are the responsibility of the Company’s management. Our responsibility is to express an opinion on these consolidated
financial  statements  based  on  our  audits.  We  are  a  public  accounting  firm  registered  with  the  Public  Company  Accounting  Oversight  Board  (United  States)
(PCAOB)  and  are  required  to  be  independent  with  respect  to  the  Company  in  accordance  with  the  U.S.  federal  securities  laws  and  the  applicable  rules  and
regulations of the Securities and Exchange Commission and the PCAOB.

We  conducted  our  audits  in  accordance  with  the  standards  of  the  PCAOB.  Those  standards  require  that  we  plan  and  perform  the  audit  to  obtain  reasonable
assurance about whether the consolidated financial statements are free of material misstatement, whether due to error or fraud. The Company is not required to
have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits, we are required to obtain an understanding of
internal  control  over  financial  reporting  but  not  for  the  purpose  of  expressing  an  opinion  on  the  effectiveness  of  the  Company’s  internal  control  over  financial
reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the consolidated financial statements, whether due to error or fraud, and
performing  procedures  that  respond  to those risks. Such procedures  included  examining,  on a test  basis, evidence  regarding  the  amounts  and disclosures  in the
consolidated financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as
evaluating the overall presentation of the consolidated financial statements. We believe that our audits provide a reasonable basis for our opinion.

Critical Audit Matter

The critical audit matter communicated below is a matter arising from the current period audit of the consolidated financial statements that was communicated or
required to be communicated to the audit committee and that: (1) relates to accounts or disclosures that are material to the consolidated financial statements and (2)
involved our especially challenging, subjective, or complex judgments. The communication of a critical audit matter does not alter in any way our opinion on the
consolidated financial statements, taken as a whole, and we are not, by communicating the critical audit matter below, providing a separate opinion on the critical
audit matter or on the accounts or disclosures to which it relates.

Evaluation of Accrued Research and Development Costs

As  discussed  in  Note  2  to  the  consolidated  financial  statements,  research  and  development  costs  are  expensed  by  the  Company  as  incurred.  Costs  for  certain
development  activities,  such  as  clinical  trials,  are  recognized  based  on  an  evaluation  of  the  progress  to  completion  of  specific  tasks  using  data  such  as  patient
enrollment, clinical site activations, or information provided to the Company by its vendors, including clinical research organizations and investigative sites, on
their actual costs incurred. Expense accruals related to clinical trials are recognized based on the Company’s estimate of the degree of completion of the

68

events specified in the specific clinical study or trial contract. Payments for these activities are based on the terms of the individual arrangements, which may differ
from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid or accrued research and development.

We identified the evaluation of accrued research and development costs relating to clinical research organizations and investigative sites as a critical audit matter.
These  estimates  are  based  on  certain  assumptions  and  inputs  that  can  be  challenging  to  assess,  including  the  evaluation  of  the  status  of  and  costs  incurred  for
outsourced research and development programs and project milestones achieved. Complex and subjective auditor judgment was involved in evaluating the status of
the clinical trials used to determine accrued research and development costs.

The  following  are  the  primary  procedures  we  performed  to  address  this  critical  audit  matter.  We  evaluated  the  design and  tested  the  operating  effectiveness  of
certain  internal  controls  related  to  the  Company’s  process  to  estimate  the  accrued  research  and  development  costs.  This  included  controls  related  to  the
development of the key assumptions listed above. For certain research and development contracts, we agreed the contract amount, duration and any key terms to
the information used in the estimation of accrued research and development costs. We examined underlying documentation and third-party evidence from clinical
research organizations and investigative sites and compared them to the assumptions and inputs that are described above. We assessed the Company’s estimate of
costs  incurred  as  of  December  31,  2020,  which  included  examining  invoices  received  after  December  31,  2020,  but  prior  to  the  issuance  of  the  Company’s
consolidated  financial  statements.  In addition,  we inquired  of the individuals  who are responsible  for monitoring  and tracking  the status  of the clinical  trials  to
understand the progress of the activities.

/s/ KPMG LLP

We have served as the Company’s auditor since 2012
San Francisco, California
February 26, 2021

69

Prothena Corporation plc and Subsidiaries
Consolidated Balance Sheets
(in thousands, except share and per share data)

Assets

December 31,

2020

2019

Current assets:

Cash and cash equivalents
Accounts receivable
Prepaid expenses and other current assets
Restricted cash, current

Total current assets
Non-current assets:

Property and equipment, net
Operating lease right-of-use assets
Deferred tax assets
Restricted cash, non-current
Other non-current assets

Total non-current assets

Total assets

Current liabilities:

Liabilities and Shareholders’ Equity

Accounts payable
Accrued research and development
Income taxes payable, current
Lease liability, current
Other current liabilities

Total current liabilities
Non-current liabilities:

Deferred revenue, non-current
Lease liability, non-current
Other liabilities

Total non-current liabilities
Total liabilities
Commitments and contingencies (Note 6)
Shareholders’ equity:

Euro deferred shares, €22 nominal value:

Authorized shares — 10,000 at December 31, 2020, and 2019
Issued and outstanding shares — none at December 31, 2020 and 2019

Ordinary shares, $0.01 par value:

Authorized shares — 100,000,000 at December 31, 2020, and 2019
Issued and outstanding shares — 39,921,413 and 39,898,561 at December 31, 2020 and 2019, respectively

Additional paid-in capital
Accumulated deficit

Total shareholders’ equity

Total liabilities and shareholders’ equity

 See accompanying Notes to Consolidated Financial Statements.

70

$

$

$

$

295,380  $
15 
2,537 
1,352 
299,284 

2,551 
17,811 
11,644 
1,352 
333 
33,691 
332,975  $

4,117  $
9,044 
36 
5,512 
7,139 
25,848 

110,242 
12,326 
553 
123,121 
148,969 

— 

399 

375,723 
68 
2,584 
— 
378,375 

3,874 
23,274 
9,956 
2,704 
1,085 
40,893 
419,268 

1,242 
5,826 
5 
5,101 
5,540 
17,714 

110,242 
17,838 
553 
128,633 
146,347 

— 

399 

966,636 
(783,029)
184,006 
332,975  $

944,407 
(671,885)
272,921 
419,268 

 
Prothena Corporation plc and Subsidiaries
Consolidated Statements of Operations
(in thousands, except per share data)

Collaboration revenue
License revenue

Total revenue

Operating expenses:

Research and development
General and administrative
Restructuring and related impairment charges (credits)

Total operating expenses

Loss from operations
Other income (expense):
Interest income, net
Other income (expense), net

Other income, net
Loss before income taxes
Provision for (benefit from) income taxes

Net loss

Basic and diluted net loss per share

Shares used to compute basic and diluted net loss per share

Year Ended  
December 31,
2019

2020

564  $
289 
853 

$

814 
— 
814 

74,884 
38,703 
— 
113,587 
(112,734)

1,369 
(62)
1,307 
(111,427)
(283)
(111,144) $
(2.78) $

39,915 

50,836 
35,736 
(61)
86,511 
(85,697)

8,203 
196 
8,399 
(77,298)
379 
(77,677)
(1.95)

39,882 

$
$

$

$

$
$

2018

955 
— 
955 

101,183 
42,482 
16,145 
159,810 
(158,855)

2,692 
48 
2,740 
(156,115)
(470)
(155,645)
(3.93)

39,559 

See accompanying Notes to Consolidated Financial Statements.

71

 
Prothena Corporation plc and Subsidiaries
Consolidated Statements of Cash Flows
(in thousands)

Operating activities
Net loss
Adjustments to reconcile net loss to cash used in operating activities:

Depreciation and amortization
Share-based compensation
Restructuring share-based compensation
Deferred income taxes
Interest expense under build-to-suit lease obligation
Amortization of right-of-use assets
Loss from disposal of fixed assets
Changes in operating assets and liabilities:

Accounts receivable
Prepaid and other assets
Deferred revenue
Accounts payable, accruals and other liabilities
Restructuring liability
Operating lease liabilities

Net cash used in operating activities

Investing activities

Purchases of property and equipment
Proceeds from disposal of fixed assets

Net cash used in investing activities

Financing activities

Proceeds from subscription of ordinary shares
Proceeds from issuance of ordinary shares upon exercise of stock options
Reduction of build-to-suit lease obligation

Net cash provided by financing activities

Net increase (decrease) in cash, cash equivalents and restricted cash
Cash, cash equivalents and restricted cash, beginning of the year
Cash, cash equivalents and restricted cash, end of the period

Supplemental disclosures of cash flow information

Cash paid (refunds received) for income taxes, net

Supplemental disclosures of non-cash investing and financing activities

Acquisition of property and equipment included in accounts payable and accrued liabilities

Right-of-use assets recorded upon adoption of ASC 842

Reduction of build-to-suit lease obligation upon adoption of ASC 842

Reduction of amounts capitalized under build-to-suit lease upon adoption of ASC 842

Reduction of capitalized interest under build-to-suit lease upon adoption of ASC 842

Year Ended December 31,

2020

2019

2018

$

(111,144) $

(77,677) $

(155,645)

1,514 
22,014 
— 
(1,688)
— 
5,463 
— 

53 
799 
— 
7,728 
— 
(5,101)
(80,362)

(196)
— 
(196)

1,564 
23,585 
— 
(1,248)
— 
5,256 
— 

— 
807 
— 
(78)
(461)
(4,717)
(52,969)

(555)
8 
(547)

— 
215 
— 
215 
(80,343)
378,427 
298,084  $

— 
228 
— 
228 
(53,288)
431,715 
378,427  $

3,216 
26,062 
948 
(1,589)
3,696 
— 
584 

238 
9,139 
110,242 
(25,628)
461 
— 
(28,276)

(1,768)
39 
(1,729)

39,758 
4,686 
(4,400)
40,044 
10,039 
421,676 
431,715 

1,367  $

1,580  $

(995)

—  $

—  $

—  $

—  $

—  $

5  $

28,530  $

(51,546) $

(46,760) $

(1,099) $

90 

— 

— 

— 

— 

$

$

$

$

$

$

$

See accompanying Notes to Consolidated Financial Statements.

72

 
The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the statement of financial position that sum to the total of
the same such amounts shown in the Consolidated Statements of Cash Flows.

Cash and cash equivalents
Restricted cash, current
Restricted cash, non-current

Total cash, cash equivalents and restricted cash, end of the period

Year Ended December 31,

2020
295,380  $
1,352 
1,352 
298,084  $

2019
375,723  $
— 
2,704 
378,427 

$

$

2018

427,659 
— 
4,056 
431,715 

73

Prothena Corporation plc and Subsidiaries
Consolidated Statements of Shareholders' Equity
(in thousands, except share data)

Ordinary Shares

Balances at December 31, 2017
Issuance of ordinary shares under share subscription agreement

with Celgene

Share-based compensation
Restructuring share-based compensation
Issuance of ordinary shares upon exercise of stock options
Net loss
Balances at December 31, 2018
Cumulative adjustment to accumulated deficit upon adoption of

ASC-842

Share-based compensation
Issuance of ordinary shares upon exercise of stock options
Net loss
Balances at December 31, 2019
Share-based compensation
Issuance of ordinary shares upon exercise of stock options
Net loss
Balances at December 31, 2020

Shares
38,482,764  $

1,174,536 
— 
— 
206,411 
— 
39,863,711 

— 
— 
34,850 
— 
39,898,561 
— 
22,852 
— 

39,921,413  $

Amount

Additional 
Paid-in 
Capital

Accumulated 
Deficit

Total 
Shareholders'
Equity

385  $

849,154  $

(442,350) $

407,189 

12 
— 
— 
2 
— 
399 

— 
— 
— 
— 
399 
— 
— 
— 
399  $

39,746 
26,062 
948 
4,684 
— 
920,594 

— 
23,585 
228 
— 
944,407 
22,014 
215 
— 
966,636  $

— 
— 
— 
— 
(155,645)
(597,995)

3,787 
— 
— 
(77,677)
(671,885)
— 
— 
(111,144)
(783,029) $

39,758 
26,062 
948 
4,686 
(155,645)
322,998 

3,787 
23,585 
228 
(77,677)
272,921 
22,014 
215 
(111,144)
184,006 

See accompanying Notes to Consolidated Financial Statements.

74

1. Organization

Description of Business

Notes to the Consolidated Financial Statements

Prothena  Corporation  plc  (“Prothena”  or  the  “Company”)  is  a  late-stage  clinical  company  with  expertise  in  protein  dysregulation  and  a  pipeline  of

investigational therapeutics with the potential to change the course of devastating rare peripheral amyloid and neurodegenerative diseases.

Fueled  by  its  deep  scientific  expertise  built  over  decades  of  research,  the  Company  is  advancing  a  pipeline  of  therapeutic  candidates  for  a  number  of
indications  and  novel  targets  for  which  its  ability  to  integrate  scientific  insights  around  neurological  dysfunction  and  the  biology  of  misfolded  proteins  can  be
leveraged.  The  Company’s  wholly-owned  programs  include  birtamimab  for  the  potential  treatment  of  AL  amyloidosis,  PRX004  for  the  potential  treatment  of
ATTR  amyloidosis,  and  a  portfolio  of  programs  for  the  potential  treatment  of  Alzheimer’s  disease  including  PRX012  that  targets  Aβ  (Amyloid  beta).  The
Company’s  partnered  programs  include  prasinezumab,  in  collaboration  with  Roche  for  the  potential  treatment  of  Parkinson’s  disease  and  other  related
synucleinopathies, and programs that target tau (PRX005), TDP-43 and an undisclosed target in collaboration with Bristol-Myers Squibb for the potential treatment
of Alzheimer’s disease, amyotrophic lateral sclerosis (ALS).

The Company was formed on September 26, 2012, under the laws of Ireland and re-registered as an Irish public limited company on October 25, 2012. The
Company's ordinary shares began trading on The Nasdaq Global Market under the symbol “PRTA” on December 21, 2012, and currently trade on The Nasdaq
Global Select Market.

Liquidity and Business Risks

As of December 31, 2020, the Company had an accumulated deficit of $783.0 million and cash and cash equivalents of $295.4 million.

Based on the Company's business plans, management believes that the Company’s cash and cash equivalents at December 31, 2020, are sufficient to meet its
obligations for at least the next twelve months. To operate beyond such period, or if the Company elects to increase its spending on research and development
programs  significantly  above  current  long-term  plans  or  enters  into  potential  licenses  and  or  other  acquisitions  of  complementary  technologies,  products  or
companies, the Company may need additional capital. The Company expects to continue to finance future cash needs that exceed its cash from operating activities
primarily through its current cash and cash equivalents, its collaborations with Roche and Bristol-Myers Squibb, and, to the extent necessary, through proceeds
from public or private equity or debt financings, loans and other collaborative agreements with corporate partners or other arrangements.

The Company is subject to a number of risks, including but not limited to: the uncertainty of the Company’s research and development (“R&D”) efforts
resulting in future successful commercial products; obtaining regulatory approval for its product candidates; its ability to successfully commercialize its product
candidates,  if  approved;  significant  competition  from  larger  organizations;  reliance  on  the  proprietary  technology  of  others;  dependence  on  key  personnel;
uncertain  patent  protection;  dependence  on  corporate  partners  and  collaborators;  the  outbreak  of  the  novel  strain  of  coronavirus  SARS-CoV-2;  and  possible
restrictions on reimbursement from governmental agencies and healthcare organizations, as well as other changes in the healthcare industry.

2. Summary of Significant Accounting Policies

Basis of Preparation and Presentation of Financial Information

These Consolidated  Financial  Statements  have been prepared  in accordance  with the  accounting  principles  generally  accepted  in the U.S. (“GAAP”) and
with the instructions for Form 10-K and Regulations S-X statements. The Consolidated Financial Statements of Prothena Corporation plc are presented in U.S.
dollars, which is the functional currency of the Company and its consolidated subsidiaries. These Consolidated Financial Statements include the accounts of the
Company and its consolidated subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Certain amounts in the Consolidated
Financial Statements have been reclassified to conform to the current year presentation.

Use of Estimates

The preparation of the Consolidated Financial Statements in conformity with GAAP requires management to make judgments, estimates and assumptions

that affect the reported amounts of assets, liabilities, revenues and expenses, and related

75

disclosures.  On  an  ongoing  basis,  management  evaluates  its  estimates,  including  critical  accounting  policies  or  estimates  related  to  revenue  recognition,  share-
based  compensation,  research  and  development  expenses  and  leases.  The  Company  bases  its  estimates  on  historical  experience  and  on  various  other  market
specific  and  other  relevant  assumptions  that  management  believes  to  be  reasonable  under  the  circumstances,  the  results  of  which  form  the  basis  for  making
judgments  about  the  carrying  values  of  assets  and  liabilities  that  are  not  readily  apparent  from  other  sources.  Because  of  the  uncertainties  inherent  in  such
estimates, actual results may differ materially from these estimates.

Significant Accounting Policies

Cash and Cash Equivalents

The Company considers all highly liquid investments held at financial institutions, such as commercial paper, money market funds, and other money market

securities with original maturities of three months or less at date of purchase to be cash equivalents.

Restricted Cash

Cash  accounts  that  are  restricted  to  withdrawal  or  usage  are  presented  as  restricted  cash.  As  of  December  31,  2020,  the  Company  had  $2.7  million  of
restricted cash held by a bank in a certificate of deposit as collateral to a standby letter of credit under an operating lease. Of this total, $1.4 million is classified as a
current  asset  and  the  remaining  amount  is  classified  as  a  non-current  asset  in  the  Company's  Consolidated  Balance  Sheets.  See  Note  6,  "Commitments  and
Contingencies" for additional information regarding our operating lease.

Property and Equipment, net

Property and equipment, net are stated at cost less accumulated depreciation and amortization. Depreciation and amortization is computed using the straight-
line method over the estimated useful lives of the related assets. Maintenance and repairs are charged to expense as incurred, and improvements and betterments
are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain
or loss is reflected in operations in the period realized. Depreciation and amortization periods for the Company’s property, plant and equipment are as follows: 

Machinery and equipment
Leasehold improvements
Purchased computer software

Impairment of Long-lived Assets

Useful Life
4-7 years
Shorter of expected useful life or lease term
4 years

Long-lived  assets  are  reviewed  for  impairment  whenever  events  or  changes  in  circumstances  indicate  that  the  carrying  amount  of  an  asset  may  not  be
recoverable or the estimated useful life is no longer appropriate. If circumstances require that a long-lived asset be tested for possible impairment, the Company
compares the undiscounted cash flows expected to be generated by the asset to the carrying amount of the asset. If the carrying amount of the long-lived asset is
not  recoverable  on  an  undiscounted  cash  flow  basis,  an  impairment  is  recognized  to  the  extent  that  the  carrying  amount  exceeds  its  fair  value.  The  Company
determines  fair  value  using  the  income  approach  based  on  the  present  value  of  expected  future  cash  flows.  The  Company’s  cash  flow  assumptions  consider
historical and forecasted revenue and operating costs and other relevant factors.

On  October  30,  2018,  the  Company  entered  into  a  surrender  agreement  for  its  office  space  in  Dún  Laoghaire,  Ireland.    The  Company  paid  €270,000,  or
$309,000  as  converted  using  an  exchange  rate  as  of  November  28,  2018,  as  full  and  final  settlement  of  outstanding  contractual  obligations  of  $1.6  million  in
exchange  for  surrender  and  assignment  to  the  landlord  including  surrender  of  approximately  $0.5  million  of  long-lived  assets,  which  was  recorded  as  an  asset
impairment in the year ended December 31, 2018. There were no impairment charges recorded during the years ended December 31, 2020, and 2019.

Leases

At the inception, the Company determines if an arrangement is a lease. If so, the Company evaluates the lease agreement to determine whether the lease is an
operating or capital using the criteria in ASC 842. The Company does not recognize right-of-use assets and lease liabilities that arise from short-term leases for any
class of underlying assets.

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When lease agreements also require the Company to make additional payments for taxes, insurance and other operating expenses incurred during the lease
period, such payments are expensed as incurred. See Note 6, “Commitments and Contingencies,” which provides additional details on the Company's current lease
arrangements.

Operating Leases

Operating leases are included in the operating lease right-of-use assets, lease liability, current and lease liability, non-current in the Company's Consolidated
Balance Sheets. Operating lease right-of-use assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the
Company’s obligation to make lease payments arising from the lease. Operating lease right-of-use assets and liabilities are recognized at the lease commencement
date  based  on  the  present  value  of  minimum  lease  payments  over  the  lease  term.  In  determining  the  present  value  of  lease  payments,  the  Company  uses  its
incremental  borrowing  rate  based  on  information  available  at  the  lease  commencement  date.  The  operating  lease  right-of-use  assets  also  include  any  lease
prepayments made and exclude lease incentives including rent abatements and/or concessions and rent holidays. Tenant improvements made by the Company as a
lessee in which they are deemed to be owned by the lessor is viewed as lease prepayments by the Company and included in the operating lease right-of-use assets.
Lease expense is recognized on a straight-line basis over the expected lease term. For lease agreements entered after the adoption of ASC 842 that include lease
and non-lease components, such components are generally accounted separately.

Revenue Recognition

Revenue is recognized only when the Company satisfies an identified performance obligation by transferring a promised good or service to a customer.

Contracts with Multiple Performance Obligations

The  Company’s  License  Agreement  with  Roche  contains  multiple  performance  obligations.  The  Company  accounts  for  the  individual  performance
obligations separately if they are distinct. Factors considered in the determination of whether the license performance obligations are distinct included, among other
things, the research and development capabilities of Roche and Roche’s sublicense rights, and for the remaining performance obligations the fact that they are not
proprietary and can be and have been provided by other vendors. The transaction price is allocated to the separate performance obligation on a relative standalone
selling price basis.

The Company does not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less and (ii)

contracts for which the Company recognize revenue at the amount to which the Company has the right to invoice for services performed.

Collaboration Revenue

Upon adoption of ASC 606, the Company recognizes research and development reimbursements as collaboration revenue earned over time as services are
performed. Prior to adoption of ASC 606, the Company recorded research reimbursement as collaboration revenue and development reimbursement as an offset to
R&D expense once the license revenue cap was met.

Milestone Revenue

The Company generally classifies each of its milestones into one of three categories: (i) clinical milestones; (ii) regulatory and development milestones; and
(iii) commercial milestones. Clinical milestones are typically achieved when a product candidate advances into or completes a defined phase of clinical research.
For example, a milestone payment may be due to the Company upon the initiation of a clinical trial for a new indication. Regulatory and development milestones
are typically achieved upon acceptance of the submission for marketing approval of a product candidate or upon approval to market the product candidate by the
FDA  or  other  regulatory  authorities.  For  example,  a  milestone  payment  may  be  due  to  the  Company  upon  submission  for  marketing  approval  of  a  product
candidate by the FDA. Commercial milestones are typically achieved when an approved product reaches certain defined levels of net royalty sales by the licensee
of a specified amount within a specified period.

In  general,  the  Company  considers  such  milestone  payments  as  variable  consideration  with  constraint  and  therefore  recognizes  the  revenue  from  such
milestone payments as collaboration revenue at point in time when the Company can conclude it is probable that a significant revenue reversal will not occur in
future periods.

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Profit Share Revenue

For  agreements,  with  profit  sharing  arrangements,  the  Company  will  record  its  share  of  the  pre-tax  commercial  profit  as  collaboration  revenue  when  the

profit sharing can be reasonably estimated and that a significant revenue reversal will not occur in future periods.

Royalty Revenue

The  Company  will  recognize  revenue  from  royalties  based  on  licensees'  sales  of  the  Company's  products  or  products  using  the  Company's  technologies.
Royalties are recognized as earned in accordance with the contract terms when royalties from licensees can be reasonably estimated and that a significant revenue
reversal will not occur in future periods. There were no royalties earned during the years ended December 31, 2020, 2019 and 2018.

Taxes, Shipping and Handling

The  Company  excludes  from  the  measurement  of  the  transaction  price  all  taxes  assessed  by  a  governmental  authority  that  are  both  imposed  on  and
concurrent  with  a  specific  revenue-producing  transaction  and  collected  by  the  Company  from  a  customer  (e.g.,  sales,  use,  value  added,  some  excise  taxes).  In
addition, the Company accounts for shipping and handling as activities that are performed after its customers obtain control of the goods as activities to fulfill our
performance obligation to transfer the goods.

Incremental Costs to Obtain or Fulfill a Contract

For costs to obtain a contract, the Company will capitalize such amounts if they are incremental and expected to be recovered. Sales commissions directly
related to obtaining new contracts will be capitalized unless the amortization period is one year or less, at which these costs will be recorded within selling and
general administrative expenses. As of December 31, 2020, the Company does not have such costs capitalized in its Consolidated Balance Sheet.

Research and Development

Research and development costs are expensed as incurred and include, but are not limited to, salary and benefits, share-based compensation, clinical trial
activities, drug development and manufacturing prior to FDA and other regulatory approval and third-party service fees, including clinical research organizations
and  investigative  sites.  Costs  for  certain  development  activities,  such  as  clinical  trials,  are  recognized  based  on  an  evaluation  of  the  progress  to  completion  of
specific tasks using data such as patient enrollment, clinical site activations, or information provided to the Company by its vendors on their actual costs incurred.
The objective of the Company’s accrual policy is to match the recording of the expenses in its Consolidated Financial Statements to the actual services received
and efforts expended. As such, expense accruals related to clinical trials are recognized based on its estimate of the degree of completion of the events specified in
the specific clinical study or trial contract. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of
costs incurred, and are reflected in the Consolidated Financial Statements as prepaid or accrued research and development. Amounts due may be fixed fee, fee for
service, and may include upfront payments, monthly payments, and payments upon the completion of milestones or receipt of deliverables.

Acquired In-Process Research and Development Expense

The  Company  has  acquired  and  may  continue  to  acquire  the  rights  to  develop  and  commercialize  new  drug  candidates  from  third  parties.  The  upfront
payments to acquire license, product or rights, as well as any future milestone payments, are immediately expensed as research and development provided that the
drug has not achieved regulatory approval for marketing and, absent obtaining such approval, has no alternative future use.

Restructuring Charges

The  Company  recognizes  restructuring  charges  related  to  its  reorganization  plan.  In  connection  with  these  activities,  the  Company  records  restructuring
charges  for  contractual  employee  termination  benefits,  one-time  employee  termination  benefits  and  contract  termination  costs.  The  Company  accounts  for  its
restructuring charges as a liability when the obligations are incurred and records such charges at fair value.

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The recognition of restructuring charges requires the Company to make certain judgments and estimates regarding the nature, timing and amount of costs
associated  with  the  planned  reorganization  plan.  To  the  extent  the  Company’s  actual  results  differ  from  its  estimates  and  assumptions,  the  Company  may  be
required to revise the estimates of future liabilities, requiring the recognition of additional restructuring charges or the reduction of liabilities already recognized.
Such changes to previously estimated amounts may be material to the Consolidated Financial Statements. Changes in the estimates of the restructuring charges are
recorded in the period the change is determined.

At the end of each reporting period, the Company evaluates the remaining accrued balances to ensure that no excess accruals are retained and the utilization
of  the  provisions  are  for  their  intended  purpose  in  accordance  with  developed  restructuring  plans.  See  Note  11,  “Restructuring”  for  additional  information
regarding restructuring charges.

Loss Contingencies

Loss contingencies, including claims and legal actions arising in the ordinary course of business, are recorded as liabilities when the likelihood of loss is
probable  and  an  amount  or  range  of  loss  can  be  reasonably  estimated.  The  Company's  accruals  for  losses  are  based  on  management's  judgment  of  all  possible
outcomes and their financial effect, the probability of losses, and where applicable, the consideration of opinions of the Company's legal counsel. The Company’s
accounting  policy  for  legal  costs  related  to  loss  contingencies  is  to  accrue  for  the  probable  fees  that  can  be  reasonably  estimated  and  expensed  as  incurred.
Additionally, the Company records insurance recovery receivable from third party insurers when recovery has been determined to be probable.

Share-based Compensation

To  determine  the  fair  value  of  share-based  payment  awards,  the  Company  uses  the  Black-Scholes  option-pricing  model.  The  determination  of  fair  value
using  the  Black-Scholes  option-pricing  model  is  affected  by  the  Company’s  share  price  as  well  as  assumptions  regarding  a  number  of  complex  and  subjective
variables.  Judgment  is  required  in  determining  the  proper  assumptions  used  in  these  models.  The  assumptions  used  include  the  risk-free  interest  rate,  expected
term, expected volatility and expected dividend yield. Share-based awards, including stock options, are measured at fair value as of the grant date and share-based
compensation  expense  is  recognized  on  a  straight-line  basis  over  the  requisite  service  period  for  each  award.  Further,  share-based  compensation  expense
recognized in the Consolidated Statements of Operations is based on awards expected to vest and therefore the amount of expense has been reduced for estimated
forfeitures. Forfeitures are estimated based on historical experience. If actual forfeitures differ from estimates at the time of grant they will be revised in subsequent
periods.  The  Company  uses  its  historical  volatility  for  the  Company's  stock  to  estimate  expected  volatility.  If  factors  change  and  different  assumptions  are
employed in determining the fair value of share-based awards, the share-based compensation expense recorded in future periods may differ significantly from what
was recorded in the current period (see Note 9, "Share-Based Compensation" for further information).

The Company records any excess tax benefits or tax shortfalls from its equity awards in its Consolidated Statements of Operations in the reporting periods in

which stock options are exercised.

Income Taxes

The Company files its own U.S. and foreign income tax returns and income taxes are presented in the Consolidated Financial Statements using the asset and
liability  method  prescribed  by  the  accounting  guidance  for  income  taxes.  Deferred  tax  assets  (“DTAs”)  and  liabilities  are  determined  based  on  the  difference
between the financial statement and tax basis of assets and liabilities using the enacted tax rates projected to be in effect for the year in which the differences are
expected to reverse. Net deferred tax assets are recorded to the extent the Company believes that these assets will more likely than not be realized. In making such
determination, all available positive and negative evidence is considered, including scheduled reversals of deferred tax liabilities, recent cumulative earnings/losses
by taxing jurisdiction, projected future taxable income, tax planning strategies and recent financial operations. Actual operating results in future years could differ
from our current assumptions, judgments and estimates.

Our significant tax jurisdictions are Ireland and the United States. Estimates are required in determining the Company’s provision for income taxes. Some of
these estimates are based on management’s interpretations of jurisdiction-specific tax laws or regulations. Various internal and external factors may have favorable
or unfavorable effects on the future effective income tax rate of the business. These factors include, but are not limited to, changes in tax laws, regulations and/or
rates, changing interpretations of existing tax laws or regulations, changes in estimates of prior years’ items, past and future levels of R&D spending, the impact of
accounting for share-based compensation, and changes in overall levels of income before taxes.

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The Company did not recognize certain tax benefits from uncertain tax positions within the provision for income taxes. The tax benefit from an uncertain tax
position is recognized only if it is more likely than not the tax position will be sustained on examination by the taxing authorities, based on the technical merits of
the position. The tax benefits recognized in the financial statements from such positions are then measured based on the largest benefit that has a greater than 50%
likelihood of being realized upon settlement. Changes in recognition or measurement are reflected in the period in which the change in judgment occurs. Interest
and penalties related to unrecognized tax benefits are accounted for in income tax expense.

Net Income (Loss) per Ordinary Share

Basic net income (loss) per ordinary share is computed by dividing net income (loss) attributable to ordinary shareholders by the weighted average number
of  ordinary  shares  outstanding  during  the  period.  Diluted  net  income  per  ordinary  share  is  computed  by  giving  effect  to  all  dilutive  potential  ordinary  shares
including options. However, potentially issuable ordinary shares are not used in computing diluted net loss per ordinary share as their effect would be anti-dilutive
due to the loss recorded. In this case, diluted net loss per share is equal to basic net loss per share.

Comprehensive Loss

Comprehensive  income  (loss)  is  comprised  of  net  income  (loss)  and  other  comprehensive  income  (loss).  The  Company  has  no  components  of  other
comprehensive  income  (loss).  Therefore  net  income  (loss)  equals  comprehensive  income  (loss)  for  all  periods  presented  and,  accordingly,  the  Consolidated
Statements of Comprehensive Income (Loss) is not presented in a separate statement.

Segment and Concentration of Risks

The Company operates in one segment. The Company’s chief operating decision maker (the “CODM”), its Chief Executive Officer, manages the Company’s
operations on a consolidated basis for purposes of allocating resources. When evaluating the Company’s financial performance, the CODM reviews all financial
information on a consolidated basis.

Financial instruments that potentially subject the Company to concentration of credit risk consist of cash and cash equivalents and accounts receivable. The
Company  places  its  cash  equivalents  with  high  credit  quality  financial  institutions  and,  by  policy,  limits  the  amount  of  credit  exposure  with  any  one  financial
institution. Deposits held with banks may exceed the amount of insurance provided on such deposits. The Company has not experienced any losses on its deposits
of cash and cash equivalents and its credit risk exposure is up to the extent recorded on the Company's Consolidated Balance Sheet.

The  receivables  recorded  in  the  Consolidated  Balance  Sheets  include  amounts  due  from  a  Roche  entity  located  in  Switzerland.  Collaboration  revenue
recorded in the Consolidated Statements of Operations consists of reimbursement from Roche for research and development services. The Company's credit risk
exposure is up to the extent recorded on the Company's Consolidated Balance Sheet.

As of December 31, 2020 and 2019, $2.6 million and $3.9 million, respectively, of the Company’s property and equipment, net were held in the U.S. and

none were in Ireland.

The Company does not own or operate facilities for the manufacture, packaging, labeling, storage, testing or distribution of nonclinical or clinical supplies of
any of its drug candidates. The Company instead contracts with and relies on third-parties to manufacture, package, label, store, test and distribute all preclinical
development  and  clinical  supplies  of  our  drug  candidates,  and  it  plans  to  continue  to  do  so  for  the  foreseeable  future.  The  Company  also  relies  on  third-party
consultants to assist in managing these third-parties and assist with its manufacturing strategy.

Recent Accounting Pronouncements

On December 18, 2019, the FASB issued Accounting Standards Update 2019-12 ("ASU 2019-12"), Income Taxes (Topic 740): Simplifying the Accounting
for  Income  Taxes,  which  simplifies  the  accounting  for  income  taxes  as  part  of  the  Board’s  overall  initiative  to  reduce  complexity  in  accounting  standards.
Amendments  include  removal  of  certain  exceptions  to  the  general  principles  of  ASC  740,  Income  Taxes  ,  and  simplification  in  several  other  areas  such  as
accounting for a franchise tax (or similar tax) that is partially based on income. While not required to be adopted until 2021 for most calendar year public business
entities  (and 2022 for  other  entities),  early  adoption  is  permitted  for  any  financial  statements.  The  Company  has  completed  its  evaluation  and  believes  that  the
adoption of ASU 2019-12 will not have a significant impact on its consolidated financial statements.

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3. Fair Value Measurements

The  Company  measures  certain  financial  assets  and  liabilities  at  fair  value  on  a  recurring  basis,  including  cash  equivalents.  Fair  value  is  an  exit  price,
representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair
value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability. A three-
tier fair value hierarchy is established as a basis for considering such assumptions and for inputs used in the valuation methodologies in measuring fair value:

Level 1 — Observable inputs such as quoted prices (unadjusted) for identical assets or liabilities in active markets.

Level 2 — Include other inputs that are based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments
in  markets  that  are  not  active,  and  model-based  valuation  techniques  for  which  all  significant  inputs  are  observable  in  the  market  or  can  be
derived from observable market data. Where applicable, these models project future cash flows and discount the future amounts to a present value
using market-based observable inputs including interest rate curves, foreign exchange rates, and credit ratings.

Level 3 — Unobservable inputs that are supported by little or no market activities, which would require the Company to develop its own assumptions.

The fair value hierarchy also requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair
value. The carrying amounts of certain financial instruments, such as cash equivalents, accounts receivable, accounts payable and accrued liabilities, approximate
fair value due to their relatively short maturities, and low market interest rates, if applicable.

Based on the fair value hierarchy, the Company classifies its cash equivalents within Level 1. This is because the Company values its cash equivalents using
quoted  market  prices.  The  Company’s  Level  1  securities  consisted  of  $226.1  million  and  $338.2  million  in  money  market  funds  included  in  cash  and  cash
equivalents at December 31, 2020, and 2019, respectively.

4. Composition of Certain Balance Sheet Items

Property and Equipment, net

Property and equipment, net consisted of the following (in thousands):

Machinery and equipment
Leasehold improvements
Purchased computer software

Less: accumulated depreciation and amortization

Property and equipment, net

December 31,

2020

2019

9,343 
1,278 
1,423 
12,044 
(9,493)
2,551  $

9,312 
1,261 
1,308 
11,881 
(8,007)
3,874 

$

Depreciation expense was $1.5 million, $1.6 million, and $3.2 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Other Current Liabilities

Other current liabilities consisted of the following (in thousands):

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Payroll and related expenses
Professional services
Other

Other current liabilities

5. Net Loss Per Ordinary Share

December 31,

2020

2019

5,927  $
696 
516 
7,139  $

4,818 
400 
322 
5,540 

$

$

Basic net income (loss) per ordinary share is calculated by dividing net income (loss) by the weighted-average number of ordinary shares outstanding during
the period. Shares used in diluted net income per ordinary share would include the dilutive effect of ordinary shares potentially issuable upon the exercise of stock
options  outstanding.  However,  potentially  issuable  ordinary  shares  are  not  used  in  computing  diluted  net  loss  per  ordinary  share  as  their  effect  would  be  anti-
dilutive due to the loss recorded during the years ended December 31, 2020, 2019 and 2018, and therefore diluted net loss per share is equal to basic net loss per
share.

Net loss per ordinary share was determined as follows (in thousands, except per share amounts):

Numerator:
Net loss
Denominator:

Weighted-average ordinary shares outstanding

Net loss per share:

Basic and diluted net loss per share

2020

Year Ended December 31,
2019

2018

$

(111,144) $

(77,677) $

(155,645)

39,915 

39,882 

39,559 

$

(2.78) $

(1.95) $

(3.93)

The equivalent ordinary shares not included in diluted net loss per share because their effect would be anti-dilutive are as follows (in thousands):

Stock options to purchase ordinary shares

6. Commitments and Contingencies

Lease Commitments

2020

Year Ended December 31,
2019

2018

8,745 

7,008 

6,727 

The Company adopted ASC 842, Leases effective January 1, 2019. Prior period amounts have not been adjusted and continued to be reported in accordance
with the Company’s historical accounting under ASC 840. For lease arrangements entered prior to the adoption of ASC 842, right-of-use asset and lease liability
are determined based on the present value of minimum lease payments over the remaining lease term and the Company’s incremental borrowing rate based on
information available as of January 1, 2019. The right-of-use asset also includes any lease prepayments made and excludes unamortized lease incentives including
rent abatements  and/or concessions and rent holidays. Tenant  improvements  made by the Company as a lessee,  in which such improvements  are deemed  to be
owned by the lessor, are viewed as lease prepayments by the Company and are included in the right-of-use asset. Lease expense is recognized on a straight-line
basis over the expected lease term. Total operating lease cost was $6.3 million and $6.4 million for the years ended December 31, 2020, and 2019, respectively.
Total cash paid against the operating lease liability was $6.0 million and $5.8 million for the years ended December 31, 2020, and 2019, respectively.

Prior to the adoption of ASC 842, the Company recognized rent expense for its operating leases on a straight-line basis over the noncancelable lease term
and recorded the difference between cash rent payments and the recognition of rent expense as a deferred rent liability. Where leases contained escalation clauses,
rent  abatements  and/or  concessions,  such  as  rent  holidays  and  landlord  or  tenant  incentives  or  allowances,  the  Company  applied  them  in  the  determination  of
straight-line rent expense over the lease term. The Company recorded the tenant improvement allowance for operating leases as deferred rent and

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associated expenditures as leasehold improvements that were being amortized over the shorter of their estimated useful life or the term of the lease. Rent expense
was $0.7 million for the year ended December 31, 2018.

For the purpose of estimating the incremental borrowing rate in the adoption of ASC 842, the Company inquired with banks that had a business relationship
with the Company to determine the Company's collateralized incremental borrowing rate. The discount rate used to determine the lease liability was 4.25%. There
was no change in the accounting of the Sub-Sublease (as defined below) of the Current SSF Facility (as defined below) upon adoption of ASC 842. Furthermore,
the Company's operating lease in Dublin is not included in the lease liability and right-of-use asset recorded due to its nominal amount.

As of December 31, 2020, the Company performed an evaluation of its other contracts with customers and suppliers in accordance with ASC 842 and have

determined that, except for the leases described below and a nominal operating lease for office equipment, none of the Company’s contracts contain a lease.

Current SSF Facility

In March 2016, the Company entered into a noncancelable operating sublease (the “Lease”) to lease 128,751 square feet of office and laboratory space in
South San Francisco, California, U.S. (the “Current SSF Facility”). Subsequently, in April 2016, the Company took possession of the Current SSF Facility. The
Lease includes a free rent period and escalating rent payments and has a remaining lease term of 3.0 years that expires on December 31, 2023, unless terminated
earlier. The Company's obligation to pay rent commenced on August 1, 2016. The Company is obligated to make lease payments totaling approximately $39.2
million over the lease term. The Lease further provides that the Company is obligated to pay to the sublandlord and master landlord certain costs, including taxes
and operating expenses. The Lease is considered an operating lease under ASC 842. Prior to the Company's adoption of ASC 842, this Lease was considered a
build-to-suit lease.

The  initial  measurement  of  right-of-use  asset  for  the  Lease  includes  the  tenant  improvement  added  by  the  Company  wherein  the  lessor  was  deemed  the
accounting owner, net of the tenant improvement allowance received from the sublandlord and the master landlord. In connection with this Lease, the Company
received a tenant improvement allowance of $14.2 million for the costs associated with the design, development and construction of tenant improvements for the
Current SSF Facility. The Company is obligated to fund all costs incurred in excess of the tenant improvement allowance. The scope of the tenant improvements
did  not  qualify  as  “normal  tenant  improvements”  under  ASC  840.  Accordingly,  for  accounting  purposes,  the  Company  was  the  deemed  owner  of  the  building
during  the  construction  period  under  ASC  840  and  the  Company  capitalized  $36.5  million  within  property  and  equipment,  net,  including  $1.2  million  for
capitalized interest and recognized a corresponding build-to-suit obligation in other non-current liabilities in the Consolidated Balance Sheets as of December 31,
2018. The Company has also recognized structural and non-structural tenant improvements totaling $15.8 million as of December 31, 2018 as an addition to the
build-to-suit lease property for amounts incurred by the Company during the construction period, of which $14.2 million were reimbursed by the landlord during
the year ended December 31, 2016 through the tenant improvement allowance. Under ASC 840, the Company increased its financing obligation for the additional
building  costs  reimbursements  received  from  the  landlord  during  the  construction  period.  For  the  year  ended  December  31,  2018,  the  Company  recorded  rent
expense  associated  with  the  ground  lease  of  $0.5  million  in  the  Consolidated  Statements  of  Operations.  Total  interest  expense,  which  represents  the  cost  of
financing obligation under the Lease agreement, was $3.7 million for the year ended December 31, 2018 which was recognized in its Consolidated Statements of
Operations.

During  the  fourth  quarter  of  2016,  construction  on  the  build-to-suit  lease  property  was  substantially  completed  and  the  build-to-suit  lease  property  was
placed  in  service.  As  such,  the  Company  evaluated  the  Lease  under  ASC  840  to  determine  whether  it  had  met  the  requirements  for  sale-leaseback  accounting,
including evaluating whether all risks of ownership have been transferred back to the landlord, as evidenced by a lack of continuing involvement in the build-to-
suit lease property. The Company determined that the construction project did not qualify for sale-leaseback accounting and was accounted for under ASC 840 as a
financing  lease,  given  the  Company’s  expected  continuing  involvement  after  the  conclusion  of  the  construction  period.  Prior  to  the  adoption  of  the  new  lease
guidance, ASC 842, the build-to-suit lease property was recorded on the Company’s Consolidated Balance Sheet as of December 31, 2018 at its historical cost of
$52.3 million and the total amount of the build-to-suit lease obligation as of December 31, 2018 was $51.5 million, of which $1.6 million and $49.9 million were
classified as current and non-current liability, respectively.

The  Lease  is  considered  an  operating  lease  under  ASC  842  as  it  did  not  meet  the  criteria  of  a  capital  lease  under  ASC  840  and  the  construction  was
completed before the adoption of ASC 842. The Company derecognized the build-to-suit property and build-to-suit lease obligations upon adoption of ASC 842
and as of December 31, 2020, the operating lease right-of-use asset and lease liability was $17.8 million and $17.8 million, respectively.

The Company obtained a standby letter of credit in April 2016 in the initial amount of $4.1 million, which may be drawn down by the sublandlord in the

event the Company fails to fully and faithfully perform all of its obligations under the Lease and

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to compensate the sublandlord for all losses and damages the sublandlord may suffer as a result of the occurrence of any default on the part of Company not cured
within the applicable cure period. This standby letter of credit is collateralized by a certificate of deposit of the same amount which is classified as restricted cash.
The  Company  was  entitled  to  a  $1.4  million  reduction  in  the  face  amount  of  the  standby  letter  of  credit  on  the  third  anniversary  of  the  contractual  rent
commencement,  which  was  received  in  2019,  and  another  $1.4  million  on  the  fifth  anniversary  of  the  contractual  rent  commencement.  As  a  condition  to  the
reduction  of  the  standby  letter  of  credit  amount,  no  uncured  default  by  the  Company  shall  then  exist  under  the  Lease.  As  of  December  31,  2020,  none  of  the
remaining standby letter of credit amount of $2.7 million has been used.

Sub-Sublease of Current SSF Facility

On July  18, 2018, the  Company  entered  into  a  Sub-Sublease  Agreement  (the  “Sub-Sublease”)  with  Assembly  Biosciences,  Inc.  (the  “Sub-Subtenant”)  to
sub-sublease approximately 46,641 square feet of office and laboratory space of the Current SSF Facility to the Sub-Subtenant. The Sub-Sublease is considered an
operating lease under ASC 842. There was no change in the accounting of the Sub-Sublease of the Current SSF Facility upon the Company's adoption of ASC 842.
For  the  years  ended  December  31,  2020,  2019  and  2018,  the  Company  recorded  $2.9  million,  $2.9  million  and  $0.8  million,  respectively,  for  sub-lease  rental
income as an offset to its operating expenses.

The  Sub-Sublease  provides  for  initial  annual  base  rent  for  the  complete  Sub-Subleased  Premises  of  approximately  $2.7  million,  with  increases  of
approximately  3.5%  in  annual  base  rent  on  September  1,  2019  and  each  anniversary  thereof.  The  Sub-Sublease  rental  income  excludes  reimbursements  for
executory costs received from the Sub-Subtenant. The Sub-Sublease became effective on September 24, 2018, and has a term of 5.2 years which terminates on
December 15, 2023. The Sub-Sublease will terminate if the Lease or the corresponding master lease terminates. The Company or the Sub-Subtenant may elect,
subject to limitations set forth in the Sub-Sublease, to terminate the Sub-Sublease following a material casualty or condemnation affecting the Subleased Premises.
The Company may terminate the Sub-Sublease following an event of default, which is defined in the Sub-Sublease to include, among other things, non-payment of
amounts owing by the Sub-Subtenant under the Sub-Sublease.

The Company is required under the Lease to pay to the sublandlord 50% of that portion of the cash sums and other economic consideration received from the

Sub-Subtenant that exceeds the base rent paid by the Company to the sublandlord after deducting certain of the Company’s costs.

Dublin

In October 2018, the Company entered into a surrender agreement for its office lease in Dún Laoghaire, Ireland. The Company paid €270,000, or $309,000
as converted using an exchange rate as of November 28, 2018, as full and final settlement of outstanding contractual obligations of $1.6 million in exchange for
surrender and assignment to the landlord including surrender of approximately $0.5 million of long-lived assets. The expenses related to this surrender agreement
were accounted for as part of the restructuring and impairment charges recognized in the year ended December 31, 2018. No additional expenses were incurred in
the years ended December 31, 2020, and 2019.

The Company entered into an agreement to lease a 133 square feet of office space in Dublin, Ireland. The current lease term expires on November 30, 2021.
The Dublin Lease also has an automatic renewal clause, pursuant to which the agreement will be extended automatically for successive periods equal to the current
term but no less than three months, unless the agreement is cancelled by the Company. This operating lease is not included in the lease liability and operating lease
right-of-use asset recorded due to its nominal amount.

As of December 31, 2020, the Company is obligated to make lease payments over the remaining term of the lease of approximately €22,000, or $27,000 as

converted using an exchange rate as of December 31, 2020.

Future  minimum  payments  under  the  above-described  noncancelable  operating  leases,  including  a  reconciliation  to  the  lease  liabilities  recognized  in  the

Consolidated Balance Sheets, and future minimum rentals to be received under the Sub-Sublease as of December 31, 2020 are as follows (in thousands):

84

Year Ended December 31,

2021
2022
2023
2024

Total
Less: Present value adjustment
Nominal lease payments

Lease liability

Indemnity Obligations

Sub-Sublease
Rental

2,944 
3,047 
3,019 
— 
9,010 

Operating Leases
6,192 
6,350 
6,535 
— 
19,077  $

(1,212)
(27)
17,838 

$

The Company has entered into indemnification agreements with its current and former directors and officers and certain key employees. These agreements
contain provisions that may require the Company, among other things, to indemnify such persons against certain liabilities that may arise because of their status or
service and advance their expenses incurred as a result of any indemnifiable proceedings brought against them. The obligations of the Company pursuant to the
indemnification agreements continue during such time as the indemnified person serves the Company and continues thereafter until such time as a claim can be
brought.  The  maximum  potential  amount  of  future  payments  the  Company  could  be  required  to  make  under  these  indemnification  agreements  is  unlimited;
however, the Company has a director  and officer liability  insurance  policy that limits  its exposure and enables the Company to recover a portion of any future
amounts  paid.  As  a  result  of  its  insurance  policy  coverage,  the  Company  believes  the  estimated  fair  value  of  these  indemnification  agreements  is  minimal.
Accordingly, the Company had no liabilities recorded for these agreements as of December 31, 2020, and 2019.

Other Commitments

In the normal course of business, the Company enters into various firm purchase commitments primarily related to research and development activities. As
of December 31, 2020, the Company had non-cancelable purchase commitments to suppliers for $10.9 million of which $3.6 million is included in accrued current
liabilities, and contractual obligations under license agreements of $0.8 million of which $0.1 million is included in accrued current liabilities. The following is a
summary of the Company's non-cancelable purchase commitments and contractual obligations as of December 31, 2020 (in thousands):

Purchase Obligations
Contractual obligations under license

 (1)

agreements

 (2)

Total

________________

Total
$ 10,900 

785 
$ 11,685 

2021
10,900 

180 
11,080 

$

$

$

$

2022

2023

2024

2025

— 

$

— 

$

— 

$

70 
70 

$

70 
70 

$

60 
60 

$

— 

60 
60 

Thereafter
— 
$

345 
345 

$

(1)

 Purchase obligations consist of non-cancelable purchase commitments to suppliers.

(2) 

Excludes future obligations pursuant to the cost-sharing arrangement under the Company's License Agreement with Roche. Amounts of such obligations, if any, cannot
be determined at this time.

Legal Proceedings

We  are  not  currently  a  party  to  any  material  legal  proceedings.  We  may  at  times  be  party  to  ordinary  routine  litigation  incidental  to  our  business.When

appropriate in management's estimation, we may record reserves in our financial statements for pending legal proceedings.

7. Significant Agreements

Roche License Agreement

In December 2013, the Company through its wholly owned subsidiary Prothena Biosciences Limited and Prothena Biosciences Inc entered into a License,

Development, and Commercialization Agreement (the “License Agreement”) with F.

85

Hoffmann-La  Roche  Ltd.  and  Hoffmann-La  Roche  Inc.  (together,  “Roche”)  to  develop  and  commercialize  certain  antibodies  that  target  α-synuclein, including
prasinezumab, which are referred to collectively as “Licensed Products.” Upon the effectiveness of the License Agreement in January 2014, the Company granted
to Roche an exclusive, worldwide license to develop, make, have made, use, sell, offer to sell, import and export the Licensed Products. The Company retained
certain rights to conduct development of the Licensed Products and an option to co-promote prasinezumab in the U.S. During the term of the License Agreement,
the Company and Roche will work exclusively with each other to research and develop antibody products targeting alpha-synuclein (or α-synuclein) potentially
including  incorporation  of  Roche’s  proprietary  Brain  Shuttle™  technology  to  potentially  increase  delivery  of  therapeutic  antibodies  to  the  brain.  The  License
Agreement provided for Roche making an upfront payment to the Company of $30.0 million, which was received in February 2014; making a clinical milestone
payment of $15.0 million upon initiation of the Phase 1 study for prasinezumab, which was received in May 2014; and making a clinical milestone payment of
$30.0 million upon dosing of the first patient in the Phase 2 study for prasinezumab, which was achieved in June 2017.

For prasinezumab, Roche is also obligated to pay:

•

•

•

up to $350.0 million upon the achievement of development, regulatory and various first commercial sales milestones;

up to an additional $175.0 million upon achievement of ex-U.S. commercial sales milestones; and

tiered, high single-digit to high double-digit royalties in the teens on ex-U.S. annual net sales, subject to certain adjustments.

Roche bore 100% of the cost of conducting the research collaboration under the License Agreement during the research term, which expired December 31,
2017. In the U.S., the parties share all development and commercialization costs, as well as profits, all of which will be allocated 70% to Roche and 30% to the
Company, for prasinezumab  in the Parkinson’s disease indication, as well as any other Licensed Products and/or indications for which the Company opts in to
participate in co-development and co-funding. After the completion of specific clinical trial activities, the Company may opt out of the co-development and cost
and profit sharing on any co-developed Licensed Products and instead receive U.S. commercial sales milestones totaling up to $155.0 million and tiered, single-
digit to high double-digit royalties in the teens based on U.S. annual net sales, subject to certain adjustments, with respect to the applicable Licensed Product.

The Company filed an Investigational New Drug Application (“IND”) with the FDA for prasinezumab and subsequently initiated a Phase 1 study in 2014.
Following  the  Phase  1  studies,  Roche  became  primarily  responsible  for  developing,  obtaining  and  maintaining  regulatory  approval  for  and  commercializing
Licensed Products. Roche also became responsible for the clinical and commercial manufacture and supply of Licensed Products.

In addition, the Company has an option under the License Agreement to co-promote prasinezumab in the U.S. in the Parkinson’s disease indication. If the
Company  exercises  such  option,  it  may  also  elect  to  co-promote  additional  Licensed  Products  in  the  U.S.  approved  for  Parkinson’s  disease.  Outside  the  U.S.,
Roche  will  have  responsibility  for  developing  and  commercializing  the  Licensed  Products.  Roche  bears  all  costs  that  are  specifically  related  to  obtaining  or
maintaining regulatory approval outside the U.S. and will pay the Company a variable royalty based on annual net sales of the Licensed Products outside the U.S.

While Roche will record product revenue from sales of the Licensed Products, the Company and Roche will share in the net profits and losses of sales of the
prasinezumab for the Parkinson's disease indication in the U.S. on a 70%/30% basis with the Company receiving 30% of the profit and losses provided that the
Company has not exercised its opt-out right.

The License Agreement continues on a country-by-country basis until the expiration of all payment obligations under the License Agreement. The License
Agreement  may  also  be  terminated  (i)  by  Roche  at  will  after  the  first  anniversary  of  the  effective  date  of  the  License  Agreement,  either  in  its  entirety  or  on  a
Licensed Product-by-Licensed Product basis, upon 90 days’ prior written notice to the Company prior to first commercial sale and 180 days’ prior written notice to
Prothena after first commercial sale, (ii) by either party, either in its entirety or on a Licensed Product-by-Licensed Product or region-by-region basis, upon written
notice in connection with a material breach uncured 90 days after initial written notice, and (iii) by either party, in its entirety, upon insolvency of the other party.
The License  Agreement  may  be  terminated  by either  party  on a  patent-by-patent  and country-by-country  basis if the  other  party  challenges  a given patent  in a
given country. The Company’s rights to co-develop Licensed Products under the License Agreement will terminate if the Company commences certain studies for
certain  types  of  competitive  products.  The  Company’s  rights  to  co-promote  Licensed  Products  under  the  License  Agreement  will  terminate  if  the  Company
commences a Phase 3 study for such competitive products.

86

The License Agreement cannot be assigned by either party without the prior written consent of the other party, except to an affiliate of such party or in the
event of a merger or acquisition of such party, subject to certain conditions. The License Agreement also includes customary provisions regarding, among other
things, confidentiality,  intellectual  property ownership, patent prosecution, enforcement  and defense, representations and warranties, indemnification,  insurance,
and arbitration and dispute resolution.

Collaboration Accounting

The License Agreement was evaluated under ASC 808, Collaborative Agreements. At the outset of the License Agreement, the Company concluded that it
did not qualify as collaboration under ASC 808 because the Company does not share significant risks due to the net profit and loss split (under which Roche incurs
substantially more of the costs of the collaboration) and because of the Company’s opt-out provision. The Company believes that Roche will be the principal in
future sales transactions with third parties as Roche will be the primary obligor bearing inventory and credit risk. The Company will record its share of pre-tax
commercial profit generated from the collaboration as collaboration revenue once the Company can conclude it is probable that a significant revenue reversal will
not occur in future periods. Prior to commercialization of a Licensed Product, the Company’s portion of the expenses related to the License Agreement reflected on
its  income  statement  will  be  limited  to  R&D  expenses.  After  commercialization,  if  the  Company  opts-in  to  co-detail  commercialization,  expenses  related  to
commercial  capabilities, including expenses related  to  the  establishment of  a  field  sales  force  and  other  activities  to  support  the  Company’s commercialization
efforts,  will  be  recorded  as  sales,  general  and  administrative  (“SG&A”)  expense  and  will  be  factored  into  the  computation  of  the  profit  and  loss  share.  The
Company will record the receivable related to commercialization activities as collaboration revenue once the Company can conclude it is probable that a significant
revenue reversal will not occur in future periods.

Adoption of ASC 606, Revenue from Contracts with Customers

The Company adopted ASC 606, Revenue from Contracts with Customers, as of January 1, 2018 using the modified retrospective transition method. The
Company recognized the cumulative effect of applying the new revenue standard as an adjustment to the opening balance of the accumulated deficit as of January
1, 2018.

As of January 1, 2018, the Company did not record any changes to the opening balance of the accumulated deficit since the cumulative effect of applying the
new revenue standard was the same as applying ASC 605. The impact  of the adoption of ASC 606 to revenues for the year ended December  31, 2018 was an
increase of $1.0 million, which represents the revenue recognized for the development services provided by the Company during the period that is reimbursable by
Roche.  Historically,  the  Company  recorded  such  reimbursement  as  an  offset  against  its  R&D  expenses  under  ASC  605.  Upon  the  adoption  of  ASC  606,  the
reimbursement for development services is now included as part of the Company’s collaboration revenue.

Performance Obligations

The License Agreement was evaluated under ASC 606. The License Agreement includes the following distinct performance obligations: (1) the Company’s
grant  of  an  exclusive  royalty  bearing  license,  with  the  right  to  sublicense  to  develop  and  commercialize  certain  antibodies  that  target  α-synuclein,  including
prasinezumab, and the initial know how transfer which was delivered at the effective date (the “Royalty Bearing License”); (2) the Company’s obligation to supply
clinical  material  as  requested  by  Roche  for  a  period  up  to  twelve  months  (the  “Clinical  Product  Supply  Obligation”);  (3)  the  Company’s  obligation  to  provide
manufacturing related services to Roche for a period up to twelve months (the “Supply Services Obligation”); (4) the Company’s obligation to prepare and file the
IND (the “IND Obligation”); and (5) the Company’s obligation to provide development activities under the development plan during Phase 1 clinical trials (the
“Development Services Obligation”). Revenue allocated to the above performance obligations under the License Agreement are recognized when the Company has
satisfied its obligations either at a point in time or over a period of time.

The Company concluded that the Royalty Bearing License and the Clinical Product Supply Obligation were satisfied at a point in time. The Royalty Bearing
License is considered to be a functional intellectual property, in which the revenue would be recognized at the point in time since (a) the Company concluded that
the license to Roche has a significant stand-alone functionality, (b) the Company does not expect the functionality of the intellectual property to be substantially
changed during the license period as a result of activities of Prothena, and (c) Prothena’s activities transfer a good or service to Roche. The Clinical Product Supply
Obligation does not meet criteria for over time recognition; as such, the revenue related to such performance obligation was recognized the point in time at which
Roche obtained control of manufactured supplies, which occurred during the first quarter of 2014.

87

The Company concluded that the Supply Services Obligation, the IND Obligation and the Development Services Obligation were satisfied over time. The
Company utilized an input method measure of progress by basing the recognition period on the efforts or inputs towards satisfying the performance obligation (i.e.
costs incurred and the time elapsed to complete the related performance obligations). The Company determined that such input method provides an appropriate
measure of progress toward complete satisfaction of such performance obligations.

As of December 31, 2020 and 2019, there were no remaining performance obligations under License Agreement since the obligations related to research and

development activities were only for the Phase 1 clinical trial and the remaining obligations were delivered or performed.

Transaction Price

According to ASC 606-10-32-2, the transaction price is the amount of consideration to which an entity expects to be entitled in exchange for transferring
promised goods or services to a customer, excluding amounts collected on behalf of third parties (for example, some sales taxes). The consideration promised in a
contract with a customer may include fixed amounts, variable amounts, or both. Factors considered in the determination of the transaction price include, among
other things, estimated selling price of the license and costs for clinical supply and development costs.

The initial transaction price under the License Agreement, pursuant to ASC 606, was $55.1 million, including $45.0 million for the Royalty Bearing License,
$9.1 million for the IND and Development Services Obligations, and $1.1 million for the Supply Services Obligation. The $45.0 million for the Royalty Bearing
License  included  the  upfront  payment  of  $30.0  million  and  the  clinical  milestone  payment  of  $15.0  million  upon  initiation  of  the  Phase  1  clinical  trial  of
prasinezumab, both of which were made in 2014. The remaining transaction price amounts the Company expected to receive as reimbursements were based on
costs expected to be paid to third parties and other costs to be incurred by the Company in order to satisfy its performance obligations. They are considered to be
variable  considerations  not  subject  to  constraint.  The  Company  did  not  incur  any  incremental  costs,  such  as  commissions,  to  obtain  or  fulfill  the  License
Agreement.

Under ASC 606, the transaction price was allocated to the performance obligations as follows: $48.9 million to the Royalty Bearing License; $4.6 million to
the IND and Development Services Obligations; $1.1 million to the Clinical Product Supply Obligation; and $0.6 million to the Supply Services Obligation. As of
December 31, 2020, the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied is nil. Prior to the adoption of ASC
606, the transaction price was allocated to the deliverables as follows: $35.6 million to the Royalty Bearing License; $3.3 million to the IND and Development
Services Obligations; $0.8 million to the Clinical Product Supply Obligation; and $0.4 million to the Supply Services Obligation.

The Company allocated the initial transaction price to the Royalty Bearing License and other performance obligations using the relative selling price method
based on its best estimate of selling price for the Royalty Bearing License and third party evidence for the remaining performance obligations. The best estimate of
selling price for the Royalty Bearing License was based on a discounted cash flow model. The key assumptions used in the discounted cash flow model used to
determine the best estimate of selling price for the Royalty Bearing License included the market opportunity for commercialization of prasinezumab in the U.S.
and the royalty territory (for licensed products that are jointly funded the royalty territory is worldwide except for the U.S., and for all licensed products that are not
jointly  funded  the  Royalty  Territory  is  worldwide),  the  probability  of  successfully  developing  and  commercializing  prasinezumab,  the  estimated  remaining
development costs for prasinezumab, and the estimated time to commercialization of prasinezumab. The Company concluded that a change in the assumptions
used  to  determine  the  best  estimate  of  selling  price  (“BESP”)  of  the  license  deliverable  would  not  have  a  significant  effect  on  the  allocation  of  arrangement
consideration.

The Company’s discounted cash  flow model  included several  market  conditions and entity-specific  inputs, including  the likelihood  that clinical  trials  for
prasinezumab will be successful, the likelihood that regulatory approval will be obtained and the product commercialized, the appropriate discount rate, the market
locations, size and potential market share of the product, the expected life of the product, and the competitive environment for the product. The market assumptions
were  generated  using  a  patient-based  forecasting  approach,  with  key  epidemiological,  market  penetration,  dosing,  compliance,  length  of  treatment  and  pricing
assumptions derived from primary and secondary market research, referenced from third-party sources.

Significant Payment Terms

Payments  for  development  services  are  due  within  45  days  after  receiving  an  invoice  from  the  Company.  Variable  considerations  related  to  clinical  and
regulatory milestone payments are constrained due to high likelihood of a revenue reversal. The payment term for all milestone payments are due within 45 days
after the achievement of the relevant milestone and receipt by Roche of an invoice for such an amount from the Company.

88

According to ASC 606-10-32-17, a significant financing component does not exist if a substantial amount of the consideration promised by the customer is
variable, and the amount or timing of that consideration varies on the basis of the occurrence or nonoccurrence of a future event that is not substantially within the
control of the customer or the entity. Since a “substantial amount of the consideration” promised by Roche to the Company is variable (i.e., is in the form of either
milestone payments or sales-based royalties) and the amount of such variable consideration varies based upon the occurrence or nonoccurrence of future events
that are not within the control of either Roche or the Company (i.e., are largely subject to regulatory approval), the License Agreement does not have a significant
financing component.

Optional Goods and Services

An option for additional goods or services exists when a customer has a present contractual right that allows it to choose the amount of additional distinct
goods or services that are purchased. Prior to the customer’s exercise of that right, the vendor is not presently obligated to provide those goods or services. ASC
606-10-25-18(j) requires recognition of an option as a distinct performance obligation when the option provides a customer with a material right.

In addition to the distinct performance obligations noted above, the Company was obligated to provide indeterminate research services for up to three years
ending  in  2017  at  rates  that  were  not  significantly  discounted  and  fully  reimbursable  by  Roche  (the  “Research  Services”).  The  amount  for  any  such  Research
Services was not fixed and determinable and was not at a significant incremental discount. There were no refund rights, concessions or performance bonuses to
consider.

The Company evaluated the obligation to perform Research Services under ASC 606-10-55-42 and 55-43 to determine whether it gave Roche a “material
right”. According to ASC 606-10-55-43, if a customer has the option to acquire an additional good or services at a price that would reflect the standalone selling
price for that good or service, that option does not provide the customer with a material right even if the option can be exercised only by entering into a previous
contract.

The Company concluded that Roche’s option to have the Company perform Research Services did not represent a “material right” to Roche that it would not
have received without entering into the License Agreement. As a result, Roche’s option to acquire additional Research Services was not considered a performance
obligation at the outset of the License Agreement under ASC 606. Accordingly, this deliverable will become new performance obligation for Prothena when Roche
asks  Prothena  to  conduct  such  Research  Services.  As  of  December  31,  2020,  there  were  no  remaining  Research  Services  performance  obligations.  Prior  to  the
adoption of ASC 606, the Company recognized Research Services as collaboration revenue as earned.

Post Contract Deliverables

Any development services provided by the Company after performance of the Development Service Obligation are not considered a contractual performance
obligation under the License Agreement, since the License Agreement does not require the Company to provide any development services after completion of the
Development Service Obligation. However, the collaboration’s Joint Steering Committee approved continued funding for additional development services to be
provided by the Company (the “Additional Development Services”). Under the License Agreement and upon the adoption of ASC 606, the Company recognizes
the reimbursements for Additional Development Services as collaboration revenue as earned.

Revenue and Expense Recognition

The Company recognized $0.6 million, $0.8 million and $1.0 million as collaboration revenue from Roche for the years ended December 31, 2020, 2019 and
2018,  respectively.  Cost  sharing  payments  to  Roche  are  recorded  as  R&D  expenses.  The  Company  recognized  $17.4  million,  $11.4  million  and  $13.0  million,
respectively in R&D expenses for payments made to Roche during the years ended December 31, 2020, 2019 and 2018, respectively. The Company had accounts
receivable from Roche of $3,000 and $2,000 at December 31, 2020 and 2019, respectively.

Milestone Accounting

Under  the  License  Agreement,  only  if  the  U.S.  and  or  global  options  are  exercised,  the  Company  is  eligible  to  receive  milestone  payments  upon  the
achievement  of  development,  regulatory  and  various  first  commercial  sales  milestones.  Milestone  payments  are  evaluated  under  ASC  Topic  606.  Factors
considered  in  this  determination  included  scientific  and  regulatory  risk  that  must  be  overcome  to  achieve  each  milestone,  the  level  of  effort  and  investment
required to achieve the milestone, and the monetary value attributed to the milestone. Accordingly, the Company estimates payments in the transaction price based
on  the  most  likely  approach,  which  considers  the  single  most  likely  amount  in  a  range  of  possible  amounts  related  to  the  achievement  of  these  milestones.
Additionally, milestone payments are included in the transaction price only when the Company can conclude it is probable that a significant revenue reversal will
not occur in future periods when the milestone is achieved.

89

The Company excludes the milestone payments and royalties in the initial transaction price calculation because such payments are considered to be variable
considerations  with  constraint.  Such  milestone  payments  and  royalties  will  be  recognized  as  revenue  once  the  Company  can  conclude  it  is  probable  that  a
significant revenue reversal will not occur in future periods.

The  clinical  and  regulatory  milestones  under  the  License  Agreement  after  the  point  at  which  the  Company  could  opt-out  are  considered  to  be  variable
considerations with constraint due to the fact that active participation in the development activities that generate the milestones is not required under the License
Agreement, and the Company can opt-out of these activities. There are no refunds or claw-back provisions and the milestones are uncertain of occurrence even
after the Company has opted out. Based on this determination, these milestones will be recognized when the Company can conclude it is probable that a significant
revenue reversal will not occur in future periods.

The Company did not achieve any clinical and regulatory milestones under the License Agreement during the years ended December 31, 2020, 2019 and

2018.

Collaboration Agreement with Bristol-Myers Squibb

Overview

On March 20, 2018, the Company, through its wholly owned subsidiary Prothena Biosciences Limited, entered into a Master Collaboration Agreement (the
“Collaboration  Agreement”)  with  Celgene  Switzerland  LLC  (“Celgene”),  a  subsidiary  of  Celgene  Corporation  (which  was  acquired  by  Bristol-Myers  Squibb
("BMS") in November 2019), pursuant to which Prothena granted to Celgene a right to elect in its sole discretion to exclusively license rights both in the U.S. (the
“US Rights”) and on a global basis (the “Global Rights”), with respect to the Company’s programs to develop and commercialize antibodies targeting Tau, TDP-
43 and an undisclosed target (the “Collaboration Targets”). For each such program, BMS may exercise its US Rights at the IND filing, and if it so exercises such
US Rights would also have a right to expand the license to Global Rights. If BMS exercises its US Rights for a program, then following the first to occur of (a)
completion  by  the  Company,  in  its  discretion  and  at  its  cost,  of  Phase  1  clinical  trials  for  such  program  or  (b)  the  date  on  which  BMS  elects  to  assume
responsibility for completing such Phase 1 clinical trials (at its cost), BMS would have decision making authority over development activities and all regulatory,
manufacturing and commercialization activities in the U.S.

The Collaboration Agreement provided for Celgene making an upfront payment to the Company of $100.0 million, which was received in April 2018, plus
future potential license exercise payments and regulatory and commercial milestones for each program under the Collaboration Agreement, as well as royalties on
net  sales  of  any  resulting  marketed  products.  In  connection  with  the  Collaboration  Agreement,  the  Company  and  Celgene  entered  into  a  Share  Subscription
Agreement  on  March  20,  2018,  under  which  Celgene  subscribed  to  1,174,536  of  the  Company’s  ordinary  shares  for  a  price  of  $42.57  per  share,  for  a  total  of
approximately $50.0 million.

BMS US and Global Rights and Licenses

On a program-by-program basis, beginning on the effective date of the Collaboration Agreement and ending on the date that the IND Option term expires for
such program (which generally occurs sixty days after the date on which Prothena delivers to BMS the first complete data package for an IND that was filed for a
lead candidate from the relevant program), BMS may elect in its sole discretion to exercise its US Rights to receive an exclusive license to develop, manufacture
and  commercialize  antibodies  targeting  the  applicable  Collaboration  Target  in  the  U.S. (the  “US License”).  If  BMS exercises  its  US Rights  for  a  collaboration
program, it is obligated to pay the Company an exercise fee of approximately $80.0 million per program. Thereafter, following the first to occur of (a) completion
by the Company, in its discretion and at its cost, of Phase 1 clinical trials for such program or (b) BMS’s election to assume responsibility to complete such Phase 1
clinical trials (at its cost), BMS would have the sole right to develop, manufacture and commercialize antibody products targeting the relevant Collaboration Target
for such program (the “Collaboration Products”) in the U.S.

On a program-by-program basis, following completion of a Phase 1 clinical trial for a collaboration program for which BMS has previously exercised its US
Rights, BMS may elect in its sole discretion to exercise its Global Rights with respect to such collaboration program to receive a worldwide, exclusive license to
develop, manufacture and commercialize antibodies targeting the applicable Collaboration Target (the “Global License”). If BMS exercises its Global Rights, BMS
would be obligated to pay the Company an additional exercise fee of $55.0 million for such collaboration program. The Global Rights would then replace the US
Rights  for  that  collaboration  program,  and  BMS  would  have  decision  making  authority  over  developing,  obtaining  and  maintaining  regulatory  approval  for,
manufacturing and commercializing the Collaboration Products worldwide.

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After BMS’s exercise of Global Rights for a collaboration program, the Company is eligible to receive up to $562.5 million in regulatory and commercial
milestones per program. Following an exercise by BMS of either US Rights or Global Rights for such collaboration program, the Company will also be eligible to
receive tiered royalties on net sales of Collaboration Products ranging from high single digit to high teen percentages, on a weighted average basis depending on
the  achievement  of  certain  net  sales  thresholds.  Such  exercise  fees,  milestones  and  royalty  payments  are  subject  to  certain  reductions  as  specified  in  the
Collaboration Agreement, the agreement for US Rights and the agreement for Global Rights.

BMS will continue to pay royalties on a Collaboration Product-by-Collaboration Product and country-by-country basis, until the latest of (i) expiration of
certain patents covering the Collaboration Product, (ii) expiration of all regulatory exclusivity for the Collaboration Product, and (iii) an agreed period of time after
the first commercial sale of the Collaboration Product in the applicable country (the “Royalty Term”).

Term and Termination

The research term under the Collaboration Agreement continues for a period of six years, which BMS may extend for up to two additional 12-month periods
by paying an extension fee of $10.0 million per extension period. The term of the Collaboration Agreement continues until the last to occur of the following: (i)
expiration of the research term; (ii) expiration of all US Rights terms; and (iii) expiration of all Global Rights terms.

The term of any US License or Global License would continue on a Licensed Product-by-Licensed Product and country-by-country basis until the expiration

of all Royalty Terms under such agreement.

The  Collaboration  Agreement  may  be  terminated  (i)  by  either  party  on  a  program-by-program  basis  if  the  other  party  remains  in  material  breach  of  the
Collaboration Agreement following a cure period to remedy the material breach, (ii) by BMS at will on a program-by-program basis or in its entirety, (iii) by either
party, in its entirety, upon insolvency of the other party, or (iv) by Prothena, in its entirety, if BMS challenges a patent licensed by Prothena to BMS under the
Collaboration Agreement.

Share Subscription Agreement

Pursuant to the terms of the Collaboration Agreement, the Company entered into a Share Subscription Agreement (the “SSA”) with Celgene, pursuant to
which  the  Company  issued,  and  Celgene  subscribed  for,  1,174,536  of  the  Company’s  ordinary  shares  (the  “Shares”)  for  an  aggregate  subscription  price  of
approximately $50.0 million, pursuant to the terms and conditions thereof.

Under the SSA, BMS (formerly Celgene) is subject to certain transfer restrictions. In addition, BMS will be entitled to request the registration of the Shares
with the U.S. Securities and Exchange Commission on Form S-3ASR or Form S-3 following termination of the transfer restrictions if the Shares cannot be resold
without restriction pursuant to Rule 144 promulgated under the U.S. Securities Act of 1933, as amended (the “Securities Act”).

Collaboration Accounting

The  Collaboration  Agreement  was  evaluated  under  ASC  808,  Collaborative  Agreements.  At  the  outset  of  the  Collaboration  Agreement,  the  Company

concluded that it does not qualify as collaboration under ASC 808 because the Company does not share significant risks due to economics of the collaboration.

Performance Obligations

The Company assessed the Collaboration Agreement and concluded that it represented a contract with a customer within the scope of ASC 606. Per ASC
606,  a  performance  obligation  is  defined  as  a  promise  to  transfer  a  good  or  service  or  a  series  of  distinct  goods  or  services.  At  inception  of  the  Collaboration
Agreement, the Company is not obligated to transfer the US License or Global License to BMS unless BMS exercises its US Rights or Global Rights, respectively,
and  the  Company  is  not  obligated  to  perform  development  activities  under  the  development  plan  during  preclinical  and  Phase  1  clinical  trials  including  the
regulatory filing of the IND.

The  discovery,  preclinical  and  clinical  development  activities  performed  by  the  Company  are  to  be  performed  at  the  Company’s  discretion  and  are  not
promised goods or services and therefore are not considered performance obligations under ASC 606, unless and until the Company agrees to perform the Phase 1
clinical  studies  (after  the  IND  option  exercise)  that  are  determined  to  be  performance  obligations  at  the  time  the  option  is  exercised.  Per  the  terms  of  the
Collaboration Agreement, the Company may conduct discovery activities to characterize, identify and generate antibodies to become collaboration candidates that
target such Collaboration Target, and thereafter may pre-clinically develop collaboration candidates to identify lead

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candidates that target such Collaboration Target and file an IND with the U.S. Food and Drug Administration (the “FDA”) for a Phase 1 clinical trial for such lead
candidates. In the event the Company agrees to be involved in a Phase 1 clinical study, the Company will further evaluate whether any such promise represents a
performance obligation at the time the option is exercised. If it is concluded that the Company has obligated itself to an additional performance obligation besides
the license granted at IND option exercise, then the effects of the changes in the arrangement will be evaluated under the modification guidance of ASC 606.

The  Company  is  not  obligated  to  perform  manufacturing  activities.  Per  the  terms  of  the  Collaboration  Agreement,  to  the  extent  that  the  Company,  at  its
discretion,  conducts  a  program,  the  Company  shall  be  responsible  for  the  manufacture  of  collaboration  candidates  and  collaboration  products  for  use  in  such
program, as well as the associated costs. Delivery of manufactured compound (clinical product supply) is not deemed a performance obligation under ASC 606 as
the Company is not obligated to transfer supply of collaboration product to BMS unless BMS exercises its right to participate in the Phase 1 development.

Compensation for the Company’s provision of inventory supply, to the extent requested by BMS would be paid to Prothena by BMS at a reasonable stand-
alone selling price for such supply. Given that (i) there is substantial uncertainty about the development of the programs, (ii) the pricing for the inventory is at its
standalone selling price and (iii) the manufacturing services require the entity to transfer additional goods or services that are incremental to the goods and services
provided prior to the resolution of the contingency, the Company’s supply of product is not a material right. Therefore, the inventory supply is not considered a
performance obligation unless and until, requested by BMS.

In addition to the grant of the US License after BMS exercises its US Rights for a program, BMS is entitled to receive certain ancillary development services

from the Company, such as technology transfer assistance, regulatory support, safety data reporting activities and transition supply, if requested by BMS.

In addition to the grant of the Global License after BMS exercises the Global Rights for a program, BMS is entitled to receive certain ancillary development
services  from  Prothena,  such  as  ongoing  clinical  trial  support  upon  request  by  BMS,  transition  supply,  if  requested  by  BMS,  and  regulatory  support  for
coordination of pharmacovigilance matters.

The Company evaluated the potential obligations to transfer the US Licenses and Global Licenses and performance of the ancillary development services
subsequent to exercise of the US Rights and Global Rights, if the options are exercised by BMS, under ASC 606-10-55-42 and 55-43 to determine whether the US
Rights or the Global Rights provided BMS a “material right” and concluded that BMS’s options to exercise its US Rights and Global Rights represented “material
rights” to BMS that it would not have received without entering into the Agreement.

There are a total of six options including US Rights and Global Rights to acquire a US License and a Global License, respectively, and rights to request
certain development services (following exercise of the US Rights and Global Rights, respectively) for each of the three programs. Per ASC 606, the US Rights
and Global Rights are material rights and therefore are performance obligations. The goods and services underlying the options are not accounted for as separate
performance obligations, but rather become performance obligations, if and when, an option is exercised.

Transaction Price

According to ASC 606-10-32-2, the transaction price is the amount of consideration to which an entity expects to be entitled in exchange for transferring
promised goods or services to a customer, excluding amounts collected on behalf of third parties (for example, some sales taxes). The consideration promised in a
contract with a customer may include fixed amounts, variable amounts, or both. Factors considered in the determination of the transaction price included, among
other things, estimated selling price of the license and costs for clinical supply and development costs.

The initial transaction price under the Collaboration Agreement, pursuant to ASC 606, was $110.2 million, including the $100.0 million upfront payment
and $10.2 million premium on the ordinary shares purchased under the SSA. The Company expects that the initial transaction price will be allocated across the US
Rights and Global Rights for each program in a range of approximately $15-$25 million and $10-$18 million, respectively.

The Company did not include the option fees in the initial transaction price because such fees are contingent on the options to the US Rights and the Global
Rights being exercised. Upon the exercise of the US Rights and the Global Rights for a program, the Company will have the obligation to deliver the US License
and  Global  License  and  provide  certain  ancillary  development  services  if  requested  by  BMS,  subsequent  to  its  exercise  of  the  US  Rights  and  Global  Rights,
respectively, for such program. The Company will include the option fees in the transaction price at the point in time a material right is exercised. In addition, the
Company did not include in the initial transaction price certain clinical and regulatory milestone

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payments  since  they  relate  to  licenses  for  which  BMS  has  not  yet  exercised  its  option  to  obtain  and  these  variable  considerations  are  constrained  due  to  the
likelihood of a significant revenue reversal.

At  the  inception  of  the  Collaboration  Agreement,  the  Company  did  not  transfer  any  goods  or  services  to  BMS  (formerly  Celgene)  that  are  material.
Accordingly, the Company has concluded that the initial transaction price will be recognized as contract liability and will be deferred until the Company transfers
control of goods or services to BMS (which would be when BMS exercises the US Right or Global Right and receives control of the US License or Global License
for at least one of the programs), or when the IND Option term expires if BMS does not exercise the US Right (which is generally sixty days after the date on
which Prothena delivers to BMS the first complete data package for an IND that was filed for a lead candidate from the relevant program), or when the Phase 1
Option term expires if BMS does not exercise the Global Right (which is generally ninety days after the date on which Prothena delivers to BMS the first complete
data package for a Phase 1 clinical trial for a lead candidate from the relevant program) or at the termination of the Collaboration Agreement, whichever occurs
first.  At  such  point  that  the  Company  transfers  control  of  goods  or  services  to  BMS,  or  when  the  option  expires,  the  Company  will  recognize  revenue  as  a
continuation  of  the  original  contract.  Under  this  approach,  the  Company  will  treat  the  consideration  allocated  to  the  material  right  as  an  addition  to  the
consideration for the goods or services underlying the contract option.

At inception of the Collaboration Agreement, the Company estimated the standalone selling price for each performance obligation (i.e., the US Rights and
Global Rights by program). The estimate of standalone selling price for the US Rights and Global Rights by program was based on the adjusted market assessment
approach using a discounted cash flow model. The key assumptions used in the discounted cash flow model included the market opportunity for commercialization
of  each  program  in  the  U.S.  or  globally  depending  on  the  license,  the  probability  of  successfully  developing  and  commercializing  a  given  program  target,  the
estimated remaining development costs for the respective program, the estimated time to commercialization of the drug for that program and a discount rate.

Significant Payment Terms

The upfront payment of $100.0 million was due within ten business days after the effective date of the Collaboration Agreement and was received in April
2018,  while  all  option  fees  and  milestone  payments  are  due  within  30  days  after  the  achievement  of  the  relevant  milestone  by  BMS  or  receipt  by  BMS  of  an
invoice for such an amount from the Company.

The  Collaboration  Agreement  does  not  have  a  significant  financing  component  since  a  substantial  amount  of  consideration  promised  by  BMS  to  the
Company is variable and the amount of such variable consideration varies based upon the occurrence or non-occurrence of future events that are not within the
control of either BMS or the Company. Variable considerations related to clinical and regulatory milestone payments and option fees are constrained due to the
likelihood of a significant revenue reversal.

Milestone and Royalties Accounting

The Company is eligible to receive milestone payments of up to $90.0 million per program upon the achievement of certain specified regulatory milestones
and milestone payments of up to $375.0 million per program upon the achievement of certain specified commercial sales milestones under the US License for such
program. The Company is also eligible to receive milestone payments of up to $187.5 million per program upon the achievement of certain specified regulatory
milestones  and  milestone  payments  of  up  $375.0  million  per  program  upon  the  achievement  of  certain  specified  commercial  sale  milestones  under  the  Global
License for such program. Milestone payments are evaluated under ASC Topic 606. Factors considered in this determination included scientific and regulatory risk
that must be overcome to achieve each milestone, the level of effort and investment required to achieve the milestone, and the monetary value attributed to the
milestone.  Accordingly,  the  Company  estimates  payments  in  the  transaction  price  based  on  the  most  likely  approach,  which  considers  the  single  most  likely
amount in a range of possible amounts related to the achievement of these milestones. Additionally, milestone payments are included in the transaction price only
when the Company can conclude it is probable that a significant revenue reversal will not occur in future periods.

The  Company  excluded  the  milestone  payments  and  royalties  in  the  initial  transaction  price  because  such  payments  are  considered  to  be  variable
considerations  with  constraint.  Such  milestone  payments  and  royalties  will  be  recognized  as  revenue  at  a  point  in  time  when  the  Company  can  conclude  it  is
probable that a significant revenue reversal will not occur in future periods.

The Company did not achieve any clinical and regulatory milestones under the Collaboration Agreement during the years ended December 31, 2020, 2019

and 2018, respectively.

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8. Shareholders' Equity

Ordinary Shares

As  of  December  31,  2020,  the  Company  had  100,000,000  ordinary  shares  authorized  for  issuance  with  a  par  value  of  $0.01  per  ordinary  share  and
39,921,413  ordinary  shares  issued  and  outstanding.  Each  ordinary  share  is  entitled  to  one  vote  and,  on  a  pro  rata  basis,  to  dividends  when  declared  and  the
remaining assets of the Company in the event of a winding up.

Euro Deferred Shares

As of December 31, 2020, the Company had 10,000 Euro Deferred Shares authorized for issuance with a nominal value of €22 per share. No Euro Deferred
Shares are outstanding at December 31, 2020. The rights and restrictions attaching to the Euro Deferred Shares rank pari passu with the ordinary shares and are
treated as a single class in all respects.

Celgene Share Subscription Agreement

In connection with the Celgene Collaboration Agreement, the Company entered into a Share Subscription Agreement (the “SSA”) with Celgene, pursuant to
which  the  Company  issued,  and  Celgene  subscribed  for,  1,174,536  of  the  Company’s  ordinary  shares  (the  “Shares”)  for  an  aggregate  subscription  price  of
approximately  $50.0  million,  of  which  the  fair  value  of  $39.8  million  was  recorded  in  shareholders'  equity  and  the  premium  of  $10.2  million  was  recorded  as
deferred revenue from Celgene.

Under  the  SSA,  Celgene  (now  part  of  Bristol-Myers  Squibb)  is  subject  to  certain  transfer  restrictions.  In  addition,  BMS  will  be  entitled  to  request  the
registration  of  the  Shares  with  the  SEC  on  Form  S-3ASR or  Form  S-3  following  termination  of  the  transfer  restrictions  if  the  Shares  cannot  be  resold  without
restriction pursuant to Rule 144 promulgated under the Securities Act.

9. Share-Based Compensation

2018 Long Term Incentive Plan

In May 2018, the Company’s shareholders approved the 2018 Long Term Incentive Plan. In May 2020, the Company's shareholders approved an amendment
to  the  2018  Long  Term  Incentive  Plan  (as  amended,  the  “2018  LTIP”)  to  increase  the  number  of  ordinary  shares  available  for  issuance  under  that  Plan  by
1,500,000 ordinary shares. Under the 2018 LTIP, the number of ordinary shares authorized for issuance under the 2018 LTIP is equal to the sum of (a) 3,300,000
ordinary shares, (b) 1,177,933 ordinary shares that were available for issuance under the 2012 LTIP as of the May 15, 2018, effective date of the 2018 LTIP, and
(c)  any  ordinary  shares  subject  to  issued  and  outstanding  awards  under  the  2012  Long  Term  Incentive  Plan  (the  “2012  LTIP”)  that  expire,  are  cancelled  or
otherwise terminate following the effective date of the 2018 LTIP; provided, that no more than 2,500,000 ordinary shares may be issued pursuant to the exercise of
ISOs.  The  2018  LTIP  provides  for  the  grant  of  ISOs,  NQSOs,  SARs,  restricted  shares,  RSUs,  performance  bonus  awards,  performance  share  units  awards,
dividend equivalents and other share or cash-based awards to eligible individuals. Options under the 2018 LTIP may be granted for periods up to ten years. All
options issued to date have had a ten year life.

Amended and Restated 2012 Long Term Incentive Plan

Prior to the effective date of the 2018 LTIP, employees and consultants of the Company, its subsidiaries and affiliates, as well as members of the Company’s
Board of Directors, received equity awards under the 2012 LTIP. Options under the 2012 LTIP were granted for periods up to ten years. All options issued to date
have had a ten year life.

2020 Employment Inducement Incentive Plan

On February 25, 2020, the Company's Board of Directors approved the 2020 Employment Inducement Incentive Plan. During the year ended December 31,
2020, the Company's Board of Directors approved amendments to the 2020 Employment Inducement Incentive Plan (as amended, the "2020 EIIP") to increase the
ordinary shares available for issuance under that Plan to an aggregate of 710,000 ordinary shares. The 2020 EIIP provides for the grant of NQSOs, SARs, restricted
shares, RSUs, performance  bonus awards, performance  share units awards, or other share or cash-based  awards to eligible  individuals. Options under the 2020
EIIP  may  be  granted  for  periods  up  to  ten  years.  All  options  issued  to date  have  had  a  ten year life. As of December  31, 2020, the number of ordinary shares
authorized  for  issuance  under  the  2020  EIIP  was  710,000  and  no  ordinary  shares  remained  available  for  future  awards  under  the  2020  EIIP,  although  the
Company's Board of Directors reserves the right to amend the 2020 EIIP to increase the number of ordinary shares available and to make additional awards to key
new hires.

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Shares Available for Grant

The Company granted 2,108,950, 1,315,975, and 4,140,800 options during the years ended December 31, 2020, 2019 and 2018, respectively, in aggregate
under its equity plans. The Company’s option awards generally vest over four years. As of December 31, 2020, 1,669,619 ordinary shares remained available for
grant under the 2018 LTIP, and options to purchase 8,744,765 ordinary shares in aggregate under the Company's equity plans were outstanding with a weighted-
average exercise price of approximately $20.42 per share.

2020 Option Exchange Program

On  May  19,  2020,  the  Company's  shareholders  approved  a  proposal  to  allow  for  a  one-time  a  stock  option  exchange  program  (the  "Option  Exchange")
designed to give its employees, including our named executive officers, and non-employee directors of the Company, who are employed by or providing services
to the Company through the completion of the Option Exchange, the opportunity to exchange eligible stock options for new replacement stock options with an
exercise price equal to the fair market value of the Company’s ordinary shares at the time the replacement stock options are granted.

On November 9, 2020, the Company commenced the Option Exchange which closed on February 12, 2021. Stock options to purchase approximately 2.5
million ordinary shares were eligible for exchange. Stock options were eligible to exchange if they had an exercise price equal to or greater than $17.63 per share,
were granted prior to April 23, 2018, under the 2012 LTIP, and were held by an eligible participant.

Share-based Compensation Expense

The  Company  estimates  the  fair  value  of  share-based  compensation  on  the  date  of  grant  using  an  option-pricing  model.  The  Company  uses  the  Black-
Scholes model to value share-based compensation, excluding RSUs, which the Company values using the fair market value of its ordinary shares on the date of
grant.  The  Black-Scholes  option-pricing  model  determines  the  fair  value  of  share-based  payment  awards  based  on  the  share  price  on  the  date  of  grant  and  is
affected  by  assumptions  regarding  a  number  of  complex  and  subjective  variables.  These  variables  include,  but  are  not  limited  to,  the  Company’s  share  price,
volatility  over the  expected  life  of the  awards  and  actual  and  projected  employee  stock  option  exercise  behaviors.  Since the  Company  does  not have  sufficient
historical employee share option exercise data, the simplified method has been used to estimate the expected life of all options. The Company uses its historical
volatility for the Company’s stock to estimate expected volatility starting January 1, 2018. Although the fair value of share options granted by the Company is
estimated by the Black-Scholes model, the estimated fair value may not be indicative of the fair value observed in a willing buyer and seller market transaction.

As  share-based  compensation  expense  recognized  in  the  Consolidated  Financial  Statements  is  based  on  awards  ultimately  expected  to  vest,  it  has  been
reduced  for estimated  forfeitures.  Forfeitures  are  estimated  at  the  time  of  grant  and  revised,  if  necessary,  in  subsequent  periods  if  actual  forfeitures  differ  from
estimates. Forfeitures were estimated based on estimated future turnover and historical experience.

Share-based compensation expense will continue to have an adverse impact on the Company’s results of operations, although it will have no impact on its
overall  financial  position.  The  amount  of  unearned  share-based  compensation  currently  estimated  to  be  expensed  from  now  through  the  year  2024  related  to
unvested share-based payment awards at December 31, 2020, is $32.7 million. The weighted-average period over which the unearned share-based compensation is
expected  to be recognized  is 2.39 years. If there  are any modifications  or cancellations  of the underlying unvested securities,  the Company may be required  to
accelerate  and/or  increase  any  remaining  unearned  share-based  compensation  expense.  Future  share-based  compensation  expense  and  unearned  share-based
compensation will increase to the extent that the Company grants additional equity awards.

Share-based  compensation  expense  recorded  in  these  Consolidated  Financial  Statements  for  the  years  ended  December  31,  2020,  2019  and  2018,
respectively was based on awards granted under the 2012 LTIP, the 2018 LTIP, and the 2020 EIIP. The following table summarizes share-based compensation
expense for the periods presented (in thousands):

95

Research and development

General and administrative

Restructuring costs

 (1)

Total share-based compensation expense

_________________

Year Ended December 31,
2019

2018

2020

$

$

8,214 

$

8,109 

$

13,800 

— 
22,014 

$

15,476 

— 
23,585 

$

9,830 

16,232 

948 
27,010 

(1)

        Restructuring  costs  for  the  year  ended  December  31,  2018,  includes  $0.9  million  of  share-based  compensation  expense  related  to  the  contractual

acceleration of vesting of certain stock options granted to executive officers.

For the years ended December 31, 2020, 2019 and 2018, the Company recognized tax benefits from share-based awards of $4.3 million, $4.7 million and

$4.7 million, respectively.

The fair value of the options granted to employees and non-employee directors during the years ended December 31, 2020, 2019 and 2018 was estimated as

of the grant date using the Black-Scholes option-pricing model assuming the weighted-average assumptions listed in the following table:

Expected volatility
Risk-free interest rate
Expected dividend yield
Expected life (in years)
Weighted average grant date fair value

2020
80.9%
0.9%
—%
6.0
$8.12

Year Ended December 31,
2019
81.4%
2.3%
—%
6.0
$8.55

2018
79.5%
2.8%
—%
6.0
$13.70

The  fair  value  of  employee  stock  options  is  being  amortized  on  a  straight-line  basis  over  the  requisite  service  period  for  each  award.  Each  of  the  inputs

discussed above is subjective and generally requires significant management judgment to determine.

The following table summarizes the Company’s stock option activity during the year ended December 31, 2020:

Outstanding at December 31, 2019

Granted
Exercised
Forfeited
Expired

Outstanding at December 31, 2020

Vested and expected to vest at December 31, 2020
Vested at December 31, 2020

Options

7,008,403  $
2,108,950 
(22,852)
(54,543)
(295,193)
8,744,765  $

8,370,141  $
4,884,436  $

Weighted 
Average 
Exercise 
Price

23.34 
11.81 
9.42 
14.65 
30.13 
20.42 

20.75 
25.45 

Weighted 
Average 
Remaining 
Contractual 
Term (years)

Aggregate 
Intrinsic 
Value 
(in thousands)

7.24 $

11,901 

7.19 $
7.12 $
6.09 $

4,656 
4,512 
3,444 

The total intrinsic value of options exercised was $0.1 million, $0.1 million and $2.4 million during the years ended December 31, 2020, 2019 and 2018,

respectively, determined as of the date of exercise.

The following table summarizes information about the Company’s options outstanding as of December 31, 2020:

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Options Outstanding

Weighted - 
Average 
Remaining 
Contractual Life 
(Years)

Number of Options

Options Exercisable

Weighted
Average Exercise
Price

Number of Options

Weighted
Average Exercise
Price

988,613 

781,500 

1,148,450 

1,034,331 

2,209,100 

1,157,992 

896,379 

488,400 

25,000 

15,000 
8,744,765 

5.11 $

9.37

9.15

8.39

7.44

5.82

5.41

6.20

6.75

4.59

7.19 $

8.05 

11.07 

12.15 

13.29 

15.04 

29.54 

41.62 

55.21 

63.27 

67.64 

20.42 

755,913 

$

18,416 

— 

385,980 

1,384,058 

971,466 

864,836 

468,976 

19,791 

15,000 
4,884,436 

$

7.46 

11.63 

— 

13.43 

15.04 

29.09 

41.67 

55.21 

63.27 

67.64 

25.45 

Range of Exercise Prices
$

6.41 

10.27 

$

11.72 

12.15 

13.53 

15.04 

33.10 

54.38 

60.45 

63.27 

67.64 

67.64 

10.31 

12.15 

12.17 

15.04 

16.42 

34.04 

55.00 

63.27 

67.64 

$

6.41 

$

10. Income Taxes

The Company files its U.S. and Irish income tax returns and income taxes are presented in the Consolidated Financial Statements using the asset and liability

method prescribed by the accounting guidance for income taxes.

Income (loss) before provision for income taxes by country for each of the fiscal periods presented is summarized as follows (in thousands):

Ireland
Switzerland
U.S.

Loss before provision for income taxes

2020

Year Ended December 31,
2019

2018

$

$

(116,981) $

8 
5,546 
(111,427) $

(84,706) $
(17)
7,425 
(77,298) $

(163,653)
384 
7,154 
(156,115)

Components of the provision for income taxes for each of the fiscal periods presented consisted of the following (in thousands):

Current:

U.S. Federal
U.S. State
Switzerland
Ireland
Total current provision

Deferred:

U.S. Federal
U.S. State
Switzerland
Ireland
Total deferred benefit

Provision for (benefit from) income taxes

2020

Year Ended December 31,
2019

2018

$

$

$

$

1,402  $
2 
1 
— 
1,405  $

(1,688) $
— 
— 
— 
(1,688)

(283) $

1,622  $
1 
5 
— 
1,628  $

(1,249) $
— 
— 
— 
(1,249) $
379  $

1,320 
1 
(197)
(5)
1,119 

(1,589)
— 
— 
— 
(1,589)
(470)

97

Pursuant to ASU 2016-09, the Company recorded a net tax shortfall of $1.0 million, $2.6 million and $1.7 million for the years ended December 31, 2020,

2019 and 2018, respectively, all of which were recorded as part of its income tax provision in the Consolidated Statements of Operations.

The provision for income taxes differs from the statutory tax rate of 12.5% applicable to Ireland primarily due to Irish net operating losses for which a tax
provision benefit is not recognized, U.S. income taxed at different rates, and net tax shortfall from cancellations  of stock options. Following is a reconciliation
between income taxes computed at the Irish statutory tax rate and the provision for income taxes for each of the fiscal periods presented (in thousands):

Taxes at the Irish statutory tax rate of 12.5%
Income tax at rates other than applicable statutory rate
Change in valuation allowance
Share-based payments
Tax credits
Other

Provision for (benefit from) income taxes

2020

Year Ended December 31,
2019

2018

$

$

(13,928) $
(3,402)
16,266 
3,409 
(2,786)
158 
(283) $

(9,662) $
(1,202)
8,248 
4,518 
(1,470)
(53)
379  $

(19,514)
(458)
26,747 
2,215 
(10,351)
891 
(470)

Deferred  income  taxes  reflect  the  net  tax  effect  of  temporary  differences  between  the  carrying  amount  of  assets  and  liabilities  for  financial  reporting

purposes and the amounts used for income tax purposes.

Significant components of the Company’s net deferred tax assets as of December 31, 2020, and 2019 are as follows (in thousands):

Deferred tax assets:

Net operating losses

Tax credits

Lease liability

Accruals

Share-based compensation

Gross deferred tax assets

Valuation allowance

Net deferred tax assets

Deferred tax liability:

Operating lease right-of-use assets

Fixed Assets

Net deferred tax assets

December 31,

2020

2019

$

118,976 

$

14,804 

4,199 

2,936 

13,048 

153,963 

(137,809)

16,154 

(4,192)

(318)
11,644 

$

$

101,897 

16,434 

5,319 

2,501 

11,186 

137,337 

(121,633)

15,704 

(5,397)

(351)
9,956 

On January 1, 2019, the Company adopted ASC 842, Leases and it recorded a reduction in deferred tax assets of $1.0 million as part of the $3.8 million

change in the opening balance of the accumulated deficit for the cumulative effect of applying ASC 842.

The Company's deferred tax assets are composed primarily of its Irish subsidiaries' net operating loss carryforwards, state net operating loss carryforwards
available  to  reduce  future  taxable  income  of  the  Company's  U.S.  subsidiaries,  federal  and  state  tax  credit  carryforwards,  share-based  compensation  and  other
temporary differences. The Company maintains a valuation allowance against certain U.S. federal and state and Irish deferred tax assets. Each reporting period, the
Company evaluates the need for a valuation allowance on its deferred tax assets by jurisdiction.

Recognition  of  deferred  tax  assets  is  appropriate  when  realization  of  such  assets  is  more  likely  than  not.  Based  upon  the  weight  of  available  evidence,
especially the uncertainties surrounding the realization of deferred tax assets through future taxable income, the Company believes it is not yet more likely than not
that the deferred tax assets will be fully

98

 
realizable. Accordingly, the Company has provided a valuation allowance of $137.8 million against its deferred tax assets as of December 31, 2020, primarily in
relation to deferred tax assets arising from tax credits and net operating losses. The deferred tax assets recognized net of the valuation allowance, $11.6 million as
of December 31, 2020, consist of U.S. federal temporary differences. Due to consistent U.S. operating income, the Company expects to realize such deferred tax
assets. The net increase of $16.2 million in the valuation allowance during the year ended December 31, 2020, was primarily due to net operating losses of the
Company and its Irish entities, and to a lesser extent from U.S. federal and state tax credits.

As of December 31, 2020, certain of the Company’s Irish entities had trading loss carryovers of $852.1 million and non-trading loss carryovers of $19.3
million, each of which can be carried forward indefinitely. Trading losses are available against income from the same trade/trades while non-trading losses (excess
management expenses) are available against future investment income in the company in which they arise. In addition, as of December 31, 2020, the Company had
state  net  operating  loss  carryforwards  of  approximately  $86.3  million,  which  are  available  to  reduce  future  taxable  income,  if  any,  for  the  Company’s  U.S.
subsidiary. If not utilized, the state net operating loss carryforward begins expiring in 2032.

The  Company  also  has  federal  and  California  research  and  development  credit  carryforwards  of  $9.8  million  and  $12.2  million,  respectively,  at
December 31, 2020. The federal research and development credit carryforwards will expire starting in 2037 if not utilized. The California tax credits can be carried
forward indefinitely.

Cumulative  unremitted  earnings  of  the  Company’s  U.S.  subsidiaries  total  approximately  $90.8  million  at  December  31,  2020.  The  Company's  U.S.
subsidiaries'  cash  balances  at  December  31, 2020, are  committed  for its  working capital  needs.  No provision  for  income  tax in  Ireland  has been  recognized  on
undistributed earnings of the Company’s U.S. subsidiaries. The Company considers the U.S. earnings to be indefinitely reinvested. Unremitted earnings may be
subject to withholding taxes (potentially at 5% in the U.S.) and Irish taxes (potentially at a rate of 12.5%) if they were to be distributed as dividends. However,
Ireland allows a credit against Irish taxes for U.S. taxes withheld, and as of December 31, 2020, the Company's current year net operating losses in Ireland are
sufficient to offset any potential dividend income received from its overseas subsidiaries. The Company's Swiss subsidiary, Prothena Switzerland GmbH (“PSG”)
has ceased operations and the Company finalized the liquidation of PSG in May 2020. In August 2019, the PSG paid out dividends out of its capital reserves and
retained earnings. Dividends paid by PSG were not subject to Swiss withholding taxes in the period the dividends are paid.

A reconciliation of the beginning and ending amounts of unrecognized tax benefits is as follows (in thousands):

Gross Unrecognized Tax Benefits at January 1

Additions for tax positions taken in the current year

Additions for tax positions taken in the prior year

Reductions for tax positions taken in the prior year

Gross Unrecognized Tax Benefits at December 31

2020

2019

$

$

6,601 

$

703 

124 

(176)
7,252 

$

6,855 

371 

— 

(625)
6,601 

If  recognized,  none  of  the  Company's  unrecognized  tax  benefits  as  of  December  31,  2020,  would  reduce  its  annual  effective  tax  rate,  primarily  due  to
corresponding  adjustments  to its deferred  tax valuation  allowance.  As of December  31, 2020, the Company has not recorded  a liability  for potential  interest  or
penalties. The Company also does not expect its unrecognized tax benefits to change significantly over the next 12 months.

The tax years 2013 to 2020 remain subject to examination by the U.S taxing authorities and the tax years 2015 to 2020 remain subject to examination by the

Irish taxing authorities as of December 31, 2020.

11. Restructuring

In May 2018, the Company commenced a reorganization plan to reduce its operating costs and better align its workforce with the needs of its business
following the Company’s April 23, 2018, announcement of its decision to discontinue further development of NEOD001. Restructuring charges incurred under
this  plan  primarily  consisted  of  employee  termination  benefits  and  contract  termination  costs  primarily  associated  with  exit  fees  relating  to  third-party
manufacturers that the Company contracted with for NEOD001 clinical and commercial supplies.

The Company completed all restructuring activities in fiscal year 2019 and do not expect to incur additional costs associated with the restructuring. The
cumulative  amount  incurred  was  $16.1  million,  including  a  restructuring  credit  recorded  for  the  year  ended  December  31,  2019  of  approximately  $61,000
primarily due to an adjustment in previously recorded employee termination benefits. Charges and other costs related to the workforce reduction and structure
realignment

99

were  presented  as  restructuring  costs  in  the  Consolidated  Statements  of  Operations.  The  following  table  summarizes  the  restructuring  charges  (credits)
recognized in the Consolidated Statements of Operations for years ended December 31, 2020, 2019 and 2018, respectively (in thousands):

Termination Benefits
Non-Cash Termination Benefits
Contract Termination Costs
Non-Cash Contract Termination Costs
Non-Cash Assets Impairment
Other

Total restructuring charges (credits)

12. Employee Retirement Plan

Year Ended December 31,
2019

2018

2020

— 
— 
— 
— 
— 
— 
—  $

(61)
— 
— 
— 
— 
— 
(61) $

8,187 
948 
5,922 
(23)
498 
613 
16,145 

$

$

In the U.S., the Company provides a qualified retirement plan under section 401(k) of the Internal Revenue Code (the “IRC”) under which participants may
contribute up to 100% of their eligible compensation, subject to maximum deferral limits specified by the IRC. In addition, the Company contributes 3% of each
participating  employee’s  eligible  compensation,  subject  to  limits  specified  by  the  IRC,  on  a  quarterly  basis.  Further,  the  Company  may  make  an  annual
discretionary matching and/or profit-sharing contribution as determined solely by the Company. The Company recorded total expense for matching contributions
of $0.6 million, $0.5 million and $0.7 million for the years ended December 31, 2020, 2019 and 2018, respectively.

In Europe, the Company recorded total expense for employer contribution of $32,000, $26,000 and $247,000, in the years ended December 31, 2020, 2019

and 2018, respectively. In Ireland, the Company operates a defined contribution plan in which it contributes up to 7.5% of an employee's eligible earnings.

13. Selected Quarterly Financial Information (Unaudited)

The following table presents selected unaudited consolidated financial data for each of the eight quarters in the two-year period ended December 31, 2020. In
the Company's opinion, this unaudited information has been prepared on the same basis as the audited information and includes all adjustments (consisting of only
normal recurring adjustments) necessary for a fair statement of the financial information for the period presented. Net loss per share - basic and diluted, for the four
quarters of each fiscal year may not sum to the total for the fiscal year because of the different number of shares outstanding during each period (in thousands,
except per share data):

Year Ended December 31, 2020
Revenues
Operating expenses
Net loss
Net loss per share - basic
Net loss per share - diluted

Year Ended December 31, 2019

Revenues

Operating expenses

Net loss

Net loss per share - basic
Net loss per share - diluted

First

Second

Third

Fourth

Quarter

$
$
$
$
$

$

$

$

$
$

141 
24,989 
(23,569)
(0.59)
(0.59)

186 

23,140 

(20,865)

(0.52)
(0.52)

$
$
$
$
$

$

$

$

$
$

195 
26,927 
(26,282)
(0.66)
(0.66)

167 

18,664 

(15,810)

(0.40)
(0.40)

$
$
$
$
$

$

$

$

$
$

157 
31,003 
(30,577)
(0.77)
(0.77)

205 

21,177 

(19,448)

(0.49)
(0.49)

$
$
$
$
$

$

$

$

$

360 
30,668 
(30,716)
(0.77)
(0.77)

256 

23,530 

(21,554)

(0.54)
(0.54)

100

ITEM 9. CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS

None.

ITEM 9A. CONTROLS AND PROCEDURES

Evaluation of Disclosure Controls and Procedures

Our  management,  with  the  participation  of  our  chief  executive  officer  (“CEO”)  and  chief  financial  officer  (“CFO”)  evaluated  the  effectiveness  of  our
disclosure controls and procedures pursuant to Rule 13a-15 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), as of the end of the
period covered by this Form 10-K.  Based on this evaluation, our CEO and CFO concluded that, as of December 31, 2020, our disclosure controls and procedures
are designed and are effective to provide reasonable assurance that information we are required to disclose in reports that we file or submit under the Exchange Act
is recorded, processed, summarized, and reported within the time periods specified in the SEC’s rules and forms, and that such information is accumulated and
communicated to our management, including our CEO and CFO, as appropriate, to allow timely decisions regarding required disclosure.

Management’s Report on Internal Control over Financial Reporting

Our  management  is  responsible  for  establishing  and  maintaining  adequate  internal  control  over  financial  reporting  as  defined  in  Rule  13a-15(f)  of  the
Exchange Act. Internal control over financial reporting is a process designed by, or under the supervision of, our CEO and CFO, and effected by our Board of
Directors,  management  and  other  personnel,  to  provide  reasonable  assurance  regarding  the  reliability  of  financial  reporting  and  the  preparation  of  financial
statements for external purposes in accordance with generally accepted accounting principles and includes those policies and procedures that:

• Pertain to the maintenance of records that accurately and fairly reflect in reasonable detail the transactions and dispositions of the assets of our company;

• Provide  reasonable  assurance  that  transactions  are  recorded  as  necessary  to  permit  preparation  of  financial  statements  in  accordance  with  generally
accepted  accounting  principles,  and that  our  receipts  and  expenditures  are  being  made  only  in accordance  with  authorizations  of  our management  and
directors; and

• Provide  reasonable  assurances  regarding  prevention  or  timely  detection  of  unauthorized  acquisition,  use  or  disposition  of  our  assets  that  could  have  a

material adverse effect on our financial statements.

Our  management  assessed  our  internal  control  over  financial  reporting  as  of  December  31,  2020,  the  end  of  our  fiscal  year.  Management  based  its
assessment  on  criteria  established  in  “Internal  Control-Integrated  Framework  (2013)”  issued  by  the  Committee  of  Sponsoring  Organizations  of  the  Treadway
Commission.  Based  on  management's  assessment  of  our  internal  control  over  financial  reporting,  management  concluded  that,  as  of  December  31,  2020,  our
internal control over financial reporting was effective.

Changes in Internal Control over Financial Reporting

There were no changes in our internal control over financial reporting identified in management’s evaluation pursuant to Rules 13a-15(d) or 15d-15(d) of the
Exchange Act during our fourth fiscal quarter ended December 31, 2020, that materially affected, or are reasonably likely to materially affect, our internal control
over financial reporting.

Limitations on Effectiveness of Controls and Procedures

Internal  control  over  financial  reporting  has  inherent  limitations.  Internal  control  over  financial  reporting  is  a  process  that  involves  human  diligence  and
compliance and is subject to lapses in judgment and breakdowns resulting from human failures. Internal control over financial reporting also can be circumvented
by  collusion  or  improper  management  override.  Because  of  such  limitations,  there  is  a  risk  that  material  misstatements  will  not  be  prevented  or  detected  on  a
timely basis by internal control over financial reporting. However, these inherent limitations are known features of the financial reporting process. Therefore, it is
possible to design into the process safeguards to reduce, though not eliminate, this risk.

Our  management  recognizes  that  any  controls  and  procedures,  no  matter  how  well  designed  and  operated,  can  provide  only  reasonable  assurance  of
achieving the desired control objectives. In addition, the design of disclosure controls and procedures must reflect the fact that there are resource constraints and
that management necessarily applies its judgment in evaluating the benefits of possible controls and procedures relative to their costs.

101

ITEM 9B. OTHER INFORMATION

None.

PART III

Certain information required by Part III is incorporated herein by reference from our definitive proxy statement relating to our Annual General Meeting of

Shareholders to be held on May 18, 2021 (our “Proxy Statement”).

ITEM 10. DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE

Except  for  the  information  about  our  executive  officers  and  Code of  Conduct  shown below,  the  information  appearing  in  our  Proxy  Statement  under  the

following headings is incorporated herein by reference:

• Proposal No. 1 - Election of Directors

Executive Officers of the Registrant

Following is certain information regarding our executive officers.

Name

Gene G. Kinney
Carol D. Karp
Michael J. Malecek
Tran B. Nguyen

Brandon S. Smith
Radhika Tripuraneni
Karin L. Walker
Wagner M. Zago

Age
52
68
55
47

46
41
57
48

Position(s)
President and Chief Executive Officer, Director
Chief Regulatory Officer
Chief Legal Officer and Company Secretary
Chief Financial Officer
Chief Operating Officer
Chief Business Officer
Chief Development Officer
Chief Accounting Officer
Chief Scientific Officer

Since
2016
2016
2019
2013
2018
2020
2018
2013
2017

Gene G. Kinney, Ph.D., has served as our President and Chief Executive Officer as well as a member of our Board of Directors since 2016. Prior to that, he
was our Chief Operating Officer for part of 2016, and prior to that he was our Chief Scientific Officer and Head of Research and Development from 2012 to 2016.
From 2009 to 2012, Dr. Kinney held various positions with Elan Pharmaceuticals, Inc.: Senior Vice President of Pharmacological Sciences (from 2011 to 2012)
and Vice President, Pharmacology (from 2009 to 2011) for Elan Pharmaceuticals, Inc; and while in those positions, he also served as Head of Nonclinical Research
for  Janssen  Alzheimer  Immunotherapy  R&D.  From  2001  to  2009,  Dr.  Kinney  was  Senior  Director,  Head  of  Central  Pharmacology  and  acting  lead  for
Bioanalytics & Pathology at the Merck Research Laboratories, where he contributed to the strategic direction and oversight of drug discovery activities and led a
number of non-clinical discovery and clinical development programs targeted for the treatment of neurodegenerative and psychiatric conditions. Dr. Kinney also
held  positions  at  Bristol-Myers  Squibb  and  was  an  Assistant  Professor  at  the  Emory  University  School  of  Medicine,  Department  of  Psychiatry  and  Behavioral
Sciences. He earned his BA from Bloomsburg University and his MA and PhD from Florida Atlantic University.

Carol  D.  Karp has  served  as  our  Chief  Regulatory  Officer  since  2016.  Prior  to  joining  Prothena,  she  was  an  independent  regulatory  consultant  to
biotechnology  and  pharmaceutical  companies.  From  2013  to  2014,  Ms.  Karp  was  Senior  Vice  President,  Regulatory  Affairs  and  Compliance  at  Esperion
Therapeutics,  Inc.,  and  from  2010  to  2013,  she  was  Vice  President,  Head  of  Global  Regulatory  Affairs,  Pharmacovigilance  &  Risk  Management  at  Janssen
Alzheimer  Immunotherapy,  a  Johnson  &  Johnson  Company.  Previously,  Ms.  Karp  held  senior  regulatory  positions  at  Janssen  Alzheimer  Immunotherapy,  CV
Therapeutics,  Inc.,  PowderJect  Technologies,  VIVUS,  Inc.,  Cygnus,  Inc.  and  Janssen  Pharmaceutica.  She  earned  her  BA  in  Biology  from  the  University  of
Rochester, where she is a member of the Board of Trustees.

Michael  J.  Malecek has  served  as  our  Chief  Legal  Officer  and  as  Company  Secretary  since  July  2019.  Prior  to  joining  Prothena  in  2019,  he  was  Vice
President,  Deputy  General  Counsel,  Intellectual  Property  and  Litigation  of  Snowflake  (a  data  warehouse  company)  from  2018.  From  2010  to  2018,  he  was  a
Partner at Arnold & Porter Kaye Scholer LLP. From 2008 to 2010 Mr. Malecek was Partner at Dewey & LeBoeuf, LLP. From 2002-2008, he was Vice President
and Chief Advocacy Counsel at Affymetrix. Mr. Malecek earned his BA in American Studies from Yale University and his JD from the University of Virginia
School of Law.

102

Tran B. Nguyen has served as our Chief Financial Officer since 2013 and as our Chief Operating Officer since 2018. Prior to joining Prothena in 2013, he
was Vice President, Chief Financial Officer (from 2010 to 2011) and then Senior Vice President, Chief Financial Officer of Somaxon Pharmaceuticals, Inc., from
2011 until its sale in 2013. Mr. Nguyen was Vice President, Chief Financial Officer at Metabasis Therapeutics, Inc. from 2009 until its sale in 2010. From 2007 to
2009, he was a Vice President in the Healthcare Investment Banking group at Citi Global Markets, Inc., and from 2004 to 2007 he served in various capacities as a
healthcare  investment  banker  at  Lehman  Brothers,  Inc.  Mr.  Nguyen  served  on  the  board  of  directors  of  Rain  Therapeutics  Inc.  (a  privately-held  clinical-stage
oncology  company)  and  served  on  the  board  of  directors  of  Sierra  Oncology,  Inc.  (a  publicly-traded  clinical-stage  oncology  company)  from  2016  to  2019.  He
earned his BA in Economics  and Psychology from  Claremont  McKenna College  and his MBA from the Anderson School of Management  at the University of
California, Los Angeles.

Brandon  S.  Smith has  served  as  our  Chief  Business  Officer  since  2020.  Prior  to  joining  Prothena  in  2020,  he  was  Chief  Operating  Officer  at  Iconic
Therapeutics, Inc. (a biopharmaceutical company) from 2017 to 2020. From 2012 to 2017, Mr. Smith held senior positions at Impax Laboratories, LLC (a specialty
pharmaceutical company), including Senior Vice President, and Vice President of Corporate Development and Strategy. Mr. Smith also held several positions of
increasing  responsibility  at  Amgen  Inc.  between  2005  and  2012,  including  Executive  Director,  Biosimilars  Strategy,  Director,  Strategy  and  Corporate
Development and Director Operations Strategy. Mr. Smith was also a Consultant and Project Leader at The Boston Consulting Group between 2002 and 2005. Mr.
Smith earned his BA in Chemical Engineering at the University of Michigan and his MBA at The University of Texas at Austin McCombs Graduate School of
Business.

Radhika Tripuraneni, M.D., M.P.H., has served as our Chief Development Officer since 2018. Prior to that, she was our Vice President, Medical Affairs
and  Development  Operations.  Prior  to  joining  Prothena  in  2018,  Dr.  Tripuraneni  was  Vice  President,  Medical  Affairs  and  Chief  of  Staff  to  the  Chief  Medical
Officer of MyoKardia Inc., positions she held from 2017 to 2018. From 2012 to 2017, she was Vice President, Medical Affairs at Synageva BioPharma Corp. and
then  Alexion  Pharmaceuticals  Inc.,  which  acquired  Synageva  in  2015.  Dr.  Tripuraneni  held  various  medical  director  positions  at  Gilead  Sciences,  Inc.  and
Genzyme Corporation from 2007 to 2012, and prior to that worked at Summer Street Research Partners (an equity research firm). She earned her BAs in business
and liberal arts and her MD from the University of Missouri, and her Master in Public Health from Harvard University. Dr. Tripuraneni did her clinical training in
general surgery at Harvard - Beth Israel Deaconess Medical Center.

Karin  L.  Walker has  served  as  our  Chief  Accounting  Officer  since  2013.  Prior  to  joining  Prothena  in  2013,  she  was  Vice  President,  Finance  and  Chief
Accounting  Officer  of  Affymax,  Inc.,  a  position  she  held  from  2012  to  2013.  From  2009  to  2012,  Ms.  Walker  was  Vice  President,  Finance  and  Corporate
Controller at Amyris Inc. From 2006 to 2009, she was Vice President, Finance and Corporate Controller for CV Therapeutics, Inc. Ms. Walker also held senior
financial leadership positions at Knight Ridder Digital, Accellion, Niku Corporation, Financial Engines, Inc. and NeoMagic Corporation. Ms. Walker serves on the
board of Cylcacel Pharmaceutical Inc. (a publicly-traded clinical-stage oncology company) and served on the board of LifeSci Acquisition Corp. (a publicly-traded
special purpose acquisition company) in 2020. She earned her BS in business from the California State Polytechnic University, San Luis Obispo, and is a certified
public accountant.

Wagner  M.  Zago,  Ph.D.,  has  served  as  our  Chief  Scientific  Officer  since  2017.  Prior  to  that,  from  2015  to  2017,  he  was  our  Vice  President,  Head  of
Research.  From  2012  to  2015,  Dr.  Zago  was  our  Head  of  Pharmacology  and  Neuropathology.  From  2006  to  2012,  he  held  various  scientific  positions  at  Elan
Pharmaceuticals, Inc, performing research aimed at developing new therapeutics for central nervous system disorders and inflammation. While in these positions,
from 2009 to 2013, Dr. Zago also served as a scientist at Janssen Alzheimer Immunotherapy, a Johnson & Johnson Company. He earned his BS in Biomedicine
from the Universidade Federal de Sao Paulo (Escola Paulista de Medicina), Brazil, and his MS and PhD (both in Pharmacology) from the Universidade de Sao
Paulo, Brazil, and was a Post-Doctoral Researcher at the University of California, San Diego and the Burnham Institute.

Code of Conduct

We  have  a  Code  of  Conduct  that  applies  to  all  of  our  directors,  executive  officers  and  employees,  including  our  principal  executive  officer,  principal
financial officer, principal accounting officer or controller, or persons performing similar functions. Our Code of Conduct is available on the Company’s website at
http://ir.prothena.com/corporate-governance. We will provide to any person without charge, upon request, a copy of that Code of Conduct; such a request may be
made by sending it to our Company Secretary, Prothena Corporation plc, 77 Sir John Rogerson’s Quay, Block C, Grand Canal Docklands, Dublin 2, D02 T804,
Ireland. If we make any amendment to, or waiver from, a provision of our Code of Conduct that we are required to disclose under SEC rules, we intend to satisfy
that  disclosure  requirement  by  posting  such  information  to  our  website  at  http://ir.prothena.com/corporate-governance.  The  contents  of  our  websites  are  not
intended to be incorporated  by reference  into this Form 10-K or in any other report or document we file with the SEC, and any references  to our websites are
intended to be inactive textual references only.

103

ITEM 11. EXECUTIVE COMPENSATION

The information appearing in our Proxy Statement under the following headings is incorporated herein by reference:

• Executive Compensation
• Director Compensation
• Report of the Compensation Committee of the Board of Directors

ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT AND RELATED STOCKHOLDER MATTERS

The information appearing in our Proxy Statement under the following headings is incorporated herein by reference:

• Equity Compensation Plan Information
• Security Ownership of Certain Beneficial Owners and Management

ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS, AND DIRECTOR INDEPENDENCE

The information appearing in our Proxy Statement under the following headings is incorporated herein by reference:

• Transactions with Related Persons and Indemnification
• Proposal No. 1 - Election of Directors

ITEM 14. PRINCIPAL ACCOUNTING FEES AND SERVICES

The information appearing in our Proxy Statement under the following headings is incorporated herein by reference:

• Proposal No. 2 - Ratification of Appointment of Independent Registered Public Accounting Firm - Fees Paid to KPMG
• Proposal No. 2 - Ratification of Appointment of Independent Registered Public Accounting Firm - Pre-Approval Policies and Procedures

With the exception of the information specifically incorporated by reference in Part III to this Form 10-K from our Proxy Statement, our Proxy Statement

shall not be deemed to be filed as part of this Form 10-K.

ITEM 15. EXHIBITS, FINANCIAL STATEMENT SCHEDULES

(a)

The following documents are filed as part of this report on Form 10-K:

PART IV

(1) Financial Statements. Reference is made to the Index to the registrant’s Financial Statements under Item 8 in Part II of this Form 10-K.

(2) Financial Statement Schedules. Financial statement schedules have been omitted because the required information is not present or not present in the
amounts sufficient to require submission of the schedule or because the information is already included in the consolidated financial statements or
notes thereto.

(3) Exhibits. The exhibits listed on the accompanying index to exhibits in Item 15(b) below are filed as part of, or hereby incorporated by reference into,

this report on Form 10-K.

(b)

Exhibits.

The exhibits listed in the Exhibit Index hereto are incorporated or filed herewith.

104

EXHIBIT INDEX

Exhibit 
No.

2.1

2.2(a)

2.2(b)

2.3

3.1

4.1

4.2

10.1(a)

10.1(b)

10.2

10.3(a)†

10.3(b)†

10.4†

10.5†

Description

Demerger Agreement, dated as of November 8, 2012, between
Elan Corporation, plc and Prothena Corporation plc

Amended and Restated Intellectual Property License and
Contribution Agreement, dated as of December 20, 2012, by
and among Neotope Biosciences Limited, Elan Pharma
International Limited, and Elan Pharmaceuticals, Inc.

Amendment Number One to the Amended and Restated
Intellectual Property License and Contribution Agreement,
effective as of December 20, 2012, among Neotope
Biosciences Limited, Elan Pharma International Limited, Elan
Pharmaceuticals, LLC, Elan Corporation, plc, and Crimagua
Limited

Intellectual Property License and Conveyance Agreement,
dated as of December 20, 2012, among Neotope Biosciences
Limited, Elan Pharma International Limited and Elan
Pharmaceuticals, Inc.

Amended and Restated Memorandum and Articles of
Association (Constitution) of Prothena Corporation plc

Amended and Restated Memorandum and Articles of
Association (Constitution) of Prothena Corporation plc

Description of Registrant’s Securities

Tax Matters Agreement, dated as of December 20, 2012,
between Elan Corporation, plc and Prothena Corporation plc

Amendment No. 1 to Tax Matters Agreement, dated as of
June 25, 2013, between Elan Corporation, plc and Prothena
Corporation plc

License Agreement, dated as of December 31, 2008, between
the University of Tennessee Research Foundation and Elan
Pharmaceuticals, Inc.

License Agreement, dated as of November 4, 2013, between
The Regents of the University of California and Neotope
Biosciences Limited

License Agreement Amendment Number One, dated as of
January 15, 2014, to License Agreement dated as of November
4, 2013, between The Regents of the University of California
and Neotope Biosciences Limited

Exclusive License Agreement, dated as of July 25, 2016,
between University Health Network and Prothena Biosciences
Limited

License, Development, and Commercialization Agreement,
dated as of December 11, 2013, among Neotope Biosciences
Limited and Prothena Biosciences Inc, F. Hoffmann-La Roche
Ltd. and Hoffmann-La Roche Inc.

105

Previously Filed

File No.

Filing Date

Exhibit

Filed Herewith

Form

10/A

001-35676

11/30/2012

8-K

001-35676

12/21/2012

2.1

2.1

S-1/A

333-191218

9/30/2013

2.2(b)

8-K

001-35676

12/21/2012

2.2

8-K

8-K

001-35676

5/25/2016

001-35676

5/25/2016

8-K

001-35676

12/21/2012

10-Q

001-35676

8/13/2013

3.1

3.1

10.1

10.2

X

10/A

001-35676

11/30/2012

10.14

10-Q/A

001-35676

8/17/2018

10.1(a)

10-Q/A

001-35676

8/17/2018

10.1(b)

10-Q/A

001-35676

8/17/2018

10.2

10-K/A

001-35676

6/6/2014

10.4

Exhibit 
No.

10.6+

10.7(a)

Description
Amendment to License, Development, and Commercialization
Agreement, entered into on October 1, 2019, among Prothena
Biosciences Limited, Prothena Biosciences Inc, F. Hoffman-La
Roche Ltd and Hoffman-La Roche Inc.

Understanding Related to License, Development, and
Commercialization Agreement, dated as of March 1, 2020,
among Prothena Biosciences Limited, Prothena Biosciences
Inc, F. Hoffman-La Roche Ltd and Hoffman-La Roche Inc.

Previously Filed

Form
10-K

File No.
001-35676

Filing Date
3/3/2020

Exhibit
10.6

Filed Herewith

10-Q

001-35676

5/6/2020

10.4(a)

10.7(b)+

License Agreement, dated as of March 1, 2020, between
Prothena Biosciences Limited and F. Hoffmann-La Roche Ltd.

10-Q

001-35676

5/6/2020

10.4(b)

10.8†

10.9

10.10†

10.11(a)

10.11(b)

10.12(a)

10.12(b)

10.13#

10.14#

10.15#

10.16#

10.17#

10.18#

10.19#

Master Collaboration Agreement, dated as of March 20, 2018,
between Prothena Biosciences Limited and Celgene
Switzerland LLC

Share Subscription Agreement, dated as of March 20, 2018,
between Celgene Switzerland LLC and Prothena Corporation
plc

Master Process Development and Clinical Supply Agreement,
dated as of June 23, 2010, as amended August 1, 2011, among
Elan Pharma International Limited, Neotope Biosciences
Limited and Boehringer Ingelheim Pharma GmbH & Co. KG

Sublease, dated as of March 22, 2016, between Prothena
Biosciences Inc and Amgen Inc.

Consent to Sublease Agreement, dated as of March 28, 2016,
among Prothena Biosciences Inc, Amgen Inc. and HCP BTC,
LLC

Sub-Sublease, dated as of July 18, 2018, between Prothena
Biosciences Inc and Assembly Biosciences, Inc.

Consent to Sub-Sublease, dated as of September 19, 2018,
among Prothena Biosciences Inc, Assembly Biosciences, Inc.,
Amgen Inc. and HCP BTC, LLC

Prothena Corporation plc Amended and Restated 2012 Long
Term Incentive Plan

Prothena Corporation plc 2018 Long Term Incentive Plan

First Amendment to the Prothena Corporation plc 2018 Long
Term Incentive Plan

Prothena Corporation plc 2020 Employment Inducement
Incentive Plan

First through Sixth Amendments to the Prothena Corporation
plc 2020 Employment Inducement Incentive Plan

Prothena Corporation plc Amended and Restated Incentive
Compensation Plan

Prothena Biosciences Inc Amended and Restated Severance
Plan

10-Q/A

001-35676

8/17/2018

10.3

10-Q

001-35676

5/9/2018

10.4

10-Q

001-35676

8/13/2013

10.3

10-Q

001-35676

5/4/2016

10.2(a)

10-Q

001-35676

5/4/2016

10.2(b)

10-Q

001-35676

11/6/2018

10.2(a)

10-Q

001-35676

11/6/2018

10.2(b)

8-K

8-K

8-K

001-35676

5/23/2017

001-35676

5/18/2018

001-35676

5/22/2020

10-Q

001-35676

5/6/2020

10-Q

001-35676

5/9/2017

8-K

001-35676

12/15/2015

10.1

10.1

10.1

10.2

10.1

10.1

X

106

Exhibit 
No.

10.20#

10.21#

10.22#

10.23#

10.24#

10.25#

10.26#

10.27#

10.28#

10.29#

10.30#

10.31#

10.32#

10.33#

10.34#

Description

Form of Deed of Indemnification between Prothena
Corporation plc and its Directors and Officers

Form of Option Award Agreement between Prothena
Corporation plc and its Non-Employee Directors under the
Prothena Corporation plc 2012 Long Term Incentive Plan
(used beginning January 29, 2013)

Form of Option Award Agreement between Prothena
Corporation plc and its Non-Employee Directors under the
Prothena Corporation plc 2018 Long Term Incentive Plan
(used beginning May 16, 2018)

Form of Option Award Agreement between Prothena
Corporation plc and its Named Executive Officers under the
Prothena Corporation plc 2012 Long Term Incentive Plan
(used beginning January 29, 2013 until February 4, 2014)

Form of Option Award Agreement between Prothena
Corporation plc and its Named Executive Officers under the
Prothena Corporation plc 2012 Long Term Incentive Plan
(used beginning February 4, 2014)

Form of Option Award Agreement between Prothena
Corporation plc and its Named Executive Officers under the
Prothena Corporation plc 2018 Long Term Incentive Plan
(used beginning June 21, 2018)

Form of Option Award Agreement under the Prothena
Corporation plc 2020 Employment Inducement Incentive Plan
(used beginning March 2, 2020)

Offer letter, dated March 20, 2013, between Prothena
Biosciences Inc and Tran B. Nguyen

Employment Agreement, dated September 30, 2016, between
Prothena Biosciences Inc and Gene G. Kinney

Offer letter, dated April 19, 2013, between Prothena
Biosciences Inc and Karin L. Walker

Offer letter, dated December 5, 2016, between Prothena
Biosciences Inc and Carol D. Karp

Promotion letter, dated June 9, 2017, between Prothena
Biosciences Inc and Wagner M. Zago

Promotion letter, dated December 11, 2018, between Prothena
Biosciences Inc and Radhika Tripuraneni

Offer letter, dated June 4, 2019, between Prothena Biosciences
Inc and Michael J. Malecek

Offer Letter, dated February 18, 2020, between Prothena
Biosciences Inc and Brandon S. Smith

107

Previously Filed

Form
8-K

File No.
001-35676

Filing Date
12/11/2014

Exhibit
10.1

Filed Herewith

S-8

333-196572

6/6/2014

99.2

10-Q

001-35676

8/7/2018

10.2

S-8

333-196572

6/6/2014

99.3

10-K

001-35676

3/13/2015

10.11

10-Q

001-35676

8/7/2018

10.3

10-Q

001-35676

8/6/2020

10.3

8-K

8-K

8-K

001-35676

3/28/2013

001-35676

11/4/2016

001-35676

5/22/2013

10.1

10.1

10.1

10-K

001-35676

2/27/2017

10.28

10-Q

001-35676

8/9/2017

10.3

10-K

001-35676

3/15/2019

10.35

10-Q

001-35676

8/6/2019

10-Q

001-35676

5/6/2020

10.1

10.1

Exhibit 
No.

10.35#

21.1

23.1

24.1

31.1

31.2

32.1*

101.INS

101.SCH

101.CAL

101.DEF

101.LAB

101.PRE

104

Description

Form

File No.

Filing Date

Exhibit

Filed Herewith

Previously Filed

Consulting Agreement, dated July 15, 2020, between Prothena
Biosciences Inc and Dennis J. Selkoe

List of Subsidiaries

Consent of KPMG LLP, independent registered public accounting
firm

Power of Attorney (see signature page hereto)

Certification of Principal Executive Officer pursuant to Rule 13a-
14(a) and 15d-14(a) of the Securities Exchange Act of 1934, as
adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002

Certification of Principal Financial Officer pursuant to Rule 13a-
14(a) and 15d-14(a) of the Securities Exchange Act of 1934, as
adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002

Certification of Principal Executive Officer and Principal Financial
Officer pursuant to 18 U.S.C. Section 1350, as adopted pursuant to
Section 906 of the Sarbanes-Oxley Act of 2002

The instance document does not appear in the Interactive Data File
because its XBRL tags are embedded within the Inline XBRL
document

Inline XBRL Taxonomy Extension Schema Document

Inline XBRL Taxonomy Extension Calculation Linkbase Document

Inline XBRL Taxonomy Extension Definition Linkbase Document

Inline XBRL Taxonomy Extension Label Linkbase Document

Inline XBRL Taxonomy Extension Presentation Linkbase
Document

Cover Page Interactive Data File (formatted as Inline 
XBRL and contained in Exhibit 101)

X

X

X

X

X

X

X

X

X

X

X

X

X

X

_______________

*    Exhibit 32.1 is being furnished and shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the
“Exchange Act”), or otherwise subject to the liability of that section, nor shall such exhibit be deemed to be incorporated by reference in any registration
statement or other document filed under the Securities Act of 1933, as amended, or the Exchange Act, except as otherwise specifically stated in such filing.

#    Indicates management contract or compensatory plan or arrangement.

†    Portions of this exhibit (indicated by asterisks) have been omitted pursuant to a request for confidential treatment and this exhibit has been filed separately

with the Securities and Exchange Commission.

+    Certain information in this exhibit (indicated by asterisks) has been excluded pursuant to Regulation S-K, Item 601(b)(10). Such information is not material

and would likely cause competitive harm to the registrant if publicly disclosed.

108

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this Annual Report

on Form 10-K to be signed on its behalf by the undersigned, thereunto duly authorized.

SIGNATURES

Dated:

February 26, 2021

Prothena Corporation plc
(Registrant)

/s/ Gene G. Kinney
Gene G. Kinney
President and Chief Executive Officer

/s/ Tran B. Nguyen
Tran B. Nguyen
Chief Operating Officer and Chief Financial Officer

109

 
POWER OF ATTORNEY

KNOW  ALL  PERSONS  BY  THESE  PRESENTS,  that  each  person  whose  individual  signature  appears  below  hereby  authorizes  and  appoints  Gene  G.
Kinney and Tran B. Nguyen, and each of them, with full power of substitution and resubstitution and full power to act without the other, as his or her true and
lawful  attorney-in-fact  and  agent  to  act  in  his  or  her  name,  place  and  stead  and  to  execute  in  the  name  and  on  behalf  of  each  person,  individually  and  in  each
capacity stated below, and to file any and all amendments to this Annual Report on Form 10-K, and to file the same, with all exhibits thereto, and other documents
in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority
to  do  and  perform  each  and  every  act  and  thing,  ratifying  and  confirming  all  that  said  attorneys-in-fact  and  agents  or  any  of  them  or  their  or  his  substitute  or
substitutes may lawfully do or cause to be done by virtue thereof.

Pursuant to the requirements of the Securities Exchange Act of 1934, this report has been signed below by the following persons on behalf of the Registrant

and in the capacities and on the dates indicated. 

Name

Title

Date

/s/Gene G. Kinney
Gene G. Kinney, Ph.D.

/s/Tran B. Nguyen

Tran B. Nguyen

/s/Karin L. Walker

Karin L. Walker

/s/Lars G. Ekman

Lars G. Ekman, M.D., Ph.D.

/s/Paula K. Cobb

Paula K. Cobb

/s/Richard T. Collier

Richard T. Collier

/s/Shane M. Cooke

Shane M. Cooke

/s/K. Anders O. Härfstrand

K. Anders O. Härfstrand, M.D., Ph.D.

/s/Christopher S. Henney

Christopher S. Henney, Ph.D., D.Sc.

/s/Oleg Nodelman

Oleg Nodelman

/s/Dennis J. Selkoe
Dennis J. Selkoe, M.D.

President and Chief Executive Officer
(Principal Executive Officer) and Director

Chief Operating Officer and Chief Financial Officer
 (Principal Financial Officer)

Chief Accounting Officer and Controller
 (Principal Accounting Officer)

February 26, 2021

February 26, 2021

February 26, 2021

Chairman of the Board

February 26, 2021

Director

Director

Director

Director

Director

Director

Director

110

February 26, 2021

February 26, 2021

February 26, 2021

February 26, 2021

February 26, 2021

February 26, 2021

February 26, 2021

EXHIBIT 4.2

DESCRIPTION OF REGISTRANT’S SECURITIES

This description is summarized from, and qualified in its entirety by reference to, our Amended and Restated Memorandum and Articles of Association
(our “Constitution”), each of which are incorporated by reference as exhibits to the Annual Report on Form 10-K of which this exhibit is a part. In this exhibit,
unless the context otherwise requires, references to “we,” “us,” “our,” “Company,” or “Prothena” refer to Prothena Corporation plc.

The following description of our ordinary shares and Euro Deferred Shares is a summary. This summary does not purport to be complete and is qualified
in its entirety by reference to the Irish Companies Act 2014 (the “Companies Act”), and the complete text of our Constitution. You should read those laws and
documents carefully.

For the avoidance of any doubt, the ordinary shares are the subject of this registration statement. The Euro Deferred Shares are not listed on any stock

exchange and are not the subject of any registration.

Capital Structure

Issued Share Capital

As of December 31, 2020, our issued share capital was 39,921,413 ordinary shares. We have no Euro Deferred Shares in issue. Our ordinary shares are

listed on Nasdaq Global Select Market (“Nasdaq”), under the symbol “PRTA.”

Authorized Share Capital

The authorized share capital of the Company is $1,000,000 and €220,000 consisting of 100,000,000 ordinary shares with a par value of $0.01 per share
and 10,000 Euro Deferred Shares with a par value of €22 per share. The authorized share capital may be increased or reduced by a resolution approved by a simple
majority of the votes cast at a general meeting of our shareholders at which a quorum is present (referred to under Irish law as an “ordinary resolution”). The shares
comprising our authorized share capital may be divided into shares of such nominal value as the resolution shall prescribe. As a matter of Irish law, our board of
directors (our “Board”), may issue new ordinary shares or Euro Deferred Shares without shareholder approval once authorized to do so by our Constitution or by
an ordinary resolution adopted by the shareholders at a general meeting. The authorization may be granted for a maximum period of five years, at which point it
must be renewed by the shareholders by an ordinary resolution.

Our Board is authorized  pursuant to an ordinary  resolution  passed by shareholders  at our annual general  meeting  held on May 17, 2017, to issue new
ordinary shares for cash without shareholder approval up to an aggregate nominal amount equal to the authorized but unissued share capital of the Company as of
May 17, 2017, for a period of five years from the date of the passing of the resolution. As a result, our shareholders must renew this authorization by an ordinary
resolution no later than May 17, 2022.

The rights and restrictions to which our ordinary shares and Euro Deferred Shares are subject are prescribed in our Constitution. We may, by ordinary
resolution and without obtaining any vote or consent of the holders of any class or series of shares, unless expressly provided by the terms of that class or series of
shares,  provide  from  time  to  time  for  the  issuance  of  other  classes  or  series  of  shares  and  to  establish  the  characteristics  of  each  class  or  series,  including  the
number  of  shares,  designations,  relative  voting  rights,  dividend  rights,  liquidation  and  other  rights,  redemption,  repurchase  or  exchange  rights  and  any  other
preferences and relative, participating, optional or other rights and limitations not inconsistent with applicable law.

Irish law does not recognize fractional shares held of record. Accordingly, our Constitution does not provide for the issuance of fractional shares of the
Company, and the official Irish share register of the Company will not reflect any fractional shares. Whenever as a result of an issuance, alteration, reorganization,
consolidation,  division,  or  subdivision  of  the  share  capital  of  the  Company  would  result  in  any  shareholder  becoming  entitled  to  fractions  of  a  share,  no  such
fractions shall be issued or delivered to any shareholder. All such fractions of a share will be aggregated into whole shares and sold in the open market at prevailing
market prices and the aggregate cash

1

proceeds from such sale (net of tax, commissions, costs and other expenses) shall be distributed on a pro rata basis, rounding down to the nearest cent, to each
shareholder who would otherwise have been entitled to receive fractions of a share.

Preemption Rights, Share Warrants and Share Options

Under  Irish  law,  certain  statutory  preemption  rights  apply  automatically  in  favor  of  shareholders  where  shares  are  to  be  issued  for  cash.  However,  as
permitted by Irish law, we have opted out of these preemption rights by way of special resolution (a “special resolution” requires the approval of not less than 75%
of the votes of our shareholders cast at a general meeting at which a quorum is present) passed at our annual general meeting on May 17, 2017. Irish law requires
this opt-out to be renewed every five years by a special resolution. As a result, our shareholders must renew this opt-out authorization by a special resolution no
later than May 17, 2022.

If  the  opt-out  is  not  renewed,  shares  issued  for  cash  must  be  offered  to  existing  shareholders  of  the  Company  on  a  pro  rata  basis  to  their  existing
shareholding  before  the  shares  may  be  issued  to  any  new  shareholders.  The  statutory  preemption  rights  do  not  apply  (i)  where  shares  are  issued  for  non-cash
consideration (such as in a share-for-share acquisition), (ii) to the issue of non-equity shares (that is, shares that have the right to participate only up to a specified
amount in any income or capital distribution) or (iii) where shares are issued pursuant to an employee share option or similar equity plan.

Our Constitution provides that, subject to any shareholder approval requirement under any laws, regulations or the rules of any stock exchange to which
we are subject, our Board is authorized, from time to time, in its discretion, to grant such persons, for such periods and upon such terms as it deems advisable,
options to purchase such number of shares of any class or classes or of any series of any class as our Board may deem advisable, and to cause warrants or other
appropriate instruments evidencing such options to be issued. The Companies Act provide that directors may issue share warrants or options without shareholder
approval  once  authorized  to  do  so  by  a  company’s  constitution  or  an  ordinary  resolution  of  shareholders.  We  are  subject  to  the  rules  of  Nasdaq  and  the
U.S. Internal Revenue Code of 1986, as amended, which require shareholder approval of certain equity plans and share issuances. Our Board may issue shares
upon exercise of warrants or options without shareholder approval or authorization (up to the relevant authorized share capital limit).

Dividends

Under Irish law, dividends and distributions may only be made from distributable reserves. Distributable reserves generally means accumulated, realized
profits, so far as not previously utilized by distribution or capitalization, less accumulated, realized losses, so far as not previously written off in a reduction or re-
organization of capital duly made. In addition, no distribution or dividend may be made unless our net assets are equal to, or in excess of, the aggregate of our
called up share capital plus undistributable reserves and the distribution does not reduce our net assets below such aggregate. Undistributable reserves include the
undenominated capital (effectively the share premium and capital redemption reserve) and the amount by which our accumulated unrealized profits, so far as not
previously utilized by any capitalization, exceed the Company’s accumulated unrealized losses, so far as not previously written off in a reduction or reorganization
of capital.

The determination as to whether or not we have sufficient distributable reserves to fund a dividend must be made by reference to the “relevant financial
statements”  of  the  Company.  The  relevant  financial  statements  are  either  the  last  set  of  unconsolidated  annual  audited  financial  statements  or  other  financial
statements properly prepared in accordance with the Companies Act, which give a “true and fair view” of our unconsolidated financial position and accord with
accepted accounting practice. The relevant financial statements must be filed in the Companies Registration Office (the official public registry for companies in
Ireland).

Our Constitution authorizes our Board to declare dividends without shareholder approval to the extent they appear justified by profits lawfully available
for distribution. Our Board may also recommend a dividend to be approved and declared by the shareholders at a general meeting. Our Board may direct that the
payment be made by distribution of assets, shares or cash, and no dividend issued may exceed the amount recommended by the directors.

2

Dividends may be declared and paid in the form of cash or non-cash assets and may be paid in dollars or any other currency.

Our Board may deduct from any dividend payable to any shareholder any amounts payable by such shareholder to the Company in relation to the shares

of the Company.

The Board may also authorize the Company to issue shares with preferred rights to participate in dividends declared by the Company from time to time,
as determined by ordinary resolution. The holders of preferred shares may, depending on their terms, rank senior to our ordinary shares in terms of dividend rights
and or be entitled to claim arrears of a declared dividend out of subsequently declared dividends in priority to ordinary shareholders.

Bonus Shares

Under our Constitution, our Board may resolve to capitalize any amount credited to any reserve available for distribution or the share premium account or
other of our undistributable reserves for issuance and distribution to shareholders as fully paid up bonus shares on the same basis of entitlement as would apply in
respect of a dividend distribution.

Share Repurchases, Redemptions and Conversions

Overview

Our Constitution provides that any ordinary share that we have agreed to acquire shall be deemed to be a redeemable share. Accordingly, for Irish law
purposes, the repurchase of ordinary shares by us may technically  be effected as a redemption of those shares as described below under  “Description of Share
Capital—Repurchases and Redemptions by Prothena.” If our Constitution did not contain such provision, repurchases by us would be subject to many of the same
rules that apply to purchases of our ordinary shares by subsidiaries described below under “Description of Share Capital—Purchases by Subsidiaries of Prothena,”
including  the  shareholder  approval  requirements  described  below,  and  the  requirement  that  any  overseas  market  purchases  be  effected  on  a  recognized  stock
exchange, which, for purposes of the Companies Act, includes Nasdaq. Neither Irish law nor any of our constituent documents places limitations on the right of
non-resident or foreign owners to vote or hold our ordinary shares. Except where otherwise noted, references in this Prospectus Supplement to repurchasing or
buying back our ordinary shares refer to the redemption of ordinary shares by us or the purchase of our ordinary shares by one of our subsidiaries, in each case in
accordance with our Constitution and Irish company law as described below.

Repurchases and Redemptions by Prothena

Under Irish law, a company may issue redeemable shares and redeem them out of distributable reserves or the proceeds of a new issue of shares for that
purpose. Please see also “Description of Share Capital—Dividends.” We may only issue redeemable shares if the nominal value of the issued share capital that is
not  redeemable  is  not  less  than  10%  of  the  nominal  value  of  our  total  issued  share  capital.  All  redeemable  shares  must  also  be  fully-paid  and  the  terms  of
redemption  of  the  shares  must  provide  for  payment  on  redemption.  Redeemable  shares  may,  upon  redemption,  be  cancelled  or  held  in  treasury.  Based  on  the
provisions of our Constitution, shareholder approval will not be required to redeem our shares.

We may also be given an additional general authority for overseas market purchases of our ordinary shares by way of ordinary resolution, which would

take effect on the same terms and be subject to the same conditions as applicable to purchases by our subsidiaries as described below.

Repurchased  and redeemed  shares  may  be cancelled  or held as treasury  shares.  The nominal  value  of treasury  shares  held by us at any time  must not
exceed 10% of the nominal  value of our issued share capital. We may not exercise any voting rights in respect of any shares held as treasury shares. Treasury
shares may be cancelled by us or re-issued subject to certain conditions.

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Purchases by Subsidiaries of Prothena

Under Irish law, an Irish or non-Irish subsidiary of the Company may purchase our shares by way of an: (i) overseas market purchase; or (ii) off-market
purchase.  For  one  of  our  subsidiaries  to  make  overseas  market  purchases  of  our  ordinary  shares,  our  shareholders  must  provide  general  authorization  for  such
purchase by way of ordinary resolution. However, as long as this general authority has been granted, no specific shareholder authority for a particular overseas
market purchase by a subsidiary of our ordinary shares is required. For a purchase by one of our subsidiaries off-market, the proposed purchase contract must be
authorized by special resolution of our shareholders before the contract is entered into. The person whose ordinary shares are to be bought back cannot vote in
favor of the special resolution and from the date of the notice of the meeting at which the resolution approving the contract is proposed, the purchase contract must
be on display or must be available for inspection by our shareholders at our registered office.

In order for one of our subsidiaries to make overseas market purchases of our shares, such shares must be purchased on a recognized stock exchange.

Nasdaq, on which our ordinary shares are listed, is specified as a recognized stock exchange for this purpose in accordance with Irish law.

The number of shares held by our subsidiaries at any time will count as treasury shares and will be included in any calculation of the permitted treasury
share threshold of 10% of the nominal value of our issued share capital. While a subsidiary holds our shares, it cannot exercise any voting rights in respect of those
shares. The acquisition of our ordinary shares by a subsidiary must be funded out of distributable reserves of the subsidiary.

Lien on Shares, Calls on Shares and Forfeiture of Shares

Our Constitution provides that we have a first and paramount lien on every share that is not a fully paid up share for all amounts payable at a fixed time or
called in respect of that share. Subject to the terms of their allotment, directors may call for any unpaid amounts in respect of any shares to be paid, and if payment
is not made, the shares may be forfeited. These provisions are standard inclusions in the constitution of an Irish public company limited by shares such as Prothena
and are only applicable to our shares that have not been fully paid up. Irish stamp duty may be payable in respect of transfers of our ordinary shares at the rate of
1%.

Consolidation and Division; Subdivision

Under our Constitution, we may, by ordinary resolution, consolidate and divide all or any of our share capital into shares of larger nominal value than our

existing shares or subdivide our shares into smaller amounts than are fixed by our Constitution.

Reduction of Share Capital

We may, by ordinary resolution, reduce our authorized share capital in any way. We also may, by special resolution and subject to confirmation by the

Irish High Court, reduce or cancel our issued share capital in any manner permitted by the Companies Act.

Annual Meetings of Shareholders

Under  Irish  company  law,  we  are  required  to  hold  annual  general  meetings  at  intervals  of  no  more  than  15  months  from  the  previous  annual  general
meeting, provided that an annual general meeting is held in each calendar year following the first annual general meeting and no more than nine months after our
fiscal  year-end.  Subject  to  compliance  with  the  Companies  Act,  any  of  our  annual  general  meetings  may  be  held  outside  Ireland.  Notice  of  an  annual  general
meeting  must  be  given  to  all  of  our  shareholders  and  to  our  auditors.  Our  Constitution  provides  for  a  minimum  notice  period  of  21  days’  notice,  which  is  the
minimum permitted by the Companies Act.

The  only  matters  which  must,  as  a  matter  of  Irish  company  law,  be  transacted  at  the  Company’s  annual  general  meeting  are  the  consideration  of  the
statutory  financial  statements,  report  of  the  directors  and  the  report  of  the  auditors  on  those  statements  and  that  report,  the  review  by  the  shareholders  of  the
Company’s affairs, the election and re-election of directors in accordance with our Constitution, the declaration of a dividend (if any), the

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appointment  or  reappointment  of  the  auditors  and  the  fixing  of  the  auditor’s  remuneration  (or  delegation  of  same).  If  no  resolution  is  made  in  respect  of  the
reappointment of an existing auditor at an annual general meeting, the existing auditor will be deemed to have continued in office.

Extraordinary General Meetings of Shareholders

Extraordinary general meetings of the Company may be convened by (i) our Board, (ii) on requisition of our shareholders holding not less than 10% of
the  paid  up  share  capital  of  our  carrying  voting  rights,  (iii)  on  requisition  of  our  auditors,  or  (iv)  in  exceptional  cases,  by  order  of  the  Irish  High  Court.
Extraordinary general meetings are generally held for the purpose of approving shareholder resolutions as may be required from time to time. At any extraordinary
general meeting only such business shall be conducted as is set forth in the notice thereof.

Notice  of  an  extraordinary  general  meeting  must  be  given  to  all  of  our  shareholders  and  to  our  auditors.  Under  Irish  law  and  our  Constitution,  the
minimum notice periods are 21 days’ notice in writing for an extraordinary general meeting to approve a special resolution and 14 days’ notice in writing for any
other extraordinary general meeting.

In the case of an extraordinary general meeting convened by the requisition of our shareholders under part (ii) above, the proposed purpose of the meeting
must be set out in the requisition notice. Upon receipt of any such valid requisition notice, our Board has 21 days to convene a meeting of our shareholders to vote
on the matters set out in the requisition notice. This meeting must be held within two months of the receipt of the requisition notice. If our Board does not convene
the meeting within such 21-day period, the requisitioning shareholders, or any of them representing more than one half of the total voting rights of all of them, may
themselves convene a meeting, which meeting must be held within three months of our receipt of the requisition notice.

If our Board becomes aware that our net assets are not greater than half of the amount of our called-up share capital, it must convene an extraordinary

general meeting of our shareholders not later than 28 days from the date that they learn of this fact to consider how to address the situation.

Quorum for General Meetings

Our Constitution provides that no business shall be transacted at any general meeting unless a quorum is present. One or more of our shareholders present

in person or by proxy holding not less than one-half of our issued and outstanding shares entitled to vote at the meeting in question constitute a quorum.

Voting

Our Constitution provides that our Board or chairman may determine the manner in which the poll is to be taken and the manner in which the votes are to

be counted.

Each Company shareholder is entitled to one vote for each ordinary share that he or she holds as of the record date for the meeting. Voting rights may be
exercised by shareholders registered in our share register as of the record date for the meeting or by a duly appointed proxy, which proxy need not be a Company
shareholder. Where interests in shares are held by a nominee trust company, such company may exercise the rights of the beneficial holders on their behalf as their
proxy.  All  proxies  must  be  appointed  in  the  manner  prescribed  by  our  Constitution,  which  permit  shareholders  to  notify  us  of  their  proxy  appointments
electronically in such manner as may be approved by our Board.

In accordance with our Constitution, we may from time to time be authorized by ordinary resolution to issue preferred shares. These preferred shares may have
such voting rights as may be specified in the terms of such preferred shares (e.g., they may carry more votes per share than ordinary shares or may entitle their
holders to a class vote on such matters as may be specified in the terms of the preferred shares). Treasury shares or our shares that are held by our subsidiaries are
not entitled to be voted at general meetings of shareholders.

Irish  law  requires  special  resolutions  of  our  shareholders  at  a  general  meeting  to  approve  certain  matters.  Examples  of  matters  requiring  special

resolutions include:

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amending our Constitution;

approving a change of name of Prothena;

authorizing  the  entering  into  of  a  guarantee  or  provision  of  security  in  connection  with  a  loan,  quasi  loan  or  credit  transaction  to  a  director  or
connected person;

opting out of preemption rights on the issuance of new shares;

re-registration of Prothena from a public limited company to a private company;

variation of class rights attaching to classes of shares (where the Constitution does not provide otherwise);

purchase of our shares off-market;

reduction of issued share capital;

sanctioning a compromise/scheme of arrangement with creditors or shareholders;

resolving that we be wound up by the Irish courts;

resolving in favor of a shareholders’ voluntary winding-up; and

setting the re-issue price of treasury shares.

Variation of Rights Attaching to a Class or Series of Shares

Under our Constitution and the Companies Act, any variation of class rights attaching to our issued shares must be approved by a special resolution of our

shareholders of the affected class or with the consent in writing of the holders of three-quarters of all the votes of that class of shares.

The  provisions  of  our  Constitution  relating  to  general  meetings  apply  to  general  meetings  of  the  holders  of  any  class  of  our  shares  except  that  the
necessary  quorum  is  determined  in  reference  to  the  shares  of the  holders  of  the  class.  Accordingly,  for general  meetings  of  holders  of  a particular  class  of  our
shares, a quorum consists of the holders present in person or by proxy representing at least one-half of the issued shares of the class.

Record Date

Our Board may from time to time fix a record date for the purposes of determining the rights of shareholders to notice of and/or to vote at any general
meeting of the Company. The record date shall not precede the date upon which the resolution fixing the record date is adopted and may not be more than 90 days
nor less than 10 days before the date of such meeting. If no record date is fixed by the Board, the record date for determining shareholders entitled to notice of, or
to vote at, a meeting shall be the date immediately preceding the date on which notice of the meeting is given.

The Board may also set a record date to determine the identity of the shareholders entitled to receive payment of any dividend or for any other proper
purpose. The record date shall not precede the date upon which the resolution fixing the record date is adopted and the record date shall not be more than ninety
days prior to such action. If no record date is fixed, the record date for determining shareholders for such purpose shall be the date on which the Board adopts the
resolution relating to the payment of any dividend.

Advance Notice Provisions

Under Irish law, there is no general right for a shareholder to put items on the agenda of an annual general meeting of the Company, other than as set out
in  the  Constitution.  Our  Constitution  permits  shareholders  to  nominate  persons  for  election  to  the  Board  at  general  meetings  called  for  the  purpose  of  electing
directors once they

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comply with certain requirements set out in the Constitution. Under our Constitution, in addition to any other applicable requirements, for director nominations to
be properly brought before a general meeting by a shareholder, such shareholder must have given timely notice thereof in writing to our corporate secretary.

To  be  timely  for  an  annual  general  meeting,  a  shareholder’s  notice  to  our  secretary  as  to  the  nominations  to  be  brought  before  the  meeting  must  be
delivered to our registered office not less than 90 days nor more than 150 days prior to the first anniversary of the notice convening our annual general meeting for
the prior year. In the event that the date of the annual general meeting is changed by more than 30 days from the first anniversary date of the prior year’s annual
general meeting, notice by the member must be delivered not earlier than 150 days prior to such annual general meeting and not later than the later of (a) 90 days
prior to the day of the contemplated annual general meeting or (b) ten days after the day on which public announcement of the date of the contemplated annual
general meeting is first made.

To be timely for nominations of a director at an extraordinary general meeting, notice must be delivered not more than 150 days prior to the date of such
extraordinary general meeting and not later than 90 days prior to such extraordinary general meeting or 10 days after the day on which public announcement is first
made of the date of the general meeting and of the nominees proposed by the Board to be elected at such meeting.

For nominations to the Board, the notice must include all information about the director nominee that is required to be disclosed by SEC rules regarding
the solicitation of proxies for the election of directors pursuant to Regulation 14A under the Exchange Act. The notice also must include information about the
shareholder  and  the  shareholder’s  holdings  of  our  shares.  The  chairman  of  the  meeting  shall  have  the  power  and  duty  to  determine  whether  any  proposed
nomination was made or proposed in accordance with these provisions (as set out in our Constitution), and if any proposed nomination is not in compliance with
these provisions, to declare that such nomination is defective and shall be disregarded.

Shareholders’ Suits

In  Ireland,  the  decision  to  institute  proceedings  on  behalf  of  a  company  is  generally  taken  by  the  company’s  board  of  directors.  In  certain  limited
circumstances, a shareholder may be entitled to bring a derivative action on our behalf. The central question at issue in deciding whether a minority shareholder
may be permitted to bring a derivative action is whether, unless the action is brought, a wrong committed against us would otherwise go unredressed. The cause of
action may be against a director, another person or both.

A shareholder may also bring proceedings against us in his or her own name where the shareholder’s rights as such have been infringed or where our
affairs are being conducted, or the powers of the board of directors are being exercised, in a manner oppressive to any shareholder or shareholders or in disregard
of  their  interests  as  shareholders.  Oppression  connotes  conduct  that  is  burdensome,  harsh  or  wrong. This  is  an  Irish  statutory  remedy  under  Section  212 of  the
Companies Act and the court can grant any order it sees fit, including providing for the purchase or transfer of the shares of any shareholder.

Inspection of Books and Records

Under Irish law, shareholders have the right to: (i) receive a copy of our Constitution; (ii) inspect and obtain copies of the minutes of our general meetings
and  resolutions;  (iii)  inspect  and  receive  a  copy  of  the  register  of  shareholders,  register  of  directors  and  secretaries,  register  of  directors’  interests;  (iv)  inspect
copies of directors’ service contracts; (v) inspect copies of instruments creating charge; (vi) receive copies of the statutory financial statements and directors’ and
auditors’ reports which have previously been sent to shareholders prior to an annual general meeting; and (vii) receive copies of the statutory financial statements
and directors’ and auditors’ reports of any of our subsidiaries which have previously been sent to the shareholders of the subsidiaries prior to an annual general
meeting for the preceding ten years. Our auditors also have the right of access, at all reasonable times, to the accounting records of the Company. The auditors’
report must be circulated to the shareholders with our financial statements prepared in accordance with Irish law 21 days (not including the day of mailing or the
day of the meeting) before the annual general meeting and must be laid before the shareholders at our annual general meeting.

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Acquisitions

The Company may be acquired in a number of ways, including:

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a court-approved scheme of arrangement under the Companies Act. A scheme of arrangement with shareholders requires a court order from the Irish
High Court and the approval of a majority in number representing  75% in value of each class of shareholders  present and voting in person or by
proxy at a meeting called to approve the scheme;

through a tender or takeover offer by a third party for all of our shares. Where the holders of 80% or more of our shares have accepted an offer for
their  shares  in  Prothena,  the  remaining  shareholders  may  also  be  statutorily  required  to  transfer  their  shares.  If  the  bidder  does  not  exercise  its
“squeeze out” right, then the non-accepting shareholders also have a statutory right to require the bidder to acquire their shares on the same terms;
and

by  way  of  a  merger  with  a  company  incorporated  in  the  European  Economic  Area  (“EEA”)  under  the  EU  Cross-Border  Mergers  Directive  (EU)
2017/1132 or with another Irish company under the Companies Act. Such a merger must be approved by a special resolution. Shareholders also may
be entitled to have their shares acquired for cash. See the section entitled “Description of Share Capital – Appraisal Rights.”

Irish law does not generally require shareholder approval for a sale, lease or exchange of all or substantially all of a company’s property and assets.

Appraisal Rights

Generally, under Irish law, shareholders of an Irish company do not have statutory appraisal rights. If we are being merged as the transferor company with
another EEA company under the EU Cross-Border Mergers Directive (EU) 2017/1132 as implemented  in Ireland by the European Communities (Cross-Border
Mergers) Regulations 2008 (as amended) or if we are being merged with another Irish company under the Irish Companies Act, (i) any of our shareholders who
voted against the special resolution approving the merger or (ii) if 90% of our shares are held by the successor company, any other of our shareholder, may be
entitled to require that the successor company acquire its shares for cash.

Disclosure of Interests in Shares

Under the Companies Act, our shareholders must notify us if, as a result of a transaction, the shareholder will become interested in three percent or more
of the Prothena voting shares, or if as a result of a transaction a shareholder who was interested in more than three percent of Prothena voting shares ceases to be so
interested. Where a shareholder is interested in more than three percent of Prothena voting shares, the shareholder must notify us of any alteration of his or her
interest  that brings his or her total  holding through the nearest  whole percentage  number, whether an increase  or a reduction.  The relevant  percentage  figure is
calculated by reference to the aggregate nominal value of the voting shares in which the shareholder is interested as a proportion of the entire nominal value of our
issued share capital (or any such class of share capital in issue). Where the percentage level of the shareholder’s interest does not amount to a whole percentage,
this figure may be rounded down to the next whole number. We must be notified within five business days of the transaction or alteration of the shareholder’s
interests that gave rise to the notification requirement. If a shareholder fails to comply with these notification requirements, the shareholder’s rights in respect of
any our shares it holds will not be enforceable, either directly or indirectly. However, such person may apply to the court to have the rights attaching to such shares
reinstated.

In addition to these disclosure requirements, we, under the Companies Act, may, by notice in writing, require a person whom we know or have reasonable
cause  to  believe  to  be,  or  at  any  time  during  the  three  years  immediately  preceding  the  date  on  which  such  notice  is  issued  to  have  been,  interested  in  shares
comprised in our relevant share capital: (i) to indicate whether or not it is the case; and (ii) where such person holds or has during that time held an interest in our
shares, to provide additional information, including the person’s own past or present

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interests in our shares. If the recipient of the notice fails to respond within the reasonable time period specified in the notice, we may apply to court for an order
directing that the affected shares be subject to certain restrictions, as prescribed by the Companies Act, as follows:

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any transfer of those shares or, in the case of unissued shares, any transfer of the right to be issued with shares and any issue of shares, shall be void;

no voting rights shall be exercisable in respect of those shares;

no further shares shall be issued in right of those shares or in pursuance of any offer made to the holder of those shares; and

no payment shall be made of any sums due from Prothena on those shares, whether in respect of capital or otherwise.

The court may also order that shares subject to any of these restrictions be sold with the restrictions terminating upon the completion of the sale.

In the event we are in an offer period pursuant to the Irish Takeover Rules (as defined below), accelerated disclosure provisions apply for persons holding

an interest in our securities of one percent or more.

Anti-Takeover Provisions

Shareholder Rights Plans and Share Issuances

Irish  law  does  not  expressly  authorize  or  prohibit  companies  from  issuing  share  purchase  rights  or  adopting  a  shareholder  rights  plan  as  an  anti-

takeover measure; there is no directly relevant case law on this issue. We do not currently have a rights plan in place.

Our Constitution expressly authorizes our Board to adopt a shareholder rights plan, subject to applicable law, including the Irish Takeover Rules and

Substantial Acquisition Rules described below and the requirement for shareholder authorization for the issue of shares described above.

Subject to the Irish Takeover Rules described below, our Board also has power to issue any of our authorized and unissued shares on such terms and
conditions as it may determine, and any such action should be taken in the best interests of the Prothena. It is possible, however, that the terms and conditions of
any issue of shares could discourage a takeover or other transaction that holders of some or a majority of the ordinary shares believe to be in their best interests
or in which holders might receive a premium for their shares over the then market price of the shares.

Irish Takeover Rules and Substantial Acquisition Rules

A transaction in which a third party seeks to acquire 30% or more of Prothena voting rights and any other acquisitions of our securities are governed by
the  Irish  Takeover  Panel  Act  1997  and  the  Irish  Takeover  Rules  made  thereunder,  which  are  referred  to  in  this  Prospectus  Supplement  as  the  “Irish  Takeover
Rules,” and are regulated by the Irish Takeover Panel. The “General Principles” of the Irish Takeover Rules and certain important aspects of the Irish Takeover
Rules are described below.

General Principles

The Irish Takeover Rules are built on the following General Principles which will apply to any transaction regulated by the Irish Takeover Panel:

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in the event of an offer, all holders of securities of the target company must be afforded equivalent treatment and, if a person acquires control of a
company, the other holders of securities must be protected;

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the holders of securities in the target company must have sufficient time and information to enable them to reach a properly informed decision on the
offer; where it advises the holders of securities, the board of directors of the target company must give its views on the effects of the implementation
of the offer on employment, employment conditions and the locations of the target company’s place of business;

a target company’s board of directors must act in the interests of the company as a whole and must not deny the holders of securities the opportunity
to decide on the merits of the offer;

false markets must not be created in the securities of the target company, the bidder or any other company concerned by the offer in such a way that
the rise or fall of the prices of the securities becomes artificial and the normal functioning of the markets is distorted;

a  bidder  can  only  announce  an  offer  after  ensuring  that  he  or  she  can  fulfill  in  full  any  cash  consideration,  if  such  is  offered,  and  after  taking  all
reasonable measures to secure the implementation of any other type of consideration;

a target company may not be hindered in the conduct of its affairs for longer than is reasonable by an offer for its securities; and

a “substantial acquisition” of securities (whether such acquisition is to be effected by one transaction or a series of transactions) shall take place only
at an acceptable speed and shall be subject to adequate and timely disclosure.

Mandatory Bid

Under  certain  circumstances,  a  person  who  acquires  our  shares,  or  other  voting  securities,  may  be  required  under  the  Irish  Takeover  Rules  to  make  a
mandatory cash offer for remaining outstanding Prothena voting securities at a price not less than the highest price paid for the securities by the acquiror, or any
parties  acting  in  concert  with  the  acquiror,  during  the  previous  12  months.  This  mandatory  bid  requirement  is  triggered  if  an  acquisition  of  securities  would
increase the aggregate holding of an acquiror, including the holdings of any parties acting in concert with the acquiror, to securities representing 30% or more of
Prothena  voting  rights,  unless  the  Irish  Takeover  Panel  otherwise  consents.  An  acquisition  of  securities  by  a  person  holding,  together  with  its  concert  parties,
securities representing between 30% and 50% of Prothena voting rights would also trigger the mandatory bid requirement if, after giving effect to the acquisition,
the  percentage  of  the  voting  rights  held  by  that  person  (together  with  its  concert  parties)  would  increase  by  0.05%  within  a  12-month  period.  Any  person
(excluding any parties acting in concert with the holder) holding securities representing more than 50% of the voting rights of a company is not subject to these
mandatory offer requirements in purchasing additional securities.

Voluntary Bid; Requirements to Make a Cash Offer and Minimum Price Requirements

If a person makes a voluntary offer to acquire our outstanding ordinary shares, the offer price must not be less than the highest price paid for our ordinary
shares by the bidder or its concert parties during the three-month period prior to the commencement of the offer period. The Irish Takeover Panel has the power to
extend the “look back” period to 12 months if the Irish Takeover Panel, taking into account the General Principles, believes it is appropriate to do so.

If the bidder or any of its concert  parties  has acquired  our ordinary  shares (i) during  the period of 12 months prior  to the commencement  of the offer
period  that  represent  more  than  10%  of  our  total  ordinary  shares  or  (ii)  at  any  time  after  the  commencement  of  the  offer  period,  the  offer  must  be  in  cash  (or
accompanied by a full cash alternative) and the price per our ordinary shares must not be less than the highest price paid by the bidder or its concert parties during,
in the case of (i), the 12-month period prior to the commencement of the offer period or, in the case of (ii), the offer period. The Irish Takeover Panel may apply
this  rule  to  a  bidder  who,  together  with  its  concert  parties,  has  acquired  less  than  10%  of  our  total  ordinary  shares  in  the  12-month  period  prior  to  the
commencement of the offer period if the Irish Takeover Panel, taking into account the General Principles, considers

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it just and proper to do so. An offer period will generally commence from the date of the first announcement of the offer or proposed offer.

Substantial Acquisition Rules

The Irish Takeover Rules also contain rules governing substantial acquisitions of shares and other voting securities which restrict the speed at which a
person may increase his or her holding of shares and rights over shares to an aggregate of between 15% and 30% of the Prothena voting rights. Except in certain
circumstances, an acquisition or series of acquisitions of shares or rights over shares representing 10% or more of the Prothena voting rights is prohibited, if such
acquisition(s),  when aggregated  with shares  or rights  already  held, would result  in the acquirer  holding 15% or more  but less than 30% of the Prothena  voting
rights and such acquisitions are made within a period of seven days. These rules also require accelerated disclosure of acquisitions of shares or rights over shares
relating to such holdings.

Frustrating Action

Under the Irish Takeover Rules, our Board is not permitted to take any action that might frustrate an offer for our shares once our Board has received an
approach that may lead to an offer or has reason to believe that such an offer is or may be imminent, subject to certain exceptions. Potentially frustrating actions
such as (i) the issue of shares, options or convertible securities, (ii) material acquisitions or disposals, (iii) entering into contracts other than in the ordinary course
of business or (iv) any action, other than seeking alternative offers, which may result in frustration of an offer, are prohibited during the course of an offer or at any
earlier time during which our Board has reason to believe an offer is or may be imminent. Exceptions to this prohibition are available where:

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the action is approved by our shareholders at a general meeting; or

the Irish Takeover Panel has given its consent, where:

it is satisfied the action would not constitute frustrating action;

our shareholders holding more than 50% of the voting rights state in writing that they approve the proposed action and would vote in favor of it at a
general meeting;

the  action  is  taken  in  accordance  with  a  contract  entered  into  prior  to  the  announcement  of  the  offer  (or  any  earlier  time  at  which  our  Board
considered the offer to be imminent); or

the decision to take such action was made before the announcement of the offer and either has been at least partially implemented or is in the ordinary
course of business.

Certain  other  provisions  of  Irish  law  or  our  Constitution  may  be  considered  to  have  antitakeover  effects,  including  advance  notice  requirements  for
director  nominations,  as  well  those  described  under  the  following  captions:  “Description  of  Share  Capital—Capital  Structure—Authorized  Share  Capital”
(regarding issuance of preferred shares), “Description of Share Capital—Preemption Rights, Share Warrants and Share Options,” “Description of Share Capital—
Disclosure of Interests in Shares” and “Description of Share Capital—Corporate Governance.”

Corporate Governance

Our  Constitution  allocates  authority  over  the  day-to-day  management  of  Prothena  to  our  Board.  Our  Board  may  then  delegate  the  management  of
Prothena to committees of the Board (consisting of one or more members of the Board) or executives, but regardless, our Board remains responsible, as a matter of
Irish law, for the proper management of the affairs of Prothena. Committees may meet and adjourn as they determine proper. A vote at any committee meeting will
be determined by a majority of votes of the members present.

The  Board  has  a  standing  audit  committee,  a  standing  compensation  committee  and  a  standing  nominating  and  corporate  governance  committee,  with

each committee comprised solely of independent directors, as prescribed

11

by  the  Nasdaq  listing  standards  and  SEC  rules  and  regulations.  We  have  adopted  corporate  governance  guidelines,  as  well  as  a  code  of  conduct  and  other
compliance policies.

The Companies Act provides for a minimum of two directors. Our Constitution provides that the Board may determine the size of the Board from time to

time.

Our Constitution provides that at least one-third of the directors serving on the Board shall come up for re-election at a given annual general meeting, and
that directors must come up for re-election at the third annual general meeting subsequent to their appointment or reappointment to the Board. Except as otherwise
provided  by  law,  vacancies  on  the  Board  may  be  filled  only  by  ordinary  resolution  or  the  affirmative  vote  of  a  majority  of  the  remaining  directors.  A  director
elected by the Board to fill a vacancy shall serve until the subsequent annual general meeting. At each annual general meeting of shareholders, the successors to
directors  whose terms  will  then  expire  will be elected  to serve  from  the time  of election  and qualification  until  the third  subsequent  annual  general  meeting  of
shareholders.

Under the Companies Act and notwithstanding anything contained in our Constitution or in any agreement between us and a director, the shareholders
may, by an ordinary resolution, remove a director from office before the expiration of his or her term at a meeting held on no less than 28 days’ notice and at which
the director is entitled to be heard. The power of removal is without prejudice to any claim for damages for breach of contract (e.g., employment contract) that the
director may have against us in respect of his removal.

Our Constitution provides that the Board may fill any vacancy occurring on the Board. If the Board fills a vacancy, the director’s term expires at the next
annual general meeting. A vacancy on the Board created by the removal of a director may be filled by the shareholders at the meeting at which such director is
removed and, in the absence of such election or appointment, the remaining directors may fill the vacancy.

Legal Name; Formation; Fiscal Year; Registered Office

Prothena  Corporation  plc  was  formed  under  the  laws  of  Ireland  on  September  26,  2012  as  a  private  limited  company,  under  the  name  “Neotope
Corporation  Limited”  (registration  number  518146),  and  reregistered  as  a  public  limited  company  and  changed  its  name  to  “Neotope  Corporation  plc”  on
October 25, 2012. On November 1, 2012, our shareholders resolved, by way of special resolution, to change the name of the company to “Prothena Corporation
plc,” and this was approved by the Irish Registrar of Companies on November 7, 2012. Our fiscal year ends on December 31 and our registered address is 77 Sir
John Rogerson’s Quay, Block C, Grand Canal Docklands, Dublin 2, D02 T804, Ireland.

Duration; Dissolution; Rights upon Liquidation

Our duration is unlimited. We may be dissolved and wound up at any time by way of a shareholders’ voluntary winding up or a creditors’ winding up. In
the  case  of  a  shareholders’  voluntary  winding  up,  a  special  resolution  of  shareholders  is  required.  We  may  also  be  dissolved  by  way  of  court  order  on  the
application of a creditor, or by the Companies Registration Office as an enforcement measure where we have failed to file certain returns.

If our Constitution contains no specific provisions in respect of a dissolution or winding up, then, subject to the priorities of any creditors, the assets will
be  distributed  to  our  shareholders  in  proportion  to  the  paid-up  nominal  value  of  the  shares  held.  Our  Constitution  provides  that  our  ordinary  shareholders  are
entitled to participate pro rata in a winding up.

Uncertificated Shares

Holders of our ordinary shares that hold their ordinary shares electronically have the right to require us to issue certificates for their shares.

12

Stock Exchange Listing

Our ordinary shares are listed on the Nasdaq Global Select Market under the symbol “PRTA.”

No Sinking Fund

Our ordinary shares have no sinking fund provisions.

Transfer and Registration of Shares

The transfer agent for our ordinary shares is Computershare Trust Company, N.A. Its address is 250 Royall Street, Canton, MA 02021. An Irish based
affiliate of the transfer agent, Computershare Investor Services (Ireland) Limited, maintains our share register, registration in which is determinative of ownership
of our ordinary shares. This affiliate provides an inspection facility in Ireland for inspection and copying of our register in accordance with the Companies Act. A
shareholder who holds shares beneficially is not the holder of record of such shares. Instead, the depository (for example, Cede & Co. as nominee for DTC) or
other nominee is the holder of record of those shares. Accordingly, a transfer of shares from a person who holds such shares beneficially to a person who also holds
such shares beneficially through a depository or other nominee will not be registered in our official share register, as the depository or other nominee will remain
the record holder of any such shares.

A written instrument of transfer is required under Irish law in order to register on our official share register any transfer of shares (i) from a person who
holds such shares directly to any other person, (ii) from a person who holds such shares beneficially to a person who holds such shares directly, or (iii) from a
person who holds such shares beneficially to another person who holds such shares beneficially where the transfer involves a change in the depository or other
nominee that is the record owner of the transferred shares. An instrument of transfer is also required for a shareholder who directly holds shares to transfer those
shares into his or her own broker account (or vice versa). Such instruments of transfer may give rise to Irish stamp duty, which must be paid prior to registration of
the transfer on our official Irish share register. However, a shareholder who directly holds shares may transfer those shares into his or her own broker account (or
vice versa) without giving rise to Irish stamp duty provided there is no change in the ultimate beneficial ownership of the shares as a result of the transfer and the
transfer is not made in contemplation of a sale of the shares.

Any transfer of our ordinary shares that is subject to Irish stamp duty will not be registered in the name of the buyer unless an instrument of transfer is
duly stamped and provided to the transfer agent. We, in our absolute discretion and insofar as the Companies Act or any other applicable law permit, may provide
that one of our subsidiaries will, pay Irish stamp duty arising on a transfer of our ordinary shares on behalf of the transferee of such ordinary shares. If stamp duty
resulting  from the transfer  of our ordinary  shares which would otherwise be payable by the transferee  is paid by us or any of our subsidiaries  on behalf of the
transferee, then in those circumstances,  we will, on our behalf or on behalf of our subsidiary (as the case may be), be entitled to (i) seek reimbursement of the
stamp  duty  from  the  transferee,  (ii)  set-off  the  stamp  duty  against  any  dividends  payable  to  the  transferee  of  those  ordinary  shares  and  (iii)  claim  a  first  and
permanent lien on our ordinary shares on which stamp duty has been paid by us or our subsidiary for the amount of stamp duty paid. Our lien shall extend to all
dividends paid on those ordinary shares. Parties to a share transfer may assume that any stamp duty arising in respect of a transaction in our ordinary shares has
been paid unless one or both of such parties is otherwise notified by us or the transfer agent.

Our Constitution delegates to any director, the secretary or any of our assistant secretaries duly appointed (or such other person as may be appointed by

the secretary for this purpose) the authority, on our behalf, to execute an instrument of transfer on behalf of a transferring party.

The directors may suspend registration of transfers from time to time, not exceeding 30 days in aggregate each year.

13

EXHIBIT 10.17

FIRST AMENDMENT TO THE
PROTHENA CORPORATION PLC
2020 EMPLOYMENT INDUCEMENT INCENTIVE PLAN

This First Amendment (this “First Amendment”) to the Prothena Corporation  plc 2020 Employment Inducement Incentive
Plan  (“2020  EIIP”),  was  made  and  adopted  by  the  Board  of  Directors  (“Board”)  of  Prothena  Corporation  plc,  a  public  limited
company organized under the laws of Ireland (the “Company”), on April 1, 2020 (the “Amendment Date”).

WHEREAS, the Company maintains the 2020 EIIP; and

RECITALS

WHEREAS, the Board believes it is in the best interests of the Company and its shareholders  to amend the 2020 EIIP to

increase the number of ordinary shares authorized for issuance under the 2020 EIIP.

NOW,  THEREFORE,  BE  IT  RESOLVED,  that  the  2020  EIIP  is  hereby  amended  as  follows,  effective  as  of  the

Amendment Date:

Section 2.28 of the 2020 EIIP is hereby amended and restated in its entirety as follows:
“2.28 “Overall Share Limit” means 360,000 Shares.”

AMENDMENT

This First Amendment shall be and hereby is incorporated into and forms a part of the 2020 EIIP, and except as expressly
provided herein, all terms and conditions of the 2020 EIIP shall remain in full force and effect.

1.

2.

1

SECOND AMENDMENT TO THE
PROTHENA CORPORATION PLC
2020 EMPLOYMENT INDUCEMENT INCENTIVE PLAN

This  Second  Amendment  (this  “Second  Amendment”)  to  the  Prothena  Corporation  plc  2020  Employment  Inducement
Incentive  Plan  (“2020  EIIP”),  was  made  and  adopted  by  the  Board  of  Directors  (“Board”)  of  Prothena  Corporation  plc,  a  public
limited company organized under the laws of Ireland (the “Company”), on July 15, 2020 (the “Amendment Date”).

WHEREAS, the Company maintains the 2020 EIIP; and

RECITALS

WHEREAS, the Board believes it is in the best interests of the Company and its shareholders  to amend the 2020 EIIP to

increase the number of ordinary shares authorized for issuance under the 2020 EIIP.

NOW,  THEREFORE,  BE  IT  RESOLVED,  that  the  2020  EIIP  is  hereby  amended  as  follows,  effective  as  of  the

Amendment Date:

1.

Section 2.28 of the 2020 EIIP is hereby amended and restated in its entirety as follows:

“2.28 “Overall Share Limit” means 420,000 Shares.”

AMENDMENT

2.

This Second Amendment shall be and hereby is incorporated into and forms a part of the 2020 EIIP, and except as expressly
provided herein, all terms and conditions of the 2020 EIIP shall remain in full force and effect.

2

THIRD AMENDMENT TO THE
PROTHENA CORPORATION PLC
2020 EMPLOYMENT INDUCEMENT INCENTIVE PLAN

This Third Amendment (this “Third Amendment”) to the Prothena Corporation plc 2020 Employment Inducement Incentive
Plan  (“2020  EIIP”),  was  made  and  adopted  by  the  Board  of  Directors  (“Board”)  of  Prothena  Corporation  plc,  a  public  limited
company organized under the laws of Ireland (the “Company”), on September 1, 2020 (the “Amendment Date”).

WHEREAS, the Company maintains the 2020 EIIP; and

RECITALS

WHEREAS, the Board believes it is in the best interests of the Company and its shareholders  to amend the 2020 EIIP to

increase the number of ordinary shares authorized for issuance under the 2020 EIIP.

NOW,  THEREFORE,  BE  IT  RESOLVED,  that  the  2020  EIIP  is  hereby  amended  as  follows,  effective  as  of  the

Amendment Date:

Section 2.28 of the 2020 EIIP is hereby amended and restated in its entirety as follows:
“2.28 “Overall Share Limit” means 480,000 Shares.”

AMENDMENT

This Third Amendment shall be and hereby is incorporated into and forms a part of the 2020 EIIP, and except as expressly
provided herein, all terms and conditions of the 2020 EIIP shall remain in full force and effect.

1.

2.

3

FOURTH AMENDMENT TO THE
PROTHENA CORPORATION PLC
2020 EMPLOYMENT INDUCEMENT INCENTIVE PLAN

This  Fourth  Amendment  (this  “Fourth  Amendment”)  to  the  Prothena  Corporation  plc  2020  Employment  Inducement
Incentive  Plan  (“2020  EIIP”),  was  made  and  adopted  by  the  Board  of  Directors  (“Board”)  of  Prothena  Corporation  plc,  a  public
limited company organized under the laws of Ireland (the “Company”), on October 1, 2020 (the “Amendment Date”).

WHEREAS, the Company maintains the 2020 EIIP; and

RECITALS

WHEREAS, the Board believes it is in the best interests of the Company and its shareholders  to amend the 2020 EIIP to

increase the number of ordinary shares authorized for issuance under the 2020 EIIP.

NOW,  THEREFORE,  BE  IT  RESOLVED,  that  the  2020  EIIP  is  hereby  amended  as  follows,  effective  as  of  the

Amendment Date:

Section 2.28 of the 2020 EIIP is hereby amended and restated in its entirety as follows:
“2.28 “Overall Share Limit” means 530,000 Shares.”

AMENDMENT

This Fourth Amendment shall be and hereby is incorporated into and forms a part of the 2020 EIIP, and except as expressly
provided herein, all terms and conditions of the 2020 EIIP shall remain in full force and effect.

1.

2.

4

FIFTH AMENDMENT TO THE
PROTHENA CORPORATION PLC
2020 EMPLOYMENT INDUCEMENT INCENTIVE PLAN

This Fifth Amendment (this “Fifth Amendment”) to the Prothena Corporation plc 2020 Employment Inducement Incentive
Plan  (“2020  EIIP”),  was  made  and  adopted  by  the  Board  of  Directors  (“Board”)  of  Prothena  Corporation  plc,  a  public  limited
company organized under the laws of Ireland (the “Company”), on November 2, 2020 (the “Amendment Date”).

WHEREAS, the Company maintains the 2020 EIIP; and

RECITALS

WHEREAS, the Board believes it is in the best interests of the Company and its shareholders  to amend the 2020 EIIP to

increase the number of ordinary shares authorized for issuance under the 2020 EIIP.

NOW,  THEREFORE,  BE  IT  RESOLVED,  that  the  2020  EIIP  is  hereby  amended  as  follows,  effective  as  of  the

Amendment Date:

Section 2.28 of the 2020 EIIP is hereby amended and restated in its entirety as follows:
“2.28 “Overall Share Limit” means 620,000 Shares.”

AMENDMENT

This Fifth Amendment shall be and hereby is incorporated into and forms a part of the 2020 EIIP, and except as expressly
provided herein, all terms and conditions of the 2020 EIIP shall remain in full force and effect.

1.

2.

5

SIXTH AMENDMENT TO THE
PROTHENA CORPORATION PLC
2020 EMPLOYMENT INDUCEMENT INCENTIVE PLAN

This Sixth Amendment (this “Sixth Amendment”) to the Prothena Corporation plc 2020 Employment Inducement Incentive
Plan  (“2020  EIIP”),  was  made  and  adopted  by  the  Board  of  Directors  (“Board”)  of  Prothena  Corporation  plc,  a  public  limited
company organized under the laws of Ireland (the “Company”), on December 1, 2020 (the “Amendment Date”).

WHEREAS, the Company maintains the 2020 EIIP; and

RECITALS

WHEREAS, the Board believes it is in the best interests of the Company and its shareholders  to amend the 2020 EIIP to

increase the number of ordinary shares authorized for issuance under the 2020 EIIP.

NOW,  THEREFORE,  BE  IT  RESOLVED,  that  the  2020  EIIP  is  hereby  amended  as  follows,  effective  as  of  the

Amendment Date:

1.

Section 2.28 of the 2020 EIIP is hereby amended and restated in its entirety as follows:

“2.28 “Overall Share Limit” means 710,000 Shares.”

AMENDMENT

2.

This Sixth Amendment shall be and hereby is incorporated into and forms a part of the 2020 EIIP, and except as expressly
provided herein, all terms and conditions of the 2020 EIIP shall remain in full force and effect.

6

EXHIBIT 10.35

CONSULTING AGREEMENT

This Consulting Agreement (this “Agreement”) is effective as of July 15, 2020 (the “Effective Date”) and is made by and between
Dennis  J.  Selkoe,  M.D.,  an  individual  (“Consultant”),  and  Prothena  Biosciences  Inc,  a  Delaware  corporation  with  offices  at  331
Oyster  Point  Boulevard,  South  San  Francisco,  CA  94080,  U.S.A.  (“Prothena”).  Consultant  and  Prothena  may  each  be  referred  to
individually herein as a “Party” and collectively as the “Parties”.

WHEREAS, Prothena is engaged in the business of researching and developing therapies for neurodegenerative diseases;

    WHEREAS, Consultant is an expert in neurodegenerative diseases; and

    WHEREAS, Prothena desires to engage Consultant to provide services to Prothena and Consultant desires to be so engaged.

NOW,  THEREFORE,  in  connection  therewith  and  for  good  and  valuable  consideration,  the  receipt  and  sufficiency  of

which are hereby acknowledged, Consultant and Prothena agree as follows:

1.

SCOPE OF SERVICES

1.1.

Services. Subject  to  the  terms  and  conditions  of  this  Agreement,  Consultant  shall  perform  services  to  Prothena  as
requested  in  connection  with  its  assessment  of  potential  business  development  opportunities  and  matters  related  to  partnered
collaboration programs (the “Services”).

1.2.

Performance. Consultant shall perform the Services (a) in a professional, diligent, workmanlike and timely manner,
that  meets  or  exceeds  the  standards  and  practices  that  are  generally  accepted  in  the  industry  and  exercised  by  others  performing
similar services, and (b) in strict compliance with all applicable laws, rules, regulations and guidelines, including but not limited to
the U.S. Federal Food, Drug and Cosmetic Act, the U.S. Federal Anti-Kickback Statute, the U.S. Foreign Corrupt Practices Act, and
the PhRMA Code on Interactions with Healthcare Professionals. None of the Services nor the Work Product (defined in Section 1.3
below) shall infringe, misappropriate or violate any proprietary rights of any third party.

1.3. Work  Product.  Consultant  shall  (a)  create  in  a  timely  and  accurate  manner,  and  (b)  maintain  during  the  Term
(defined in Section 7.1 below), written records of the results, data and other materials and deliverables generated or recorded in the
performance of the Services (the “Work Product”), which Work Product shall be owned by, and shall be Confidential Information
(defined below) of, Prothena. Promptly upon completion of the Services or termination of this Agreement, or upon earlier request by
Prothena, Consultant shall deliver the Work Product to Prothena.

1

1.4.

Independent  Contractor.  Consultant  is  an  independent  contractor  and  nothing  in  this  Agreement  or  the  Services
provided  hereunder  is  intended  to  reflect  or  create,  or  shall  be  construed  as  reflecting  or  creating,  the  relationship  of  partners,
principal and agent, or employer and employee. Neither Party shall have any express or implied authority to assume or create any
obligation on behalf of, or in the name of, the other Party to any contract or undertaking with any third party directly or indirectly as
a  result  of  this  Agreement.  Any  taxes,  insurance  or  benefits  imposed  on  Consultant  due  to  his  business  activities,  including  any
Services provided hereunder, shall be the sole responsibility of Consultant.

1.5.

Prothena Affiliates. Prothena  may  specify  that  the  Consultant’s  Services  will  be  for  the  benefit  of  an  Affiliate  of

Prothena. The term “Affiliate” means any entity that controls, is controlled by or is under common control with Prothena.

2

Compensation, Expenses and Invoicing

2.1. Compensation. Prothena shall pay Consultant at the rate of $500.00 for each hour of Services actually performed by
Consultant. For the avoidance of doubt, travel time, if any, required to perform the Services shall not be billable except to the extent
that Services are actually performed during such time.

2.2.

Travel and Other Expenses. Prothena shall reimburse Consultant for reasonable travel and other expenses actually

incurred by Consultant, without commission or mark-up, to the extent necessary to perform the Services.

2.3. Maximum  Amount  Payable. Notwithstanding  anything  to  the  contrary  herein,  the  maximum  aggregate  amount

payable to Consultant under this Agreement, including for reimbursement of expenses, shall not exceed $60,000.

2.4.

Invoicing. Consultant shall submit to Prothena a written invoice (“Invoice”) monthly for Services actually performed
and expenses actually incurred. Each such Invoice shall include (a) a description of the Services performed, by date, and the amount
of  time  spent  for  each  Service,  (b)  the  compensation  earned  by  Consultant  in  accordance  with  Section  2.1  above,  and  (c)  the
reimbursable  expenses  incurred  by  Consultant  in  accordance  with  Section  2.2  above.  Invoices  shall  be  sent  by  e-mail  to
Accounting@Prothena.com.  Prothena  shall  pay  to  Consultant  all  undisputed  amounts  due  no  later  than  thirty  (30)  days  from
Prothena’s  receipt  of  the  applicable  Invoice;  provided,  however,  that  Prothena  may  withhold  payment  pending  delivery  by
Consultant to Prothena of any Work Product.

3.

CONFIDENTIALITY

3.1.

Confidential Information. “Confidential Information” means any and all confidential, proprietary and/or trade secret
information  or  materials  that  are  directly  or  indirectly  disclosed  by  or  on  behalf  of  Prothena  or  its  Affiliates  to  Consultant  or  its
Affiliates in connection with this Agreement. Confidential Information includes, without limitation, trade secrets,

2

processes, formulae, data, know-how, improvements,  inventions, techniques, marketing plans, strategies, forecasts, employees and
customer and contact lists.

3.2.

Exceptions. Confidential  Information  shall  not  include  any  information  that  Consultant  can  demonstrate  by
competent  written  evidence  (a)  previously  was  in  his  possession,  as  shown  by  its  pre-existing  records,  without  violation  of  any
obligation of confidentiality, (b) has become publicly known through no wrongful act of or breach of this Agreement by Consultant,
(c) was received by Consultant without breach of this Agreement from a third party without restriction as to the use and disclosure of
the information, or (d) was independently developed by Consultant without use of the Confidential Information.

3.3.

Confidentiality. Consultant shall maintain in confidence and shall not disclose or use for any purpose other than as
expressly provided for in this Agreement any Confidential Information. Consultant may use and disclose Confidential Information
only  to  its  directors,  officers,  employees  and  permitted  subcontractors,  and  solely  to  the  extent  required  and  for  the  purpose  of
performing  the  Services.  Consultant  shall  not  use  the  Confidential  Information  for  any  purpose  or  in  any  manner  that  would
constitute a violation of any law, rule, regulation or guideline. Consultant shall ensure that any of its directors, officers, employees
and subcontractors receiving any Confidential Information as permitted under this Agreement shall be informed of the confidential
nature  of  such  Confidential  Information  and  shall  be  bound  by  confidentiality  obligations  at  least  as  strict  as  the  confidentiality
obligations  in  this  Agreement  to  protect  the  confidentiality  of  such  Confidential  Information.  Any  failure  by  any  such  directors,
officers, employee or subcontractors of Consultant to meet the foregoing obligations shall be deemed to be a breach by Consultant.

3.4.

Authorized  Disclosures. If  Consultant  is  required  by  a  valid  order  of  a  court  or  other  governmental  body  or
otherwise required by the law to disclose Confidential Information, it shall give Prothena timely written notice of such a requirement
before doing so and shall cooperate with Prothena to seek a protective order, confidential treatment or other appropriate protections
of such Confidential Information.

3.5.

Notice. Consultant will promptly report to Prothena any actual or suspected breach of the terms of this Section 3, and

will take all reasonable further steps requested by Prothena to prevent, control or remedy any such breach.

3.6.

Return  of  Confidential  Information. Upon  request  of  Prothena  or  the  termination  of  this  Agreement,  Consultant
shall (a) return to Prothena all tangible forms of the Confidential Information and (b) destroy all electronic forms of the Confidential
Information,  including  all  notes,  reports  or  other  documents  prepared  by  Consultant  that  contain  any  Confidential  Information  in
Consultant’s  possession,  custody  or  control,  within  thirty  (30)  days  of  such  request  or  termination;  provided,  however,  that
Consultant may retain a single copy of the Confidential Information in a secure format for the sole purpose of determining the scope
of Consultant’s obligations under this Agreement.

3

3.7.

Survival. The  confidentiality  and  non-use  obligations  set  forth  in  this  Section  3  shall  survive  termination  of  this

Agreement and continue for a period of seven (7) years following the date of such termination of this Agreement.

3.8.

Injunctive Relief and Irreparable Harm. Consultant agrees that its breach of any of the obligations of this Section
3  may  cause  Prothena  irreparable  damage  for  which  recovery  of  money  damages  may  be  inadequate.  Prothena  will,  therefore,  be
entitled  to  seek  timely  injunctive  relief  without  the  necessity  of  proving  money  damages,  in  addition  to  any  and  all  remedies
available at law or equity.

3.9.

Defend Trade Secrets Act Notice of Immunity Rights. Consultant acknowledges that the Company has provided
Consultant with the following notice of immunity rights in compliance with the requirements of the Defend Trade Secrets Act: (a)
Consultant will not be held criminally or civilly liable under any Federal or State trade secret law for the disclosure of Confidential
Information  that is made in confidence to a Federal, State or local government official or to an attorney solely for the purpose of
reporting or investigating a suspected violation of law; (b) Consultant will not be held criminally or civilly liable under any Federal
or  State  trade  secret  law  for  the  disclosure  of  Confidential  Information  that  is  made  in  a  complaint  or  other  document  filed  in  a
lawsuit or other proceeding, if such filing is made under seal; and (c) if Consultant files a lawsuit for retaliation by the Company for
reporting a suspected violation of law, Consultant may disclose the Confidential Information to its attorney and use the Confidential
Information in the court proceeding, if Consultant files any document containing the Confidential Information under seal, and does
not disclose the Confidential Information, except pursuant to court order.

4.

IntelLectual Property

4.1.

Intellectual  Property.  “Intellectual  Property”  means  any  and  all  ideas,  concepts,  discoveries,  inventions,
developments,  formulae,  processes,  know-how,  trade  secrets,  techniques,  materials,  methodologies,  modifications,  inventions,
innovations, improvements, processes, writings, documentation, electronic code, data and rights (whether or not protectable under
state,  federal  or  other  jurisdictions’  patent,  trademark,  copyright  or  similar  laws)  or  the  like,  whether  or  not  written  or  otherwise
fixed in any form or medium, regardless of the media on which contained and whether or not patentable or copyrightable, and all
intellectual property rights therein.

4.2.

Project IP. Prothena shall solely and exclusively own all right, title and interest in and to the Work Product and all
Intellectual Property arising during the course of performance of the Services, whether made solely by either Party or jointly by the
Parties (collectively, the “Project IP”). Consultant hereby assigns to Prothena, its successors or assigns, as the case may be, all rights,
titles  and  interest  in  the  Project  IP.  Consultant  shall  promptly  notify  Prothena  in  writing  of  any  inventions  within  the  Project  IP
conceived of, or reduced to practice, by Consultant, together with a reasonable description of any such invention.

4

4.3.

Assistance. Consultant  agrees  to  execute  such  documents  and  take  such  action  as  Prothena  may  request  to
memorialize, secure and perfect Prothena’s interest in the Project IP. If Prothena is unable for any reason, after reasonable effort, to
secure  Consultant’s  signature  on  any  document  needed  in  connection  with  the  actions  specified  above,  Consultant  hereby
irrevocably designates and appoints Prothena as Consultant’s duly authorized officers and agents as Consultant’s agent and attorney-
in-fact,  which  appointment  is  coupled  with  an  interest,  to  act  for  and  on  Consultant’s  behalf  to  execute,  verify  and  file  any  such
documents and to do all other lawfully permitted acts to further the purposes of the preceding paragraph with the same legal force
and effect as if executed by Consultant.

4.4.

No Other Rights. Delivery of any Intellectual Property or Confidential Information of Prothena to Consultant shall
not be deemed to grant to Consultant any right or licenses under such Confidential Information or under any Intellectual Property of
Prothena, including without limitation the Work Product or any Project IP, except as expressly set forth in this Agreement.

5.

Representations and Warranties

5.1.

By Each Party. Each Party represents and warrants to the other Party that (a) it has the full power and authority to

enter into this Agreement, (b) this Agreement has been duly authorized, and (c) this Agreement is binding upon it.

5.2.

By Consultant. Consultant represents and warrants that (a) entering into this Agreement and performing the Services
and  obligations  contemplated  under  this  Agreement  would  not  violate  any  law,  rule,  regulation  or  judicial  order  applicable  to
Consultant, and would not violate or constitute a default under any agreement to which Consultant is a party, and (b) Consultant is
not (i) under investigation by the U.S. Food and Drug Administration or any other governmental agency or authority that could result
in any debarment, sanction or exclusion action (a “Debarment”), (ii) subject to a Debarment, or (iii) currently excluded or otherwise
ineligible  from  participating  in  any  governmental  health  care  program.  In  the  event  that  Consultant  becomes  the  subject  of  an
investigation that could result in a Debarment or becomes subject to a Debarment, Consultant shall immediately notify Prothena in
writing.  Upon  the  receipt  of  such  notice  by  Prothena,  or  if  Prothena  otherwise  becomes  aware  of  such  Debarment  or  threatened
Debarment, Prothena shall have the right to terminate this Agreement immediately.

6.

INDEMNIFICATION

6.1.

By  Consultant. Consultant  shall  indemnify  and  hold  Prothena  and  its  Affiliates,  and  their  respective  directors,
officers, employees and agents (each a “Prothena Indemnitee”), harmless from and against any and all liabilities, losses, damages or
expenses  of  any  kind,  including  costs  and  reasonable  attorneys’  fees  (collectively,  “Losses”)  arising  out  of  or  resulting  from  any
third party suit, proceeding, action, claim or demand (collectively, “Claims”) to the extent resulting from (a) any grossly negligent or
willful act or omission by Consultant; or (b) any breach of this Agreement by Consultant. Notwithstanding the foregoing, Consultant
shall

5

not  be  obligated  to  indemnify  any  Prothena  Indemnitee  to  the  extent  that  the  applicable  Claim  is  subject  to  Prothena’s
indemnification obligations under Section 6.2 below.

6.2.

By  Prothena.  Prothena  shall  indemnify  and  hold  Consultant  harmless  from  any  and  all  Losses  arising  out  of  or
resulting from Claims to the extent resulting from (a) any grossly negligent or willful acts or omissions by Prothena or any of its
directors, officers, employees or agents, or (b) any breach of this Agreement by Prothena. Notwithstanding the foregoing, Prothena
shall  not  be  obligated  to  indemnify  Consultant  to  the  extent  that  the  applicable  Claim  is  subject  to  Consultant’s  indemnification
obligations under Section 6.1 above.

6

7.

TERM AND TERMINATION

7.1.

Term. The term of this Agreement (the “Term”) shall commence as of the Effective Date and shall terminate on the

date that is one (1) year after the Effective Date, unless terminated earlier pursuant to Section 7.2 below.

7.2.

Termination. Either Party may terminate this Agreement by providing at least ten (10) business days prior written

notice to the other Party.

7.3.

Effect of Termination. Upon any termination of this Agreement:

(a)

(b)

(c)

(d)

Work Product.

Consultant shall immediately cease all Services;

Prothena shall pay to Consultant all amounts due for Services performed under this Agreement;

Consultant shall return or destroy, at Prothena’s election, Prothena’s Confidential Information; and

Consultant  shall  promptly  deliver  to  Prothena  the  Work  Product,  or  at  Prothena’s  instruction,  destroy  the

7.4    Survival. Sections 1.3, 3, 4, 6, 7.3 and 8 shall survive any termination of this Agreement.

8.

Miscellaneous

8.1.

Entire Agreement; Amendments. This Agreement contains the entire understanding of the Parties with respect to
the subject matter herein and supersedes all previous agreements (oral and written), negotiations and discussions. The Parties may
modify or amend the provisions hereof only in a writing duly executed by authorized representatives of the Parties.

8.2.

Remedies. If  (a)  Consultant’s  Services  fail  to  meet  standards  set  forth  in  this  Agreement,  (b)  Consultant  fails  to
provide appropriate and timely Services, or (c) Consultant commits any other material error in performance of the Services, Prothena
shall  in  its  sole  discretion  have  the  right,  in  addition  to  any  other  remedy  it  may  have  at  law  or  equity,  to  (i)  require  that  the
applicable Services be remedied or re-performed without charge to Prothena, or (ii) set off the costs of the loss, damage or defect
against monies owed to Consultant and/or require Consultant to provide a refund of all amounts paid for such Services.

8.3.

Notices. All legal notices from one Party to the other will be in writing and will be given by addressing the same to
the applicable address set forth below, or at such other address as either may specify in writing to the other. Notices shall be sent by
overnight courier, certified mail with return receipt requested, or by other means of delivery requiring an

7

acknowledged receipt. For purposes of clarity, notice may be provided via electronic mail with read receipt requested. All notices
shall be effective upon receipt.

To Prothena:         Prothena Biosciences Inc
            331 Oyster Point Boulevard
            South San Francisco, CA 94080, U.S.A.
            Attention: Chief Legal Officer and Secretary

michael.malecek@prothena.com

To Consultant:        Dennis J. Selkoe, M.D.

                 166 Moss Hill road
                 Boston, MA 02130
                 dselkoe@partners.org

8.4.

Assignment.  This  Agreement  and  the  Services  contemplated  hereunder  are  personal  to  Consultant  and  Consultant
shall not assign, transfer or subcontract any of Consultant’s obligations under this Agreement without the prior written consent of
Prothena. Any attempted assignment, transfer or subcontracting in violation hereof shall be null and void. The Company may freely
assign this Agreement, and Consultant expressly agrees that any intellectual property rights licensed to the Company are transferable
to the Company’s assignee without Consultant’s consent.

8.5. Waiver. No waiver by either Party of any obligation under this Agreement, or non-performance thereof, of the other

Party shall constitute a waiver of any other obligation or non-performance of such other Party.

8.6.

Severability. If any provision of this Agreement is declared void or unenforceable, such provision shall be deemed
modified to the extent necessary to allow enforcement, and all other portions of this Agreement shall remain in full force and effect.

8.7. Governing Law. This  Agreement  shall  be  governed  by  and  construed  in  accordance  with  the  laws  of  the  State  of

California, without giving effect to any conflicts of laws principles thereof.

8.8.

Arbitration. To  ensure  rapid  and  economical  resolution  of  any  disputes  unrelated  to  patent  rights  regarding  this
Agreement, in the event any dispute is not resolved by action taken under Section 8.2 above, the Parties hereby agree that any and all
claims,  disputes  or  controversies  of  any  nature  whatsoever  arising  out  of,  or  relating  to,  this  Agreement,  or  its  interpretation,
enforcement, breach, performance or execution, or services thereunder, shall be resolved, to the fullest extent permitted by law, by
final,  binding  and  confidential  arbitration  in  San  Francisco,  CA  under  the  then  applicable  American  Arbitration  Association
arbitration  rules.  The  Parties  each  acknowledge  that  by agreeing  to this  arbitration  procedure,  they  waive  the right  to resolve  any
such dispute, claim or demand through a trial by jury or judge or by administrative proceeding. The Parties will share the costs of
arbitration equally. Both Parties will be responsible for their own attorney’s fees, and the arbitrator may not award attorney’s fees
unless

8

a  statute  or  contract  at  issue  specifically  authorizes  such  an  award.  Nothing  in  this  Agreement  is  intended  to  prevent  either  Party
from  obtaining  injunctive  relief  in  court  to  prevent  irreparable  harm  pending  the  conclusion  of  any  arbitration.  With  respect  to
injunctive relief, the Parties agree to personal jurisdiction and venue in the state or federal courts of San Francisco, California. With
respect to any dispute relating to patent rights, including without limitation the validity, enforceability or scope of any patent, the
laws of the applicable country of the patent shall govern and the courts of such applicable country shall have jurisdiction with regard
to any patent dispute.

8.9.

Execution. This Agreement may be executed in one or more counterparts, each of which shall be deemed an original
but  all  of  which  together  shall  constitute  one  and  the  same  document.  This  Agreement  may  be  executed  electronically  (including
PDF). The Parties agree that electronic copies of signatures have the same effect as original signatures.

(Signature Page Follows)

9

IN WITNESS WHEREOF, this Agreement has been executed by the Parties hereto effective as of the Effective Date.

PROTHENA BIOSCIENCES INC            DENNIS J. SELKOE, M.D.

By: /s/ Gene G. Kinney        /s/ Dennis J. Selkoe
Name: Gene G. Kinney, Ph.D.        Date: July 15, 2020
Title: President and Chief Executive Officer    
Date: July 15, 2020        

[Signature Page to Consulting Agreement]

List of Subsidiaries

Exhibit 21.1

Subsidiary Name

   Jurisdiction of Incorporation or Organization

Prothena Biosciences Limited
Prothena Biosciences Inc
Prothena Finance Inc
Neotope Neuroscience Limited
Othair Prothena Limited

Ireland
Delaware
Delaware
Ireland
Ireland

 
  
  
Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

The Board of Directors
Prothena Corporation plc:

We  consent  to  the  incorporation  by  reference  in  the  registration  statements  (Nos.  333-244366,  333-226724,  333-218184,  333-211653,  333-196572  and  333-
187726)  on  Form  S-8  and  the  registration  statements  (Nos.  333-231675,  333-223207,  333-203258,  333-197006,  333-196965  and  333-193416)  on  Form  S-3  of
Prothena Corporation plc of our reports dated February 26, 2021, with respect to the consolidated balance sheets of Prothena Corporation plc as of December 31,
2020  and  2019,  the  related  consolidated  statements  of  operations,  shareholders’  equity,  and  cash  flows  for  each  of  the  years  in  the  three-year  period  ended
December 31, 2020, and the related notes, which report appears in the December 31, 2020 annual report on Form 10‑K of Prothena Corporation plc.

Our report refers to a change in the Company’s method of accounting for leases as of January 1, 2019 due to the adoption of the Financial Accounting Standards
Board’s Accounting Standards Codification (ASC) Topic 842, Leases.

San Francisco, California
February 26, 2021

/s/ KPMG LLP

CERTIFICATION OF CHIEF EXECUTIVE OFFICER
PURSUANT TO RULE 13a-14(a)/15d-14(a), AS ADOPTED PURSUANT TO SECTION 302 OF
THE SARBANES-OXLEY ACT OF 2002

Exhibit 31.1

I, Gene G. Kinney, certify that:

1.

I have reviewed this Annual Report on Form 10-K of Prothena Corporation plc;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements

made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial

condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange
Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant
and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure
that  material  information  relating  to  the  registrant,  including  its  consolidated  subsidiaries,  is  made  known  to  us  by  others  within  those  entities,
particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to
provide  reasonable  assurance  regarding  the  reliability  of  financial  reporting  and  the  preparation  of  financial  statements  for  external  purposes  in
accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of

the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal
quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the
registrant’s internal control over financial reporting; and

5. The  registrant’s  other  certifying  officer(s)  and  I  have  disclosed,  based  on  our  most  recent  evaluation  of  internal  control  over  financial  reporting,  to  the

registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

(a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to

adversely affect the registrant’s ability to record, process, summarize and report financial information; and

(b) Any  fraud,  whether  or  not  material,  that  involves  management  or  other  employees  who  have  a  significant  role  in  the  registrant’s  internal  control  over

financial reporting.

Date:

February 26, 2021

/s/ Gene G. Kinney
Gene G. Kinney
President and Chief Executive Officer
(Principal Executive Officer)

CERTIFICATION OF CHIEF FINANCIAL OFFICER
PURSUANT TO RULE 13a-14(a)/15d-14(a), AS ADOPTED PURSUANT TO SECTION 302 OF
THE SARBANES-OXLEY ACT OF 2002

Exhibit 31.2

I, Tran B. Nguyen, certify that:

1.

I have reviewed this Annual Report on Form 10-K of Prothena Corporation plc;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements

made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial

condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange
Act Rules 13a-15(e) and 15d-15(e)) and internal control over financial reporting (as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant
and have:

(a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure
that  material  information  relating  to  the  registrant,  including  its  consolidated  subsidiaries,  is  made  known  to  us  by  others  within  those  entities,
particularly during the period in which this report is being prepared;

(b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to
provide  reasonable  assurance  regarding  the  reliability  of  financial  reporting  and  the  preparation  of  financial  statements  for  external  purposes  in
accordance with generally accepted accounting principles;

(c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of

the disclosure controls and procedures, as of the end of the period covered by this report based on such evaluation; and

(d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal
quarter (the registrant’s fourth fiscal quarter in the case of an annual report) that has materially affected, or is reasonably likely to materially affect, the
registrant’s internal control over financial reporting; and

5. The  registrant’s  other  certifying  officer(s)  and  I  have  disclosed,  based  on  our  most  recent  evaluation  of  internal  control  over  financial  reporting,  to  the

registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

(a)

 All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to
adversely affect the registrant’s ability to record, process, summarize and report financial information; and

(b)  Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over

financial reporting.

Date: February 26, 2021

/s/ Tran B. Nguyen
Tran B. Nguyen
Chief Financial Officer
(Principal Financial Officer)

CERTIFICATION OF PRINCIPAL EXECUTIVE OFFICER
AND PRINCIPAL FINANCIAL OFFICER
PURSUANT TO 18 U.S.C. SECTION 1350,
AS ADOPTED PURSUANT TO SECTION 906
OF THE SARBANES-OXLEY ACT OF 2002

Exhibit 32.1

Pursuant to the requirement set forth in Rule 13a-14(b) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and Section 1350 of Chapter 63
of Title 18 of the United States Code (18 U.S.C. §1350), Gene G. Kinney, President and Chief Executive Officer of Prothena Corporation plc (the “Company”) and
Tran B. Nguyen, Chief Financial Officer of the Company, each hereby certify that, to the best of his knowledge:

1. The  Company’s  Annual  Report  on  Form  10-K  for  the  fiscal  year  ended  December  31,  2020,  to  which  this  Certification  is  attached  as  Exhibit  32.1  (the

“Report”) fully complies with the requirements of Section 13(a) or Section 15(d) of the Exchange Act; and

2. The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date:

February 26, 2021

/s/ Gene G. Kinney
Gene G. Kinney
President and Chief Executive Officer
(Principal Executive Officer)

/s/ Tran B. Nguyen
Tran B. Nguyen
Chief Financial Officer
(Principal Financial Officer)

    A signed original of this written statement required by Rule 13a-14(b) of the Securities Exchange Act of 1934 and 18 U.S.C. Section 1350 has been provided to
the Company and will be retained by the Company and furnished to the Securities and Exchange Commission or its staff upon request.

    This certification accompanies the Form 10-K to which it relates, is not deemed filed with the Securities and Exchange Commission and is not to be
incorporated by reference into any filing of the Company under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended
(whether made before or after the date of the Form 10-K), irrespective of any general incorporation language contained in such filing.