SecProbe.io

April 3, 2019
Tran Nguyen
Chief Operating Officer and Financial Officer
Prothena Corporation plc
Adelphi Plaza
Upper George's Street
Dún Laoghaire
Co. Dublin, A96 T927, Ireland
Re:Prothena Corp plc
Form 10-K for the Fiscal Year Ended December 31, 2017
Filed February 26, 2018
Form 10-Q for the Quarterly Period Ended September 30, 2018
Filed November 6, 2018
File No. 001-35676
Dear Mr. Nguyen:
            We have reviewed your January 22, 2019 response as supplemented by your February 28,
2019 response to our comment letter and have the following comments.  In our comments, we
may ask you to provide us with information so we may better understand your disclosure.
            Please respond to the comments within ten business days by providing the requested
information or advise us as soon as possible when you will respond.  If you do not believe our
comments apply to your facts and circumstances, please tell us why in your response.
            After reviewing your response to the comments, we may have additional
comments.  Unless we note otherwise, our references to prior comments are to comments in
our December 19, 2018 letter.
Form 10-Q for the Quarterly Period Ended September 30, 2018
Item 1. Financial Statements (unaudited)
Notes to the Condensed Consolidated Financial Statements
8. Significant Agreements
Celgene Collaboration Agreement, page 18
1. Please propose revised disclosure that:
•articulates consistently when Celgene would have “decision making authority over

 FirstName LastNameTran Nguyen
 Comapany NameProthena Corporation plc
 April 3, 2019 Page 2
 FirstName LastNameTran Nguyen
Prothena Corporation plc
April 3, 2019
Page 2
development activities and all regulatory, manufacturing and commercialization
activities in the U.S.” We note that the first paragraph of the Overview section
indicates this occurs upon Celgene’s exercise of the option to acquire U.S. Rights
whereas the first paragraph of the Celgene U.S. and Global Rights and Licenses
section indicates this occurs “following Phase 1.”
•clarifies whether the exclusive license to develop and commercialize that Celgene will
receive upon exercise of its options for U.S. Rights and Global Rights includes the
right to manufacture.
•quantifies the regulatory and commercial milestones per program the Company is
eligible to receive after Celgene’s exercise of U.S. Rights.
2.Please analyze for us whether your contract with Celgene includes one or more implied
promises by Prothena to perform research and development services prior to the filing of
an IND. We make this request because your response appears to be limited to whether an
explicit promise exists, nonetheless promises may be implied by an entity’s customary
business practices, published policies or specific statements (ASC 606-10-25-16); implied
promises need not be enforceable at law (ASC No. 2014-09 BC87); and the illustrative
statements below appear to imply such a promise.
•“And that's essentially the way we kind of move that into the R&D. So again to
reiterate, we're responsible for research and development through Phase I. So to be
clear, that includes CMC, that includes regulatory, basically every other function in
there.” – March 20, 2018 Prothena Corporation PLC Neuroscience R&D
Collaboration Investor Call
•“Prothena will lead and have final decision-making authority over all programs
through Phase I, unless Celgene elects otherwise at its expense.” - March 20, 2018
Prothena Corporation PLC Neuroscience R&D Collaboration Investor Call
•“And as you may recall, Prothena is responsible for the execution of these programs
through the preclinical and early clinical stages, dependent upon various clinical
option exercise [indiscernible] by Celgene.” –Q4 2018 Earnings Transcript
•"… this collaboration provides Prothena the opportunity to work with a premier
scientific partner and the resources and flexibility to advance these programs while
continuing to expand our proprietary discovery activities …." March 20, 2018 Press
Release.
•“For Prothena, it offers the opportunity to work with a premier scientific partner with
complementary biological expertise and also provides the resources and flexibility to
advance in parallel both the programs within the scope of this collaboration as well as
our proprietary discovery activities…” March 20, 2018 Press Release.
•“…from the Prothena side, this provides an opportunity to accelerate and expand our
discovery activities and to do it with expertise and input that we may not otherwise
have access to. And so from our perspective, being able to work with a scientific team
is actually quite attractive. And obviously from a resource perspective, we do think
that this not only advantages the collaboration but advantages our discovery
organization beyond the collaboration as well. So we actually see this as an

 FirstName LastNameTran Nguyen
 Comapany NameProthena Corporation plc
 April 3, 2019 Page 3
 FirstName LastName
Tran Nguyen
Prothena Corporation plc
April 3, 2019
Page 3
opportunity to accelerate things that we were looking forward to working on. And
actually these are targets that were obviously high on our list and we were doing an
extensive amount of work on in any event.” - March 20, 2018 Prothena Corporation
PLC Neuroscience R&D Collaboration Investor Call
3.With respect to your assertion that the license rights conveyed to Celgene are not material
in the context of the contract, please reconcile for us why the following rights granted to
Celgene would nonetheless not be viewed as important by Celgene.
•right to access intellectual property for six years through the requirement to be notified
on a regular basis of the Company’s ongoing research activities, material
developments, and new material data or information (see for example Section 2.2.2.a.
and b.)
•right to use the Company’s licensed intellectual property to conduct its activities and
perform its obligations under the Agreement (see for example Section 7.1.1)
•right to use the Company’s licensed intellectual property for six years for purposes
other than evaluating whether to exercises its option (see for example Section 2.9.1)
•right to use for research and development purposes (see page PRTA 1003 of your
January 22, 2019 response).
4.Please reconcile for us the statements in your most recent disclosure in Note 8 to the
financial statements included in your December 31, 2018 Form 10-K that the options for
U.S. Rights and Global Rights represent material rights and the Company’s conclusion
that it does not have a material distinct performance obligation at the inception of the
Collaboration Agreement. In your reply, please provide your analysis as to whether one or
more material rights exists, including whether the exercise price of each option reflects the
standalone selling price for the goods and services subject to each option and how you
made that determination.
5.Please consider updating your analysis of the performance obligations in the contract
based on your responses to the foregoing comments.
6.Tell us how you considered the guidance in ASC 730-20 in accounting for this
arrangement.
            You may contact Tabatha McCullom at 202-551-3658 or Frank Wyman at 202-551-3660,
if you have any questions regarding the comments.
Sincerely,
Division of Corporation Finance
Office of Healthcare & Insurance