Prothena Corporation plc (NASDAQ:PRTA), a late-stage clinical biotechnology company with a robust pipeline of investigational therapeutics built on protein dysregulation expertise, today announced updates to its leadership team. Annie Kingston is being promoted to Chief Strategy Officer and Michael Isaacs is being promoted to General Counsel and Corporate Secretary. Mr. Isaacs succeeds Michael Malecek who will be departing from Prothena. Ms. Kingston and Mr. Isaacs will join Prothena's leadership team and will report to Gene Kinney, Ph.D., President and Chief Executive Officer. Ms. Kingston's promotion is effective immediately and Mr. Isaacs' promotion will take effect following Mr. Malecek's departure in June.

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Annie Kingston, Prothena

Ms. Kingston will lead the Company's growth strategy aimed at driving sustainable value creation and Mr. Isaacs will be the Company's most senior legal officer, overseeing the corporate legal function. Tran Nguyen, who previously served as Chief Financial Officer and Chief Strategy Officer, continues to serve as the Company's Chief Financial Officer.

"Prothena is focused on supporting our partnered clinical programs, investing in our wholly-owned preclinical programs and technology, and exploring research collaborations and licensing partnerships to further drive our mission," said Gene Kinney, Ph.D., President and Chief Executive Officer, Prothena. "Annie has played a key role supporting Prothena's evolving corporate strategy and I am excited to expand her current responsibilities to further elucidate the potential of our preclinical programs and CYTOPE^® technology. On behalf of our Board and all Prothenians, I would like to thank Mike Malecek for his leadership over the past seven years, as well as his succession planning leading to the seamless transition to Mike Isaacs. I look forward to continuing to work with Mike Isaacs in his new role leading our corporate legal functions. Having already made significant contributions to the Company, both Annie and Mike are well positioned to step into their expanded roles. I am delighted to continue to work closely with them, our Board, and the rest of the leadership team as we execute our long-term strategy."

Executive Biographies

Ms. Kingston joined Prothena in 2023, serving most recently as Vice President, Corporate Strategy and Chief of Staff. Prior to joining Prothena, Ms. Kingston was an Associate Principal and Project Leader at ClearView Healthcare Partners (a life sciences strategy consultancy), where she advised pharmaceutical and biotechnology companies on both product-level and corporate strategy from 2017 to 2023. Prior to that role, she was a consultant at The Dedham Group. She earned her B.A. in Biology and Psychology from Fairfield University.

Mr. Isaacs joined Prothena in 2020, serving most recently as Deputy General Counsel. Prior to joining Prothena, he was a Corporate Associate at Arnold & Porter Kaye Scholer LLP from 2015 to 2020. Prior to entering the legal profession, he held multiple research positions, including at the Salk Institute for Biological Studies and Biogen Idec. Mr. Isaacs earned his B.S. in Biology (Microbiology) and his M.S. in Biology (Biochemistry and Biophysics) both from the University of California, San Diego, and his J.D. from Santa Clara University School of Law.

About Prothena

Prothena Corporation plc is a late-stage clinical biotechnology company with expertise in protein dysregulation with the potential to change the course of devastating neurodegenerative and rare peripheral amyloid diseases. Fueled by its deep scientific expertise built over decades of research, Prothena 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. Prothena's pipeline includes both wholly-owned and partnered programs being developed for the potential treatment of diseases including Parkinson's disease, ATTR amyloidosis with cardiomyopathy, Alzheimer's disease, Amyotrophic lateral sclerosis (ALS) and a number of other neurodegenerative diseases. Prothena is developing and applying CYTOPE^®, a novel technology that incorporates a cell-internalizing domain to drive efficient cytosolic delivery with highly specific marcomolecular effectors. For more information, please visit the Company's website at www.prothena.com and follow the Company on X (formerly Twitter) @ProthenaCorp.

Forward-Looking Statements

This press release contains forward-looking statements. These statements relate to, among other things, the continued advancement of our preclinical and clinical pipeline, including the potential and advancement of CYTOPE. These statements are based on estimates, projections and assumptions that may prove not to be accurate, and actual results could differ materially from those anticipated due to known and unknown risks, uncertainties and other factors, as well as those described in the "Risk Factors" sections of our Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) on February 27, 2026, and discussions of potential risks, uncertainties, and other important factors in our subsequent filings with the SEC. We undertake no obligation to update publicly any forward-looking statements contained in this press release as a result of new information, future events, or changes in our expectations.

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Mark Johnson, CFA

Senior Vice President, Head of Investor Relations and Corporate Communications

650-837-8550

IR@prothena.com

Media@prothena.com

Prothena Announces Leadership Team Updates