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

This UNDERSTANDING RELATED TO LICENSE, DEVELOPMENT, AND COMMERCIALIZATION AGREEMENT (the “Understanding”) is made effective March 1, 2020 (the “Understanding Effective Date”) and hereby reflects the Parties’ understanding related to the LICENSE, DEVELOPMENT, AND COMMERCIALIZATION AGREEMENT (collectively, with all amendments thereto, being referred to as the “Agreement”) dated December 11, 2013 by and between Neotope Biosciences Limited (as of January 5, 2015 Prothena Biosciences limited, “Prothena Ireland”) with respect to all rights and obligations under this Agreement outside of the United States, and Prothena Biosciences Inc. (“Prothena US”) with respect to all rights and obligations under this Agreement in the United States (Prothena US, together with Prothena Ireland, “Prothena”), on the one hand, and F. Hoffmann-La Roche Ltd (“Roche Basel”) with respect to all rights and obligations under this Agreement outside of the United States, and Hoffmann-La Roche Inc. (“Roche Nutley”) with respect to all rights and obligations under this Agreement in the United States (Roche Nutley, together with Roche Basel, “Roche”), on the other hand. All capitalized terms used herein shall have the meaning ascribed herein or in the Agreement.

WHEREAS, Prothena Ireland and Roche Basel have entered into a license agreement dated March 1, 2020 (the “Diagnostics Agreement”);

WHEREAS, Prothena and Roche view the Diagnostics Agreement as separate from and independent of the Agreement, the Diagnostics Agreement raises potential conflicts with the Agreement, including with respect to termination, compensation and exclusivity;

WHEREAS, Prothena and Roche want to avoid having to amend the Agreement and therefore agree to the provisions set forth in this Understanding.

NOW, THEREFORE, in consideration of the foregoing and the covenants and promises contained in this Amendment and intending to be legally bound, the Parties agree as follows:

IN WITNESS WHEREOF, the Parties have caused this Understanding to be executed effective as of the Understanding Effective Date by their duly authorized representatives as set forth below.