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Prothena Corporation (PRTA) Loss Submission Form

The Klein Law Firm announces that a class action complaint has been filed on behalf of shareholders of Prothena Corporation (NASDAQ: PRTA) who purchased shares between October 15, 2015 and April 20, 2018. The action, which was filed in the United States District Court for the Northern District of California, alleges that the Company violated federal securities laws.

In particular, the PRTA lawsuit alleges that (1) relevant trial data showed that Prothena’s antibody NEOD001, designed to treat amyloid light chain amyloidosis (“AL amyloidosis”), was not an effective treatment; (2) the Company made misleading comparisons of NEOD001’s “best response” rates against certain prior studies; and (3) the Company touted Prothena’s ongoing Phase 1/2 study of NEOD001 as providing a strong basis for late-stage Phase 2b and Phase 3 studies of NEOD001, even though the full Phase 1/2 study data demonstrated that NEOD001 was not an effective treatment. On October 15, 2015, Prothena announced its late-stage Phase 2b “PRONTO” study and expansion of its Phase 1/2 clinical trial for the antibody NEOD001. On April 23, 2018, Prothena announced it was ending development of NEOD001 after its Phase 2b PRONTO trial failed to reach either its primary or secondary endpoints. Following this news, shares of Prothena fell from a close of $36.84 on April 20, 2018, to a close of $11.50 per share on April 23, 2018.

Shareholders have until July 16, 2018 to petition the court for lead plaintiff status. Your ability to share in any recovery does not require that you serve as lead plaintiff. You may choose to be an absent class member.

Keep Me Informed

The Klein Law Firm does not share your information with others. There is no cost or obligation. This submission does not create an attorney-client relationship. If we believe that you might be an appropriate lead plaintiff, we will contact you to discuss whether to establish an attorney-client relationship.

This letter confirms that you have retained The Klein Law Firm to represent you as a named plaintiff in a shareholder action involving Prothena Corporation.

We agree to advance all expenses in the litigation, which means that you are not liable to pay any of the expenses of the lawsuit, whether attorneys' fees or costs. Regardless of the result, we will never ask you to directly pay for any attorneys' fees or costs. Should we obtain a favorable result, we may ask the court to award us compensation to be paid by the defendants or as a portion of any class benefit, but, again, we will never ask you to directly pay any of the costs of this litigation.

As the client you are entitled to direct the litigation in any way you deem proper, and may at any time order us to dismiss the case or opt-out. Should you choose to do so, we will never ask you to reimburse us directly for any legal fees or expenses. During the course of this litigation, we may employ and/or work with other law firms to prosecute your case.

We look forward to representing you and other Prothena Corporation shareholders.

Sincerely,

The Klein Law Firm

Joseph Klein

AGREED: Sign Name Clear