SCHEDULE 13D/A: EcoR1 Capital Fully Divests Prothena Stake, Ceases 5% Beneficial Ownership

Investment firm EcoR1 Capital, LLC and its affiliates have sold their entire holdings in Prothena Corp Public Ltd Co, no longer beneficially owning more than five percent of the company's Ordinary Shares as of May 28, 2025.

Summary

• EcoR1 Capital, LLC, Oleg Nodelman, and EcoR1 Capital Fund Qualified, L.P. (the "reporting persons") have filed an Amendment No. 6 to Schedule 13D regarding their holdings in Prothena Corp Public Ltd Co.
• As of May 28, 2025, the reporting persons ceased to be beneficial owners of more than five percent of Prothena's outstanding Ordinary Shares.
• The filing indicates that the reporting persons now beneficially own 0 shares, representing 0% of the class.
• Over several transactions between May 23, 2025, and May 29, 2025, the Funds sold a total of 5,304,596 Ordinary Shares of Prothena Corp.
• The sales occurred at dollar-weighted average prices ranging from $4.6492 to $7.2708 per share.
• The initial acquisition of shares was for investment purposes, based on the belief that Prothena's Ordinary Shares were undervalued and represented an attractive investment opportunity.

Sentiment

Score: 4

Explanation: The sentiment is slightly negative because a significant investor has fully exited their position, which can be interpreted as a lack of continued confidence or a strategic shift away from the company. While some sales were at a higher price, the overall action is a complete divestment.

Positives

• The reporting persons initially acquired Prothena's Ordinary Shares for investment purposes, believing them to be undervalued and an attractive investment opportunity.
• The sales included a significant block of 1,400,000 shares at a dollar-weighted average price of $7.2708, which is higher than other reported sale prices, potentially indicating a profitable exit for a portion of their holdings.

Negatives

• The reporting persons have divested their entire stake in Prothena Corp, ceasing to be a beneficial owner of more than five percent of the company's Ordinary Shares.
• The majority of the reported sales occurred at prices between $4.6492 and $5.0357 per share, which could be lower than their initial acquisition cost, though the document does not specify the acquisition cost.

Risks

• The divestment by a significant institutional investor like EcoR1 Capital could be perceived negatively by the market, potentially leading to downward pressure on Prothena's share price.
• The reporting persons retain the flexibility to re-enter the market, either by purchasing additional shares or selling any future acquisitions, which could introduce volatility.

Future Outlook

The reporting persons have no present plan or proposal that would result in specific corporate actions, but they will continue to monitor the Issuer and may take various actions regarding their holdings, including purchasing additional shares, selling existing shares, or entering into hedging transactions. They may also recommend actions to the Issuer's management, board, and stockholders.

Management Comments

• "The reporting persons acquired Ordinary Shares for investment purposes based on their belief that the Issuer's Ordinary Shares, when purchased, was undervalued and represented an attractive investment opportunity."
• "The reporting persons will routinely monitor the Issuer regarding a wide variety of factors that affect their investment considerations, including, current and anticipated future trading prices of the Ordinary Shares and other securities, the Issuer's operations, assets, prospects, financial position, and business development, Issuer's management, Issuer-related competitive and strategic matters, general economic, financial market and industry conditions, and other investment considerations."
• "The reporting persons have no present plan or proposal that relates to or would result in any of the actions specified in clauses (a) through (j) of Item 4 of Schedule 13D. However, the reporting persons may recommend action to the Issuer's management, board of directors and stockholders."

Industry Context

This filing reflects a significant divestment by a specialized healthcare investment fund from a biotechnology company. While the document does not provide specific reasons for the exit beyond general investment considerations, such a move by a previously significant shareholder could signal a change in their investment thesis regarding Prothena's prospects or the broader biotech market, or simply a portfolio rebalancing.

Comparison to Industry Standards

• NA This document reports a change in beneficial ownership by an investment fund, not the financial or operational performance of Prothena Corp. Therefore, a comparison to industry standards for company performance is not applicable.

Legal Proceedings

• None of the reporting persons have been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors) in the last five years.
• None of the reporting persons were a party to a civil proceeding of a judicial or administrative body of competent jurisdiction that resulted in a judgment, decree, or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws in the last five years.

Related Party Transactions

• EcoR1 Capital, LLC acts as an investment adviser to its clients, including EcoR1 Capital Fund Qualified, L.P., pursuant to investment management agreements or limited partnership agreements.
• These agreements grant EcoR1 the authority to invest, vote, and dispose of Ordinary Shares on behalf of its clients.
• EcoR1 is entitled to allocations or fees based on assets under management and realized and unrealized gains from these agreements.

Stakeholder Impact

• Shareholders: The divestment by a significant institutional investor could lead to increased selling pressure and potentially a decrease in share price, impacting existing shareholders. It might also signal a loss of institutional confidence.
• Management/Board: The reporting persons explicitly state they may recommend actions to management and the board, indicating potential future engagement or pressure, even after divesting their stake.

Next Steps

• The reporting persons may purchase additional Ordinary Shares in the open market or through privately negotiated transactions.
• The reporting persons may sell at any time, in the open market or privately, any Ordinary Shares they now own or acquire in the future.
• The reporting persons may enter into or unwind hedging or other derivative transactions.
• The reporting persons and their representatives may communicate with other stockholders, industry participants, and interested parties about the Issuer.
• The reporting persons may recommend action to the Issuer's management, board of directors, and stockholders.

Key Dates

Keywords

Prothena Corp, EcoR1 Capital, Schedule 13D, Beneficial Ownership, Share Sale, Institutional Investor, Investment Management, Biotechnology, Pharmaceuticals, SEC Filing