Common Stock, par value $0.0001 per share

Rallybio Corp

234 CHURCH STREET, NEW HAVEN, CT, 06510

This Schedule 13D/A is being filed on behalf of 5AM Ventures V, L.P. ("5AM V"), 5AM Partners V, LLC ("5AM Partners V"), 5AM Opportunities I, L.P. ("5AM Opportunities"), 5AM Opportunities I (GP), LLC ("5AM Opportunities GP"), Andrew J. Schwab ("Schwab"), Dr. Kush Parmar ("Dr. Parmar") and Dr. Scott M. Rocklage ("Dr. Rocklage"). 5AM V, 5AM Partners V, 5AM Opportunities, 5AM Opportunities GP, Schwab, Dr. Parmar and Dr. Rocklage are collectively referred to herein as the "Reporting Persons." The agreement among the Reporting Persons to file this Schedule 13D/A jointly in accordance with Rule 13d-1(k) of the Securities Exchange Act of 1934, as amended, (the "Act") is attached hereto as Exhibit 99.1.

The principal business and principal business office of the Reporting Persons is 4 Embarcadero Center, Suite 3110, San Francisco, CA 94111.

The principal business of the Reporting Persons is venture capital investments. Each of the individuals serves as a Managing Member of 5AM Partners V, which is the general partner of 5AM V. Schwab and Dr. Parmar serve as Managing Members of 5AM Opportunities GP, which is the general partner of 5AM Opportunities.

During the last five years, none of the Reporting Persons was a party to a civil proceeding of a judicial of administrative body of competent jurisdiction or were subject to 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.

Each of 5AM V, 5AM Partners V, 5AM Opportunities and 5AM Opportunities GP was organized in the state of Delaware and each of the individuals is a citizen of the United States.

Rows 11 and 13 of each Reporting Person's cover page to this Schedule 13D/A set forth the aggregate number of shares of common stock and percentages of the shares of common stock beneficially owned by such Reporting Person and are incorporated by reference. The percentage set forth in each row 13 is based upon 5,280,471 shares of common stock outstanding as of December 30, 2025 as reported in the Issuer's definitive proxy statement filed with the SEC on January 2, 2026 and giving effect to an 8-for-1 reverse split of the Issuer's common stock, which was effected on February 2, 2026. The Reporting Persons' beneficial ownership of the Issuer's common stock consists of (i) 135,319 shares of common stock directly held by 5AM V; and (ii) 156,469 shares of common stock directly held by 5AM Opportunities. 5AM Partners V is the sole general partner of 5AM V and shares voting and dispositive power over the securities held by 5AM Partners V. 5AM Opportunities GP is the sole general partner of 5AM Opportunities and shares voting and dispositive power over the securities held by 5AM Opportunities. Schwab and Drs. Parmar and Rocklage are the managing members of 5AM Partners V and share voting and dispositive power over the securities held by 5AM V. Schwab and Dr. Parmar are the managing members of 5AM Opportunities GP and share voting and dispositive power over the securities held by 5AM Opportunities.

Rows 7 through 10 of each Reporting Person's cover page to this Schedule 13D/A set forth the number of shares of common stock as to which such Reporting Person has the sole or shared power to vote or direct the vote and sole or shared power to dispose or to direct the disposition and are incorporated by reference.

Except as set forth below, none of the Reporting Persons has effected any transactions with respect to the securities of the Issuer during the past sixty days. On February 25, 2025, 5AM V sold an aggregate of 87,052 shares in open market transactions at prices ranging from $6.00 to $6.15 (weighted average sales price of $6.07 per share). On February 26, 2025, 5AM V sold an aggregate of 75,000 shares in open market transactions at prices ranging from $6.00 to $6.14 (weighted average sales price of $6.06 per share).

No other person is known to have the right to receive or the power to direct the receipt of dividends from, or any proceeds from the sale of, the securities beneficially owned by any of the Reporting Persons.

Not Applicable.