Form SCHEDULE 13D/A Vor Biopharma Inc. Filed by: RA CAPITAL MANAGEMENT, L.P.

This Schedule 13D/A is being filed on behalf of RA Capital Management, L.P. ("RA Capital"), Peter Kolchinsky, Rajeev Shah, and RA Capital Healthcare Fund, L.P. (the "Fund"). RA Capital, Dr. Kolchinsky, Mr. Shah and the Fund 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 Reporting Persons' beneficial ownership of the Issuer's common stock consists of (i) 3,197,619 shares of common stock directly held by the Fund; (ii) Common Stock Warrants exercisable for up to 1,056,072 shares of common stock held directly by the Fund; (iii) pre-funded warrants (the "Pre-Funded Warrants" and, together with the Common Stock Warrants, the "Warrants") exercisable for up to 10,000,000 shares of common stock directly held by the Fund; (iv) a total of 6,190 shares of common stock underlying vested stock options (right to buy) held by Joshua Resnick for the benefit of RA Capital; and (v) a total of 249 shares of common stock underlying vested stock options (right to buy) and 167 shares of common stock underlying stock options (right to buy) scheduled to vest within 60 days of this filing held by Andrew Levin for the benefit of RA Capital. The Common Stock Warrants contain a provision (the "Common Stock Warrant Beneficial Ownership Blocker") which precludes exercise of the Common Stock Warrants to the extent that, following exercise, the Fund, together with its affiliates and other attribution parties, would own more than 9.99% of the common stock outstanding. The Fund is currently prohibited from exercising the Common Stock Warrants by virtue of the Common Stock Warrant Beneficial Ownership Blocker. The Pre-Funded Warrants contain a provision (the "Pre-Funded Warrant Beneficial Ownership Blocker") which precludes exercise of the Pre-Funded Warrants to the extent that, following exercise, the Fund, together with its affiliates and other attribution parties, would own more than 19.99% of the common stock outstanding. The Fund is currently prohibited from exercising the Pre-Funded Warrants to the extent that such exercise would result in beneficial ownership of more than 12,739,024 shares of common stock by virtue of the Pre-Funded Warrant Beneficial Ownership Blocker. RA Capital Healthcare Fund GP, LLC is the general partner of the Fund. The general partner of RA Capital is RA Capital Management GP, LLC, of which Dr. Kolchinsky and Mr. Shah are the controlling persons. RA Capital serves as investment adviser for the Fund and may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the Issuer held by the Fund. The Fund has delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in its portfolio, including the shares of the Issuer's common stock reported herein. Because each of the Fund has divested itself of voting and investment power over the reported securities it holds and may not revoke that delegation on less than 61 days' notice, the Fund disclaims beneficial ownership of the securities it holds for purposes of Section 13(d) of the Act and therefore disclaims any obligation to report ownership of the reported securities under Section 13(d) of the Act. As managers of RA Capital, Dr. Kolchinsky and Mr. Shah may be deemed beneficial owners, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of the securities reported in this Schedule 13D/A other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13D/A shall not be deemed an admission that either RA Capital, Dr. Kolchinsky, or Mr. Shah is the beneficial owner of such securities for any other purpose.