X0306 4 2022-11-30 0 0001690585 Magenta Therapeutics, Inc. MGTA 0001741286 GARDNER JASON C/O MAGENTA THERAPEUTICS, INC. 100 TECHNOLOGY SQUARE CAMBRIDGE MA 02139 1 1 0 0 See Remarks Common Stock 2022-11-30 5 A 0 E 3000 0.94 A 292872 D Common Stock 292990 I By J.P. Gardner Irrevocable Trust Common Stock 359092 I By P.S. Gardner Irrevocable Trust The reporting person is voluntarily reporting the acquisition of shares of the Issuer's common stock pursuant to the Magenta Therapeutics, Inc. 2019 Employee Stock Purchase Plan (the "ESPP") for the ESPP purchase period of June 1, 2022 through November 30, 2022. This transaction is exempt under both Rule 16b-3(c) and Rule 16b-3(d). In accordance with the ESPP, these shares were purchased based on 85% of the closing price of the Issuer's common stock on June 1, 2022. Title: President and Chief Executive Officer /s/ Cindy Driscoll, Attorney-in-Fact for Jason Gardner 2022-12-02