X0306 4 2018-06-25 1 0001690585 Magenta Therapeutics, Inc. MGTA 0001722201 GV 2016 GP, L.L.C. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW CA 94043 0 0 1 0 0001722204 GV 2016 GP, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW CA 94043 0 0 1 0 0001721789 GV 2016, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW CA 94043 0 0 1 0 0001652044 Alphabet Inc. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW CA 94043 0 0 1 0 Common Stock 2018-06-25 4 C 0 3339137 A 3339137 I By GV 2016, L.P. Series A Preferred Stock 2018-06-25 4 C 0 133400 D Common Stock 51626 0 I By GV 2016, L.P. Series B Preferred Stock 2018-06-25 4 C 0 8494864 D Common Stock 3287511 0 I By GV 2016, L.P. The reported securities converted into shares of the Issuer's common stock on a 2.58398:1 basis automatically immediately prior to the closing of the Issuer's initial public offering without payment of further consideration. The shares had no expiration date. The reported securities are directly held by GV 2016, L.P. GV 2016 GP, L.P., the general partner of GV 2016, L.P., GV 2016 GP, L.L.C., the general partner of GV 2016 GP, L.P., Alphabet Holdings LLC, the sole member of GV 2016 GP, L.L.C., XXVI Holdings Inc., the managing member of Alphabet Holdings LLC, and Alphabet Inc., the sole stockholder of XXVI Holdings Inc., may each be deemed to have sole power to vote or dispose of these shares. Each of GV 2016 GP, L.P., GV 2016 GP, L.L.C., Alphabet Holdings LLC, XXVI Holdings Inc. and Alphabet Inc. disclaim beneficial ownership of the shares except to the extent of any pecuniary interest therein. /s/Zoran Zdraveski, as Attorney-in-Fact for GV 2016 GP, L.L.C. 2018-06-27 /s/Zoran Zdraveski, as Attorney-in-Fact for GV 2016 GP, L.P. 2018-06-27 /s/Zoran Zdraveski, as Attorney-in-Fact for GV 2016, L.P. 2018-06-27 /s/Zoran Zdraveski, as Attorney-in-Fact for Alphabet Inc. 2018-06-27