X0306 4 2022-06-28 0 0001690585 Magenta Therapeutics, Inc. MGTA 0001451612 Booth Bruce C/O MAGENTA THERAPEUTICS, INC. 100 TECHNOLOGY SQUARE CAMBRIDGE MA 02139 1 0 0 0 Stock Option (Right to Buy) 1.21 2022-06-28 4 A 0 20000 0.00 A 2032-06-27 Common Stock 20000 20000 D This option shall vest and become exercisable in full upon the earlier to occur of (a) June 28, 2023 or (b) the next annual meeting of the Issuer's stockholders. This option was granted to the Reporting Person, a director of the Issuer. The proceeds of any sale of shares of common stock issued to the Reporting Person upon exercise of this option will be transferred to Atlas Venture Life Science Advisors, LLC and as such, the Reporting Person disclaims ownership of such securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, except to the extent of his pecuniary interest therein, if any. /s/ Ommer Chohan, Attorney-in-Fact for Bruce Booth 2022-06-30