X0306 4 2021-09-14 0 0001690585 Magenta Therapeutics, Inc. MGTA 0001741389 Mahoney Stephen F. C/O MAGENTA THERAPEUTICS, INC. 100 TECHNOLOGY SQUARE CAMBRIDGE MA 02139 0 1 0 0 See Remarks Common Stock 2021-09-14 4 A 0 20000 0.00 A 20000 D On February 11, 2021, the reporting person was granted 40,000 restricted stock units. The restricted stock units vest in two equal installments subject to the achievement of certain performance milestones related to the issuer's business plans. The first performance milestone was achieved, resulting in vesting of 20,000 restricted stock units and the corresponding issuance of 20,000 shares of issuer common stock. Chief Financial and Operating Officer /s/ Stephen F. Mahoney 2021-09-16