X0306 4 2022-05-17 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 Stock Option (Right to Buy) 1.18 2022-05-17 4 A 0 62500 0.00 A 2032-05-16 Common Stock 62500 62500 D This option shall vest and become exercisable in three equal installments, each installment vesting every six months, over the 18 months following the vesting commencement date. The vesting commencement date is May 15, 2022. Title: Chief Financial and Operating Officer /s/ Cindy Driscoll, Attorney-in-Fact for Stephen F. Mahoney 2022-05-19