X0306 4/A 2021-04-19 2021-04-20 0 0001690585 Magenta Therapeutics, Inc. MGTA 0001857488 Nichols David Wayne C/O MAGENTA THERAPEUTICS, INC. 100 TECHNOLOGY SQUARE CAMBRIDGE MA 02139 0 1 0 0 Chief Technical Officer Stock Option (Right to Buy) 10.50 2021-04-19 4 A 0 175000 0.00 A 2031-04-18 Common Stock 175000 175000 D This option shall vest and become exerciseable over four years, with 25% of this option vesting on April 19, 2022, and the remainder vesting in 36 equal monthly installments thereafter. This amendment has been filed to revise the vesting terms of Mr. Nichols' stock option, which were reported incorrectly on Mr. Nichols' prior Form 4. The corrected vesting schedule is included in Footnote 1 above. /s/ Cindy Driscoll, Attorney-in-Fact for David Nichols 2021-05-17