On August 3, 2021, Michael W. Bonney notified Magenta Therapeutics, Inc. of his intent to resign from the Company’s Board of Directors (the “Board”) and its committees effective August 3, 2021, to focus on his newly expanded role as Executive Chair of Alnylam Pharmaceuticals, Inc. Mr. Bonney’s decision to resign from the Board was not the result of any dispute or disagreement with the Company or the Board on any matter relating to the Company’s operations, policies, or practices. In connection with Mr. Bonney’s resignation, effective August 4, 2021, the size of the Board was reduced from ten members to nine members, Alison F. Lawton, currently a member of the Board, was appointed Chair of the Board, and Jeffrey W. Albers, also a current member of the Board, was appointed to the Board’s audit committee.