X0206 3 2018-06-20 0 0001690585 Magenta Therapeutics, Inc. MGTA 0001319446 Borisy Alexis C/O MAGENTA THERAPEUTICS, INC. 50 HAMPSHIRE STREET CAMBRIDGE MA 02139 1 0 0 0 Common Stock 0 I See Footnote Series A Preferred Stock Common Stock 0 I See Footnote Series B Preferred Stock Common Stock 0 I See Footnote Third Rock Ventures IV, L.P. (the "Fund") holds 96,749 shares of Common Stock of the Issuer. The reporting person is a partner of Third Rock Ventures GP IV, L.P., which is the general partner of the Fund. The reporting person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares. The Fund holds 7,779,656 and 131,799 shares of Series A and Series B Preferred Stock of the Issuer on an as converted to Common Stock basis. The reporting person disclaims beneficial ownership over such shares, except to the extent of his pecuniary interest therein, if any, and this report shall not be deemed an admission that he is the beneficial owner of such shares. Each share of Series A Preferred Stock is convertible into shares of the Issuer's Common Stock on a 2.58398:1 basis. Upon the closing of the Issuer's initial public offering, all shares of Series A Preferred Stock will convert into shares of Common Stock of the Issuer. The Series A Preferred Stock has no expiration date. Each share of Series B Preferred Stock is convertible into shares of the Issuer's Common Stock on a 2.58398:1 basis. Upon the closing of the Issuer's initial public offering, all shares of Series B Preferred Stock will convert into shares of Common Stock of the Issuer. The Series B Preferred Stock has no expiration date. Exhibit 24.1: Power of Attorney /s/ Zoran Zdraveski, Attorney-in-Fact for Alexis A. Borisy 2018-06-20