X0306 4/A 2019-12-23 2019-12-26 false 0001690585 Magenta Therapeutics, Inc. MGTA 0001741285 ZDRAVESKI ZORAN C/O MAGENTA THERAPEUTICS, INC. 50 HAMPSHIRE STREET CAMBRIDGE MA 02139 false true false false See Remarks Common Stock 2019-12-23 4 M false 9.00 7.71 A 140101.00 D Common Stock 2019-12-23 4 M false 4172.00 9.49 A 144273.00 D Common Stock 2019-12-23 4 S false 4181.00 16.0347 D 140092.00 D Common Stock 2019-12-24 4 M false 820.00 7.71 A 140912.00 D Common Stock 2019-12-24 4 S false 7902.00 16.00 D 133010.00 D Stock Option (Right to Buy) 9.49 2019-12-23 4 M false 4172.00 0.00 D 2028-05-08 Common Stock 4172.00 129342.00 D Stock Option (Right to Buy) 7.71 2019-12-23 4 M false 9.00 0.00 D 2028-01-30 Common Stock 9.00 17676.00 D Stock Option (Right to Buy) 7.71 2019-12-24 4 M false 820.00 0.00 D 2028-01-30 Common Stock 820.00 16856.00 D Shares were not previously reported on the form 4 filed 12/26/2019 as an option exercise. This trade is pursuant to an active 10b5-1 plan. This transaction was executed in multiple trades at prices ranging from $16.00 to $16.16. The price reported above reflects the weighted average price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected. This transaction was executed in multiple trades at prices ranging from $16.00 to $16.10. The price reported above reflects the weighted average price. The reporting person hereby undertakes to provide upon request by the staff of the U.S. Securities and Exchange Commission, the issuer or a security holder of the issuer, full information regarding the number of shares and prices at which the transaction was effected. Balance has been updated to reflect the shares acquired and sold on the form 4 filed 12/26/2019. This option vests and becomes exercisable in 48 equal monthly installments beginning on the date of effectiveness of the Issuer's Registration Statement on Form S-1. This option vests and becomes exercisable in 16 equal quarterly installments beginning on January 1, 2018. Secretary and Chief Legal Officer /s/Zoran Zdraveski 2019-12-30