Sec Form 4 Filing - GV 2016 GP, L.L.C. @ Magenta Therapeutics, Inc. - 2018-06-25

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person GV 2016 GP, L.L.C. 2. Issuer Name and Ticker or Trading Symbol Magenta Therapeutics, Inc. [ MGTA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 1600 AMPHITHEATRE PARKWAY 3. Date of Earliest Transaction (MM/DD/YY) 06/25/2018 (Street) MOUNTAIN VIEW, CA94043 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 06/25/2018 C 3,339,137 A 3,339,137 I ( 2 ) By GV 2016, L.P. ( 2 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Series A Preferred Stock ( 1 ) 06/25/2018 C 133,400 ( 1 ) ( 1 ) Common Stock 51,626 ( 1 ) 0 I ( 2 ) By GV 2016, L.P. ( 2 ) Series B Preferred Stock ( 1 ) 06/25/2018 C 8,494,864 ( 1 ) ( 1 ) Common Stock 3,287,511 ( 1 ) 0 I ( 2 ) By GV 2016, L.P. ( 2 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other GV 2016 GP, L.L.C. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X GV 2016 GP, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X GV 2016, L.P. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X Alphabet Inc. 1600 AMPHITHEATRE PARKWAY MOUNTAIN VIEW, CA94043 X Signatures /s/Zoran Zdraveski, as Attorney-in-Fact for GV 2016 GP, L.L.C. 06/27/2018 Signature of Reporting Person Date /s/Zoran Zdraveski, as Attorney-in-Fact for GV 2016 GP, L.P. 06/27/2018 Signature of Reporting Person Date /s/Zoran Zdraveski, as Attorney-in-Fact for GV 2016, L.P. 06/27/2018 Signature of Reporting Person Date /s/Zoran Zdraveski, as Attorney-in-Fact for Alphabet Inc. 06/27/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The reported securities converted into shares of the Issuer's common stock on a 2.58398:1 basis automatically immediately prior to the closing of the Issuer's initial public offering without payment of further consideration. The shares had no expiration date. ( 2 )The reported securities are directly held by GV 2016, L.P. GV 2016 GP, L.P., the general partner of GV 2016, L.P., GV 2016 GP, L.L.C., the general partner of GV 2016 GP, L.P., Alphabet Holdings LLC, the sole member of GV 2016 GP, L.L.C., XXVI Holdings Inc., the managing member of Alphabet Holdings LLC, and Alphabet Inc., the sole stockholder of XXVI Holdings Inc., may each be deemed to have sole power to vote or dispose of these shares. Each of GV 2016 GP, L.P., GV 2016 GP, L.L.C., Alphabet Holdings LLC, XXVI Holdings Inc. and Alphabet Inc. disclaim beneficial ownership of the shares except to the extent of any pecuniary interest therein.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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