Sec Form 4 Filing - Borisy Alexis @ 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 Borisy Alexis 2. Issuer Name and Ticker or Trading Symbol Magenta Therapeutics, Inc. [ MGTA] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O MAGENTA THERAPEUTICS, INC., 50 HAMPSHIRE STREET 3. Date of Earliest Transaction (MM/DD/YY) 06/25/2018 (Street) CAMBRIDGE, MA02139 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ 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 0 ( 1 ) A 0 I See Footnote ( 3 )

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 ( 2 ) 06/25/2018 C 0 ( 4 ) ( 2 ) ( 2 ) Common Stock 0 ( 5 ) ( 2 ) 0 I See Footnote ( 3 ) Series B Preferred Stock ( 2 ) 06/25/2018 C 0 ( 4 ) ( 2 ) ( 2 ) Common Stock 0 ( 5 ) ( 2 ) 0 I See Footnote ( 3 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Borisy Alexis C/O MAGENTA THERAPEUTICS, INC. 50 HAMPSHIRE STREET CAMBRIDGE, MA02139 X Signatures /s/ Zoran Zdraveski, Attorney-in-Fact for Alexis A. Borisy 06/27/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents 7,911,455 shares held by Third Rock Ventures IV, L.P. (the "Fund") received by the Fund upon conversion of Series A Preferred Stock and Series B Preferred Stock (collectively, the "Preferred Stock") upon closing of the Issuer's initial public offering on June 25, 2018. ( 2 )The Preferred Stock converted into Common Stock on a 2.58398:1 basis upon the closing of the Issuer's initial public offering on June 25, 2018. The Preferred Stock had no expiration date. ( 3 )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 the shares held by the Fund, 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. ( 4 )Prior to the conversion, the Fund held 20,102,478 shares of Series A Preferred Stock and 340,566 shares of Series B Preferred Stock. ( 5 )Prior to the conversion, the shares of Common Stock underlying the Series A Preferred Stock and Series B Preferred Stock held by the Fund were 7,779,656 and 131,799, respectively.

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