Sec Form 3 Filing - RENSCHLER MARKUS MD @ Cyteir Therapeutics, Inc. - 2021-06-17

FORM 3 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 RENSCHLER MARKUS MD 2. Issuer Name and Ticker or Trading Symbol Cyteir Therapeutics, Inc. [ CYT] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) See Remarks (Last) (First) (Middle) 128 SPRING ST, BUILDING A, SUITE 510 3. Date of Earliest Transaction (MM/DD/YY) 06/17/2021 (Street) LEXINGTON, MA02421 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 841,954 ( 1 ) D

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 Stock Option (Right to Buy) $ 1.02 ( 2 ) 12/10/2028 Common Stock 106,342 D Stock Option (Right to Buy) $ 1.19 ( 3 ) 02/24/2030 Common Stock 63,408 D Stock Option (Right to Buy) $ 7.09 ( 4 ) 02/21/2031 Common Stock 500,344 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other RENSCHLER MARKUS MD 128 SPRING ST, BUILDING A, SUITE 510 LEXINGTON, MA02421 X See Remarks Signatures By: /s/ Andrew Gengos, Attorney-in-Fact 06/17/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Includes 125,226 shares acquired upon early exercise of an option, which are subject to forfeiture until they vest. ( 2 )The option vests at a rate of 18,337 shares per month at the end of each successive one-month period beginning January 3, 2019, for 40 months, and at a rate of 14,670 shares per month at the end of the 41st month, at which point the option is fully vested, subject to the Reporting Person's continued employment with the Issuer through the applicable vesting date. ( 3 )The option vested as to 1/48th of the underlying shares of common stock on February 1, 2020, and at the same rate at the end of each successive one-month period following such date until the fourth anniversary of such date, subject to the Reporting Person's continued employment with the Issuer through the applicable vesting date. ( 4 )The option will become exercisable as to 1/36th of the underlying shares of common stock at the end of each successive one-month period following the vesting commencement date, February 5, 2021, until the option is fully vested on the third anniversary of the vesting commencement date, subject to the Reporting Person's continued employment with the Issuer through the applicable vesting date .

Remarks: President and Chief Executive OfficerExhibit List: Exhibit 24 - Power of Attorney

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