Sec Form 4 Filing - MCGUIRE TERRANCE @ Tectonic Therapeutic, Inc. - 2024-06-20

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 MCGUIRE TERRANCE 2. Issuer Name and Ticker or Trading Symbol Tectonic Therapeutic, Inc. [ TECX] 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 TECTONIC THERAPEUTIC, INC., 490 ARSENAL WAY, SUITE 210 3. Date of Earliest Transaction (MM/DD/YY) 06/20/2024 (Street) WATERTOWN, MA02472 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 06/20/2024 A 1,073,062 A 1,073,062 I See Footnote ( 2 ) Common Stock 06/20/2024 A 20,262 A 20,262 I See Footnote ( 4 ) Common Stock 06/20/2024 A 64,652 A 64,652 I See Footnote ( 6 )

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) $ 16.8 06/20/2024 A 11,760 ( 7 ) 06/19/2034 Common Stock 11,760 $ 0 11,760 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other MCGUIRE TERRANCE C/O TECTONIC THERAPEUTIC, INC. 490 ARSENAL WAY, SUITE 210 WATERTOWN, MA02472 X Signatures /s/ Daniel Lochner, Attorney-in-Fact 06/24/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Received in exchange for 2,007,902 shares of common stock of Tectonic Therapeutic, Inc., a Delaware corporation ("Tectonic"), pursuant to an Agreement and Plan of Merger dated as of January 30, 2024 (the "Merger Agreement") by and among AVROBIO, Inc., a Delaware corporation ("AVROBIO"), Tectonic and Alpine Merger Subsidiary, Inc., a direct, wholly owned subsidiary of AVROBIO (the "Merger Sub"). Under the terms of the Merger Agreement, on June 20, 2024, Merger Sub merged with and into Tectonic (the "Merger"), with Tectonic surviving the Merger as a wholly owned subsidiary of AVROBIO. Upon the closing of the Merger, each share of Tectonic common stock was converted into the right to receive 0.534419990 shares of the Issuer's common stock, after giving effect to a reverse stock split of the Issuer's common stock of 1-for-12. Subsequent to the Merger, the name of the Issuer was changed from AVROBIO, Inc. to Tectonic Therapeutic, Inc. ( 2 )The reportable securities are owned directly by Polaris Partners IX, L.P. ("PP IX"). Polaris Partners GP IX, L.L.C. ("PP GP IX") is the general partner of PP IX. Each of David Barrett, Brian Chee, Amir Nashat and Amy Schulman are the managing members of PP GP IX (collectively, the "PP IX GP Managing Members"), and the Reporting Person, a member of the Issuer's board of directors, holds an interest in PP GP IX. Each of PP GP IX, the PP IX GP Managing Members and the Reporting Person, in their respective capacities with respect to PP GP IX, may be deemed to have shared voting, investment and dispositive power with respect to the securities held by PP IX, and each disclaims beneficial ownership of these securities, except to the extent of their respective pecuniary interests therein. ( 3 )Received in exchange for 37,914 shares of common stock of Tectonic on the same terms and conditions as set forth in footnote (1) herein. ( 4 )The reportable securities are owned directly by Polaris Founders Capital I, LP. ("PFC I"). Polaris Founders Capital Management Co. I, L.L.C. ("PFCM I") is the general partner of PFC I. Each of the Reporting Person, a member of the Issuer's board of directors, and Jonathan Flint are the managing members of PFCM I (the "PFCM I Managing Members"). Each of PFCM I and the PFCM I Managing Members, in their respective capacities with respect to PFCM I, may be deemed to have shared voting, investment and dispositive power with respect to the securities held by PFC I, and each disclaims beneficial ownership of these securities, except to the extent of their respective pecuniary interests therein. ( 5 )Received in exchange for 120,976 shares of common stock of Tectonic on the same terms and conditions as set forth in footnote (1) herein. ( 6 )The reportable securities are owned directly by Polaris Founders Capital II, LP. ("PFC II"). Polaris Founders Capital Management Co. I, L.L.C. ("PFCM II") is the general partner of PFC II. Each of the Reporting Person, a member of the Issuer's board of directors, and Jonathan Flint are the managing members of PFCM II (the "PFCM II Managing Members"). Each of PFCM II and the PFCM II Managing Members, in their respective capacities with respect to PFCM II, may be deemed to have shared voting, investment and dispositive power with respect to the securities held by PFC II, and each disclaims beneficial ownership of these securities, except to the extent of their respective pecuniary interests therein. ( 7 )1/3rd of the shares subject to the option will vest on June 20, 2025, and the balance will vest in equal monthly installments thereafter over the next 24 months, subject in each case to the continuous service of the Reporting Person to the Issuer through the applicable vesting date.

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).

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