Sec Form 3 Filing - SCHULMAN AMY W @ SQZ Biotechnologies Co - 2020-10-29

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

OMB APPROVAL OMB Number: 3235-0287 Expires: November 30, 2011 Estimated average burden hours per response... 0.5

1. Name and Address of Reporting Person SCHULMAN AMY W 2. Issuer Name and Ticker or Trading Symbol SQZ Biotechnologies Co [ SQZ] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 200 ARSENAL YARDS BLVD, SUITE 210 3. Date of Earliest Transaction (MM/DD/YY) 10/29/2020 (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 168,480 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 Series A Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 30,392 I See footnotes ( 2 ) ( 3 ) Series A Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 434,476 I See footnotes ( 4 ) ( 3 ) Series B Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 59,454 I See footnotes ( 2 ) ( 3 ) Series B Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 849,872 I See footnotes ( 4 ) ( 3 ) Series C Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 46,458 I See footnotes ( 2 ) ( 3 ) Series C Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 664,097 I See footnotes ( 4 ) ( 3 ) Series C Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 177,638 I See footnotes ( 5 ) Series C Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 22,204 D Series D Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 25,690 I See footnotes ( 2 ) ( 3 ) Series D Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 367,207 I See footnotes ( 4 ) ( 3 ) Series D Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 98,222 I See footnotes ( 5 ) Stock Option $ 2.02 ( 6 ) 03/04/2028 Common Stock 10,530 D Stock Option $ 4.59 ( 7 ) 02/18/2029 Common Stock 10,530 D Stock Option $ 4.59 ( 8 ) 06/05/2029 Common Stock 10,530 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other SCHULMAN AMY W 200 ARSENAL YARDS BLVD, SUITE 210 WATERTOWN, MA02472 X X Signatures /s/ Lawrence Knopf, Attorney-in-Fact for Amy W. Schulman 10/29/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The Issuer's preferred stock is convertible into common stock on a 1.053 for 1 basis at the holder's election and will automatically convert upon closing of the initial public offering of the Issuer's common stock. The shares have no expiration date. ( 2 )These shares are held of record by Polaris Entrepreneurs' Fund VII, L.P. ("EF VII"). Polaris Management Co. VII, L.L.C. ("PMC VII") is the general partner of EF VII. David Barrett, Brian Chee, Amir Nashat and Bryce Youngren (the "Managing Members") are the managing members of PMC VII. The Reporting Person, a member of the Issuer's board of directors, holds an interest in PMC VII. ( 3 )Each of the Managing Members and the Reporting Person, in their respective capacities with respect to PMC VII, may be deemed to have shared investment, voting and dispositive power over these shares. Each of PMC VII, the Managing Members and the Reporting Person disclaim beneficial ownership of these shares and this report shall not be deemed an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interests therein. ( 4 )These shares are held of record by Polaris Partners VII, L.P. ("PP VII"). PMC VII is the general partner of PP VII. The Managing Members are the managing members of PMC VII. The Reporting Person, a member of the Issuer's board of directors, holds an interest in PMC VII. ( 5 )These shares are held of record by LS Polaris Innovation Fund, L.P. ("LSPIF"). LS Polaris Innovation Fund GP, L.L.C. ("LSPIF GP") is the general partner of LSPIF. The Reporting Person is the sole managing member of LSPIF GP. Each of LSPIF GP and the Reporting Person may be deemed to have sole investment, voting and dispositive power over these shares. LSPIF GP and the Reporting Person disclaim beneficial ownership of the shares held by LSPIF and this report shall not be deemed an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or for any other purpose, except to the extent of their respective pecuniary interests therein. ( 6 )The option vests and becomes exercisable as to 25% of the underlying securities on January 23, 2019 and in 36 equal monthly installments thereafter. ( 7 )The option vests and becomes exercisable as to 25% of the underlying securities on February 1, 2020 and in 36 equal monthly installments thereafter. ( 8 )The option vests and becomes exercisable in 48 equal monthly installments commencing on July 5, 2019.

Remarks: Exhibit 24 - Power of Attorney.

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).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.