Sec Form 4 Filing - Polaris Management Co. VII, L.L.C. @ SQZ Biotechnologies Co - 2020-11-03

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 Polaris Management Co. VII, L.L.C. 2. Issuer Name and Ticker or Trading Symbol SQZ Biotechnologies Co [ SQZ] 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) ONE MARINA PARK DRIVE, 10TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 11/03/2020 (Street) BOSTON, MA02210 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 11/03/2020 C 161,994 A 161,994 I See footnotes ( 2 ) ( 3 ) Common Stock 11/03/2020 C 2,315,652 A 2,315,652 I See footnotes ( 3 ) ( 4 ) Common Stock 11/03/2020 P 16,346 A $ 16 178,340 I See footnotes ( 2 ) ( 3 ) Common Stock 11/03/2020 P 233,654 A $ 16 2,549,306 I See footnotes ( 3 ) ( 4 )

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 ) 11/03/2020 C 28,863 ( 1 ) ( 1 ) Common Stock 30,392 ( 1 ) 0 I See footnotes ( 2 ) ( 3 ) Series A Convertible Preferred Stock ( 1 ) 11/03/2020 C 412,608 ( 1 ) ( 1 ) Common Stock 434,476 ( 1 ) 0 I See footnotes ( 3 ) ( 4 ) Series B Convertible Preferred Stock ( 1 ) 11/03/2020 C 56,462 ( 1 ) ( 1 ) Common Stock 59,454 ( 1 ) 0 I See footnotes ( 2 ) ( 3 ) Series B Convertible Preferred Stock ( 1 ) 11/03/2020 C 807,096 ( 1 ) ( 1 ) Common Stock 849,872 ( 1 ) 0 I See footnotes ( 3 ) ( 4 ) Series C Convertible Preferred Stock ( 1 ) 11/03/2020 C 44,120 ( 1 ) ( 1 ) Common Stock 46,458 ( 1 ) 0 I See footnotes ( 2 ) ( 3 ) Series C Convertible Preferred Stock ( 1 ) 11/03/2020 C 630,672 ( 1 ) ( 1 ) Common Stock 664,097 ( 1 ) 0 I See footnotes ( 3 ) ( 4 ) Series D Convertible Preferred Stock ( 1 ) 11/03/2020 C 24,397 ( 1 ) ( 1 ) Common Stock 25,690 ( 1 ) 0 I See footnotes ( 2 ) ( 3 ) Series D Convertible Preferred Stock ( 1 ) 11/03/2020 C 348,725 ( 1 ) ( 1 ) Common Stock 367,207 ( 1 ) 0 I See footnotes ( 3 ) ( 4 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Polaris Management Co. VII, L.L.C. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON, MA02210 X Polaris Entrepreneurs' Fund VII, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON, MA02210 X Polaris Partners VII, L.P. ONE MARINA PARK DRIVE, 10TH FLOOR BOSTON, MA02210 X Signatures Polaris Management Co. VII, L.L.C., /s/ Lauren Crockett, Attorney-in-fact for Polaris Management Co . VII, L.L.C. 11/03/2020 Signature of Reporting Person Date Polaris Entrepreneurs' Fund VII, L.P., /s/ Lauren Crockett, Attorney-in-fact for Polaris Entrepreneurs' Fund VII, L.P. 11/03/2020 Signature of Reporting Person Date Polaris Partners VII, L.P., /s/ Lauren Crockett, Attorney-in-fact for Polaris Partners VII, L.P. 11/03/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each share of preferred stock automatically converted on a 1.053 for one basis into common stock upon the closing of the Issuer's initial public offering. 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. Amy Schulman ("Ms. Schulman"), a member of the Issuer's board of directors, holds an interest in PMC VII. ( 3 )Each of the Managing Members and Ms. Schulman, 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 Ms. Schulman 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. Ms. Schulman, a member of the Issuer's board of directors, holds an interest in PMC VII.

Remarks: This Form 4 does not include certain shares held by LS Polaris Innovation Fund, L.P. ("LSPIF"). Ms. Schulman, a member of the Issuer's board of directors, is the sole managing member of LS Polaris Innovation Fund GP, L.L.C. ("LSPIF GP"), the general partner of LSPIF, and files her own Section 16 reports. The shares held by LSPIF are reported in Ms. Schulman's Section 16 reports. LSPIF is a specialized affiliate fund of Polaris Partners and, through its general partner, LSPIF GP, is under separate management and control from PP VII and PEF VII.

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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