Sec Form 3 Filing - Bain Capital Life Sciences Investors, LLC @ Xilio Therapeutics, Inc. - 2021-10-26

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 Bain Capital Life Sciences Investors, LLC 2. Issuer Name and Ticker or Trading Symbol Xilio Therapeutics, Inc. [ XLO] 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) 200 CLARENDON STREET 3. Date of Earliest Transaction (MM/DD/YY) 10/26/2021 (Street) BOSTON, MA02116 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 2,762,944 I See footnotes ( 1 ) ( 2 ) ( 3 ) ( 4 ) ( 5 )

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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Ot her Bain Capital Life Sciences Investors, LLC 200 CLARENDON STREET BOSTON, MA02116 X Bain Capital Life Sciences Fund II, L.P. 200 CLARENDON STREET BOSTON, MA02116 X Bain Capital Life Sciences Investors II, LLC 200 CLARENDON STREET BOSTON, MA02116 X BCLS II Investco, LP 200 CLARENDON STREET BOSTON, MA02116 X BCLS II Investo (GP), LLC 200 CLARENDON STREET BOSTON, MA02116 X BCIP Life Sciences Associates, LP 200 CLARENDON STREET BOSTON, MA02116 X Signatures See Signatures Included in Exhibit 99.1 11/05/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents 1,348,682 shares of the Issuer's common stock held by Bain Capital Life Sciences Fund II, L.P. ("BCLS II"), 1,250,000 shares of the Issuer's common stock held by BCLS II Investco, LP ("BCLS II Investco") and 164,262 shares of the Issuer's common stock held by BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS II and BCLS II Investco, the "Bain Capital Life Sciences Entities"). ( 2 )Bain Capital Life Sciences Investors II, LLC ("BCLSI II") is the general partner of BCLS II. As a result, BCLSI II may be deemed to share voting and dispositive power with respect to the securities held by BCLS II. BCLSI II disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 3 )BCLS II Investco (GP), LLC ("BCLS II Investco GP"), whose manager is BCLS II, is the general partner of BCLS II Investco. As a result, each of BCLSI II, BCLS II and BCLS II Investco GP may be deemed to share voting and dispositive power with respect to the securities held by BCLS II Investco. Each of BCLSI II, BCLS II and BCLS II Investco GP disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 4 )Boylston Coinvestors, LLC is the general partner of BCIPLS. ( 5 )Bain Capital Life Sciences Investors, LLC ("BCLSI") is the manager of BCLSI II and governs the investment strategy and decision-making process with respect to investments held by BCIPLS. As a result, BCLSI may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. BCLSI disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein.

Remarks: Exhibit 99.1: Joint Filer Information

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

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