Sec Form 3 Filing - Rock Springs Capital Management LP @ Xilio Therapeutics, Inc. - 2021-10-21

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 Rock Springs Capital Management LP 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) 650 SOUTH EXETER ST., SUITE 1070 3. Date of Earliest Transaction (MM/DD/YY) 10/21/2021 (Street) BALTIMORE, MD21202 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

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 C Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 756,472 I See footnote ( 2 ) Series C Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 151,294 I See footnote ( 3 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Rock Springs Capital Management LP 650 SOUTH EXETER ST., SUITE 1070 BALTIMORE, MD21202 X Rock Springs Capital LLC 650 SOUTH EXETER ST., SUITE 1070 BALTIMORE, MD21202 X Rock Springs Capital Master Fund LP 190 ELGIN AVENUE GEORGE TOWN, E9KY1 9001 X Four Pines Master Fund LP 650 SOUTH EXETER ST., SUITE 1070 BALTIMORE, MD21202 X Signatures By: /s/ Mark Bussard, Authorized Signatory, Rock Springs Capital Management LP 10/21/2021 Signature of Reporting Person Date By: /s/ Mark Bussard, Authorized Signatory, Rock Springs Capital LLC 10/21/2021 Signature of Reporting Person Date By: /s/ Mark Bussard, Authorized Signatory, Rock Springs Capital Master Fund LP 10/21/2021 Signature of Reporting Person Date By: /s/ Mark Bussard, Authorized Signatory, Four Pines Master Fund LP 10/21/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The Series C Preferred Stock automatically converts into the number of shares of Common Stock as shown in Column 3 without payment of further consideration at the holder's election or upon closing of the initial public offering of the Issuer's common stock. The shares have no expiration date. ( 2 )The securities reported herein are held of record by Rock Springs Capital Master Fund LP ("Master Fund"). Rock Springs Capital LLC ("RSC") is the general partner of Rock Springs Capital Management LP ("RSCM") which is the investment manager to Master Fund. RSC and RSCM may therefore be deemed to have or share beneficial ownership of the Series C Preferred Stock held directly by Master Fund. ( 3 )The securities reported herein are held of record by Four Pines Master Fund LP ("Four Pines"). RSC is the general partner of RSCM which is the investment manager to Four Pines. RSC and RSCM may therefore be deemed to have or share beneficial ownership of the Series C Preferred Stock held directly by Four Pines.

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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