Filing Details

The remainder of this cover page shall be filled out for a reporting persons initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

  NAME OF REPORTING PERSON

  I.R.S. IDENTIFICATION NO. (ENTITIES ONLY)

   RiverVest Venture Fund IV, L.P.

  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

  (a)  ☐        (b)  ☐

  SEC USE ONLY

  SOURCE OF FUNDS

  WC

  CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)

  ☐

  CITIZENSHIP OR PLACE OF ORGANIZATION

  Delaware, USA

NUMBER OF

SHARES

  BENEFICIALLY  

OWNED BY

EACH

REPORTING

PERSON

WITH

  SOLE VOTING POWER

  0

  SHARED VOTING POWER

  1,441,444

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  1,441,444

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  1,441,444

  CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

  5.4%⁽¹⁾

  TYPE OF REPORTING PERSON

   PN

The percentage set forth in row (13) is based on the 26,666,008 outstanding shares of common stock, par value $0.0001 per share (Common Stock), of Xilio Therapeutics, Inc., a Delaware corporation (the Issuer), reported by the Issuer to be outstanding immediately after the Issuers initial public offering on the Issuers prospectus filed under Rule 424(b)(4), filed with the Securities and Exchange Commission (SEC) on October 22, 2021.

  NAME OF REPORTING PERSON

  I.R.S. IDENTIFICATION NO. (ENTITIES ONLY)

  RiverVest Venture Partners IV, L.P.

  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

  (a)  ☐        (b)  ☐

  SEC USE ONLY

  SOURCE OF FUNDS

  AF

  CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)

  ☐

  CITIZENSHIP OR PLACE OF ORGANIZATION

  Delaware, USA

NUMBER OF

SHARES

  BENEFICIALLY  

OWNED BY

EACH

REPORTING

PERSON

WITH

  SOLE VOTING POWER

  0

  SHARED VOTING POWER

  1,441,444⁽²⁾

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  1,441,444⁽²⁾

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  1,441,444⁽²⁾

  CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

  5.4%⁽¹⁾

  TYPE OF REPORTING PERSON

   PN

Represents 1,441,444 shares of Common Stock owned by RiverVest Venture Fund IV, L.P., a Delaware limited partnership (RiverVest IV). RiverVest Venture Partners IV, L.P., a Delaware limited partnership (RiverVest Partners IV), is the general partner of RiverVest IV.

  NAME OF REPORTING PERSON

  I.R.S. IDENTIFICATION NO. (ENTITIES ONLY)

   RiverVest Venture Partners IV, LLC

  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

  (a)  ☐        (b)  ☐

  SEC USE ONLY

  SOURCE OF FUNDS

  AF

  CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)

  ☐

  CITIZENSHIP OR PLACE OF ORGANIZATION

  Delaware, USA

NUMBER OF

SHARES

  BENEFICIALLY  

OWNED BY

EACH

REPORTING

PERSON

WITH

  SOLE VOTING POWER

  0

  SHARED VOTING POWER

  1,441,444⁽³⁾

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  1,441,444⁽³⁾

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  1,441,444⁽³⁾

  CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

  5.4%⁽¹⁾

  TYPE OF REPORTING PERSON

   OO

Represents 1,441,444 shares of Common Stock owned by RiverVest IV. RiverVest Venture Partners IV, LLC, a Delaware limited liability company, is the general partner of RiverVest Partners IV, which is the general partner of RiverVest IV.

  NAME OF REPORTING PERSON

  I.R.S. IDENTIFICATION NO. (ENTITIES ONLY)

   Niall ODonnell, Ph.D.

  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

  (a)  ☐        (b)  ☐

  SEC USE ONLY

  SOURCE OF FUNDS

  AF

  CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)

  ☐

  CITIZENSHIP OR PLACE OF ORGANIZATION

  USA

NUMBER OF

SHARES

  BENEFICIALLY  

OWNED BY

EACH

REPORTING

PERSON

WITH

  SOLE VOTING POWER

  0

  SHARED VOTING POWER

  1,441,444⁽⁴⁾

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  1,441,444⁽⁴⁾

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  1,441,444⁽⁴⁾

  CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

  5.4%⁽¹⁾

  TYPE OF REPORTING PERSON

   IN

Represents 1,441,444 shares of Common Stock owned by RiverVest IV. Dr. ODonnell is a member of RiverVest Venture Partners IV, LLC, which is the general partner of RiverVest Partners IV, which is the general partner of RiverVest IV.

  NAME OF REPORTING PERSON

  I.R.S. IDENTIFICATION NO. (ENTITIES ONLY)

   John P. McKearn, Ph.D

  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

  (a)  ☐        (b)  ☐

  SEC USE ONLY

  SOURCE OF FUNDS

  AF

  CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)

  ☐

  CITIZENSHIP OR PLACE OF ORGANIZATION

  USA

NUMBER OF

SHARES

  BENEFICIALLY  

OWNED BY

EACH

REPORTING

PERSON

WITH

  SOLE VOTING POWER

  0

  SHARED VOTING POWER

  1,441,444⁽⁵⁾

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  1,441,444⁽⁵⁾

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  1,441,444⁽⁵⁾

  CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

  5.4%⁽¹⁾

  TYPE OF REPORTING PERSON

   IN

Represents 1,441,444 shares of Common Stock owned by RiverVest IV. Dr. McKearn is a member of RiverVest Venture Partners IV, LLC, which is the general partner of RiverVest Partners IV, which is the general partner of RiverVest IV.

  NAME OF REPORTING PERSON

  I.R.S. IDENTIFICATION NO. (ENTITIES ONLY)

   Jay Schmelter

  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

  (a)  ☐        (b)  ☐

  SEC USE ONLY

  SOURCE OF FUNDS

  AF

  CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(d) OR 2(e)

  ☐

  CITIZENSHIP OR PLACE OF ORGANIZATION

  USA

NUMBER OF

SHARES

  BENEFICIALLY  

OWNED BY

EACH

REPORTING

PERSON

WITH

  SOLE VOTING POWER

  0

  SHARED VOTING POWER

  1,441,444⁽⁶⁾

  SOLE DISPOSITIVE POWER

  0

  SHARED DISPOSITIVE POWER

  1,441,444⁽⁶⁾

  AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

  1,441,444⁽⁶⁾

  CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

  ☐

  PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

  5.4%⁽¹⁾

  TYPE OF REPORTING PERSON

   IN

Represents 1,441,444 shares of Common Stock owned by RiverVest IV. Mr. Schmelter is a member of RiverVest Venture Partners IV, LLC, which is the general partner of RiverVest Partners IV, which is the general partner of RiverVest IV.

Name of Person Filing (each a Reporting Person and collectively, the Reporting Persons)

Residence or Business Address

Present Principal Occupation or Employment

During the last five years, none of the Reporting Persons has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

During the last five years, none of the Reporting Persons has been named as a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

Each of the Reporting Persons who is a natural person is a citizen of the United States of America.

The acquisition by any person of additional securities of the Issuer, or the disposition of securities of the Issuer;

An extraordinary corporate transaction, such as a merger, reorganization or liquidation, involving the Issuer or any of its subsidiaries;

A sale or transfer of a material amount of assets of the Issuer or any of its subsidiaries;

Any change in the present board of directors or management of the Issuer, including any plans or proposals to change the number or term of directors or to fill any existing vacancies on the board;

Any material change in the present capitalization or dividend policy of the Issuer;

Any other material change in the Issuers business or corporate structure;

Changes in the Issuers charter, bylaws or instruments corresponding thereto or other actions which may impede the acquisition of control of the Issuer by any person;

Causing a class of securities of the Issuer to be delisted from a national securities exchange or to cease to be authorized to be quoted in an inter-dealer quotation system of a registered national securities association;

A class of equity securities of the Issuer becoming eligible for termination of registration pursuant to Section 12(g)(4) of the Securities Exchange Act of 1934, as amended (the Act); or

Any action similar to any of those enumerated above.

Entity or Individual

RiverVest Venture Fund IV, L.P.

RiverVest Venture Partners IV, L.P.⁽¹⁾

RiverVest Venture Partners IV, LLC⁽²⁾

Niall ODonnell, Ph.D⁽³⁾

John P. McKearn, Ph.D⁽⁴⁾

Jay Schmelter⁽⁵⁾

Based on the 26,666,008 outstanding shares of Common Stock of the Issuer, reported by the Issuer to be outstanding immediately after the IPO on the Issuers prospectus filed under Rule 424(b)(4), filed with the SEC on October 22, 2021.

RiverVest Partners IV is the general partner of RiverVest IV, and as a result, may be deemed to beneficially own the 1,441,444 shares of Common Stock owned by RiverVest IV.

RiverVest Venture Partners IV, LLC is the sole general partner of RiverVest Partners IV, which is the general partner of RiverVest IV, and as a result, may be deemed to beneficially own the 1,441,444 shares of Common Stock owned by RiverVest IV.

Dr. ODonnell is a member of RiverVest Venture Partners IV, LLC, which is the sole general partner of RiverVest Partners IV. RiverVest Partners IV is the general partner of RiverVest IV. As a result, Dr. ODonnell may be deemed to beneficially own the 1,441,444 shares of Common Stock owned by RiverVest IV.

Dr. McKearn is a member of RiverVest Venture Partners IV, LLC, which is the sole general partner of RiverVest Partners IV. RiverVest Partners IV is the general partner of RiverVest IV. As a result, Dr. McKearn may be deemed to beneficially own the 1,441,444 shares of Common Stock owned by RiverVest IV.

Mr. Schmelter is a member of RiverVest Venture Partners IV, LLC, which is the sole general partner of RiverVest Partners IV. RiverVest Partners IV is the general partner of RiverVest IV. As a result, Mr. Schmelter may be deemed to beneficially own the 1,441,444 shares of Common Stock owned by RiverVest IV.

Except as set forth herein, none of the Reporting Persons has effected any transactions in shares of the Issuers Common Stock during the last 60 days.

No other person is known to have the right to receive or the power to direct the receipt of dividends from, or any proceeds from the sale of, the shares of Common Stock beneficially owned by any of the Reporting Persons.

Not applicable.

RiverVest Venture Partners IV, LLC,

its sole general partner

/s/ Jay Schmelter

Name: Jay Schmelter

Title: Member

/s/ Jay Schmelter

/s/ Jay Schmelter

/s/ Niall ODonnell, Ph.D

/s/ John P. McKearn, Ph.D

/s/ Jay Schmelter