Sec Form 3 Filing - MPM BioVentures 2014, L.P. @ iTeos Therapeutics, Inc. - 2020-07-23

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 MPM BioVentures 2014, L.P. 2. Issuer Name and Ticker or Trading Symbol iTeos Therapeutics, Inc. [ ITOS] 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) C/O MPM CAPITAL, 450 KENDALL STREET 3. Date of Earliest Transaction (MM/DD/YY) 07/23/2020 (Street) CAMBRIDGE, MA02142 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 B Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 1,269,230 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 5 ) Series B Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 84,655 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 5 ) Series B Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 43,687 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 5 ) Series B Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 801,619 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 6 ) Series B Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 42,605 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 6 ) Series B Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 15,820 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 6 ) Series B-2 Preferred Stock ( 7 ) ( 7 ) ( 7 ) Common Stock 724,702 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 5 ) Series B-2 Preferred Stock ( 7 ) ( 7 ) ( 7 ) Common Stock 48,336 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 5 ) Series B-2 Preferred Stock ( 7 ) ( 7 ) ( 7 ) Common Stock 24,944 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 5 ) Series B-2 Preferred Stock ( 7 ) ( 7 ) ( 7 ) Common Stock 457,706 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 6 ) Series B-2 Preferred Stock ( 7 ) ( 7 ) ( 7 ) Common Stock 24,326 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 6 ) Series B-2 Preferred Stock ( 7 ) ( 7 ) ( 7 ) Common Stock 9,033 ( 2 ) ( 3 ) ( 4 ) I Footnote ( 6 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other MPM BioVentures 2014, L.P. C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM BioVentures 2018 LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM BioVentures 2018 GP LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X Signatures /s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC 07/23/2020 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC 07/23/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each share of Series B Convertible Preferred stock is convertible at any time, at the Reporting Person's election, into Common Stock, based on the then-applicable conversion rate and has no expiration date. Each Reporting Person disclaims beneficial ownership of the securities except to the extent of his or its pecuniary interest therein. ( 2 )The shares of Series B Convertible Preferred stock held by MPM BioVentures 2014 LP ("BV 2014") will convert automatically into 1,269,230 shares of Common Stock upon the closing of the Issuer's initial public offering. The shares of Series B Convertible Preferred stock held by MPM BioVentures 2014 (B) LP ("BV 2014(B)") will convert automatically into 84,655 shares of Common Stock upon the closing of the Issuer's initial public offering. The shares of Series B Convertible Preferred stock held by MPM Asset Management Investors BV 2014 LLC will convert automatically into 43,687 shares of Common Stock upon the closing of the Issuer's initial public offering. The shares of Series B Convertible Preferred stock held by MPM BioVentures 2018 LP ("BV 2018") will convert automatically into 801,619 shares of Common Stock upon the closing of the Issuer's initial public offering. ( 3 )(Continued from footnote 2) The shares of Series B Convertible Preferred stock held by MPM BioVentures 2018 (B) LP ("BV 2018(B)") will convert automatically into 42,605 shares of Common Stock upon the closing of the Issuer's initial public offering. The shares of Series B Convertible Preferred stock held by MPM Asset Management Investors BV 2018 LLC will convert automatically into 15,820 shares of Common Stock upon the closing of the Issuer's initial public offering. The shares of Series B-2 Convertible Preferred stock held by BV 2014 will convert automatically into 724,702 shares of Common Stock upon the closing of the Issuer's initial public offering. The shares of Series B-2 Convertible Preferred stock held by BV 2014(B) will convert automatically into 48,336 shares of Common Stock upon the closing of the Issuer's initial public offering. ( 4 )(Continued from footnote 3) The shares of Series B-2 Convertible Preferred stock held by MPM Asset Management Investors BV 2014 LLC will convert automatically into 24,944 shares of Common Stock upon the closing of the Issuer's initial public offering. The shares of Series B-2 Convertible Preferred stock held by BV 2018 will convert automatically into 457,706 shares of Common Stock upon the closing of the Issuer's initial public offering. The shares of Series B-2 Convertible Preferred stock held by BV 2018(B) will convert automatically into 24,326 shares of Common Stock upon the closing of the Issuer's initial public offering. The shares of Series B-2 Convertible Preferred stock held by MPM Asset Management Investors BV 2018 LLC will convert automatically into 9,033 shares of Common Stock upon the closing of the Issuer's initial public offering. These amounts reflect a 1-for-3.3115 reverse stock split which became effective on July 20, 2020. ( 5 )MPM BioVentures 2014 GP LLC and MPM BioVentures 2014 LLC ("2014 BV LLC") are the direct and indirect general partners of BV 2014 and BV 2014(B). Luke Evnin, Ansbert Gadicke and Todd Foley are the managing directors of 2014 BV LLC and members of MPM Asset Management Investors BV2014 LLC. ( 6 )MPM BioVentures 2018 GP LLC and MPM BioVentures 2018 LLC ("2018 BV LLC") are the direct and indirect general partners of BV 2018 and BV 2018(B). Luke Evnin, Ansbert Gadicke, Todd Foley and Edward Hurwitz are the managing directors of 2018 BV LLC and members of MPM Asset Management Investors BV2018 LLC. ( 7 )Each share of Series B-2 Convertible Preferred stock is convertible at any time, at the Reporting Person's election, into Common Stock, based on the then-applicable conversion rate and has no expiration date. Each Reporting Person disclaims beneficial ownership of the securities except to the extent of his or its pecuniary interest therein.

Remarks: Form 2 of 2.

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).

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