Sec Form 4 Filing - MPM BIOVENTURES 2018, L.P. @ iTeos Therapeutics, Inc. - 2022-01-04

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 MPM BIOVENTURES 2018, 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) 01/04/2022 (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 Common Stock 01/04/2022 S 94,745( 1 ) D $ 42.05( 2 ) 2,790,725 I See Footnote( 3 ) Common Stock 01/04/2022 S 19,366( 4 ) D $ 43.2( 5 ) 2,771,359 I See Footnote( 6 ) Common Stock 01/04/2022 S 6,768( 7 ) D $ 45.32( 8 ) 2,764,591 I See Footnote( 9 ) Common Stock 01/04/2022 S 7,671( 10 ) D $ 46.47( 11 ) 2,756,920 I See Footnote( 12 ) Common Stock 01/05/2022 S 18,135( 13 ) D $ 42.03( 14 ) 2,738,785 I See Footnote( 15 )

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 Cod e (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 Other MPM BIOVENTURES 2018, 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, the managing member of MPM BioVentures 2018 GP LLC, the general partner of MPM BioVentures 2018, L.P. 01/06/2022 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC 01/06/2022 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC 01/06/2022 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The shares were sold as follows: 56,414 by MPM BioVentures 2014, L.P. ("BV 2014"), 1,959 by MPM Asset Management Investors BV2014 LLC ("AM BV2014"), 35,653 by MPM BioVentures 2018, L.P. ("BV 2018") and 719 by MPM Asset Management Investors BV2018 LLC ("AM BV2018"). MPM BioVentures 2014 GP LLC and MPM BioVentures 2014 LLC ("BV 2014 LLC") are the direct and indirect general partners of BV 2014 and BV 2014(B). BV 2014 LLC is the manager of AM BV2014. MPM BioVentures 2018 GP LLC and MPM BioVentures 2018 LLC ("BV 2018 LLC") are the direct and indirect general partners of BV 2018 and BV 2018(B). BV 2018 LLC is the manager of AM BV2018. Messrs. Evnin and Foley are managing directors of BV 2014 LLC and BV 2018 LLC. ( 2 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $42.00 to $42.58 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 3 )The shares are held as follows: 1,575,558 by BV 2014, 97,289 by MPM BioVentures 2014(B), L.P. ("BV 2014(B)"), 54,213 by AM BV2014, 995,065 by BV 2018, 48,966 by MPM BioVentures 2018(B), L.P. ("BV 2018(B)") and 19,634 by AM BV2018. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 4 )The shares were sold as follows: 11,534 by BV 2014, 390 by AM BV2014, 7,300 by BV 2018 and 142 by AM BV2018. ( 5 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $43.00 to $43.79 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 6 )The shares are held as follows: 1,564,024 by BV 2014, 97,289 by BV 2014(B), 53,823 by AM BV2014, 987,765 by BV 2018, 48,966 by BV 2018(B) and 19,492 by AM BV2018. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 7 )The shares were sold as follows: 4,050 by BV 2014, 133 by AM BV2014, 2,544 by BV 2018 and 41 by AM BV2018. ( 8 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $45.00 to $45.90 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 9 )The shares are held as follows: 1,559,974 by BV 2014, 97,289 by BV 2014(B), 53,690 by AM BV2014, 985,221 by BV 2018, 48,966 by BV 2018(B) and 19,451 by AM BV2018. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 10 )The shares were sold as follows: 4,590 by BV 2014, 154 by AM BV2014, 2,874 by BV 2018 and 53 by AM BV2018. ( 11 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $46.025 to $46.965 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 12 )The shares are held as follows: 1,555,384 by BV 2014, 97,289 by BV 2014(B), 53,536 by AM BV2014, 982,347 by BV 2018, 48,966 by BV 2018(B) and 19,398 by AM BV2018. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 13 )The shares were sold as follows: 10,804 by BV 2014, 372 by AM BV2014, 6,824 by BV 2018 and 135 by AM BV2018. ( 14 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $42.00 to $42.38 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 15 )The shares are held as follows: 1,544,580 by BV 2014, 97,289 by BV 2014(B), 53,164 by AM BV2014, 975,523 by BV 2018, 48,966 by BV 2018(B) and 19,263 by AM BV2018. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any.

Remarks: See Form 4 for MPM BioVentures 2014, L.P for additional members of this joint filing.

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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