X0306 4 2022-01-04 0 0001808865 iTeos Therapeutics, Inc. ITOS 0001609492 MPM BioVentures 2014, L.P. C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001134657 EVNIN LUKE C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001473930 Foley Todd C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001609493 MPM BioVentures 2014 (B), L.P. C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001609495 MPM Asset Management Investors BV2014 LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001765021 MPM BioVentures 2014 LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001765091 MPM BioVentures 2014 GP LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001729504 MPM BIOVENTURES 2018 (B), L.P. C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 0001734817 MPM ASSET MANAGEMENT INVESTORS BV2018 LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 0 0 1 0 Common Stock 2022-01-04 4 S 0 94745 42.05 D 2790725 I See Footnote Common Stock 2022-01-04 4 S 0 19366 43.20 D 2771359 I See Footnote Common Stock 2022-01-04 4 S 0 6768 45.32 D 2764591 I See Footnote Common Stock 2022-01-04 4 S 0 7671 46.47 D 2756920 I See Footnote Common Stock 2022-01-05 4 S 0 18135 42.03 D 2738785 I See Footnote 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. See Form 4 for MPM BioVentures 2018, L.P for additional members of this joint filing. /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC, the general partner of MPM BioVentures 2014, L.P. 2022-01-06 /s/ Luke Evnin 2022-01-06 /s/ Todd Foley 2022-01-06 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC, the general partner of MPM BioVentures 2014 (B), L.P. 2022-01-06 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the manager of MPM Asset Management Investors BV2014 LLC 2022-01-06 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC 2022-01-06 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC 2022-01-06 /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 (B), L.P. 2022-01-06 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the manager of MPM Asset Management Investors BV2018 LLC 2022-01-06