X0306 4 2021-09-07 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 2021-09-07 4 S 0 30474 29.18 D 3635313 I See Footnote Common Stock 2021-09-07 4 J 0 31340 0.00 D 3603793 I See Footnote Common Stock 2021-09-08 4 S 0 11152 28.61 D 3592821 I See Footnote Common Stock 2021-09-08 4 S 0 940 29.10 D 3591881 I See Footnote Transaction effected pursuant to a plan established pursuant to Rule 10b5-1. The shares were sold as follows: 18,156 by MPM BioVentures 2014, L.P. ("BV 2014"), 625 by MPM Asset Management Investors BV2014 LLC ("AM BV2014"), 11,467 by MPM BioVentures 2018, L.P. ("BV 2018") and 226 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 $28.89 to $29.64 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: 2,050,714 by BV 2014, 128,561 by MPM BioVentures 2014(B), L.P. ("BV 2014(B)"), 70,585 by AM BV2014, 1,295,187 by BV 2018, 64,705 by MPM BioVentures 2018(B), L.P. ("BV 2018(B)") and 25,561 by AM BV2018. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein. Represents a pro rata in-kind distribution from BV 2014(B) and BV 2018(B) to its respectve limited partners for no consideration. The shares were distributed as follows: 20,848 by BV 2014(B) and 10,492 by AM BV 2018(B). The shares are held as follows: 2,050,714 by BV 2014, 107,713 by BV 2014(B), 70,585 by AM BV2014, 1,295,187 by BV 2018, 54,213 by BV 2018(B) and 25,561 by AM BV2018. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein. The shares were sold as follows: 6,644 by BV 2014, 229 by AM BV2014, 4,196 by BV 2018 and 83 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 $28.02 to $29.01 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: 2,044,070 by BV 2014, 107,713 by BV 2014(B), 70,356 by AM BV2014, 1,290,991 by BV 2018, 54,213 by BV 2018(B) and 25,478 by AM BV2018. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein. The shares were sold as follows: 560 by BV 2014, 19 by AM BV2014, 354 by BV 2018 and 7 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 $29.04 to $29.21 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: 2,043,510 by BV 2014, 107,713 by BV 2014(B), 70,337 by AM BV2014, 1,290,637 by BV 2018, 54,213 by BV 2018(B) and 25,471 by AM BV2018. The Reporting Person disclaims beneficial ownership of the securities except to the extent of his pecuniary interest therein. Page 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. 2021-09-08 /s/ Luke Evnin 2021-09-08 /s/ Todd Foley 2021-09-08 /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. 2021-09-08 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the manager of MPM Asset Management Investors BV2014 LLC 2021-09-08 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC 2021-09-08 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC 2021-09-08 /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. 2021-09-08 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the manager of MPM Asset Management Investors BV2018 LLC 2021-09-08