X0206 3 2020-07-23 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 0001729505 MPM BIOVENTURES 2018, L.P. 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 Series B Preferred Stock Common Stock 1269230 I Footnote Series B Preferred Stock Common Stock 84655 I Footnote Series B Preferred Stock Common Stock 43687 I Footnote Series B Preferred Stock Common Stock 801619 I Footnote Series B Preferred Stock Common Stock 42605 I Footnote Series B Preferred Stock Common Stock 15820 I Footnote Series B-2 Preferred Stock Common Stock 724702 I Footnote Series B-2 Preferred Stock Common Stock 48336 I Footnote Series B-2 Preferred Stock Common Stock 24944 I Footnote Series B-2 Preferred Stock Common Stock 457706 I Footnote Series B-2 Preferred Stock Common Stock 24326 I Footnote Series B-2 Preferred Stock Common Stock 9033 I Footnote 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. 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. (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. (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. 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. 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. 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. Form 1 of 2. /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. 2020-07-23 /s/ Luke Evnin 2020-07-23 /s/ Todd Foley 2020-07-23 /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. 2020-07-23 /s/ Howard Rubin, director of MPM Asset Management Investors BV2014 LLC 2020-07-23 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC 2020-07-23 /s/ Ansbert Gadicke, managing director of MPM BioVentures 2014 LLC, the managing member of MPM BioVentures 2014 GP LLC 2020-07-23 /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. 2020-07-23 /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. 2020-07-23 /s/ Howard Rubin, director of MPM Asset Management Investors BV2018 LLC 2020-07-23