X0306 4 2019-02-19 0 0001750019 TCR2 THERAPEUTICS INC. TCRR 0001134655 GADICKE ANSBERT C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE MA 02142 1 0 1 0 Common Stock 2019-02-19 4 C 0 79644 A 79644 I See Footnote Common Stock 2019-02-19 4 C 0 52469 A 52469 I See Footnote Common Stock 2019-02-19 4 C 0 146447 A 146447 I See Footnote Common Stock 2019-02-19 4 C 0 2195681 A 2195681 I See Footnote Common Stock 2019-02-19 4 C 0 351155 A 351155 I See Footnote Common Stock 2019-02-19 4 C 0 2421775 A 2421775 I See Footnote Common Stock 2019-02-19 4 C 0 9291 A 88935 I See Footnote Common Stock 2019-02-19 4 C 0 5247 A 57716 I See Footnote Common Stock 2019-02-19 4 C 0 17085 A 163532 I See Footnote Common Stock 2019-02-19 4 C 0 256163 A 2451844 I See Footnote Common Stock 2019-02-19 4 C 0 35115 A 386270 I See Footnote Common Stock 2019-02-19 4 C 0 282540 A 2704315 I See Footnote Common Stock 2019-02-19 4 P 0 1373333 15.00 A 1569235 I See Footnote Series A Preferred Stock 2019-02-19 4 C 0 493306 D Common Stock 79644 0 I See Footnote Series A Preferred Stock 2019-02-19 4 C 0 325002 D Common Stock 52469 0 I See Footnote Series A Preferred Stock 2019-02-19 4 C 0 907073 D Common Stock 146447 0 I See Footnote Series A Preferred Stock 2019-02-19 4 C 0 13599621 D Common Stock 2195681 0 I See Footnote Series A Preferred Stock 2019-02-19 4 C 0 2174998 D Common Stock 351155 0 I See Footnote Series A Preferred Stock 2019-02-19 4 C 0 15000000 D Common Stock 2421775 0 I See Footnote Series B Preferred Stock 2019-02-19 4 C 0 57552 D Common Stock 9291 0 I See Footnote Series B Preferred Stock 2019-02-19 4 C 0 32500 D Common Stock 5247 0 I See Footnote Series B Preferred Stock 2019-02-19 4 C 0 105825 D Common Stock 17085 0 I See Footnote Series B Preferred Stock 2019-02-19 4 C 0 1586623 D Common Stock 256163 0 I See Footnote Series B Preferred Stock 2019-02-19 4 C 0 217500 D Common Stock 35115 0 I See Footnote Series B Preferred Stock 2019-02-19 4 C 0 1750000 D Common Stock 282540 0 I See Footnote Each share of Series A Preferred Stock converted into shares of the Issuer's common stock, par value $0.0001 ("Common Stock"), on a 6.1938:1 basis upon the closing of the Issuer's initial public offering. The reported securities are owned directly by MPM Asset Management Investors BV2014 LLC. The Reporting Person disclaims beneficial ownership of the securities reported herein except to the extent of his pecuniary interest therein. The reported securities are owned directly by MPM Asset Management Investors SunStates Fund LLC. The Reporting Person disclaims beneficial ownership of the securities reported herein except to the extent of his pecuniary interest therein. The reported securities are owned directly by MPM BioVentures 2014 (B), L.P. MPM BioVentures 2014 GP LLC is the general partner of MPM BioVentures 2014 (B), L.P. MPM BioVentures 2014 LLC is the managing member of MPM BioVentures 2014 GP LLC. The Reporting Person is a member of MPM BioVentures 2014 LLC and disclaims beneficial ownership of the securities reported herein except to the extent of his pecuniary interest therein. The reported securities are owned directly by MPM BioVentures 2014, L.P. MPM BioVentures 2014 GP LLC is the general partner of MPM BioVentures 2014, L.P. MPM BioVentures 2014 LLC is the managing member of MPM BioVentures 2014 GP LLC. The Reporting Person is a member of MPM BioVentures 2014 LLC and disclaims beneficial ownership of the securities reported herein except to the extent of his pecuniary interest therein. The reported securities are owned directly by MPM SunStates Fund, L.P. MPM SunStates Fund GP LLC is the general partner of MPM SunStates Fund, L.P. MPM SunStates GP Managing Member LLC is the managing member of MPM SunStates Fund GP LLC. The Reporting Person is a member of MPM SunStates Fund GP LLC and disclaims beneficial ownership of the securities reported herein except to the extent of his pecuniary interest therein. The reported securities are held directly by UBS Oncology Impact Fund, L.P. The general partner of UBS Oncology Impact Fund, L.P. is Oncology Impact Fund (Cayman) Management L.P. The general partner of Oncology Impact Fund (Cayman) Management L.P. is MPM Oncology Impact Management LP. The general partner of MPM Oncology Impact Management LP is MPM Oncology Impact Management GP LLC. The Reporting Person is the managing director of MPM Oncology Impact Management GP LLC and disclaims beneficial ownership of the securities reported herein except to the extent of his pecuniary interest therein. Each share of Series B Preferred Stock converted into shares of the Issuer's Common Stock on a 6.1938:1 basis upon the closing of the Issuer's initial public offering. The reported securities are owned directly by MPM Asset Management LLC. The Reporting Person is a member of MPM Asset Management LLC and disclaims beneficial ownership of the securities reported herein except to the extent of his pecuniary interest therein. /s/ Ansbert Gadicke 2019-02-21