X0306 4 2017-02-01 0 0001640455 Jounce Therapeutics, Inc. JNCE 0001488495 Third Rock Ventures II, L.P. C/O THIRD ROCK VENTURES, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001614061 Third Rock Ventures GP II, L.P. C/O THIRD ROCK VENTURES, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001614073 TRV GP II, LLC C/O THIRD ROCK VENTURES, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001569705 Third Rock Ventures III, L.P. C/O THIRD ROCK VENTURES, LLC, 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001637300 Third Rock Ventures GP III, L.P. 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001637299 TRV GP III, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001180428 LEVIN MARK J C/O THIRD ROCK VENTURES, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001192603 STARR KEVIN P C/O THIRD ROCK VENTURES, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 Common Stock 2017-02-01 4 C 0 9688344 A 10230349 D Common Stock 2017-02-01 4 C 0 3048780 A 3048780 D Series A Preferred Stock 2017-02-01 4 C 0 35750000 0.00 D Common Stock 9688344 0 D Series A Preferred Stock 2017-02-01 4 C 0 11250000 0.00 D Common Stock 3048780 0 D Represents the total number of shares of Common Stock received by Third Rock Ventures II, L.P. ("TRV II") upon conversion of Series A Preferred Stock in connection with the closing of the Issuer's initial public offering. Represents the total number of shares of Common Stock received by Third Rock Ventures III, L.P. ("TRV III") upon conversion of Series A Preferred Stock in connection with the closing of the Issuer's initial public offering. Each share of Series A Preferred Stock converted into Common Stock on a one-for-3.69 basis upon the closing of the Issuer's initial public offering without payment or consideration. Each share of Series A Preferred Stock was convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The Preferred Stock had no expiration date. These shares are directly held by TRV II. The general partner of TRV II is Third Rock Ventures GP II, L.P. ("TRV GP II"). The general partner of TRV GP II is TRV GP II, LLC ("TRV GP II LLC"). The individual managers of TRV GP II LLC are Mark Levin ("Levin"), Kevin Starr ("Starr") and Dr. Robert Tepper ("Tepper"). Each of TRV GP II, TRV GP II LLC, Levin, Starr and Tepper disclaims beneficial ownership of these shares except to the extent of its or his pecuniary interest therein, if any, and this report shall not be deemed an admission that it or he is the beneficial owner of such shares. These shares are directly held by TRV III. The general partner of TRV III is Third Rock Ventures GP III, L.P. ("TRV GP III"). The general partner of TRV GP III is TRV GP III, LLC ("TRV GP III LLC"). The individual managers of TRV GP III LLC are Levin, Starr and Tepper. Each of TRV GP III, TRV GP III LLC, Levin, Starr and Tepper disclaims beneficial ownership of the shares except to the extent of its or his pecuniary interest therein, if any, and this report shall not be deemed an admission that it or he is the beneficial owner of such shares. /s/ Kevin Gillis, Chief Financial Officer of TRV GP II, LLC, general partner of Third Rock Ventures GP II, L.P., general partner of Third Rock Ventures II, L.P. 2017-02-03 /s/ Kevin Gillis, Chief Financial Officer of TRV GP II, LLC, general partner of Third Rock Ventures GP II, L.P. 2017-02-03 /s/ Kevin Gillis, Chief Financial Officer of TRV GP II, LLC 2017-02-03 /s/ Kevin Gillis, Chief Financial Officer of TRV GP III, LLC, general partner of Third Rock Ventures GP III, L.P., general partner of Third Rock Ventures III, L.P. 2017-02-03 /s/ Kevin Gillis, Chief Financial Officer of TRV GP III, LLC, general partner of Third Rock Ventures GP III, L.P. 2017-02-03 /s/ Kevin Gillis, Chief Financial Officer of TRV GP III, LLC 2017-02-03 /s/ Kevin Gillis by power of attorney for Mark Levin 2017-02-03 /s/ Kevin Gillis by power of attorney for Kevin Starr 2017-02-03