Security	Date	Code	Shares	Price	A/D	Owned after	D/I
Common Stock^F2	Jun 19, 2015	J	1,000,000	$0.00	D	8,773,073	D
Common Stock^F4	Jun 19, 2015	J	64,607	$0.00	A	64,607	D
Common Stock^F4	Jun 19, 2015	J	64,607	$0.00	D	0	D
Common Stock	Jun 19, 2015	J	9,402	$0.00	A	27,330	D
Common Stock	Jun 19, 2015	J	9,403	$0.00	A	27,331	D

Table II — derivative securities

No Table II lines on this filing.

Explanation of responses

F1Distribution of shares in kind by Third Rock Ventures II, L.P. ("TRV") on a pro rata basis to its partners.
F2The shares are directly held by Third Rock Ventures II, L.P. ("TRV"). The general partner of TRV is Third Rock Ventures GP II, L.P. ("TRV GP"). The general partner of TRV GP is TRV GP II, LLC ("TRV GP LLC"). The individual managers of TRV GP LLC are Mark Levin ("Levin"), Kevin Starr ("Starr") and Dr. Robert Tepper ("Tepper") and, as such, each of TRV GP, TRV GP LLC, Levin, Starr and Tepper exercises shared voting and investment power over the shares held of record by TRV. Each of the Reporting Persons disclaims beneficial ownership of the shares except to the extent of their pecuniary interest therein, if any.
F3TRV GP received shares distributed in kind by TRV on a pro rata basis to its partners.
F4The shares are directly held by TRV GP. As such, each of TRV GP LLC, Levin, Starr and Tepper exercises shared voting and investment power over the shares held of record TRV GP. Each of the Reporting Persons disclaims beneficial ownership of the shares except to the extent of its pecuniary interest therein, if any.
F5Distribution of shares in kind by TRV GP on a pro rata basis to its partners.
F6Levin received shares distributed in kind by TRV GP on a pro rata basis to its partners.
F7Tepper received shares distributed in kind by TRV GP on a pro rata basis to its partners.