Security	Date	Code	Shares	Price	A/D	Owned after	D/I	Nature of ownership
Common Stock^F1,F2	Feb 8, 2016	C	2,039,549	—	A	2,039,549	D
Common Stock^F1,F2	Feb 8, 2016	C	1,617,015	—	A	3,656,564	D
Common Stock^F1,F2	Feb 8, 2016	C	307,692	—	A	3,964,256	D
Common Stock^F1,F3	Feb 8, 2016	C	509,885	—	A	509,885	I	See Footnote
Common Stock^F1,F3	Feb 8, 2016	C	404,253	—	A	914,138	I	See Footnote
Common Stock^F1,F3	Feb 8, 2016	C	76,922	—	A	991,060	I	See Footnote

Table II — derivative securities

Security	Conv. / exercise price	Date	Code	Shares	A/D	Exercisable	Expires	Underlying	Underlying shares	D/I
Series A-1 Preferred Stock^F2,F1	—	Feb 8, 2016	C	5,302,834	D	—	—	Common Stock	2,039,549	D
Series A-2 Preferred Stock^F2,F1	—	Feb 8, 2016	C	4,204,240	D	—	—	Common Stock	1,617,015	D
Series B Preferred Stock^F2,F1	—	Feb 8, 2016	C	800,001	D	—	—	Common Stock	307,692	D
Series A-1 Preferred Stock^F3,F1	—	Feb 8, 2016	C	1,325,708	D	—	—	Common Stock	509,885	I
Series A-2 Preferred Stock^F3,F1	—	Feb 8, 2016	C	1,051,060	D	—	—	Common Stock	404,253	I
Series B Preferred Stock^F3,F1	—	Feb 8, 2016	C	199,999	D	—	—	Common Stock	76,922	I

Explanation of responses

F1The Series A-1, Series A-2 and Series B Preferred Stock converted into Common Stock on a 2.6-for-one basis upon the closing of the Issuer's initial public offering without payment of consideration. The Series A-1, Series A-2 and B Preferred Stock were convertible at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering. The shares had no expiration date.
F2Held by Flagship Ventures Fund IV, L.P. ("Flagship IV"). Flagship Ventures Fund IV General Partner LLC ("Flagship IV LLC") is the general partner of Flagship IV. Noubar B. Afeyan, Ph.D. and Edwin M. Kania, Jr. are the managers of Flagship IV LLC. Flagship IV LLC and each of these individuals may be deemed to share voting and investment power with respect to all shares held by Flagship IV. Each of the filing persons other than Flagship IV disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.
F3Held by Flagship Ventures Fund IV-Rx, L.P. ("Flagship IV-Rx"). Flagship IV LLC is the general partner of Flagship IV-Rx. Noubar B. Afeyan, Ph.D. and Edwin M. Kania, Jr. are the managers of Flagship IV LLC. Flagship IV LLC and each of these individuals may be deemed to share voting and investment power with respect to all shares held by Flagship IV-Rx. Each of the filing persons other than Flagship IV-Rx disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.