Security	Date	Code	Shares	Price	A/D	Owned after	D/I	Nature of ownership
Common Stock, $0.001 par value^F4,F1	Jun 26, 2015	C	8,822,420	—	A	8,822,420	I	See Footnote
Common Stock, $0.001 par value^F4,F2	Jun 26, 2015	C	2,205,603	—	A	2,205,603	I	See Footnote
Common Stock, $0.001 par value^F4,F3	Jun 26, 2015	C	599,297	—	A	599,297	I	See Footnote
Common Stock, $0.001 par value^F6	holding	—	—		—	3,055,556	I	See Footnote

Table II — derivative securities

Security	Conv. / exercise price	Date	Code	Shares	A/D	Exercisable	Expires	Underlying	Underlying shares	Owned after	D/I
Series A Convertible Preferred Stock^F1,F4	—	Jun 26, 2015	C	6,105,362	D	—	—	Common Stock	6,105,362	0	I
Series A Convertible Preferred Stock^F2,F4	—	Jun 26, 2015	C	1,526,338	D	—	—	Common Stock	1,526,338	0	I
Series A Convertible Preferred Stock^F3,F4	—	Jun 26, 2015	C	599,297	D	—	—	Common Stock	599,297	0	I
Series A-2 Convertible Preferred Stock^F1,F4	—	Jun 26, 2015	C	898,877	D	—	—	Common Stock	898,877	0	I
Series A-2 Convertible Preferred Stock^F2,F4	—	Jun 26, 2015	C	224,719	D	—	—	Common Stock	224,719	0	I
Series B Convertible Preferred Stock^F1,F4	—	Jun 26, 2015	C	1,818,181	D	—	—	Common Stock	1,818,181	0	I
Series B Convertible Preferred Stock^F2,F4	—	Jun 26, 2015	C	454,546	D	—	—	Common Stock	454,546	0	I
Stock Option (right to buy)^F5	$18.00	Jun 25, 2015	A	15,000	A	—	Jun 24, 2025	Common Stock	15,000	15,000	I

Explanation of responses

F1Held by Flagship Ventures Fund IV, L.P. ("Flagship Fund IV"). Flagship Ventures Fund IV General Partner LLC ("Flagship Fund IV GP") is the general partner of Flagship Fund IV. Noubar B. Afeyan, Ph.D. and Edwin M. Kania, Jr. are the managers of Flagship Fund IV GP and each of these individuals may be deemed to share voting and investment power with respect to all shares held by Flagship Fund IV. Each of the filing persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.
F2Held by Flagship Ventures Fund IV-Rx, L.P. ("Flagship IV-Rx"). Flagship Fund IV GP is the general partner of Flagship IV Rx. Noubar B. Afeyan, Ph.D. and Edwin M. Kania, Jr. are the managers of Flagship Fund IV GP 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 disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.
F3Held by Flagship Ventures Fund 2007, L.P. ("Flagship 2007"). Flagship Ventures 2007 General Partner LLC ("Flagship 2007 LLC") is the general partner of Flagship 2007. Noubar B. Afeyan, Ph.D. and Edwin M. Kania, Jr. are the managers of Flagship 2007 LLC and each of these individuals may be deemed to share voting and investment power with respect to all shares held by Flagship 2007. Each of the filing persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.
F4Each class of preferred stock converted into Common Stock on a one-for-one basis upon the listing of the issuer's securities on The NASDAQ Global Select Exchange and had no expiration date.
F5Held by Noubar B. Afeyan, Ph.D. The option will vest as to 25% of the shares on June 25, 2016. The remainder of the shares will vest in 12 equal monthly installments.
F6Held by Flagship VentureLabs IV LLC ("Flagship VentureLabs"). Flagship Fund IV is a member of Flagship VentureLabs and also serves as its manager. Flagship Fund IV GP is the general partner of Flagship Fund IV. Noubar B. Afeyan, Ph.D. and Edwin M. Kania, Jr. are the managers of Flagship Fund IV GP. Each of these individuals and entities may be deemed to share voting and investment power with respect to all shares held by Flagship VentureLabs. Each of the filing persons disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.