Security	Date	Code	Shares	Price	A/D	Owned after	D/I	Nature of ownership
Common Stock^F2,F3	Jul 20, 2018	C	15,323,593	—	A	15,323,593	I	See Footnote
Common Stock^F2,F4	Jul 20, 2018	C	3,830,402	—	A	3,830,402	I	See Footnote
Common Stock^F2,F5	Jul 20, 2018	C	5,000,000	—	A	5,000,000	I	See Footnote
Common Stock^F2,F6	Jul 20, 2018	C	5,000,000	—	A	5,000,000	I	See Footnote
Common Stock^F2,F5	Jul 20, 2018	C	593,948	—	A	5,593,948	I	See Footnote
Common Stock^F2,F6	Jul 20, 2018	C	593,948	—	A	5,593,948	I	See Footnote
Common Stock^F2,F7	Jul 20, 2018	C	1,781,843	—	A	1,781,843	I	See Footnote
Common Stock^F2,F5	Jul 20, 2018	C	195,466	—	A	5,789,414	I	See Footnote
Common Stock^F2,F6	Jul 20, 2018	C	195,466	—	A	5,789,414	I	See Footnote
Common Stock^F2,F7	Jul 20, 2018	C	781,860	—	A	2,563,703	I	See Footnote
Common Stock^F1	holding	—	—		—	5,000,000	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 Preferred Stock^F2,F3	—	Jul 20, 2018	C	15,323,593	D	—	—	Common Stock	15,323,593	I
Series A Preferred Stock^F2,F4	—	Jul 20, 2018	C	3,830,402	D	—	—	Common Stock	3,830,402	I
Series A Preferred Stock^F2,F5	—	Jul 20, 2018	C	5,000,000	D	—	—	Common Stock	5,000,000	I
Series A Preferred Stock^F2,F6	—	Jul 20, 2018	C	5,000,000	D	—	—	Common Stock	5,000,000	I
Series B Preferred Stock^F2,F5	—	Jul 20, 2018	C	593,948	D	—	—	Common Stock	593,948	I
Series B Preferred Stock^F2,F6	—	Jul 20, 2018	C	593,948	D	—	—	Common Stock	593,948	I
Series B Preferred Stock^F2,F7	—	Jul 20, 2018	C	1,781,843	D	—	—	Common Stock	1,781,843	I
Series C Preferred Stock^F2,F5	—	Jul 20, 2018	C	195,466	D	—	—	Common Stock	195,466	I
Series C Preferred Stock^F2,F6	—	Jul 20, 2018	C	195,466	D	—	—	Common Stock	195,466	I
Series C Preferred Stock^F2,F7	—	Jul 20, 2018	C	781,860	D	—	—	Common Stock	781,860	I

Explanation of responses

F1Shares held by Flagship VentureLabs IV LLC ("VentureLabs IV"). Flagship Ventures Fund IV, L.P. ("Flagship Fund IV") is a member of VentureLabs IV and also serves as its manager. 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. Each of these individuals and entities may be deemed to share voting and investment power with respect to all shares held by VentureLabs IV. Each of the filing persons disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.
F2The preferred stock is convertible into the Issuer's common stock on a one-for-one basis at the holder's election and has no expiration date. The preferred stock automatically convert into common stock upon the closing of the Issuer's initial public offering held on July 20, 2018.
F3Shares held by Flagship Fund IV. 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 such shares except to the extent of his or its pecuniary interest therein.
F4Shares held by Flagship Ventures Fund IV-Rx, L.P. ("Flagship Fund 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. 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 such shares except to the extent of his or its pecuniary interest therein.
F5Shares held by Flagship Ventures Fund V, L.P. ("Flagship Fund V"). Flagship Ventures Fund V General Partner LLC ("Flagship Fund V GP") is the general partner of Flagship Fund V. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Fund V GP and may be deemed to possess sole voting and investment power with respect to all shares held by Flagship Fund V. Each of the filing persons disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.
F6Shares held by Flagship V VentureLabs Rx Fund, L.P. ("VentureLabs Rx V"). Flagship Fund V GP is the general partner of VentureLabs Rx V. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Fund V GP and may be deemed to possess sole voting and investment power with respect to all shares held by VentureLabs Rx V. Each of the filing persons disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.
F7Shares held by Flagship Ventures Opportunities Fund I, L.P. ("Flagship Opportunities Fund I"). Flagship Ventures Opportunities Fund I General Partner LLC ("Flagship Opportunities GP") is the general partner of Flagship Opportunities I. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Opportunities GP and may be deemed to possess sole voting and investment power with respect to all shares held by Flagship Opportunities I. Each of the filing persons disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein.