X0306 4 2020-05-18 0 0001633070 Axcella Health Inc. AXLA 0001508051 Flagship Ventures Fund IV General Partner LLC C/O FLAGSHIP PIONEERING INC. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001503559 Flagship Ventures Fund IV, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001590973 Flagship Ventures Fund IV-Rx, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001725004 Flagship Ventures Opportunities Fund I General Partner LLC 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001677345 Flagship Ventures Opportunities Fund I, L.P. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001222012 AFEYAN NOUBAR 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 Common Stock 2020-05-18 4 P 0 1520000 4.75 A 4808780 I See Footnote Common Stock 2020-05-18 4 P 0 380000 4.75 A 1056752 I See Footnote Common Stock 2020-05-18 4 P 0 1900000 4.75 A 2886023 I See Footnote Common Stock 2035830 I See Footnote Common Stock 1761029 I See Footnote Shares held 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. is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for Flagship Fund IV disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Edwin M. Kania, Jr. is retired both from Flagship Pioneering, Inc. and as a manager of Flagship Fund IV GP. Shares held by Flagship Ventures Fund IV-Rx, L.P. ("Flagship Fund IV-Rx"). Flagship Fund IV GP is the general partner of Flagship Fund IV-Rx. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for Flagship Fund IV-Rx disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship Ventures Opportunities Fund I, L.P. ("Flagship Opportunities 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. Each of the reporting persons except for Flagship Opportunities I disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship VentureLabs IV, LLC ("VentureLabs IV"). Flagship Fund IV is a member of VentureLabs IV and also serves as its manager. Flagship Fund IV GP is the general partner of Flagship Fund IV. Noubar B. Afeyan, Ph.D. is the sole manager of Flagship Fund IV GP. Each of the reporting persons except for VentureLabs IV disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship Ventures Fund 2007, L.P. ("Flagship Fund 2007"). Flagship Ventures 2007 General Partner LLC ("Fund 2007 GP") is the general partner of Flagship Fund 2007. Noubar B. Afeyan, Ph.D. is the sole manager of Fund 2007 GP. Each of the reporting persons except for Flagship Fund 2007 disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Edwin M. Kania, Jr. is retired both from Flagship Pioneering, Inc. and as a manager of Fund 2007 GP. Flagship Ventures Fund IV General Partner LLC, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 2020-05-20 Flagship Ventures Fund IV, L.P., By: Flagship Ventures Fund IV General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 2020-05-20 Flagship Ventures Fund IV-Rx, L.P., By: Flagship Ventures Fund IV General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 2020-05-20 Flagship Ventures Opportunities Fund I General Partner LLC, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 2020-05-20 Flagship Ventures Opportunities Fund I, L.P. By: Flagship Ventures Opportunities Fund I General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan, Ph.D., Name: Noubar B. Afeyan, Ph.D., Title: Manager 2020-05-20 Noubar B. Afeyan, Ph.D. By: /s/ Noubar B. Afeyan, Ph.D. 2020-05-20