X0206 3 2020-12-03 0 0001821323 Sigilon Therapeutics, Inc. SGTX 0001724575 Flagship Ventures Fund V General Partner LLC C/O FLAGSHIP PIONEERING INC. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001627639 Flagship Ventures Fund V, L.P. C/O FLAGSHIP PIONEERING INC. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001761283 Flagship Pioneering Special Opportunities Fund II, L.P. C/O FLAGSHIP PIONEERING INC. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001826217 Flagship Pioneering Special Opportunities Fund II General Partner LLC C/O FLAGSHIP PIONEERING INC. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001400240 Flagship Pioneering Inc. C/O FLAGSHIP PIONEERING INC. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 0001222012 AFEYAN NOUBAR C/O FLAGSHIP PIONEERING INC. 55 CAMBRIDGE PARKWAY, SUITE 800E CAMBRIDGE MA 02142 0 0 1 0 Series A Convertible Preferred Stock Common Stock 4444444 I See Footnote Series A-1 Convertible Preferred Stock Common Stock 4074074 I See Footnote Series B Convertible Preferred Stock Common Stock 370370 I See Footnote Series B Convertible Preferred Stock Common Stock 1481481 I See Footnote The Series A Convertible Preferred Stock, Series A-1 Convertible Preferred Stock and Series B Convertible Preferred Stock (collectively, the "Preferred Stock") is convertible into the number of shares of the Registrant's common stock shown in column 3 and has no expiration date. The Preferred Stock will automatically convert into common stock upon the closing of the Registrant's initial public offering. Shares held by Flagship Ventures Fund V, L.P. ("Flagship Fund V"). Flagship Ventures Fund V General Partner LLC ("Fund V GP") is the general partner of Flagship Fund V. Noubar B. Afeyan Ph.D. serves as the sole manager of Fund V GP. Each of Fund V GP and Noubar B. Afeyan Ph.D. disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Shares held by Flagship Pioneering Special Opportunities Fund II, L.P. ("Flagship Opportunities Fund II"). Flagship Pioneering Special Opportunities Fund II General Partner LLC ("Opportunities Fund II GP") is the general partner of Flagship Opportunities Fund II. Flagship Pioneering, Inc. ("Flagship Pioneering") is the manager of Opportunities Fund II GP. Noubar B. Afeyan, Ph.D. is sole director of Flagship Pioneering. Each of Noubar B. Afeyan Ph.D., Flagship Pioneering, and Opportunities Fund II GP disclaims beneficial ownership of such shares except to the extent of his or its pecuniary interest therein. Flagship Ventures Fund V, L.P., By: Flagship Ventures Fund V General Partner LLC, its general partner, By: /s/ Noubar B. Afeyan Ph.D., Title: Manager 2020-12-03 Flagship Ventures Fund V General Partner LLC, By: /s/ Noubar B. Afeyan Ph.D., Title: Manager 2020-12-03 Flagship Pioneering Special Opportunities Fund II, L.P., By: Flagship Pioneering, Inc. its manager, By: /s/ Noubar B. Afeyan Ph.D., Title: CEO, Flagship Pioneering, Inc. 2020-12-03 Flagship Pioneering Special Opportunities Fund II General Partner LLC, By: /s/ Noubar B. Afeyan Ph.D., Title: Manager 2020-12-03 Flagship Pioneering, Inc., /s/ Noubar B. Afeyan Ph.D., Title: CEO 2020-12-03 /s/ Noubar B. Afeyan Ph.D. 2020-12-03