X0306 4 2018-07-20 0 0001709401 Rubius Therapeutics, Inc. RUBY 0001508051 Flagship Ventures Fund IV General Partner LLC C/O RUBIUS THERAPEUTICS, INC. 325 VASSAR STREET, SUITE 1A CAMBRIDGE MA 02139 1 0 1 0 0001642578 Flagship VentureLabs IV, LLC C/O RUBIUS THERAPEUTICS, INC. 325 VASSAR STREET, SUITE 1A CAMBRIDGE MA 02139 0 0 1 0 0001503559 Flagship Ventures Fund IV, L.P. C/O RUBIUS THERAPEUTICS, INC. 325 VASSAR STREET, SUITE 1A CAMBRIDGE MA 02139 0 0 1 0 0001590973 Flagship Ventures Fund IV-Rx, L.P. C/O RUBIUS THERAPEUTICS, INC. 325 VASSAR STREET, SUITE 1A CAMBRIDGE MA 02139 0 0 1 0 0001627639 Flagship Ventures Fund V, L.P. C/O RUBIUS THERAPEUTICS, INC. 325 VASSAR STREET, SUITE 1A CAMBRIDGE MA 02139 0 0 1 0 0001724939 Flagship V VentureLabs Rx Fund, L.P. C/O RUBIUS THERAPEUTICS, INC. 325 VASSAR STREET, SUITE 1A CAMBRIDGE MA 02139 0 0 1 0 0001677345 Flagship Ventures Opportunities Fund I, L.P. C/O RUBIUS THERAPEUTICS, INC. 325 VASSAR STREET, SUITE 1A CAMBRIDGE MA 02139 0 0 1 0 0001222012 AFEYAN NOUBAR C/O RUBIUS THERAPEUTICS, INC. 325 VASSAR STREET, SUITE 1A CAMBRIDGE MA 02139 1 0 1 0 0001255927 KANIA EDWIN M JR C/O RUBIUS THERAPEUTICS, INC. 325 VASSAR STREET, SUITE 1A CAMBRIDGE MA 02139 0 0 1 0 Common Stock 5000000 I See Footnote Common Stock 2018-07-20 4 C 0 15323593 A 15323593 I See Footnote Common Stock 2018-07-20 4 C 0 3830402 A 3830402 I See Footnote Common Stock 2018-07-20 4 C 0 5000000 A 5000000 I See Footnote Common Stock 2018-07-20 4 C 0 5000000 A 5000000 I See Footnote Common Stock 2018-07-20 4 C 0 593948 A 5593948 I See Footnote Common Stock 2018-07-20 4 C 0 593948 A 5593948 I See Footnote Common Stock 2018-07-20 4 C 0 1781843 A 1781843 I See Footnote Common Stock 2018-07-20 4 C 0 195466 A 5789414 I See Footnote Common Stock 2018-07-20 4 C 0 195466 A 5789414 I See Footnote Common Stock 2018-07-20 4 C 0 781860 A 2563703 I See Footnote Series A Preferred Stock 2018-07-20 4 C 0 15323593 D Common Stock 15323593 0 I See Footnote Series A Preferred Stock 2018-07-20 4 C 0 3830402 D Common Stock 3830402 0 I See Footnote Series A Preferred Stock 2018-07-20 4 C 0 5000000 D Common Stock 5000000 0 I See Footnote Series A Preferred Stock 2018-07-20 4 C 0 5000000 D Common Stock 5000000 0 I See Footnote Series B Preferred Stock 2018-07-20 4 C 0 593948 D Common Stock 593948 0 I See Footnote Series B Preferred Stock 2018-07-20 4 C 0 593948 D Common Stock 593948 0 I See Footnote Series B Preferred Stock 2018-07-20 4 C 0 1781843 D Common Stock 1781843 0 I See Footnote Series C Preferred Stock 2018-07-20 4 C 0 195466 D Common Stock 195466 0 I See Footnote Series C Preferred Stock 2018-07-20 4 C 0 195466 D Common Stock 195466 0 I See Footnote Series C Preferred Stock 2018-07-20 4 C 0 781860 D Common Stock 781860 0 I See Footnote Shares 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. The 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. Shares 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. Shares 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. Shares 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. Shares 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. Shares 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. Flagship Ventures Fund IV General Partner LLC By: /s/ Noubar B. Afeyan Name: Noubar B. Afeyan, Ph.D. Title: Manager 2018-07-23 Flagship VentureLabs IV LLC By: Flagship Ventures Fund IV, L.P., its manager By: Flagship Ventures Fund IV General Partner LLC, its general partner By: /s/ Noubar B. Afeyan Name: Noubar B. Afeyan, Ph.D. Title: Manager 2018-07-23 Flagship Ventures Fund IV, L.P. By: Flagship Ventures Fund IV General Partner LLC, its general partner By: /s/ Noubar B. Afeyan Name: Noubar B. Afeyan, Ph.D. Title: Manager 2018-07-23 Flagship Ventures Fund V, L.P. By: Flagship Ventures Fund V General Partner LLC, its general partner By: /s/ Noubar B. Afeya Name: Noubar B. Afeyan, Ph.D. Title: Manager 2018-07-23 Flagship VentureLabs Rx Fund, L.P. By: Flagship Ventures Fund V General Partner LLC, its general partner By: /s/ Noubar B. Afeya Name: Noubar B. Afeyan, Ph.D. Title: Manager 2018-07-23 Flagship Ventures Opportunities Fund I, L.P. By: Flagship Ventures Fund V General Partner LLC, its general partner By: /s/ Noubar B. Afeya Name: Noubar B. Afeyan, Ph.D. Title: Manager 2018-07-23 /s/ Noubar B. Afeyan Ph.D. 2018-07-23 /s/ Edwin M. Kania, Jr. 2018-07-23