X0306 4 2022-01-29 0 0001709401 Rubius Therapeutics, Inc. RUBY 0001205703 CAGNONI PABLO J C/O RUBIUS THERAPEUTICS, INC. 399 BINNEY STREET, SUITE 300 CAMBRIDGE MA 02139 1 1 0 0 CEO and President Common Stock 2022-01-29 4 M 0 21250 A 42250 D Common Stock 2022-02-01 4 S 0 6730 6.573 D 35520 D Restricted Stock Units 2022-01-29 4 M 0 21250 0 D Common Stock 21250 63750 D Stock Option (Right to Buy) 6.75 2022-01-31 4 A 0 365000 0 A 2032-01-30 Common Stock 365000 365000 D Restricted Stock Units 2022-01-31 4 A 0 100000 0 A Common Stock 100000 100000 D Each restricted stock unit represents a contingent right to receive one share of the Issuer's common stock. Represents the number of shares required to be sold to cover the statutory tax withholding obligations in connection with the vesting of the restricted stock units listed in Table II. This sale is mandated by the Issuer's election under its equity incentive plans to require the satisfaction of minimum statutory tax withholding obligations to be funded by a "sell to cover" transaction and does not represent a discretionary sale by the reporting person. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $6.57 to $6.72, inclusive. The reporting person undertakes to provide to Rubius Therapeutics, Inc., any security holder of Rubius Therapeutics, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in this footnote. The shares underlying the restricted stock units vest in four equal annual installments beginning on January 29, 2022. 25% of this option shall vest on January 31, 2023, then in 12 equal quarterly installments thereafter. The shares underlying the restricted stock units vest in four equal annual installments beginning on January 31, 2023. /s/ Joanne M. Protano, Attorney-in-Fact 2022-02-01