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                Shares beneficially owned 
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| 
                Name and address of beneficial owner 
               |  |  | 
                Number 
               |  |  | 
                Percentage 
               |  | ||||||
| 5% Stockholders: |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| 
                Entities affiliated with the Flagship Pioneering Funds(1) 
               |  |  |  |  | 38,506,526 |  |  |  |  |  | 42.6% |  |  | 
| 
                FMR LLC(2) 
               |  |  |  |  | 12,376,153 |  |  |  |  |  | 13.7% |  |  | 
| 
                David R. Epstein(3) 
               |  |  |  |  | 4,900,012 |  |  |  |  |  | 5.4% |  |  | 
| 
                Named Executive Officers and Directors: 
               |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| 
                Pablo J. Cagnoni, M.D.(4) 
               |  |  |  |  | 4,617,478 |  |  |  |  |  | 4.9% |  |  | 
| 
                Jose Carmona(5) 
               |  |  |  |  | — |  |  |  |  |  | — |  |  | 
| 
                Craig Jalbert   |  |  |  |  | — |  |  |  |  |  | — |  |  | 
| 
                Dannielle Appelhans(6)   |  |  |  |  | 87,500 |  |  |  |  |  | * |  |  | 
| 
                Maiken Keson-Brookes(7)   |  |  |  |  | 5,343 |  |  |  |  |  | * |  |  | 
| 
                Laurence Turka, M.D.(8)   |  |  |  |  | 382,452 |  |  |  |  |  | * |  |  | 
| 
                All executive officers and directors as a group (6 persons)(9)   |  |  |  |  | 5,092,773 |  |  |  |  |  | 5.3% |  |  | 
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