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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% |  |  | 
| 
                Baillie Gifford & Co(4)
               |  |  |  |  | 4,869,126 |  |  |  |  |  | 5.4% |  |  | 
| Named Executive Officers and Directors: |  |  |  |  |  |  |  |  |  |  |  |  |  | 
| 
                Pablo J. Cagnoni, M.D.(5) 
               |  |  |  |  | 4,617,478 |  |  |  |  |  | 4.9% |  |  | 
| 
                Jose Carmona(6) 
               |  |  |  |  | — |  |  |  |  |  | — |  |  | 
| 
                Dannielle Appelhans(7) 
               |  |  |  |  | 97,885 |  |  |  |  |  | * |  |  | 
| 
                Maiken Keson-Brookes(8) 
               |  |  |  |  | 5,343 |  |  |  |  |  | * |  |  | 
| 
                Laurence Turka, M.D.(9) 
               |  |  |  |  | 382,452 |  |  |  |  |  | * |  |  | 
| 
                Catherine A. Sohn, Pharm.D.(10) 
               |  |  |  |  | 232,500 |  |  |  |  |  | * |  |  | 
| 
                Sir Jonathan R. Symonds, CBE(11) 
               |  |  |  |  | 295,000 |  |  |  |  |  | * |  |  | 
| 
                All executive officers and directors as a group (7 persons)(12)
               |  |  |  |  | 5,630,658 |  |  |  |  |  | 5.9% |  |  |