| Explanation of Responses: |
| (1) | These sales were effected by the reporting person pursuant to a Rule 10b5-1 trading plan adopted on September 15, 2021, as amended on March 11, 2022. |
| (2) | Represents (i) 63,512 shares sold by Flagship Ventures Fund IV, L.P. ("Flagship Fund IV") and (ii) 12,432 shares sold by Flagship Ventures Fund IV-Rx, L.P. ("Flagship Fund IV-Rx"). The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $129.00 to $129.93, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, 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 range. Following the reported transactions, 3,212,827 shares are held directly by Flagship Fund IV and 2,827,886 shares are held directly by Flagship Fund IV-Rx. |
| (3) | Shares held directly by Flagship Fund IV and Flagship Fund IV-Rx. Flagship Ventures Fund IV General Partner LLC ("Flagship Fund IV GP") is the general partner of each of Flagship Fund IV and Flagship Fund IV-Rx. The reporting person is the sole manager of Flagship Fund IV GP and disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein. |
| (4) | Represents (i) 34,589 shares sold by Flagship Fund IV and (ii) 6,593 shares sold by Flagship Fund IV-Rx. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $130.00 to $130.36, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, 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 range. Following the reported transactions, 3,178,238 shares are held directly by Flagship Fund IV and 2,821,293 shares are held directly by Flagship Fund IV-Rx. |
| (5) | Represents (i) 43,035 shares sold by Flagship Fund IV and (ii) 8,221 shares sold by Flagship Fund IV-Rx. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $131.00 to $131.99, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, 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 range. Following the reported transactions, 3,135,203 shares are held directly by Flagship Fund IV and 2,813,072 shares are held directly by Flagship Fund IV-Rx. |
| (6) | Represents (i) 26,546 shares sold by Flagship Fund IV and (ii) 5,072 shares sold by Flagship Fund IV-Rx. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $132.00 to $132.62, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, 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 range. Following the reported transactions, 3,108,657 shares are held directly by Flagship Fund IV and 2,808,000 shares are held directly by Flagship Fund IV-Rx. |
| (7) | Represents (i) 21,250 shares sold by Flagship Fund IV and (ii) 4,183 shares sold by Flagship Fund IV-Rx. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $133.00 to $133.70, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, 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 range. Following the reported transactions, 3,087,407 shares are held directly by Flagship Fund IV and 2,803,817 shares are held directly by Flagship Fund IV-Rx. |
| (8) | Represents (i) 20,621 shares sold by Flagship Fund IV and (ii) 3,946 shares sold by Flagship Fund IV-Rx. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $134.00 to $134.27, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, 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 range. Following the reported transactions, 3,066,786 shares are held directly by Flagship Fund IV and 2,799,871 shares are held directly by Flagship Fund IV-Rx. |
| (9) | Represents (i) 41,885 shares sold by Flagship Fund IV and (ii) 8,015 shares sold by Flagship Fund IV-Rx. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $135.00 to $135.98, inclusive. The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, 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 range. Following the reported transactions, 3,024,901 shares are held directly by Flagship Fund IV and 2,791,856 shares are held directly by Flagship Fund IV-Rx. |
| (10) | Represents (i) 84 shares sold by Flagship Fund IV and (ii) 16 shares sold by Flagship Fund IV-Rx. Following the reported transactions, 3,024,817 shares are held directly by Flagship Fund IV and 2,791,840 shares are held directly by Flagship Fund IV-Rx. |
| (11) | 11,460,435 shares are held directly by Flagship VentureLabs IV LLC ("VentureLabs IV") and 3,924 shares are held directly by Flagship Pioneering, Inc. ("Flagship Pioneering"). Flagship Fund IV is a member of VentureLabs IV and also serves as its manager. Flagship Fund IV GP is the general partner of Flagship Fund IV. The reporting person is the sole manager of Flagship Fund IV GP and CEO and sole stockholder of Flagship Pioneering and disclaims beneficial ownership of such shares except to the extent of his pecuniary interest therein. |