X0306 4 2023-01-03 0 0001287098 MAXCYTE, INC. MXCT 0001874482 Doerfler Douglas C/O MAXCYTE, INC. 9713 KEY WEST AVENUE, SUITE 400 ROCKVILLE MD 20850 1 1 0 0 President and CEO Common Stock 2023-01-03 4 M 0 10613 0.04 A 343810 D Common Stock 2023-01-03 4 S 0 10613 5.13 D 333197 D Common Stock 2023-01-04 4 M 0 9153 0.04 A 342350 D Common Stock 2023-01-04 4 S 0 9153 5.07 D 333197 D Common Stock 2023-01-05 4 M 0 10234 0.04 A 343431 D Common Stock 2023-01-05 4 S 0 10234 5.04 D 333197 D Employee Stock Option (right to buy) 0.04 2023-01-03 4 M 0 10613 0.00 D 2024-11-11 Common Stock 10613 434467 D Employee Stock Option (right to buy) 0.04 2023-01-04 4 M 0 9153 0.00 D 2024-11-11 Common Stock 9153 425314 D Employee Stock Option (right to buy) 0.04 2023-01-05 4 M 0 10234 0.00 D 2024-11-11 Common Stock 10234 415080 D The sales and option exercises reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on November 18, 2022 relating solely to the sale of shares acquired from exercise of an option that expires on November 11, 2024. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $5.00 to $5.49, 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 set forth in this footnote to this Form 4. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $5.00 to $5.19, 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 set forth in this footnote to this Form 4. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $5.00 to $5.14, 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 set forth in this footnote to this Form 4. This option is fully vested and exercisable. /s/ Brian F. Leaf, attorney-in-fact 2023-01-05