X0407 4 2023-04-10 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 1 Common Stock 2023-04-10 4 M 0 100 0.04 A 333297 D Common Stock 2023-04-10 4 S 0 100 5.00 D 333197 D Common Stock 2023-04-11 4 M 0 2182 0.04 A 335379 D Common Stock 2023-04-11 4 S 0 2182 5.00 D 333197 D Common Stock 2023-04-12 4 M 0 12718 0.04 A 345915 D Common Stock 2023-04-12 4 S 0 12718 5.00 D 333197 D Employee Stock Option (right to buy) 0.04 2023-04-10 4 M 0 100 0.00 D 2024-11-11 Common Stock 100 339980 D Employee Stock Option (right to buy) 0.04 2023-04-11 4 M 0 2182 0.00 D 2024-11-11 Common Stock 2182 337798 D Employee Stock Option (right to buy) 0.04 2023-04-12 4 M 0 12718 0.00 D 2024-11-11 Common Stock 12718 325080 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 $5.025, 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. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $5.00 to $5.001, 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. This option is fully vested and exercisable. /s/ Brian F. Leaf, Attorney-in-Fact 2023-04-12