X0306 4 2021-11-12 0 0001287098 MAXCYTE, INC. MXCT 0001874571 Masoud Maher C/O MAXCYTE, INC. 22 FIRSTFIELD ROAD, SUITE 110 GAITHERSBURG MD 20878 0 1 0 0 EVP and General Counsel Common Stock 2021-11-12 4 M 0 25722 2.08 A 25722 D Common Stock 2021-11-12 4 S 0 25722 12.66 D 0 D Common Stock 2021-11-15 4 M 0 24278 2.08 A 24278 D Common Stock 2021-11-15 4 M 0 6438 3.25 A 30716 D Common Stock 2021-11-15 4 S 0 30716 12.16 D 0 D Common Stock 2021-11-16 4 M 0 18562 3.25 A 18562 D Common Stock 2021-11-16 4 S 0 18562 12.08 D 0 D Employee Stock Option (right to buy) 2.08 2021-11-12 4 M 0 25722 0.00 D 2030-02-25 Common Stock 25722 99278 D Employee Stock Option (right to buy) 2.08 2021-11-15 4 M 0 24278 0.00 D 2030-02-25 Common Stock 24278 75000 D Employee Stock Option (right to buy) 3.25 2021-11-15 4 M 0 6438 0.00 D 2027-07-14 Common Stock 6438 18562 D Employee Stock Option (right to buy) 3.25 2021-11-16 4 M 0 18562 0.00 D 2027-07-14 Common Stock 18562 0 D This exercise price is in U.S. Dollars and reflects the conversion of GBP to USD at an exchange rate of GBP 1.00 to $1.34. The price reported is a weighted average price. The shares were sold in multiple transactions at prices ranging from $12.56 to $12.765, 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 $12.03 to $12.615, 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 $12.00 to $12.20, 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 shares underlying this option vested or shall vest monthly in forty-eight (48) equal monthly installments commencing on March 25, 2020, subject to the Reporting Person's continued service to the Issuer through each vesting date. This option is fully vested and exercisable. /s/ Brian F. Leaf, attorney-in-fact 2021-11-16