X0306 4 2021-02-01 0 0001661998 Homology Medicines, Inc. FIXX 0001754067 Kelly Timothy P C/O HOMOLOGY MEDICINES, INC. ONE PATRIOTS PARK BEDFORD MA 01730 0 1 0 0 See Remarks Common Stock 2021-02-01 4 M 0 2000 6.6314 A 2000 D Common Stock 2021-02-01 4 M 0 2000 2.8947 A 4000 D Common Stock 2021-02-01 4 S 0 4000 12.365 D 0 D Employee Stock Options 6.6314 2021-02-01 4 M 0 2000 0.00 D 2027-12-06 Common Stock 2000 43500 D Employee Stock Options 2.8947 2021-02-01 4 M 0 2000 0.00 D 2027-09-06 Common Stock 2000 34001 D The sale reported in the Form 4 was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on December 3, 2020. The price reported is a weighted average price. The shares were sold in multiple transactions at per share prices ranging from $12.13 to $12.3680. The Reporting Person undertakes to provide upon request to the SEC staff, the Issuer, or any stockholder of the Issuer, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The option vests and becomes exercisable upon the Reporting Person's completion of each full month of service after January 1, 2018, so that such option will become fully vested on January 1, 2022. The option vests and becomes exercisable as to 25% of the total grant on the first anniversary of the vesting commencement date and vests in equal monthly installments over a three year period thereafter. The vesting commencement date for this option was May 30, 2017. Chief Technical Operations Officer /s/ Bradford Smith, Attorney-in-Fact for Timothy P. Kelly 2021-02-03