SGTX Sigilon Therapeutics Inc

+ Online Go to www.envisionreports.com/SGTX or scan the QR code — login details are located in the shaded bar below. Votes submitted electronically must be received by May 26, 2022, at 1:00 A.M. EDT. Important Notice Regarding the Availability of Proxy Materials for the Sigilon Therapeutics, Inc. Stockholder Meeting to be Held on May 26, 2022 Under Securities and Exchange Commission rules, you are receiving this notice that the proxy materials for the annual stockholders’ meeting are available on the Internet. Follow the instructions below to view the materials and vote online or request a copy. The items to be voted on and location of the annual meeting are on the reverse side. Your vote is important! This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. We encourage you to access and review all of the important information contained in the proxy materials before voting. The 2022 proxy statement and annual report to stockholders are available at: www.envisionreports.com/SGTX Easy Online Access — View your proxy materials and vote. Step 1: Step 2: Step 3: Step 4: Step 5: Go to www.envisionreports.com/SGTX. Click on Cast Your Vote or Request Materials. Follow the instructions on the screen to log in. Make your selections as instructed on each screen for your delivery preferences. Vote your shares. When you go online, you can also help the environment by consenting to receive electronic delivery of future materials. Obtaining a Copy of the Proxy Materials – If you want to receive a copy of the proxy materials, you must request one. There is no charge to you for requesting a copy. Please make your request as instructed on the reverse side on or before May 13, 2022 to facilitate timely delivery. + 2 N O T 03M2QD Stockholder Meeting Notice

The 2022 Annual Meeting of Stockholders of Sigilon Therapeutics, Inc. will be held on May 26, 2022 at 8 am EDT, at Sigilon Therapeutics, Inc., 100 Binney Street, Suite 600, Cambridge, Massachusetts. Proposals to be voted on at the meeting are listed below along with the Board of Directors’ recommendations. The Board of Directors recommend a vote FOR all the nominees listed and FOR Proposal 2: 1.Election of Directors: 01 - Rogerio Vivaldi Coelho, M.D. 02 - John Cox 03 – Kavita Patel, M.D. 2.To ratify the appointment of PricewaterhouseCoopers LLP as Sigilon Therapeutic, Inc.’s independent registered public accounting firm for the fiscal year ending December 31, 2022. PLEASE NOTE – YOU CANNOT VOTE BY RETURNING THIS NOTICE. To vote your shares you must go online or request a paper copy of the proxy materials to receive a proxy card. Here’s how to order a copy of the proxy materials and select delivery preferences: Current and future delivery requests can be submitted using the options below. If you request an email copy, you will receive an email with a link to the current meeting materials. PLEASE NOTE: You must use the number in the shaded bar on the reverse side when requesting a copy of the proxy materials. — — — Internet – Go to www.envisionreports.com/SGTX. Click Cast Your Vote or Request Materials. Phone – Call us free of charge at 1-866-641-4276. Email – Send an email to investorvote@computershare.com with “Proxy Materials Sigilon Therapeutics, Inc.” in the subject line. Include your full name and address, plus the number located in the shaded bar on the reverse side, and state that you want a paper copy of the meeting materials. To facilitate timely delivery, all requests for a paper copy of proxy materials must be received by May 13, 2022. Stockholder Meeting Notice