#1editas January 2024 MEDICINE Corporate Presentation Dima, Tristan, & Stephanie#2Forward Looking Statements This presentation contains forward-looking statements and information within the meaning of The Private Securities Litigation Reform Act of 1995. The words "anticipate," "believe," "continue," "could," "estimate," "expect," "intend," "may," "plan," "potential," "predict," "project," "target," "should," "would," and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. Forward-looking statements in this presentation include statements regarding the initiation, timing, progress and results of the Company's preclinical and clinical studies and its research and development programs, including initiating the adolescent cohort in the RUBY trial in 2024 and establishing in vivo proof-of-concept for an undisclosed indication in 2024, the timing for the Company's receipt and presentation of data from its clinical trials and preclinical studies, including RUBY clinical updates in mid-2024 and by year-end 2024, the potential of, and expectations for, the Company's product candidates, the timing or likelihood of regulatory filings and approvals, the Company's expectations regarding commercial readiness, and the Company's expectations regarding cash runway. The Company may not actually achieve the plans, intentions, or expectations disclosed in these forward-looking statements, and you should not place undue reliance on these forward- looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these forward-looking statements as a result of various important factors, including: uncertainties inherent in the initiation and completion of pre-clinical studies and clinical trials, including the RUBY and EdiTHAL trials, and clinical development of the Company's product candidates, including reni-cel; availability and timing of results from pre-clinical studies and clinical trials; whether interim results from a clinical trial will be predictive of the final results of the trial or the results of future trials; expectations for regulatory approvals to conduct trials or to market products and availability of funding sufficient for the Company's foreseeable and unforeseeable operating expenses and capital expenditure requirements. These and other risks are described in greater detail under the caption "Risk Factors" included in the Company's most recent Annual Report on Form 10-K, which is on file with the Securities and Exchange Commission, as updated by the Company's subsequent filings with the Securities and Exchange Commission, and in other filings that the Company may make with the Securities and Exchange Commission in the future. Any forward-looking statements contained in this presentation represent Company's views only as of the date hereof and should not be relied upon as representing its views as of any subsequent date. Except as required by law, the Company explicitly disclaims any obligation to update any forward-looking statements. editas MEDICINE 2#3Editas Medicine is a Leader in the CRISPR-based Gene Editing Medicine Field Reni-cel is an investigational gene editing medicine that is a potential "best in class" treatment for sickle cell disease and beta thalassemia Ongoing RUBY and EdiTHAL clinical trials. Editas holds exclusive foundational IP for Cas9 and Cas12a for the prevention or treatment of human disease • Source of non-dilutive capital o Recently granted sublicenses to Vertex Pharmaceuticals and Vor Bio editas MEDICINE Proprietary As Cas12a is a high fidelity and high efficiency CRISPR nuclease • Core expertise in guide RNA design and chemistry for high precision editing Longer-term focus on creating important medicines based on in vivo gene editing Scaled CMC 8.8 • Leadership team with a proven track record of drug development and commercialization 3#4Strategic Framework (From the 2023 J.P. Morgan Healthcare Conference) Drive reni-cel (EDIT-301) toward BLA and Commercialization editas Platform MEDICINE Strengthen and Focus Discovery to Build in vivo Editing Pipeline Commercial Stage CH Increase Business Development Activities and Monetize IP Long-Term Vision: A Leader in In Vivo Programmable Gene Editing 4#5Strategic Transformation Toward Long-Term Vision (From the 2023 J.P. Morgan Healthcare Conference) Drive reni-cel (EDIT-301) toward BLA and Commercialization Platform Continue ex vivo development of reni-cel (EDIT- 301) for SCD, TDT Enroll 20 patients in RUBY study by year-end Provide RUBY and EdiTHAL data updates by mid-year and year-end Divest wholly-owned cell therapy program, continue supporting partnered cell therapy programs Terminate AAV IRD programs editas MEDICINE Strengthen and Focus Discovery to Build in vivo Editing Pipeline Focus on in vivo pipeline build Hire new CSO with specific expertise aligned with Editas' vision Reset discovery and technology group Initiate discovery of in vivo editing of HSCs and in other tissues Commercial Stage CH Increase Business Development Activities and Monetize IP Create value through business development to complement core gene editing technology capabilities Leverage robust IP portfolio Vertex sublicense for exa-cel Long-Term Vision: A Leader in In Vivo Programmable Gene Editing 5#62024 Strategic Objectives Drive reni-cel (EDIT-301) toward BLA and Commercialization Continue enrollment and dosing in the RUBY and EdiTHAL trials of reni-cel Initiate the adolescent cohort in the RUBY trial • Present a substantive clinical data set of Sickle cell patients with considerable clinical follow-up in the RUBY study in mid-2024 and by year-end 2024 Strengthen and Focus Discovery to Build in vivo Editing Pipeline • Establish in vivo preclinical proof-of-concept for an undisclosed indication o Focus on disease targets with high probability of technical, clinical, regulatory, and commercial success o Initial focus on hematopoietic stem cells (HSCS) Increase Business Development Activities and Monetize IP Derive revenue from the Company's foundational IP, building on the recently announced license agreements with Vertex Pharmaceuticals and Vor Bio editas MEDICINE 01 02 03 6#7Sickle Cell Disease (SCD) is an Inherited Life-Threatening Hematological Disorder Manifesting Shortly After Birth y ● SICKLE CELL DISEASE is a genetic blood disorder caused by mutations in the HBB gene that causes sickling of RBCs; this leads to anemia, hemolysis, and VOEs ¹,2 ● UPREGULATION OF FETAL HEMOGLOBIN (HbF) is a naturally validated therapeutic strategy to control complications of SCD SCD AFFECTS 3,4,5 -100K de EDITAS EDITS THE HBG1 AND HBG2 PROMOTERS USING ASCAS12a ENZYME, AN APPROACH THAT IS DESIGNED TO: Upregulate HbF robustly Correct anemia with superior red blood cell production and health vs. BCL11A approach Reduce risk of off-target editing with high fidelity and high efficiency proprietary AsCas12a enzyme to huk PEOPLE IN THE U.S. Reni-cel is potentially a “best in class” medicine with consistent correction of anemia HBB, B-globin gene; RBC, red blood cell; SCD, sickle cell disease; VOE, vaso-occlusive event. 1. Kato GJ et al. Nat Rev Dis Primers 2018; 4: 18010. 2. Williams TN et al. Annu Rev Genomics Hum Genet 2018; 19: 113-147. 3. Sickle Cell Disorders. Available at: https://www.thelancet.com/pb- editas assets/Lancet/gbd/summaries/diseases/sickle-cell-disorders.pdf. Accessed June 2023. 4. Wastnedge E et al. J Glob Health 2018; 8 (2): 021103. 5. Sickle Cell Disease. Available at: https://www.nhlbi.nih.gov/health/sickle-cell-disease. Accessed June 2023. MEDICINE 7#8All Treated RUBY Patients Successfully Engrafted, Showed a Favorable Ruby Safety Profile editas MEDICINE DEMOGRAPHICS Genotype, n (%) BS/Bs Sex, n (%) Female Age, years, mean (SD) Severe VOEs, pre-study annual rate*, mean (SD) INFUSION AND ENGRAFTMENT Total reni-cel dose administered, x106 CD34+ cells/kg, mean (SD) Follow-up duration, months, mean (SD) Time to neutrophil engraftmentt. ‡, days, mean (SD) Time to platelet engraftment¹.⁹, days, mean (SD) (N=11) 11 (100) 6 (54.5) 27.6 (4.2) 3.9 (1.4) (N=11¹) 5.2 (2.5) 6.5 (5.3) 23.7 (2.8) 26.1 (7.7) Safety profile is consistent. with myeloablative busulfan conditioning and autologous HSCT No serious adverse events (SAES) related to reni-cel were reported after reni-cel infusion. Data cutoff November 22, 2023. *The pre-study period is defined as the 2-year period prior to informed consent. One patient had 23 days of follow-up after infusion as of the data cut; neutrophil engraftment and platelet engraftment were not achieved yet; engraftment values are therefore based on n=10. *Three consecutive measurements with absolute neutrophil count (ANC) 20.5 × 10%/L. $Three consecutive measurements with platelet count 250 × 10%/L starting at least 7 days after the platelet transfusion, and 10 days after thrombopoietin (TPO). No TPO was used for patients after reni-cel infusion. HSCT, hematopoietic stem cell transplant; reni-cel, renizgam glogene autogedtem cel; SCD, sickle cell disease; SD, standard deviation; SAE, serious adverse event; VOE, vaso-occlusive event. Hanna R et al. Poster presented at ASH 2023; San Diego, CA, USA, 9-12 December. 8#9All Treated RUBY Patients are VOE-free Since Reni-cel Infusion editas MEDICINE Patient 1 Patient 2 Patient 3 Patient 4 Patient 5 Patient 6 Patient 7 Patient 8 Patient 9 Patient 10 6 11 11 7 7 7 9 4 12 VOES Prior to Informed Consent -25 -20 -15 -10 -5 Months Prior to Informed Consent 0* 0^ VOE-free After Reni-cel Infusion 5 Months of Post-Reni-cel Follow-up 10 Data cutoff November 22, 2023. Due to limited follow up period after dosing, Patient 11 was not included. Left panel ends at informed consent date: *Day of informed consent. Right panel starts at infusion date: ^Day reni-cel was infused. reni-cel, renizgamglogene autogedtem cel; VOE, vaso-occlusive event. Hanna R et al. Poster presented at ASH 2023; San Diego, CA, USA, 9-12 December. 15 All 10 patients who reached the Month 1 visit have been VOE-free since reni-cel infusion Ruby Severe VOE Non-severe VOE 9#10RUBY Patients Show Total Hb Rapidly Returning to the Normal Range and Clinically Meaningful Improvements in HbF Levels of >40% Mean Total Hemoglobin (g/dL) editas MEDICINE 18 16 14 12 10 8 6 4 2 0 9.6 Reni-cel infusion 4.2% Baseline (n=10) 10.9 10.7% 12.3 Day 15t 21.9% 13.0 29.6% 13.8 39.9% 3 1 1.5 2 (n=9) (n=9) (n=8) (n=7) 14.3 47.7% 15.1 48.9% 14.1 14.5 14.6 49.4% 49.5% 46.5% 15.6 47.2% *Central laboratory reference range. The last RBC transfusion in patients occurred a mean (SD) of 15.4 (6.0) days after reni-cel infusion (n=10). Hb, hemoglobin; HbF, fetal hemoglobin; RBC, red blood cell; reni-cel, renizgam glogene autogedtem cel; SCD, sickle cell disease. Hanna R et al. Poster presented at ASH 2023; San Diego, CA, USA, 9-12 December. 16.2 43.4% 10 12 15 4 5 6 8 (n=6) (n=6) (n=4) (n=4) (n=2) (n=2) (n=1) Months After Reni-cel Infusion 16.9 43.7% 18 (n=1) Ruby 13.6-18.0 g/dL normal range in males* 12.0-16.0 g/dL normal range in females* Data cutoff November 22, 2023. Number of male patients = 5; number of female patients = 5. Bars show mean Hb (g/dL). Labels inside / next to the bars indicate mean proportion of HbF as a percentage of total Hb. Mean total Hb concentrations are shown directly above bars. HbF Total Hb Last RBC transfusion, meant 10