Editas Medicine : Review of BRILLIANCE Phase 1/2 Single Ascending Dose Study of EDIT-101 Presentation

BRILLIANCE: A Phase 1/2 Single Ascending Dose Study of EDIT-101,

an in vivo CRISPR Gene Editing Therapy in CEP290-Related Retinal Degeneration

September 29, 2021

Forward 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 the safety and efficacy of EDIT-101 and the application of results achieved in the study to any future studies, the timing for the Company's receipt and presentation of additional data from its clinical trials and preclinical studies, the timing or likelihood of regulatory filings and approvals, and the therapeutic value, development, and commercial potential of the Company's gene editing technologies. 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 factors, including: uncertainties inherent in the initiation and completion of pre-clinical studies and clinical trials and clinical development of the Company's product candidates; 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.

2 © 2021 Editas Medicine

Agenda

Introduction

Overview of LCA10 and CEP290-Related Retinal Degeneration

Overview of EDIT-101

Phase 1/2 Brilliance Trial

Safety Assessments

Efficacy Assessments

Summary

SPEAKERS:

James Mullen

Chairman & CEO, Editas Medicine

Lisa A. Michaels, M.D.

Chief Medical Officer, Editas Medicine

Mark Shearman, Ph.D.

Chief Scientific Officer, Editas Medicine

Eric A. Pierce, M.D., Ph.D.

Director of the Ocular Genomics Institute at Massachusetts Eye and Ear

Professor of Ophthalmology, Harvard Medical School Principal Investigator, BRILLIANCE Clinical Trial

3 © 2021 Editas Medicine

EDIT-101 Timeline

TODAY

September 29, 2021

Editas Medicine

Presents Clinical

Data on First In Vivo

Gene Editing

Treatment for LCA10

2014

4 © 2021 Editas Medicine

Key Findings & Acknowledgements

Initial Observations

Thank You

EDIT-101 was associated with no serious adverse events (AE) or dose- limiting toxicities (DLT) to date.

Early efficacy signals in the mid-dose cohort suggest positive biological activity and potential early clinical benefits.

Editas Medicine extends utmost gratitude to all trial participants and their families for their trust and support.

Thank you to all investigative sites for your partnership and ongoing collaboration.

Massachusetts Eye	W.K. Kellogg Eye Center -
and Ear Infirmary*	University of Michigan
Boston, Massachusetts	Ann Arbor, Michigan
Casey Eye Institute - OHSU*	Bascom Palmer Eye Institute
Portland, Oregon	Miami, Florida

*Primary Surgical Sites	5 © 2021 Editas Medicine