UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

Filed by the Registrant  ☒                            Filed by a Party other than the Registrant  ☐

Check the appropriate box:

MAGENTA THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check the appropriate box):

MAGENTA THERAPEUTICS, INC.

100 Technology Square

Cambridge, Massachusetts 02139

NOTICE OF 2021 ANNUAL MEETING OF STOCKHOLDERS

To be held June 1, 2021

Notice is hereby given that the 2021 Annual Meeting of Stockholders (the “Annual Meeting”) of Magenta Therapeutics, Inc. will be held on June 1, 2021 at 9:00 a.m. Eastern Time. Due to health concerns about the coronavirus, or COVID-19, and to support the health and well-being of our stockholders, employees and partners, the Annual Meeting will be a virtual meeting. You will be able to attend and participate in the Annual Meeting online by visiting www.proxydocs.com/MGTA, where you will be able to listen to the meeting live, submit questions and vote.

The purpose of the Annual Meeting is the following:

Only Magenta Therapeutics, Inc. stockholders of record at the close of business on April 5, 2021, will be entitled to vote at the Annual Meeting and any adjournment or postponement thereof.

We are pleased to take advantage of Securities and Exchange Commission rules that allow companies to furnish their proxy materials over the Internet. We are mailing to our stockholders a Notice of Internet Availability of Proxy Materials (“Notice and Access Card”), instead of a paper copy of our proxy materials and our 2020 Annual Report to Stockholders (the “2020 Annual Report”). The Notice and Access Card contains instructions on how to access those documents and to cast your vote via the Internet. The Notice and Access Card also contains instructions on how to request a paper copy of our proxy materials and our 2020 Annual Report. This process allows us to provide our stockholders with the information they need on a more timely basis, while reducing the environmental impact and lowering the costs of printing and distributing our proxy materials.

To be admitted to the Annual Meeting and vote your shares, you must register in advance at www.proxydocs.com/MGTA prior to the Annual Meeting. You will be required to enter the control number provided in the Notice and Access Card or proxy card at www.proxydocs.com/MGTA and beneficial owners of shares held in street name will need to follow the instructions provided in the voting instructions form by the broker, bank or other nominee that holds their shares. Upon completing your registration, you will receive further instructions via email, including unique links to access the Annual Meeting and to submit questions in advance of the Annual Meeting. Please see the “General Information” section of the proxy statement that accompanies this notice for more details regarding the logistics of the virtual Annual Meeting, including the ability of stockholders to submit questions in advance of and during the Annual Meeting, and technical details and support related to accessing the virtual platform.

Your vote is important. Whether or not you are able to attend the Annual Meeting and vote your shares online, it is important that your shares be represented. To ensure that your vote is recorded promptly, please vote as soon as possible, even if you plan to attend the Annual Meeting, by submitting your proxy via the Internet at the address listed on the proxy card or by signing, dating and returning the proxy card.

By order of our Board of Directors,

Jason Gardner President and Chief Executive Officer

Cambridge, Massachusetts

April 21, 2021

Table of Contents

MAGENTA THERAPEUTICS, INC.

100 Technology Square

Cambridge, Massachusetts 02139

PROXY STATEMENT

FOR THE 2021 ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD JUNE 1, 2021

This proxy statement contains information about the 2021 Annual Meeting of Stockholders (the “Annual Meeting”) of Magenta Therapeutics, Inc., which will be held on June 1, 2021 at 9:00 a.m. Eastern Time. Due to health concerns about the coronavirus, or COVID-19, and to support the health and well-being of our stockholders, employees and partners, the Annual Meeting will be a virtual meeting. You will be able to attend and participate in the Annual Meeting online by visiting www.proxydocs.com/MGTA, where you will be able to listen to the meeting live, submit questions and vote. The Board of Directors of Magenta Therapeutics, Inc. is using this proxy statement to solicit proxies for use at the Annual Meeting. In this proxy statement, the terms “Magenta,” “we,” “us,” and “our” refer to Magenta Therapeutics, Inc. The mailing address of our principal executive offices is Magenta Therapeutics, Inc., 100 Technology Square, Cambridge, Massachusetts 02139.

To be admitted to the Annual Meeting and vote your shares, you must register in advance at www.proxydocs.com/MGTA prior to the Annual Meeting. You will be required to enter the control number provided in the Notice and Access Card or proxy card at www.proxydocs.com/MGTA and beneficial owners of shares held in street name will need to follow the instructions provided in the voting instructions form by the broker, bank or other nominee that holds their shares. Upon completing your registration, you will receive further instructions via email, including unique links to access the Annual Meeting and to submit questions in advance of the Annual Meeting. Please see the “General Information” section of the proxy statement for more details regarding the logistics of the virtual Annual Meeting, including the ability of stockholders to submit questions in advance of and during the Annual Meeting, and technical details and support related to accessing the virtual platform.

All properly submitted proxies will be voted in accordance with the instructions contained in those proxies. If no instructions are specified, the proxies will be voted in accordance with the recommendation of our Board of Directors with respect to each of the matters set forth in the accompanying Notice of Meeting. You may revoke your proxy at any time before it is exercised at the meeting by giving our corporate secretary written notice to that effect.

We made this proxy statement and our Annual Report to Stockholders for the fiscal year ended December 31, 2020 available to stockholders on or about April 21, 2021.

We are an “emerging growth company” under applicable federal securities laws and therefore are permitted to comply with certain reduced public company reporting requirements. As an emerging growth company, we provide in this proxy statement the scaled disclosure permitted under the Jumpstart Our Business Startups Act of 2012, including the compensation disclosures required of a “smaller reporting company,” as that term is defined in Rule 12b-2 promulgated under the Securities Exchange Act of 1934, as amended (the “Exchange Act”). In addition, as an emerging growth company, we are not required to conduct votes seeking approval, on an advisory basis, of the compensation of our named executive officers or the frequency with which such votes must be conducted. We will remain an “emerging growth company” until the earliest of (i) the last day of the fiscal year following the fifth anniversary of our initial public offering in June 2018; (ii) the last day of the fiscal year in

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which our total annual gross revenue is equal to or more than $1.07 billion; (iii) the date on which we have issued more than $1 billion in nonconvertible debt during the previous three years; or (iv) the date on which we are deemed to be a large accelerated filer under the rules of the Securities and Exchange Commission (the “SEC”). Even after we are no longer an “emerging growth company,” we may remain a “smaller reporting company.”

Important Notice Regarding the Availability of Proxy Materials for

the Annual Meeting of Stockholders to be Held on June 1, 2021:

This proxy statement and our 2020 Annual Report to Stockholders are

available for viewing, printing and downloading at www.proxydocs.com/MGTA.

A copy of our Annual Report on Form 10-K for the fiscal year ended December 31, 2020, as filed with the SEC, except for exhibits, will be furnished without charge to any stockholder upon written request to Magenta Therapeutics, Inc., 100 Technology Square, Cambridge, Massachusetts 02139, Attention: Corporate Secretary. This proxy statement and our Annual Report on Form 10-K for the fiscal year ended December 31, 2020 are also available on the SEC’s website at www.sec.gov.

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MAGENTA THERAPEUTICS, INC.

PROXY STATEMENT

FOR THE 2021 ANNUAL MEETING OF STOCKHOLDERS

GENERAL INFORMATION

When are this proxy statement and the accompanying materials scheduled to be sent to stockholders?

We have elected to provide access to our proxy materials to our stockholders via the Internet. Accordingly, on or about April 21, 2021, we will begin mailing a Notice of Internet Availability of Proxy Materials (the “Notice and Access Card”). Our proxy materials, including the Notice of 2021 Annual Meeting of Stockholders, this proxy statement and the accompanying proxy card or, for shares held in street name (i.e., held for your account by a broker or other nominee), a voting instruction form, and the 2020 Annual Report to Stockholders (the “2020 Annual Report”), will be mailed or made available to stockholders on the Internet on or about the same date.

Why did I receive a Notice of Internet Availability of Proxy Materials instead of a full set of proxy materials?

Pursuant to rules adopted by the SEC, for most stockholders, we are providing access to our proxy materials over the Internet rather than printing and mailing our proxy materials. We believe following this process will expedite the receipt of such materials and will help lower our costs and reduce the environmental impact of our annual meeting materials. Therefore, the Notice and Access Card was mailed to holders of record and beneficial owners of our common stock starting on or about April 21, 2021. The Notice and Access Card provides instructions as to how stockholders may access and review our proxy materials, including the Notice of 2021 Annual Meeting of Stockholders, this proxy statement, the proxy card and our 2020 Annual Report, on the website referred to in the Notice and Access Card or, alternatively, how to request that a copy of the proxy materials, including a proxy card, be sent to them by mail. The Notice and Access Card also provides voting instructions. In addition, stockholders of record may request to receive the proxy materials in printed form by mail or electronically by e-mail on an ongoing basis for future stockholder meetings. Please note that, while our proxy materials are available at the website referenced in the Notice and Access Card and our Notice of 2021 Annual Meeting of Stockholders, this proxy statement and our 2020 Annual Report are available on our website. No other information contained on either website is incorporated by reference in, or considered to be a part of, this proxy statement.

Who is soliciting my vote?

Our Board of Directors is soliciting your vote for the matters to be acted on at the Annual Meeting.

When is the record date for the Annual Meeting?

The record date for determination of stockholders entitled to vote at the Annual Meeting is the close of business on April 5, 2021.

How many votes can be cast by all stockholders?

There were 48,603,205 shares of our common stock, par value $0.001 per share, outstanding on April 5, 2021, all of which are entitled to vote with respect to all matters to be acted upon at the Annual Meeting. Each stockholder of record is entitled to one vote for each share of our common stock held by such stockholder. None of our shares of undesignated preferred stock were outstanding as of April 5, 2021.

How do I vote my shares without attending the Annual Meeting?

If you do not wish to vote in person or will not be attending the Annual Meeting, you may vote by proxy. You can vote by proxy over the Internet by following the instructions provided in the Notice and Access Card, or, if

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you requested printed copies of the proxy materials by mail, you can vote by mailing your proxy as described in the proxy materials. Proxies submitted by mail must be received before the start of the Annual Meeting.

If you complete and submit your proxy before the Annual Meeting, the persons named as proxies will vote the shares represented by your proxy in accordance with your instructions. If you submit a proxy without giving voting instructions, your shares will be voted in the manner recommended by our Board of Directors on all matters presented in this proxy statement, and as the persons named as proxies may determine in their discretion with respect to any other matters properly presented at the Annual Meeting. You may also authorize another person or persons to act for you as proxy in a writing, signed by you or your authorized representative, specifying the details of those proxies’ authority. The original writing must be given to each of the named proxies, although it may be sent to them by electronic transmission if, from that transmission, it can be determined that the transmission was authorized by you.

If any other matters are properly presented for consideration at the Annual Meeting, including, among other things, consideration of a motion to adjourn the Annual Meeting to another time or place (including, without limitation, for the purpose of soliciting additional proxies), the persons named in your proxy and acting thereunder will have discretion to vote on those matters in accordance with their best judgment. We do not currently anticipate that any other matters will be raised at the Annual Meeting.

How can I attend and vote at the Annual Meeting?

To attend and participate in the Annual Meeting, stockholders will need to access the live audio webcast of the meeting. To do so, stockholders of record will need to visit www.proxydocs.com/MGTA and enter the control number provided in the Notice and Access Card to pre-register for the Annual Meeting, and beneficial owners of shares held in street name will need to follow the instructions provided in the voting instructions form by the broker, bank or other nominee that holds their shares.

To be admitted to the Annual Meeting and vote your shares, stockholders must register in advance at www.proxydocs.com/MGTA prior to the Annual Meeting and provide the control number located in the shaded gray box in the Notice and Access Card or proxy card. Stockholders who have completed registration will receive an email on the morning of the Annual Meeting with further instructions, including a unique link to access the Annual Meeting.

The live audio webcast of the Annual Meeting will begin promptly at 9:00 a.m. Eastern Time. We encourage stockholders to login to this website and access the webcast before the Annual Meeting’s start time by following the instructions in the email received on the morning of the Annual Meeting. You should allow ample time in advance of the meeting.

Additionally, questions regarding how to attend and participate via the Internet can be answered by following the assistance instructions included at www.proxydocs.com/MGTA or by calling the phone number provided in the email received on the morning of the Annual Meeting.

As part of the Annual Meeting, we will hold a live question and answer session, during which we intend to answer questions that were submitted during the pre-registration process (described above) and during the meeting in accordance with the Annual Meeting’s Rules of Conduct that are pertinent to Magenta and the meeting matters, as time permits. Questions and answers will be grouped by topic and substantially similar questions will be grouped and answered once. Only stockholders who register prior to the Annual Meeting and subsequently log in to attend the Annual Meeting will be able to ask questions at the Annual Meeting.

The Annual Meeting’s Rules of Conduct will be posted on www.proxydocs.com/MGTA approximately two weeks prior to the date of the Annual Meeting.

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How do I revoke my proxy?

You may revoke your proxy by (1) following the instructions on the Notice and Access Card and entering a new vote by mail that we receive before the start of the Annual Meeting or over the Internet, (2) attending and voting at the Annual Meeting (although attendance at the Annual Meeting will not in and of itself revoke a proxy), or (3) by filing an instrument in writing revoking the proxy or another duly executed proxy bearing a later date with our Corporate Secretary. Any written notice of revocation or subsequent proxy card must be received by our Corporate Secretary prior to the taking of the vote at the Annual Meeting. Such written notice of revocation or subsequent proxy card should be hand delivered to our Corporate Secretary or sent to our principal executive offices at Magenta Therapeutics, Inc., 100 Technology Square, Cambridge, Massachusetts 02139, Attention: Corporate Secretary.

If a broker, bank, or other nominee holds your shares, you must contact such broker, bank, or nominee in order to find out how to change your vote.

How is a quorum reached?

Our Amended and Restated By-laws (the “By-laws”) provide that a majority of the shares entitled to vote, present in person or represented by proxy, will constitute a quorum for the transaction of business at the Annual Meeting.

Under the General Corporation Law of the State of Delaware, shares that are voted “abstain” or “withheld” and broker “non-votes” are counted as present for purposes of determining whether a quorum is present at the Annual Meeting. If a quorum is not present, the meeting may be adjourned until a quorum is obtained.

How is the vote counted?

Under our By-laws, any proposal other than an election of directors (which is decided by a plurality of votes) is decided by a majority of the votes properly cast for and against such proposal, except where a larger vote is required by law or by our Amended and Restated Certificate of Incorporation (the “Certificate of Incorporation”) or By-laws. Abstentions and broker “non-votes” are not included in the tabulation of the voting results on any such proposal and, therefore, do not have an impact on such proposals. A broker “non-vote” occurs when a nominee holding shares for a beneficial owner does not vote on a particular proposal because the nominee does not have discretionary voting power with respect to that item, and has not received instructions from the beneficial owner.

If your shares are held in “street name” by a brokerage firm, your brokerage firm is required to vote your shares according to your instructions. If you do not give instructions to your brokerage firm, the brokerage firm will still be able to vote your shares with respect to certain “discretionary” items, but will not be allowed to vote your shares with respect to “non-discretionary” items. Proposal No. 1 is a “non-discretionary” item. If you do not instruct your broker how to vote with respect to this proposal, your broker may not vote for this proposal, and that vote will be counted as a broker “non-vote.” Proposal No. 2 is considered to be a discretionary item, and your brokerage firm will be able to vote on this proposal even if it does not receive instructions from you.

Who pays the cost for soliciting proxies?

We are making this solicitation and will pay the entire cost of preparing and distributing the Notice and Access Card and our proxy materials and soliciting votes. If you choose to access the proxy materials or vote over the Internet, you are responsible for any Internet access charges that you may incur. Our officers and employees may, without compensation other than their regular compensation, solicit proxies through further mailings, personal conversations, facsimile transmissions, e-mails, or otherwise.

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How may stockholders submit matters for consideration at an annual meeting?

The required notice must be in writing and received by our corporate secretary at our principal executive offices not less than 90 days nor more than 120 days prior to the first anniversary of the preceding year’s annual meeting. However, in the event that the date of the annual meeting is advanced by more than 30 days, or delayed by more than 60 days, from the first anniversary of the preceding year’s annual meeting, or if no annual meeting were held in the preceding year, a stockholder’s notice must be so received no earlier than the 120th day prior to such annual meeting and not later than the close of business on the later of (A) the 90th day prior to such annual meeting and (B) the tenth day following the day on which notice of the date of such annual meeting was mailed or public disclosure of the date of such annual meeting was made, whichever first occurs.

In addition, any stockholder proposal intended to be included in the proxy statement for the next annual meeting of our stockholders in 2022 must also satisfy the requirements of Rule 14a-8 under the Exchange Act and be received not later than December 22, 2021. If the date of the annual meeting is moved by more than 30 days from the date contemplated at the time of the previous year’s proxy statement, then notice must be received within a reasonable time before we begin to print and send proxy materials. If that happens, we will publicly announce the deadline for submitting a proposal in a press release or in a document filed with the SEC.

How can I know the voting results?

We plan to announce preliminary voting results at the Annual Meeting and will publish final results in a Current Report on Form 8 -K to be filed with the SEC within four business days following the Annual Meeting.

What is householding?

Some banks, brokers and other nominee record holders may be participating in the practice of “householding” proxy statements and annual reports. This means that only one copy of our documents, including the annual report to stockholders and proxy statement, may have been sent to multiple stockholders in your household. We will promptly deliver a separate copy of either document to you upon written or oral request to Magenta Therapeutics, Inc., 100 Technology Square, Cambridge, Massachusetts 02139, Attention: Corporate Secretary, telephone: 857-242-0170. If you want to receive separate copies of the proxy statement or annual report to stockholders in the future, or if you are receiving multiple copies and would like to receive only one copy per household, you should contact your bank, broker or other nominee record holder, or you may contact us at the above address and phone number.

What interest do officers and directors have in matters to be acted upon?

Members of the Board of Directors and executive officers of Magenta do not have any interest in any proposal that is not shared by all other stockholders of Magenta, except for Proposal 1 (nominees to our Board of Directors will be elected).

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PROPOSAL NO. 1 – ELECTION OF CLASS III DIRECTORS

Our Board of Directors currently consists of eleven members. In accordance with the terms of our Certificate of Incorporation and By-laws, our Board of Directors is divided into three classes, class I, class II and class III, with members of each class serving staggered three-year terms. The members of the classes are divided as follows:

Upon the expiration of the term of a class of directors, directors in that class will be eligible to be elected for a new three-year term at the annual meeting of stockholders in the year in which their term expires.

Our Certificate of Incorporation and By-laws provide that the authorized number of directors may be changed only by resolution of our Board of Directors. Our Certificate of Incorporation also provides that our directors may be removed only for cause by the affirmative vote of the holders of at least two-thirds (2/3) of the outstanding shares of capital stock then entitled to vote in an annual election of directors, and that any vacancy on our Board of Directors, including a vacancy resulting from an enlargement of our Board of Directors, may be filled only by vote of a majority of our directors then in office.

Our Board of Directors has nominated Bruce Booth, D.Phil., Thomas O. Daniel, M.D., Jason Gardner, D.Phil. and Alison F. Lawton for election as the class III directors at the Annual Meeting. Each of the nominees are currently directors and have consented to serve as our directors if elected. If the nominees become unable or unwilling to serve, however, the proxies may be voted for a substitute nominee selected by our Board of Directors.

The biographies of each of the nominees and continuing directors below contain information regarding each such person’s service as a director, business experience, director positions held currently or at any time during the last five years and the experiences, qualifications, attributes or skills that caused the Nominating and Corporate Governance Committee of our Board of Directors to determine that the person should serve as a director of Magenta. In addition to the information presented below regarding each such person’s specific experience, qualifications, attributes and skills that led our Board of Directors and our Nominating and Corporate Governance Committee to the conclusion that he or she should serve as a director, we also believe that each of our directors has a reputation for integrity, honesty and adherence to high ethical standards. Each of our directors has demonstrated business acumen and an ability to exercise sound judgment, as well as a commitment of service to Magenta and our Board of Directors. There are no material legal proceedings to which any of our nominees and continuing directors is a party adverse to us or our subsidiary or in which any such person has a material interest adverse to us or our subsidiary.

The proxies will be voted in favor of the above nominees unless a contrary specification is made in the proxy. However, if the nominees are unable to serve or for good cause will not serve as a director, the proxies will be voted for the election of such substitute nominee as our Board of Directors may designate.

Vote Required

The nominees for class III director who receive the most votes (also known as a plurality) will be elected. You may vote either FOR all the nominees, FOR any one of the nominees, WITHHOLD your vote from all the

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nominees or WITHHOLD your vote from any one of the nominees. Votes that are withheld will not be included in the vote tally for the election of directors. Brokerage firms do not have authority to vote your unvoted shares held by the firms in street name for the election of directors. As a result, any shares not voted by you will be treated as a broker non-vote. Such broker non-votes will have no effect on the results of this vote.

OUR BOARD RECOMMENDS A VOTE FOR THE ELECTION OF THE NOMINEES NAMED ABOVE AS CLASS III DIRECTORS, AND PROXIES SOLICITED BY THE BOARD WILL BE VOTED IN FAVOR THEREOF UNLESS A STOCKHOLDER HAS INDICATED OTHERWISE ON THE PROXY.

Nominees for Election as Class III Directors

The following table identifies our director nominees, and sets forth their principal occupation and business experience during the last five years and their ages as of April 5, 2021.

Bruce Booth, D.Phil., one of our founding investors and board members, has served as a member of our Board of Directors since February 2016. Dr. Booth joined Atlas Venture in 2005, and currently serves as partner. Previously, from 2004 to 2005, Dr. Booth was a principal at Caxton Health Holdings L.L.C., a healthcare-focused investment firm, where he focused on the firm’s venture capital activities. Prior to Caxton, from 1999 to 2004, he was an associate principal at McKinsey & Company, a global strategic management consulting firm, where he advised clients on R&D productivity, corporate strategy and business development issues across the biopharmaceutical sector. Dr. Booth serves on the board of several privately held companies, as well as on the board of AVROBIO Inc., where he is the chairman, and Kymera Therapeutics, Inc., where he is the chairman and a co-founder. Dr. Booth previously served on the Board of miRagen Therapeutics, Inc. from 2007 to December 2018, Zafgen, Inc. from 2007 to June 2018 and Unum Therapeutics, Inc. from 2018 to July 2020. Dr. Booth also serves on UCB Pharma’s New Medicines Scientific Advisory Board, and participates on several other advisory boards for pharmaceutical companies and academic medical centers. As a British Marshall Scholar, Dr. Booth holds a D.Phil in molecular immunology from Oxford University’s Nuffield Department of Medicine and a B.S. in biochemistry, summa cum laude, from Pennsylvania State University. We believe Dr. Booth’s extensive leadership, executive, managerial and business experience with life sciences companies, including experience in the formation, development and business strategy of multiple start-up companies in the life sciences sector qualifies him to serve on our Board of Directors.

Thomas O. Daniel, M.D. has served as a member of our Board of Directors since October 2016. Dr. Daniel has 20 years of experience in biopharmaceutical discovery and development. He is currently Chairman of Locana Inc., is a venture partner at ARCH Venture Partners, Inc., and is a director at Larimar Therapeutics, Inc. (formerly Zafgen, Inc. until the completion of its merger with Chondrial Therapeutics, Inc. in May 2020) and Gossamer Bio, Inc. He was recently Chairman of Research at Celgene Corporation, and served as President of Research and Early Development from December 2006 until February 2012, and as Executive Vice President and President of Research and Early Development until December 2015. Previously, he served as Chief Scientific Officer and Director at Ambrx Inc., from August 2003 to November 2006. Dr. Daniel also served as Vice President of Research at Amgen Inc. from August 2002 to April 2003, where he was Research Site Head of Amgen Washington and Therapeutic Area Head of Inflammation. Prior to Amgen Inc.’s acquisition of Immunex Corporation, Dr. Daniel served as Senior Vice President of Discovery Research at Immunex Corporation from May 2000 to August 2002. Dr. Daniel previously served on the boards of Juno Therapeutics, Inc. from July 2015 to March 2018, and Epizyme, Inc. from May 2013 to June 2014. Dr. Daniel is a Trustee of Reed College, serves

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on the Board of the Alliance for Lupus Research, and advises privately-held biotechnology companies including Brii Biosciences Limited, Epirium Bio, Inc. and BlackThorn Therapeutics. Dr. Daniel serves as Chairman of the Board of Overseers of The Scripps Research Institute and on the Biomedical Science Advisory Board of Vanderbilt University Medical Center. A nephrologist and former academic investigator, Dr. Daniel was previously the C.M. Hakim Professor of Medicine and Cell Biology at Vanderbilt University. He formerly conducted research in the Howard Hughes Medical Institute at UC San Francisco, earned an M.D. from the University of Texas, Southwestern, and completed medical residency at Massachusetts General Hospital. Dr. Daniel’s qualifications to serve on our Board of Directors include his extensive experience in biotechnology research and development and his prior experience as both an executive officer and a director of publicly traded companies.

Jason Gardner, D.Phil., co-founder of Magenta, has served as our President and Chief Executive Officer and as a member of our Board of Directors since February 2016. Dr. Gardner has more than 20 years of experience in stem cell science, drug development and industry leadership roles. He joined Atlas Venture in November 2015 as an Entrepreneur-in-Residence to create Magenta with Third Rock Ventures. He previously worked at GlaxoSmithKline plc. from 2005, most recently as Vice President and Head of the R&D Satellite in Boston. He created and led the Regenerative Medicine Unit, established partnerships with The Harvard Stem Cell Institute, and The Telethon Institute for Gene Therapy, from which the first stem cell gene therapy (Strimvelis) was approved. Prior to that, Dr. Gardner was the Head of the Center of Excellence for External Drug Discovery and was a member of the clinical project team that led the late stage development and NDA approval for Tykerb for breast cancer. Dr. Gardner held scientific leadership roles at Progenics Pharmaceuticals, Inc. and Chiron Corporation working on drug discovery and development. Dr. Gardner completed a postdoctoral fellowship in stem cell biology with Professor David Scadden at Harvard Medical School. He was educated in the U.K. and holds a doctorate from Oxford University, and graduate and undergraduate degrees in Natural Sciences (Biochemistry) from Cambridge University. Dr. Gardner currently serves on the Board of Directors of Obsidian Therapeutics, Inc. Dr. Gardner is qualified to serve on our Board of Directors because of his insight into our operations and strategy as a result of being our Chief Executive Officer and his experience in the life sciences industry.

Alison F. Lawton has served as a member of our Board of Directors since December 2020. Ms. Lawton is an executive leader with more than 30 years of experience in biopharma. She served as President and Chief Executive Officer of Kaleido Biosciences, Inc. from August 2018 to June 2020, and served as President and Chief Operating Officer from December 2017 to August 2018. Prior to joining Kaleido Biosciences, Inc., Ms. Lawton served as Chief Operating Officer at Aura Biosciences, Inc., an oncology therapeutics company, from January 2015 until December 2017, and, prior to joining Aura, served as a consultant to Aura from March 2014 to December 2014. From January 2013 to January 2014, Ms. Lawton served as Chief Operating Officer at OvaScience Inc., a life sciences company. From 2014 to 2017, Ms. Lawton served as a biotech consultant for various companies, including as Chief Operating Officer consultant at X4 Pharmaceuticals. Prior to that, Ms. Lawton spent more than 20 years in various positions of increasing responsibility including Senior VP and General Manager of Biosurgery and prior, Senior VP of Market Access at Genzyme Corporation, a global biopharmaceutical company, and subsequently at Sanofi S.A., also a global biopharmaceutical company, following the acquisition of Genzyme by Sanofi in 2011. Additionally, Ms. Lawton previously served two terms as the industry representative on the U.S. Food & Drug Administration’s Cell & Gene Therapy Advisory Committee and as Chairman of the Board of the Regulatory Affairs Professional Society. Ms. Lawton currently serves on the board of directors of ProQR Therapeutics N.V., X4 Pharmaceuticals Inc. and Aeglea Biotherapeutics Inc. and the private company SwanBio. Ms. Lawton previously served on the boards of directors of Kaleido Biosciences Inc. from August 2018 to October 2020, Verastem, Inc. from November 2012 to May 2020, CoLucid Pharmaceuticals, Inc. from March 2016 until its acquisition by Eli Lilly in March 2017, and Cubist Pharmaceuticals, Inc. from February 2012 to December 2014 prior to its acquisition by Merck & Co. in January 2015. Ms. Lawton holds a B.Sc. in pharmacology from Kings College, University of London. We believe that Ms. Lawton is qualified to serve on our Board of Directors based on her extensive regulatory affairs and quality systems experience and leadership in the biopharma industry.

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Directors Continuing in Office

The following table identifies our continuing directors, and sets forth their principal occupation and business experience during the last five years and their ages as of April 5, 2021.

Class I Directors (Term Expires at the 2022 annual meeting of stockholders)

Alexis A. Borisy, one of our founding investors and board members, has served as a member of our Board of Directors since June 2015. Mr. Borisy currently serves as the Chairman and Chief Executive Officer of EQRx, Inc., a biotechnology company. From 2010 to June 2019, Mr. Borisy was a partner at Third Rock Ventures, LLC, a life sciences venture capital firm focused on the formation, development and strategy of new companies. Mr. Borisy co-founded Blueprint Medicines Corporation and served as the interim chief executive officer from May 2013 through July 2014 and has served as a member of its Board of Directors since April 2011. Mr. Borisy also co-founded Foundation Medicine, Inc., where he served as its interim chief executive officer from 2009 to 2011 and served as a member of its Board of Directors from 2009 to July 2018, including as chairman of Foundation Medicine, Inc.’s Board of Directors from 2011 to February 2017. Mr. Borisy currently serves on the board of directors of Revolution Medicines, Inc. and Relay Therapeutics, Inc. and previously served as a member of the board of directors of Editas Medicine, Inc. from November 2013 to March 2018 and as executive chairman of Warp Drive Bio, LLC from 2011 to October 2018, when it was acquired by Revolution Medicine, Inc. In addition, Mr. Borisy currently serves on the Board of Directors of the following privately held biopharmaceutical companies: Tango Therapeutics, Inc., Celsius Therapeutics, Inc. and Dascena, Inc.. Mr. Borisy received an A.B. in chemistry from the University of Chicago and an A.M. from Harvard University. We believe Mr. Borisy’s detailed knowledge of our company and long tenure with us, along with his experience working with and serving on the boards of directors of life sciences companies, and his experience working in the venture capital industry qualifies him to serve on our Board of Directors.

Blake Byers, Ph.D. has served as a member of our Board of Directors since April 2017. From 2010 to March 2021, Dr. Byers worked at GV as an investor and general partner. During his time at GV, Dr. Byers partnered with founders of life science and digital companies – from drug development and healthcare delivery to financial services and information security. Dr. Byers served as President of Pact Pharma, Inc. from February 2018 to October 2018 and is currently chairman of their Board of Directors. Dr. Byers also serves on the Board of Directors of IonQ Inc.. Prior to joining GV, Dr. Byers helped start two companies, led research projects on biomedical engineering and stem cells at Stanford University and was an angel investor. Dr. Byers received a Ph.D. and M.S. in bioengineering from Stanford University and holds a B.S in biomedical engineering and economics from Duke University. We believe Dr. Byers’ experience working in the venture capital industry and history with stem cell technology qualifies him to serve on our Board of Directors.

Amy Lynn Ronneberg has served on our Board of Directors since March 2018. Ms. Ronneberg is the Chief Executive Officer of Be The Match, a healthcare organization. Ms. Ronneberg joined Be The Match as the Chief Financial Officer in 2013 and served as Acting Chief Executive Officer from February 2020 until her June 2020 appointment as Chief Executive Officer. Ms. Ronneberg also served as the President at Be The Match BioTherapies, LLC, a start-up company within the organization, and as Chief of Staff of the organization from

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February 2018 to February 2020. Within the organization, Ms. Ronneberg formulated a new organizational operating model, established international operations, transformed several struggling areas within the organization and directed the completion of a seven story headquarters. Ms. Ronneberg has 20 years of experience in financial and operational leadership, serving as Executive Vice President, CFO and Chief Operating Officer of North American Membership Group, a private equity-owned media company. Prior to that, Ms. Ronneberg spent 12 years at Capella University, where she served in roles such as Vice President of Finance and Vice President of Operations, lead enterprise-wide operations and customer service. Ms. Ronneberg also worked for Ernst & Young for several years as an Audit Manager. Ms. Ronneberg is a member of the board of directors and finance committee for Allina Health and board of directors for Medical Alley Association and previously served on the executive committee for the World Marrow Donor Association and chairman of the board of Twin Cities in Motion, Minneapolis. Ms. Ronneberg earned a Master’s in Business Administration from Capella University, Minneapolis, Minnesota and a B.B.A. in Accounting from University of Wisconsin-Eau Claire. We believe Ms. Ronneberg’s financial expertise and knowledge of the transplant industry qualifies her to serve on our Board of Directors.

Class II Directors (Term Expires at the 2023 annual meeting of stockholders)

Jeffrey W. Albers has served as a member of our Board of Directors since July 2017. Mr. Albers has over fifteen years of experience in leadership roles in the biopharmaceutical industry and is currently the president and chief executive officer of Blueprint Medicines Corporation. Prior to joining Blueprint Medicines Corporation in July 2014, Mr. Albers was president of Algeta ASA, a Norwegian biotechnology company from January 2012 to April 2014, where he oversaw the commercial and business functions. Prior to Algeta ASA, from July 2005 to November 2011, Mr. Albers was at Genzyme, a biotechnology company that is now a wholly-owned subsidiary of Sanofi S.A., most recently as vice president of the U.S. hematology and oncology business unit. Mr. Albers serves on the Board of Directors of Blueprint and Kymera Therapeutics, Inc. Mr. Albers received a B.S. from Indiana University and an M.B.A. and a J.D. from Georgetown University. We believe that Mr. Albers’ leadership in the life sciences industry qualifies him to serve on our Board of Directors.

Michael W. Bonney has been a member of our Board of Directors since October 2016 and the Chair of our Board of Directors since June 2018 and previously served as the Executive Chairman of our Board of Directors from November 2016 to June 2018. Mr. Bonney is Managing Director of Sasanoa Advisory Group Enterprises, LLC, a CEO advisory firm, a position he has held since June 2019. Mr. Bonney served as the Executive Chair of Kaleido Biosciences, Inc. from August 2018 to November 2020 and has served as Chair of the Board of Directors of Kaleido Biosciences, Inc. since November 2020. Previously, Mr. Bonney served as the Chief Executive Officer of Kaleido Biosciences, Inc. from June 2017 until August 2018. Prior to that, he served as Partner at Third Rock Ventures, LLC, a venture capital firm, from January 2016 to July 2016. Before joining Third Rock Ventures, LLC, Mr. Bonney served as CEO and Director at Cubist Pharmaceuticals, Inc., a biopharmaceutical company, from June 2003 until January 2015, when it was acquired by Merck. In addition to his role as Chair of the Board of Directors of Magenta, Mr. Bonney chairs the board of directors of Alnylam Pharmaceuticals, Inc. Mr. Bonney served as a board member of Celgene Corporation from April 2015 until its acquisition by Bristol-Myers Squibb Company in November 2019 and currently serves as a board member of Bristol-Myers Squibb Company. Mr. Bonney previously served on the boards of Sarepta Therapeutics, Inc. from December 2017 to March 2020, Syros Pharmaceuticals, Inc. from June 2018 to March 2020, Global Blood Therapeutics from April 2016 to June 2017, Revolution Medicines, Inc. from August 2016 to September 2017 and NPS Pharmaceuticals, Inc. from January 2005 to February 2015. Mr. Bonney also serves on the board of directors of X-Biotix Therapeutics, Inc., a private company. He received a B.A. in economics from Bates College. We believe that Mr. Bonney is qualified to serve on our Board of Directors based on our review of his experience, qualifications, attributes and skills, including his extensive experience in leadership roles at other biotech ventures.

Anne McGeorge has been a member of our Board of Directors since June 2019. Ms. McGeorge has over 35 years of experience providing strategic guidance and operational oversight to health care organizations.

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Ms. McGeorge currently works as an operating partner for Havencrest Healthcare Partners and as an adjunct professor at the University of North Carolina at Chapel Hill. Ms. McGeorge is a director at SOC Telemed, CitiusTech, a private health care technology company, and several entities associated with the Be The Match Foundation, and is on the advisory board at Dioko Ventures. Prior to her retirement in July 2017, Ms. McGeorge worked at Grant Thornton LLP where she routinely advised clients on audit and financial matters relating to the healthcare industry. During her time at Grant Thornton LLP, Ms. McGeorge was Managing Partner of Grant Thornton LLP’s Health Care Industry Practice from January 2006 to July 2017 as well as Global Managing Partner for Grant Thornton International’s Health Care Industry Practice from August 2015 to July 2017. Ms. McGeorge was formerly a partner at Deloitte LLP from 2002 to 2005 and at Arthur Andersen LLP from 1994 to 2002. Ms. McGeorge received a BBA, Business, Accounting from the College of William and Mary, and an MS, Accounting/Taxation from the University of Virginia. We believe that Ms. McGeorge is qualified to serve on our Board of Directors based on her extensive experience providing auditing and financial services for the healthcare industry.

David T. Scadden, M.D., one of our co-founders, has served on our Board of Directors and as chair of our Scientific Advisory Board since November 2016. Dr. Scadden is the Gerald and Darlene Jordan Professor of Medicine at Harvard University. He and Professor Douglas Melton founded and jointly direct the Harvard Stem Cell Institute, which is the largest institute dedicated to bringing stem cell biology to medical care in the world. With Professor Melton, Dr. Scadden founded the Department of Stem Cell and Regenerative Biology Department at Harvard University, the first department to span faculties in Harvard’s history, and served as chair of the department from January 2009 to September 2018. He is a hematologist/oncologist and directs the Center for Regenerative Medicine at the Massachusetts General Hospital and previously chaired the Hematologic Malignancies program in the MGH Cancer Center. Dr. Scadden is an expert on the medical applications of stem cell biology with a particular emphasis on their use in the settings of cancer and AIDS. He has published over 300 scientific papers and book chapters, and his laboratory has made fundamental contributions in how the stem cell niche regulates stem cell function and in normal and disease-corrupted hematopoiesis. Dr. Scadden serves as a director on the board of Agios Pharmaceuticals, Inc and Editas Medicine, Inc. In addition, Dr. Scadden is a member of the board of several private companies, including Clear Creek Bio, Inc., Red Oak Medicines Inc. and LifeVault Bio, Inc., and also serves on several scientific advisory boards, including Magenta’s. In addition, he has served or serves on the Board of Scientific Counselors for the National Cancer Institute, the Board of External Experts for the National Heart, Lung and Blood Institute and the Board of Directors of the International Society for Stem Cell Research. He is an elected member of the National Academy of Medicine and the American Academy of Arts and Sciences and is a fellow of the American Association for the Advancement of Science and the American College of Physicians. He is the recipient of numerous awards from scholarly societies and honorary degrees from multiple universities. We believe Dr. Scadden’s experience as a physician and medical researcher qualifies him to serve on our Board of Directors.

There are no family relationships between or among any of our directors or executive officers. The principal occupation and employment during the past five years of each of our directors was carried on, in each case except as specifically identified above, with a corporation or organization that is not a parent, subsidiary or other affiliate of us. There is no arrangement or understanding between any of our directors and any other person or persons pursuant to which he or she is to be selected as a director.

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Executive Officers Who Are Not Directors

The following table identifies our executive officers, and sets forth their current positions at Magenta, the year they became an executive officer and their ages.

John C. Davis, Jr., M.D. joined Magenta in February 2018 as Chief Medical Officer and currently serves as our Head of Research and Development and Chief Medical Officer, effective as of April 2020. Prior to joining Magenta, Dr. Davis was Senior Vice President and Head of Early Clinical Development at Pfizer Inc. from 2016 to 2018. Prior to his role at Pfizer, Dr. Davis served as Vice President and Global Therapeutic Area Head of Immunology at Baxalta which is now wholly-owned by Shire plc, from 2015 to 2016. Dr. Davis had multiple roles at Genentech, Inc. from 2007 to 2015 and ultimately was Senior Group Director and Head of the Inflammation and Cardiovascular/Metabolism Group in the Early Clinical Development Group. Dr. Davis spent nearly 10 years on faculty at The University of California San Francisco leading clinical research in autoimmune diseases, where he most recently was Professor of Clinical Medicine until 2015. He continues to see patients, teach, and serve as volunteer faculty at the Boston VA Medical Center. Dr. Davis earned an M.D. from the University of Maryland. Dr. Davis trained in Internal Medicine and Rheumatology at The University of California San Francisco. He continued training in clinical research and rheumatology at The National Institutes of Health NIAMS Intramural Program. He holds a Master’s in Public Health in Epidemiology from the University of California Berkeley, and a Master of Science in Anatomy from the University of Maryland School of Medicine.

Stephen F. Mahoney joined Magenta as Chief Financial and Operating Officer in November 2020, with more than 20 years of global biotechnology sector industry experience. Most recently, Mr. Mahoney served as President and Chief Operating Officer of Kiniksa Pharmaceuticals, Ltd., from August 2015 to November 2019 where he was responsible for overseeing all operational aspects of Kiniksa Pharmaceuticals, Ltd, including advancement of its existing programs, and as a senior advisor from November 2019 through December 2019. Prior to his time at Kiniksa Pharmaceuticals, Ltd., Mr. Mahoney served as Chief Commercial Officer, among other executive titles of increasing responsibilities, at Synageva Biopharma Corp. Previous to that, he was Regional Director, Legal – Asia Pacific Region for Genzyme Corporation, following other roles for the organization. Mr. Mahoney holds an M.B.A. from the Boston College Carroll School of Management, a J.D. from Boston College Law School and a B.A. from Colorado College.

David Nichols joined Magenta in April 2021 as Chief Technical Officer. Mr. Nichols has over 30 years of comprehensive experience in all clinical and commercial phases of process and analytical development, GMP manufacturing for drug substance and drug product, combination product development and manufacture, quality control, and supply chain logistics. Before joining Magenta, Mr. Nichols served most recently as the Senior Vice President of Technical Operations at Kiniksa Pharmaceuticals, Ltd. from February 2019 to April 2021 and as the Vice President, Technical Operations from August 2016 to February 2019. In this role, he was responsible for leading the strategic integration of technical operations across their portfolio, including process development and

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oversight of internal and external GMP manufacturing. Prior to his time at Kiniksa Pharmaceuticals Ltd., Mr. Nichols was the Head of CMC for the biologics division at Tesaro, Inc. from April 2015 to August 2016. Prior to Tesaro, Inc., David held various positions of increasing responsibility over his 20-year tenure with Shire plc and Transkaryotic Therapies Inc. (acquired by Shire in 2005), where he was able to bring three biologics from early phase development through commercialization. Mr. Nichols holds a Bachelor of Science degree in Chemistry from the University of Massachusetts, a Master of Science degree in Biochemistry from University of New Hampshire and a Master’s in Business Administration from Northeastern University.

Lisa Olson joined Magenta as Head of Research and Chief Scientific Officer in September 2020. Prior to joining Magenta, Dr. Olson served for over fifteen years in leadership positions at the AbbVie Bioresearch Center (formerly the Abbott Bioresearch Center), where she most recently served as Vice President, Immunology Discovery and Site Head from January 2013 to September 2020. In her role as Vice President, Immunology Discovery and Site Head, Dr. Olson was responsible for all immunology discovery scientific and portfolio decisions, including new target approval, project advancement and licensing opportunities. Prior to her time at the AbbVie Bioresearch Center, she served as a Research Fellow and Group Leader in Inflammation & Immunology at Pfizer, Inc. She began her career as an Assistant Professor at Washington University School of Medicine in St. Louis, MO, following a post-doctoral cardiovascular fellowship at the University of Chicago. Dr. Olson holds a Ph.D. from the University of Illinois at Urbana-Champaign and a B.S. in Biological Sciences from Iowa State University.

Kristen Stants joined Magenta as Chief People Officer in January 2020. Prior to joining Magenta, Ms. Stants was the VP of Talent Strategy at Alexion Pharmaceuticals Inc. from October 2017 to December 2019 where she was responsible for talent acquisition and leadership development. Prior to Alexion, Ms. Stants worked in multiple capacities at Patheon Pharmaceuticals Inc., including as VP, Global Talent Management from January 2016 to October 2017 and as VP, HR Business Partner, Global Pharmaceutical Development from January 2016 to August 2016, and spent ten years at Biogen Inc., where she most recently held the position of Senior Director, Human Resources Business Partner (HRBP), R&D from May 2013 to December 2016. Ms. Stants’ early career began in management consulting at Hewitt Associates (now Aon Hewitt) where she led the research for Fortune Magazine’s 100 Best Companies to Work For. Ms. Stants completed a Master of Industrial and Labor Relations, with a concentration in Organizational Behavior, from Cornell University and earned a Bachelor of Science in Psychology and Business from the University of Oregon.

Zoran Zdraveski, J.D., Ph.D. joined Magenta as our Chief Legal Officer in April 2017 and served as our Secretary from March 2018 and as our Chief Legal and Technology Operations Officer from September 2020 until April 21, 2021. After such date, Dr. Zdraveski was no longer an executive officer of the Company. As Chief Legal and Technology Operations Officer, Dr. Zdraveski was responsible for all aspects of Magenta’s legal, intellectual property, and compliance functions. Dr. Zdraveski has more than 19 years of experience in the legal field in the biopharmaceutical industry. Most recently he served as Vice President and Associate General Counsel at Epizyme Inc., from July 2012 to April 2017, where he established the legal team and managed all aspects of legal, intellectual property and compliance both before and after the company’s 2013 initial public offering. Prior to joining Epizyme Inc., he held patent counsel positions at Ironwood from April 2011 to July 2012 and Genzyme Therapeutics, from September 2009 to April 2011. Dr. Zdraveski earned a doctorate in biochemistry from the Massachusetts Institute of Technology, holds a J.D. from Suffolk University Law School, a graduate degree in chemistry and undergraduate degrees in chemistry and studio art, all from Southern Methodist University.

The principal occupation and employment during the past five years of each of our executive officers was carried on, in each case except as specifically identified above, with a corporation or organization that is not a parent, subsidiary or other affiliate of us. There is no arrangement or understanding between any of our executive officers and any other person or persons pursuant to which he was or is to be selected as an executive officer.

There are no material legal proceedings to which any of our executive officers is a party adverse to us or our subsidiary or in which any such person has a material interest adverse to us or our subsidiary.

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PROPOSAL NO. 2 – RATIFICATION OF THE APPOINTMENT OF KPMG LLP

Magenta’s stockholders are being asked to ratify the appointment by the Audit Committee of our Board of Directors of KPMG LLP as Magenta’s independent registered public accounting firm for the fiscal year ending December 31, 2021. KPMG LLP has served as Magenta’s independent registered public accounting firm since 2017.

The Audit Committee is solely responsible for selecting Magenta’s independent registered public accounting firm for the fiscal year ending December 31, 2021. Stockholder approval is not required to appoint KPMG LLP as Magenta’s independent registered public accounting firm. However, our Board of Directors believes that submitting the appointment of KPMG LLP to the stockholders for ratification is good corporate governance. If the stockholders do not ratify this appointment, the Audit Committee will reconsider whether to retain KPMG LLP. If the selection of KPMG LLP is ratified, the Audit Committee, at its discretion, may direct the appointment of a different independent registered public accounting firm at any time it decides that such a change would be in the best interest of Magenta and its stockholders.

A representative of KPMG LLP is expected to be present at the Annual Meeting and will have an opportunity to make a statement if he or she desires to do so and to respond to appropriate questions from our stockholders.

Vote Required

The affirmative vote of a majority of the votes cast for this proposal is required to ratify the appointment of our independent public accountant. Abstentions will be counted towards the tabulation of votes cast on this proposal and will have the same effect as a negative vote. Brokerage firms have authority to vote your unvoted shares held by the firms in street name on this proposal. If a broker does not exercise this authority, such broker non-votes will have no effect on the results of this vote.

OUR BOARD RECOMMENDS A VOTE FOR THE RATIFICATION OF THE APPOINTMENT OF KPMG LLP AS INDEPENDENT PUBLIC ACCOUNTANT, AND PROXIES SOLICITED BY THE BOARD WILL BE VOTED IN FAVOR THEREOF UNLESS A STOCKHOLDER HAS INDICATED OTHERWISE ON THE PROXY.

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CORPORATE GOVERNANCE

Director Nomination Process

Our Nominating and Corporate Governance Committee is responsible for identifying individuals qualified to serve as directors, consistent with criteria approved by our Board of Directors, and recommending such persons to be nominated for election as directors, except where we are legally required by contract, law or otherwise to provide third parties with the right to nominate.

The process followed by our Nominating and Corporate Governance Committee to identify and evaluate director candidates includes soliciting recommendations from any or all of the following sources: non-management directors, the Chief Executive Officer, other executive officers, third-party search firms or any other source our Nominating and Corporate Governance Committee deems appropriate. The qualifications, qualities and skills that our Nominating and Corporate Governance Committee believes must be met by a committee-recommended nominee for a position on our Board of Directors are as follows:

During 2020, our Board of Directors, based on the recommendation of our Nominating and Corporate Governance Committee, appointed Alison F. Lawton to serve as a class III member of our Board of Directors. Ms. Lawton previously served as a member of our Board of Directors from May 2017 to February 2018 and was recommended by Jason Gardner, our President and Chief Executive Officer, for consideration as our Board of Directors sought to further diversify the mix of skills and experience among our board members.    

Stockholders may recommend individuals to the Nominating and Corporate Governance Committee for consideration as potential director candidates. Any such proposals should be submitted to our corporate secretary at our principal executive offices no later than the close of business on the 90th day nor earlier than the close of business on the 120th day prior to the one-year anniversary of the date of the preceding year’s annual meeting and should include appropriate biographical and background material to allow the Nominating and Corporate Governance Committee to properly evaluate the potential director candidate and the number of shares of our stock beneficially owned by the stockholder proposing the candidate. Stockholder proposals should be addressed to Magenta Therapeutics, Inc., 100 Technology Square, Cambridge, Massachusetts 02139, Attention: Corporate Secretary. Assuming that biographical and background material has been provided on a timely basis in accordance with our By-laws, any recommendations received from stockholders will be evaluated in the same manner as potential nominees proposed by the Nominating and Corporate Governance Committee. If our Board of Directors determines to nominate a stockholder-recommended candidate and recommends his or her election, then his or her name will be included on our proxy card for the next annual meeting of stockholders. See the section entitled “Stockholder Proposals” below for a discussion regarding submitting stockholder proposals.

We have no formal policy regarding board diversity. Our priority in selection of board members is identification of members who will further the interests of our stockholders through their established record of professional accomplishment, their ability to contribute positively to the collaborative culture among board members, and their knowledge of our business and understanding of the competitive landscape.

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Director Independence

Applicable Nasdaq Stock Market LLC (“Nasdaq”) rules require a majority of a listed company’s board of directors to be comprised of independent directors within one year of listing. In addition, the Nasdaq rules require that, subject to specified exceptions, each member of a listed company’s audit, compensation and nominating and corporate governance committees be independent and that audit committee members also satisfy independence criteria set forth in Rule 10A-3 under the Exchange Act and that compensation committee members satisfy independence criteria set forth in Rule 10C-1 under the Exchange Act. Under applicable Nasdaq rules, a director will only qualify as an “independent director” if, in the opinion of the listed company’s board of directors, that person does not have a relationship that would interfere with the exercise of independent judgment in carrying out the responsibilities of a director. In order to be considered independent for purposes of Rule 10A-3, a member of an audit committee of a listed company may not, other than in his or her capacity as a member of the audit committee, the board of directors, or any other board committee, accept, directly or indirectly, any consulting, advisory, or other compensatory fee from the listed company or any of its subsidiaries or otherwise be an affiliated person of the listed company or any of its subsidiaries. In addition, in affirmatively determining the independence of any director who will serve on a company’s compensation committee, Rule 10C-1 under the Exchange Act requires that a company’s board of directors must consider all factors specifically relevant to determining whether a director has a relationship to such company which is material to that director’s ability to be independent from management in connection with the duties of a compensation committee member, including: the source of compensation to the director, including any consulting, advisory or other compensatory fee paid by such company to the director, and whether the director is affiliated with the company or any of its subsidiaries or affiliates.

Our Board of Directors has determined that all members of our Board of Directors, except Dr. Gardner, are independent directors, including for purposes of the rules of Nasdaq and the SEC. In making such independence determination, our Board of Directors considered the relationships that each non-employee director has with us and all other facts and circumstances that our Board of Directors deemed relevant in determining their independence, including the beneficial ownership of our capital stock by each non-employee director. In considering the independence of the directors listed above, our Board of Directors considered the association of our directors with the holders of more than 5% of our common stock and also considered Ms. Lawton’s prior relationship with Magenta as a member of our Board of Directors from May 2017 to February 2018 and as a consultant from February 2018 to her re-appointment to our Board of Directors in December 2020. There are no family relationships among any of our directors or executive officers. Dr. Gardner is not an independent director under these rules because he is an executive officer of Magenta.

Board Committees

Our Board of Directors has established an Audit Committee, a Compensation Committee and a Nominating and Corporate Governance Committee. Each of the Audit Committee, Compensation Committee and Nominating and Corporate Governance Committee operates under a charter that satisfies the applicable standards of the SEC and Nasdaq. Each such committee reviews its respective charter at least annually. A current copy of the charter for each of the Audit Committee, Compensation Committee and Nominating and Corporate Governance Committee is posted on the corporate governance section of our website, https://investor.magentatx.com/corporate-governance/governance-overview. In addition, in October 2020, our Board of Directors established an R&D Committee to advise the members of our management and provide oversight and input regarding our research and clinical development strategies. The R&D Committee operates pursuant to the authority granted to it by our Board of Directors. Our Board of Directors may from time to time establish other special or standing committees to facilitate the management of Magenta or to discharge specific duties delegated by the full Board of Directors.

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The table below shows current membership for each of the standing committees of our Board of Directors.

Audit Committee

Our Board of Directors has determined that each member of the Audit Committee is “independent” for Audit Committee purposes as that term is defined in the rules of the SEC and the applicable Nasdaq rules, and each has sufficient knowledge in financial and auditing matters to serve on the Audit Committee. Our Board of Directors has designated Michael W. Bonney and Anne McGeorge as “Audit Committee financial experts,” as defined under the applicable rules of the SEC.

During the fiscal year ended December 31, 2020, the Audit Committee met five times and each of the members attended at least 75% of the meetings of the Audit Committee held during the period for which such person served as a member.

Pursuant to its written charter, the Audit Committee’s responsibilities include:

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Compensation Committee

Our Board of Directors has determined that each member of the Compensation Committee is “independent” as defined in the applicable Nasdaq rules.

During the fiscal year ended December 31, 2020, the Compensation Committee met eight times and each of the members attended 100% of the meetings of the Compensation Committee held during the period for which such person served as a member.

Pursuant to its written charter, the Compensation Committee’s responsibilities include:

Nominating and Corporate Governance Committee

Our Board of Directors has determined that each member of the Nominating and Corporate Governance Committee is “independent” as defined in the applicable Nasdaq rules.

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During the fiscal year ended December 31, 2020, the Nominating and Corporate Governance Committee met three times and each of the members attended 100% of the meetings of the Nominating and Corporate Governance Committee held during the period for which such person served as a member.

Pursuant to its written charter, the Nominating and Corporate Governance Committee’s responsibilities include:

The Nominating and Corporate Governance Committee considers candidates for Board of Director membership suggested by its members and the Chief Executive Officer. Additionally, in selecting nominees for directors, the Nominating and Corporate Governance Committee will review candidates recommended by stockholders in the same manner and using the same general criteria as candidates recruited by the committee and/or recommended by our Board of Directors. Any stockholder who wishes to recommend a candidate for consideration by the committee as a nominee for director should follow the procedures described later in this proxy statement under the heading “Stockholder Proposals.” The Nominating and Corporate Governance Committee will also consider whether to nominate any person proposed by a stockholder in accordance with the provisions of our By-laws relating to stockholder nominations as described later in this proxy statement under the heading “Stockholder Proposals.”

Our Board of Directors is responsible for filling vacancies on our Board of Directors and for nominating candidates for election by our stockholders each year in the class of directors whose term expires at the relevant annual meeting. Our Board of Directors delegates the identification and evaluation process to the Nominating and Corporate Governance Committee, with the expectation that other members of our Board of Directors, and of management, will be requested to take part in the process as appropriate.

Generally, the Nominating and Corporate Governance Committee identifies candidates for director nominees in consultation with management, through the use of search firms or other advisors, through the recommendations submitted by stockholders or through such other methods as the Nominating and Corporate Governance Committee deems to be helpful to identify candidates. Once candidates have been identified, the Nominating and Corporate Governance Committee confirms that the candidates meet all of the minimum qualifications for director nominees established by the Nominating and Corporate Governance Committee. The Nominating and Corporate Governance Committee may gather information about the candidates through interviews, detailed questionnaires, comprehensive background checks or any other means that the Nominating and Corporate Governance Committee deems to be appropriate in the evaluation process. The Nominating and Corporate Governance Committee then meets as a group to discuss and evaluate the qualities and skills of each candidate, both on an individual basis and taking into account the overall composition and needs of our Board of Directors. Based on the results of the evaluation process, the Nominating and Corporate Governance Committee recommends candidates for our Board of Directors’ approval to fill a vacancy or as director nominees for

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election to our Board of Directors by our stockholders each year in the class of directors whose term expires at the relevant annual meeting.

Board and Committee Evaluations

The Nominating and Corporate Governance Committee oversees our annual board and committee evaluation process. Generally, our Board of Directors and each committee conducts self-evaluations by means of written questionnaires completed by each director and committee member. The anonymous responses are summarized and provided to our Board of Directors and each committee at their next meetings in order to facilitate an examination and discussion by our Board of Directors and each committee of the effectiveness of our Board of Directors and committees, Board of Directors and committee structure and dynamics and areas for possible improvement. The Nominating and Corporate Governance Committee establishes the Board of Directors and committee evaluation process each year and may determine to use an independent third party evaluation process from time to time in the future.

Board and Committee Meetings Attendance

The full Board of Directors met seven times during 2020. During 2020, each member of our Board of Directors attended in person or participated in 90% or more of the aggregate of (i) the total number of meetings of our Board of Directors (held during the period for which such person has been a director) and (ii) the total number of meetings held by all committees of our Board of Directors on which such person served (during the periods that such person served).

Director Attendance at Annual Meeting of Stockholders

Directors are encouraged to attend the annual meeting of stockholders. Seven of our directors serving on our Board of Directors at the time of the 2020 annual meeting of stockholders attended the 2020 annual meeting of stockholders.

Policy on Trading, Pledging and Hedging of Company Stock

Certain transactions in our securities (such as purchases and sales of publicly traded put and call options, and short sales) create a heightened compliance risk or could create the appearance of misalignment between management and stockholders. In addition, securities held in a margin account or pledged as collateral may be sold without consent if the owner fails to meet a margin call or defaults on the loan, thus creating the risk that a sale may occur at a time when an officer or director is aware of material, non-public information or otherwise is not permitted to trade in our securities. Our insider trading policy expressly prohibits short sales and derivative transactions of our stock by our executive officers, directors, employees and certain designated consultants and contractors, including short sales of our securities. Our insider trading policy expressly prohibits, without the advance approval of our Audit Committee, purchases or sales of puts, calls, or other derivative securities of the company or any derivative securities that provide the economic equivalent of ownership.

Code of Business Conduct and Ethics

We have adopted a written code of business conduct and ethics that applies to our directors, officers and employees, including our principal executive officer, principal financial officer, principal accounting officer or controller, or persons performing similar functions. A current copy of the code is posted on the corporate governance section of our website, which is located at https://investor.magentatx.com/corporate-governance/governance-overview. If we make any substantive amendments to, or grant any waivers from, the code of business conduct and ethics for any officer or director, we will disclose the nature of such amendment or waiver on our website or in a current report on Form 8-K.

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Board Leadership Structure and Board’s Role in Risk Oversight

Michael W. Bonney currently serves as the chair of our Board of Directors. We believe that separating the role of chair of our Board and Chief Executive Officer allows our Chief Executive Officer to focus on our day-to-day business, while allowing the chair of our Board to lead our Board of Directors in its fundamental role of providing advice to, and independent oversight of, management. Our Board of Directors recognizes the time, effort and energy that the Chief Executive Officer is required to devote to his position in the current business environment, as well as the commitment required to serve as chair of our Board, particularly as our Board of Directors’ oversight responsibilities continue to grow as we mature as a public company. While our By-laws and corporate governance guidelines do not require that we appoint a separate chair and Chief Executive Officer, our Board of Directors believes that having separate positions is the appropriate leadership structure for us at this time and demonstrates our commitment to good corporate governance.

Risk is inherent to every business, and how well a business manages risk can ultimately determine its success. We face a number of risks, including risks relating to our financial condition, operations, strategic direction and intellectual property. Management is responsible for the day-to-day management of risks we face, while our Board of Directors, as a whole and through its committees, has responsibility for the oversight of risk management. In its risk oversight role, our Board of Directors has the responsibility to satisfy itself that the risk management processes designed and implemented by management are adequate and functioning as designed.

The role of our Board of Directors in overseeing the management of our risks is conducted primarily through committees of our Board, as disclosed in the descriptions of each of the committees above and in the charters of each of the committees. The full Board of Directors (or the appropriate board committee in the case of risks that are under the purview of a particular committee) discusses with management our major risk exposures, their potential impact on us, and the steps we take to manage them. When a board committee is responsible for evaluating and overseeing the management of a particular risk or risks, the chair of the relevant committee reports on the discussion to the full Board of Directors during the committee reports portion of the next Board meeting. This enables our Board of Directors and its committees to coordinate the risk oversight role, particularly with respect to risk interrelationships.

Communication with the Directors of Magenta

Any interested party with concerns about our company may report such concerns to our Board of Directors or the chair of our Board of Directors and Nominating and Corporate Governance Committee, by submitting a written communication to the attention of such director at the following address:

c/o Magenta Therapeutics, Inc.

Attn: [Director]

100 Technology Square

Cambridge, Massachusetts 02139

United States

You may submit your concern anonymously or confidentially by postal mail. You may also indicate whether you are a stockholder, customer, supplier, or other interested party.

A copy of any such written communication may also be forwarded to Magenta’s legal counsel and a copy of such communication may be retained for a reasonable period of time. The director may discuss the matter with Magenta’s legal counsel, with independent advisors, with non-management directors, or with Magenta’s management, or may take other action or no action as the director determines in good faith, using reasonable judgment, and applying his or her own discretion.

Communications may be forwarded to other directors if they relate to important substantive matters and include suggestions or comments that may be important for other directors to know. In general, communications relating

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to corporate governance and long-term corporate strategy are more likely to be forwarded than communications relating to ordinary business affairs, personal grievances, and matters as to which we tend to receive repetitive or duplicative communications.

The Audit Committee oversees the procedures for the receipt, retention, and treatment of complaints received by Magenta regarding accounting, internal accounting controls, or audit matters, and the confidential, anonymous submission by employees of concerns regarding questionable accounting, internal accounting controls or auditing matters, or potential violations of the federal securities laws, including any rules and regulations thereunder, or the U.S. Foreign Corrupt Practices Act. Magenta has also established a toll-free telephone number, which is 866-244-3167, and has established a webform, which can be accessed at https://www.whistleblowerservices.com/magentatx, for the reporting of such activity.

Director Compensation

The table below shows all compensation paid to our non-employee directors during 2020. Jason Gardner, D.Phil., our President and Chief Executive Officer, receives no compensation for his service as a director, and, consequently, is not included in this table. The compensation received by Dr. Gardner as an employee during 2020 is presented in “—Executive Compensation—2020 Summary Compensation Table” below.

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Under our director compensation program, we pay our non-employee directors a cash retainer for service on our Board of Directors and for service on each committee on which the director is a member. The chair of each committee receives a higher retainer for such service. These fees are payable in arrears in four equal quarterly installments pro-rated based on the number of actual days served by the director during such calendar quarter. The fees paid to non-employee directors for service on our Board of Directors and for service on each committee of our Board of Directors on which the director is a member are as follows:

We also reimburse our non-employee directors for reasonable travel and out-of-pocket expenses incurred in connection with attending our Board of director and committee meetings.

In addition, each new non-employee director elected to our Board of Directors will be granted an initial, one-time equity award of a stock option to purchase 36,377 shares of our common stock which shall vest 33% on the first anniversary of the grant, then the remainder shall vest monthly in equal installments over the following two years, provided, however, that all vesting shall cease if the director resigns from our Board of Directors or otherwise ceases to serve as a director of Magenta. On the date of each annual meeting of stockholders of Magenta, each continuing non-employee director will receive an annual equity award of a stock option to purchase 18,188 shares, which shall vest in full upon the earlier to occur of the first anniversary of the date of grant or the date of the next Annual Meeting; provided, however, that vesting shall cease if the director resigns from our Board of Directors or otherwise ceases to serve as a director, unless our Board of Directors determines that the circumstances warrant continuation of vesting.

This program is intended to provide a total compensation package that enables us to attract and retain qualified and experienced individuals to serve as directors and to align our directors’ interests with those of our stockholders.

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Executive Compensation

Our named executive officers for the year ended December 31, 2020 are as follows:

2020 Summary Compensation Table

The following table presents the compensation awarded to, earned by or paid to each of our named executive officers for the years indicated.

Narrative to Summary Compensation Table

Our Board of Directors and Compensation Committee review compensation annually for all employees, including our executives. In setting executive base salaries and annual incentives and granting equity incentive

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awards, we consider compensation for comparable positions in the market, the historical compensation levels of our executives, internal equity, individual performance as compared to our expectations and objectives, our desire to motivate our employees to achieve short- and long-term results that are in the best interests of our stockholders, and a long-term commitment to Magenta. We target a general competitive position, based on independent third-party benchmark analytics to inform the mix of compensation of base salary, annual incentives or long-term incentives.

Our Compensation Committee is responsible for determining the compensation for all executives other than the chief executive officer and our Board of Directors, with the recommendation of the Compensation Committee, is responsible for determining the compensation of our chief executive officer. Our Compensation Committee typically reviews and discusses management’s proposed compensation with the chief executive officer for all executives other than the chief executive officer. Based on those discussions and its discretion, taking into account the factors noted above, the Compensation Committee then sets the compensation for each executive officer other than the chief executive officer and recommends the compensation for the chief executive officer to our Board of Directors for approval. Our Board of Directors discusses the Compensation Committee’s recommendation and ultimately approves the compensation of our chief executive officer without members of management present.

In 2020, the Compensation Committee retained the services of Pay Governance LLC, as its external independent compensation consultant. After review of the independence factors set forth by Nasdaq, the Compensation Committee determined that Pay Governance is an independent compensation consultant. Our Board of Directors and the Compensation Committee considered Pay Governance’s input on certain compensation matters as they deemed appropriate.

Annual base salary

Each named executive officer’s base salary is a fixed component of annual compensation for performing specific duties and functions, and has been established by our Compensation Committee or Board of Directors, as applicable, taking into account each individual’s role, responsibilities, skills, and experience. Base salaries for our named executive officers are reviewed annually by our Compensation Committee or Board of Directors, as applicable, typically in connection with our annual performance review process, and adjusted from time to time to realign salaries with market levels after taking into account individual responsibilities, internal equity, performance, and experience.

Cash annual incentive

Our annual incentive program is intended to reward our named executive officers for meeting objective or subjective performance goals for a fiscal year. From time to time, our Compensation Committee or Board of Directors, as applicable, may approve annual incentives for our named executive officers based on individual performance, company performance, or as otherwise determined appropriate. Each of our named executive officers was eligible to receive a target bonus with respect to 2020 (as a percentage of base salary as set forth below) based upon the achievement of corporate performance goals. The Compensation Committee approved a corporate multiplier for the 2020 annual incentive at 90%.

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Long-term equity incentives

Our equity grant program is intended to align the interests of our named executive officers with those of our stockholders and to motivate them to make important contributions to our performance. For more detail, please refer to “Outstanding Equity Awards at 2020 Fiscal Year End.”

Outstanding Equity Awards at 2020 Fiscal Year End

The following table presents information regarding all outstanding stock options held by each of our named executive officers on December 31, 2020.

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Employment arrangements with our named executive officers

Jason Gardner, D.Phil.

Dr. Gardner’s employment agreement provides for the payment of an annual base salary and annual incentive compensation, which are subject to review and redetermination by our Board of Directors. Dr. Gardner’s current base salary for fiscal year 2021 is $545,000 and he is eligible to earn an annual incentive with a target amount equal to 55% of his base salary. Dr. Gardner is also eligible to participate in the employee benefit plans available to our employees, subject to the terms of those plans.

Pursuant to his employment agreement, in the event Dr. Gardner is terminated by us without “cause” (as defined in the agreement) or he resigns for “good reason” (as defined in the agreement), subject to the delivery of a fully effective release of claims, Dr. Gardner will be entitled to receive (i) a cash severance equal to one (1) times his base salary, plus a pro-rata portion of his target annual incentive compensation, payable over the 12-month period following the termination of his employment, and (ii) up to 12 monthly cash payments equal to the monthly contribution for health insurance for Dr. Gardner.

In the event Dr. Gardner is terminated by us without cause or he resigns for good reason, each within 12 months following a change in control (as defined in the agreement), subject to the delivery of a fully effective release of claims, Dr. Gardner will not be entitled to receive the severance benefits described above, but will instead be entitled to the following: (i) a lump sum cash severance equal to 1.5 times his base salary, plus 150% of his target annual incentive compensation, (ii) for all outstanding time-based stock options and other time-based stock-based awards held by Dr. Gardner, full accelerated vesting of such awards, and (iii) up to 18 monthly cash payments equal to the monthly contribution for health insurance for Dr. Gardner.

The payments and benefits provided under Dr. Gardner’s employment agreement in connection with a change in control may not be eligible for federal income tax deduction for Magenta pursuant to Section 280G of the Internal Revenue Code. These payments and benefits may also be subject to an excise tax under Section 4999 of the Internal Revenue Code. If the payments or benefits payable to Dr. Gardner in connection with a change in control would be subject to the excise tax imposed under Section 4999 of the Internal Revenue Code, then those payments or benefits will be reduced if such reduction would result in a higher net after-tax benefit to him.

Pursuant to his employment agreement, Dr. Gardner is subject to standard confidentiality and nondisclosure, assignment of intellectual property work product and post-termination noncompetition and non-solicitation of employees, consultants and customers covenants.

John C. Davis, Jr., M.D.

Dr. Davis’ employment agreement provides for the payment of an annual base salary and annual incentive compensation, which are subject to review and redetermination by our Compensation Committee. Dr. Davis’ base salary for fiscal year 2021 is $464,000, and he is eligible to earn an annual incentive with a target amount equal to 40% of his base salary. Dr. Davis is also eligible to participate in the employee benefit plans available to our employees, subject to the terms of those plans.

Pursuant to his employment agreement, in the event Dr. Davis is terminated by us without “cause” (as defined in the agreement) or he resigns for “good reason” (as defined in the agreement), subject to the delivery of a fully effective release of claims, Dr. Davis will be entitled to receive (i) a cash severance equal to 0.75 times his base salary, payable over the nine-month period following the termination of his employment and (ii) up to nine monthly cash payments equal to the monthly contribution for health insurance for Dr. Davis.

In the event Dr. Davis is terminated by us without cause or he resigns for good reason, each within 12 months following a change in control (as defined in the agreement), subject to the delivery of a fully effective release of claims, Dr. Davis will not be entitled to receive the severance benefits described above, but will instead be

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entitled to the following: (i) a lump sum cash severance equal to one (1) times his base salary, plus 100% of his target annual incentive compensation, (ii) for all outstanding time-based stock options and other time-based stock-based awards held by Dr. Davis, full accelerated vesting of such awards, and (iii) up to 12 monthly cash payments equal to the monthly contribution for health insurance for Dr. Davis.

The payments and benefits provided under Dr. Davis’ employment agreement in connection with a change in control may not be eligible for federal income tax deduction for Magenta pursuant to Section 280G of the Internal Revenue Code. These payments and benefits may also be subject to an excise tax under Section 4999 of the Internal Revenue Code. If the payments or benefits payable to Dr. Davis in connection with a change in control would be subject to the excise tax imposed under Section 4999 of the Internal Revenue Code, then those payments or benefits will be reduced if such reduction would result in a higher net after-tax benefit to him.

Pursuant to his employment agreement, Dr. Davis is subject to standard confidentiality and nondisclosure, assignment of intellectual property work product and post-termination noncompetition and non-solicitation of employees, consultants and customers covenants.

Stephen F. Mahoney

Mr. Mahoney’s employment agreement provides for the payment of an annual base salary and annual incentive compensation, which are subject to review and redetermination by our Compensation Committee. Mr. Mahoney’s base salary for fiscal year 2021 is $433,000, and he is eligible to earn an annual incentive with a target amount equal to 40% of his base salary. Mr. Mahoney is also eligible to participate in the employee benefit plans available to our employees, subject to the terms of those plans.

Pursuant to his employment agreement, in the event Mr. Mahoney is terminated by us without “cause” (as defined in the agreement) or he resigns for “good reason” (as defined in the agreement), subject to the delivery of a fully effective release of claims, Mr. Mahoney will be entitled to receive (i) a cash severance equal to 0.75 times his base salary, payable over the nine-month period following the termination of his employment and (ii) up to nine monthly cash payments equal to the monthly contribution for health insurance for Mr. Mahoney.

In the event Mr. Mahoney is terminated by us without cause or he resigns for good reason, each within 12 months following a change in control (as defined in the agreement), subject to the delivery of a fully effective release of claims, Mr. Mahoney will not be entitled to receive the severance benefits described above, but will instead be entitled to the following: (i) a lump sum cash severance equal to one (1) times his base salary, plus 100% of his target annual incentive compensation, (ii) for all outstanding time-based stock options and other time-based stock-based awards held by Mr. Mahoney, full accelerated vesting of such awards, and (iii) up to 12 monthly cash payments equal to the monthly contribution for health insurance for Mr. Mahoney.

The payments and benefits provided under Mr. Mahoney’s employment agreement in connection with a change in control may not be eligible for federal income tax deduction for Magenta pursuant to Section 280G of the Internal Revenue Code. These payments and benefits may also be subject to an excise tax under Section 4999 of the Internal Revenue Code. If the payments or benefits payable to Mr. Mahoney in connection with a change in control would be subject to the excise tax imposed under Section 4999 of the Internal Revenue Code, then those payments or benefits will be reduced if such reduction would result in a higher net after-tax benefit to him.

Pursuant to his employment agreement, Mr. Mahoney is subject to standard confidentiality and nondisclosure, assignment of intellectual property work product and post-termination noncompetition and non-solicitation of employees, consultants and customers covenants.

Compensation Risk Assessment

We believe that although a portion of the compensation provided to our executive officers and other employees is performance-based, our executive compensation program does not encourage excessive or unnecessary risk

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taking. This is primarily due to the fact that our compensation programs are designed to encourage our executive officers and other employees to remain focused on both short-term and long-term strategic goals, in particular in connection with our pay-for-performance compensation philosophy. As a result, we do not believe that our compensation programs are reasonably likely to have a material adverse effect on us.

Equity Compensation Plan Information

The following table sets forth information as of December 31, 2020 regarding shares of common stock that may be used under our equity compensation plans.

The 2019 ESPP has an evergreen provision whereby the number of shares of common stock reserved and available for purchase under the 2019 ESPP is subject to an automatic increase on each January 1, beginning in 2020, by the lesser of (i) 1% of the number of shares issued and outstanding on the immediately preceding December 31, (ii) 1,000,000 shares and (iii) such number of shares as determined by the Administrator (as defined in the 2019 ESPP). The number of shares reserved for purchase under the ESPP did not increase on January 1, 2021.

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CERTAIN RELATIONSHIPS AND RELATED PARTY TRANSACTIONS

Certain Relationships and Transactions

Other than the compensation agreements and other arrangements described under “Executive Compensation” and “Director Compensation” in this proxy statement and the transactions described below, since January 1, 2019, there has not been and there is not currently proposed, any transaction or series of similar transactions to which we were, or will be, a party in which the amount involved exceeded, or will exceed, $120,000 (or, if less, 1% of the average of our total assets amounts at December 31, 2019 and 2020) and in which any director, executive officer, holder of five percent or more of any class of our capital stock or any member of the immediate family of, or entities affiliated with, any of the foregoing persons, had, or will have, a direct or indirect material interest.

Collaboration and Advisory Services

During the years ended December 31, 2019 and 2020, we made payments for advisory and related services from Be the Match BioTherapies Collection Services, LLC (f/k/a Be the Match BioTherapies, LLC) (“BTMB”) and its affiliates, including National Marrow Donor Program (“NMDP”), in the amount of $523,046 and $533,937, respectively. We have a collaboration agreement with NMDP (as successor in interest to BTMB) and a research agreement with an affiliated organization, Center for International Blood and Marrow Transplant Research. Amy Lynn Ronneberg was formerly the president of BTMB, and is the Chief Executive Officer of NMDP and a member of our Board of Directors. These fees were paid to BTMB and its affiliates pursuant to the collaboration agreement in amounts mutually agreed upon in advance by us and BTMB. None of these fees were paid directly to Ms. Ronneberg. The fees paid to BTMB did not exceed 5% of the consolidated gross revenue of BTMB (or NMDP) during fiscal years 2019 and 2020.

Public Offering of Common Stock

On June 29, 2020, we completed a registered public offering pursuant to which we issued and sold 8,625,000 shares of our common stock at a public offering price of $8.00 per share. Certain of our existing stockholders, including the affiliate of one of our directors, purchased shares of our common stock in the offering. The following table summarizes purchase in the offering by related persons.

Limitation of Liability and Indemnification of Officers and Directors

Our Certificate of Incorporation contains provisions that limit the liability of our directors for monetary damages to the fullest extent permitted by Delaware law. Consequently, our directors will not be personally liable to us or

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our stockholders for monetary damages for any breach of fiduciary duties as directors, except liability for the following:

Any amendment to, or repeal of, these provisions will not eliminate or reduce the effect of these provisions in respect of any act, omission or claim that occurred or arose prior to that amendment or repeal. If the Delaware General Corporation Law is amended to provide for further limitations on the personal liability of directors of corporations, then the personal liability of our directors will be further limited to the greatest extent permitted by the Delaware General Corporation Law.

In addition, our By-laws provide that we will indemnify, to the fullest extent permitted by law, any person who is or was a party or is threatened to be made a party to any action, suit or proceeding by reason of the fact that he or she is or was one of our directors or officers or is or was serving at our request as a director or officer of another corporation, partnership, joint venture, trust, or other enterprise. Our By-laws provide that we may indemnify to the fullest extent permitted by law any person who is or was a party or is threatened to be made a party to any action, suit, or proceeding by reason of the fact that he or she is or was one of our employees or agents or is or was serving at our request as an employee or agent of another corporation, partnership, joint venture, trust or other enterprise. Our By-laws also provide that we must advance expenses incurred by or on behalf of a director or officer in advance of the final disposition of any action or proceeding, subject to very limited exceptions.

We have entered into, and in the future plan to enter into, agreements to indemnify our directors and executive officers. These agreements, among other things, require us to indemnify these individuals for certain expenses (including attorneys’ fees), judgments, fines and settlement amounts reasonably incurred by such person in any action or proceeding, including any action by or in our right, on account of any services undertaken by such person on behalf of our company or that person’s status as a member of our Board of Directors to the maximum extent allowed under Delaware law.

Related Person Transaction Policy

Our Board of Directors adopted a written related person transactions policy providing that transactions with our directors, officers and holders of five percent or more of our voting securities and their affiliates must be approved by our Audit Committee. This policy became effective on June 20, 2018. Pursuant to this policy, the Audit Committee has the primary responsibility for reviewing and approving or disapproving “related person transactions,” which are transactions between us and related persons and in which a related person has or will have a direct or indirect material interest. For purposes of this policy, a related person is defined as a director, executive officer, nominee for director, or greater than 5% beneficial owner of our common stock, in each case since the beginning of the most recently completed year, and their immediate family members.

As appropriate for the circumstances, the Audit Committee will review and consider:

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PRINCIPAL STOCKHOLDERS

The following table sets forth information, to the extent known by us or ascertainable from public filings, with respect to the beneficial ownership of our common stock as of March 31, 2021 by:

The column entitled “Shares Beneficially Owned” is based on a total of 48,603,205 shares of our common stock outstanding as of March 31, 2021.

Beneficial ownership is determined in accordance with the rules and regulations of the SEC and includes voting or investment power with respect to our common stock. Shares of our common stock subject to options that are currently exercisable or exercisable within 60 days of March 31, 2021 are considered outstanding and beneficially owned by the person holding the options for the purpose of calculating the percentage ownership of that person but not for the purpose of calculating the percentage ownership of any other person. Except as otherwise noted, the persons and entities in this table have sole voting and investing power with respect to all of the shares of our common stock beneficially owned by them, subject to community property laws, where applicable.

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INFORMATION ABOUT OUR INDEPENDENT ACCOUNTANTS

KPMG LLP has served as our independent auditor since 2017. Magenta incurred the following fees from KPMG LLP for the audit of the consolidated financial statements and for other services provided during the years ended December 31, 2020 and 2019.

Audit Committee Pre-Approval Policy and Procedures

Our Board of Directors has adopted and our Audit Committee has ratified policies and procedures relating to the approval of all audit and non-audit services that are to be performed by our independent registered public accounting firm. This policy provides that we will not engage our independent registered public accounting firm to render audit or non-audit services unless the service is specifically approved in advance by our Audit Committee or the engagement is entered into pursuant to the pre-approval procedure described below.

From time to time, our Audit Committee may pre-approve specified types of services that are expected to be provided to us by our independent registered public accounting firm during the next 12 months. Any such pre-approval details the particular service or type of services to be provided and is also generally subject to a maximum dollar amount.

During our 2020 and 2019 fiscal years, no services were provided to us by KPMG LLP other than in accordance with the pre-approval policies and procedures described above.

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REPORT OF THE AUDIT COMMITTEE

The Audit Committee is appointed by our Board of Directors to assist our Board of Directors in fulfilling its oversight responsibilities with respect to (1) the integrity of Magenta’s financial statements and financial reporting process and systems of internal controls regarding finance, accounting, and compliance with legal and regulatory requirements, (2) the qualifications, independence, and performance of Magenta’s independent registered public accounting firm, (3) the performance of Magenta’s internal audit function, if any, and (4) other matters as set forth in the charter of the Audit Committee approved by our Board of Directors.

Management is responsible for the preparation of Magenta’s financial statements and the financial reporting process, including its system of internal control over financial reporting and its disclosure controls and procedures. The independent registered public accounting firm is responsible for performing an audit of Magenta’s financial statements in accordance with the standards of the Public Company Accounting Oversight Board (the “PCAOB”) and issuing a report thereon. The Audit Committee’s responsibility is to monitor and oversee these processes.

In connection with these responsibilities, the Audit Committee reviewed and discussed with management the audited consolidated financial statements of Magenta for the fiscal year ended December 31, 2020. The Audit Committee also discussed with the independent registered public accounting firm the matters required to be discussed by the applicable requirements of the PCAOB and the SEC. In addition, the Audit Committee received written communications and the letter from the independent registered public accounting firm confirming their independence as required by the applicable requirements of the PCAOB and has discussed with the independent registered public accounting firm their independence.

Based on the reviews and discussions referred to above, the Audit Committee recommended to our Board of Directors that the audited consolidated financial statements of Magenta be included in Magenta’s Annual Report on Form 10-K for the fiscal year ended December 31, 2020 that was filed with the SEC. The information contained in this report shall not be deemed to be (1) “soliciting material,” (2) “filed” with the SEC, (3) subject to Regulations 14A or 14C of the Exchange Act, or (4) subject to the liabilities of Section 18 of the Exchange Act. This report shall not be deemed incorporated by reference into any of our other filings under the Exchange Act or the Securities Act, except to the extent that we specifically incorporate it by reference into such filing.

April 21, 2021

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STOCKHOLDER PROPOSALS

A stockholder who would like to have a proposal considered for inclusion in our 2022 proxy statement must submit the proposal in accordance with the procedures outlined in Rule 14a-8 of the Exchange Act so that it is received by us no later than December 22, 2021. However, if the date of the 2022 Annual Meeting of Stockholders is changed by more than 30 days from the date of the previous year’s meeting, then the deadline is a reasonable time before we begin to print and send our proxy statement for the 2022 Annual Meeting of Stockholders. SEC rules set standards for eligibility and specify the types of stockholder proposals that may be excluded from a proxy statement. Stockholder proposals should be addressed to 100 Technology Square, Cambridge, Massachusetts 02139, Attention: Corporate Secretary.

If a stockholder wishes to propose a nomination of persons for election to our Board of Directors or present a proposal at an annual meeting but does not wish to have the proposal considered for inclusion in our proxy statement and proxy card, our By-laws establish an advance notice procedure for such nominations and proposals. Stockholders at an annual meeting may only consider proposals or nominations specified in the notice of meeting or brought before the meeting by or at the direction of our Board of Directors or by a stockholder of record on the record date for the meeting, who is entitled to vote at the meeting and who has delivered timely notice in proper form to our corporate secretary of the stockholder’s intention to bring such business before the meeting.

The required notice must be in writing and received by our corporate secretary at our principal executive offices not less than 90 days nor more than 120 days prior to the first anniversary of the preceding year’s annual meeting. However, in the event that the date of the annual meeting is advanced by more than 30 days, or delayed by more than 60 days, from the first anniversary of the preceding year’s annual meeting, a stockholder’s notice must be so received no earlier than the 120th day prior to such annual meeting and not later than the close of business on the later of (A) the 90th day prior to such annual meeting and (B) the tenth day following the day on which notice of the date of such annual meeting was mailed or public disclosure of the date of such annual meeting was made, whichever first occurs. For stockholder proposals to be brought before the 2022 Annual Meeting of Stockholders, the required notice must be received by our corporate secretary at our principal executive offices no earlier than February 1, 2022 and no later than March 3, 2022. Stockholder proposals and the required notice should be addressed to 100 Technology Square, Cambridge, Massachusetts 02139, Attention: Corporate Secretary.

OTHER MATTERS

Our Board of Directors does not know of any other matters to be brought before the Annual Meeting. If any other matters not mentioned in this proxy statement are properly brought before the meeting, the individuals named in the enclosed proxy intend to use their discretionary voting authority under the proxy to vote the proxy in accordance with their best judgment on those matters.

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		YOUR VOTE IS IMPORTANT! PLEASE VOTE BY:
				INTERNET Go To: www.proxypush.com/MGTA •  Cast your vote online •  Have your Proxy Card ready •  Follow the simple instructions to record your vote
				PHONE  Call 1-866-230-6343 •  Use any touch-tone telephone •  Have your Proxy Card ready •  Follow the simple recorded instructions
				MAIL •  Mark, sign and date your Proxy Card •  Fold and return your Proxy Card in the postage-paid envelope provided

Annual Meeting of Stockholders

For Stockholders as of record on April 5, 2021

This proxy is being solicited on behalf of the Board of Directors

The undersigned hereby appoints Jason Gardner and Stephen F. Mahoney as the “Named Proxies”, and each or either of them, as the true and lawful attorneys of the undersigned, with full power of substitution and revocation, and authorizes them, and each of them, to vote all the shares of capital stock of Magenta Therapeutics, Inc. which the undersigned is entitled to vote at said meeting and any adjournment thereof upon the matters specified and upon such other matters as may be properly brought before the meeting or any adjournment thereof, conferring authority upon such true and lawful attorneys to vote in their discretion on such other matters as may properly come before the meeting and revoking any proxy heretofore given.

THE SHARES REPRESENTED BY THIS PROXY WILL BE VOTED AS DIRECTED OR, IF NO DIRECTION IS GIVEN, SHARES WILL BE VOTED FOR THE ELECTION OF THE DIRECTORS IN PROPOSAL 1 AND FOR PROPOSAL 2.

You are encouraged to specify your choice by marking the appropriate box (SEE REVERSE SIDE) but you need not mark any box if you wish to vote in accordance with the Board of Directors’ recommendation. The Named Proxies cannot vote your shares unless you sign (on the reverse side) and return this card.

PLEASE BE SURE TO SIGN AND DATE THIS PROXY CARD AND MARK ON THE REVERSE SIDE

Magenta Therapeutics, Inc.

Annual Meeting of Stockholders

Please make your marks like this: ☒ Use dark black pencil or pen only

THE BOARD OF DIRECTORS RECOMMENDS A VOTE:

FOR THE ELECTION OF THE DIRECTOR NOMINEES LISTED IN PROPOSAL 1 AND FOR PROPOSAL 2

		PROPOSAL				YOUR VOTE				BOARD OF DIRECTORS RECOMMENDS
1.		To elect four class III directors to our Board of Directors, to serve until the 2024 annual meeting of stockholders and until his or her successor has been duly elected and qualified, or until his or her earlier death, resignation or removal.		FOR		WITHHOLD
		1.01 Bruce Booth, D.Phil.		☐		☐				FOR
		1.02 Thomas O. Daniel, M.D.		☐		☐				FOR
		1.03 Jason Gardner, D.Phil.		☐		☐				FOR
		1.04 Alison F. Lawton		☐		☐				FOR
				FOR		AGAINST		ABSTAIN
2.		To ratify the appointment of KPMG LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2021.		☐		☐		☐		FOR
		Note: In their discretion, the Named Proxies are authorized to vote upon any other matters that are properly brought by or at the discretion of the Board of Directors before the Annual Meeting and at any adjournments or postponements thereof.

You must register to attend the meeting online and/or participate at www.proxydocs.com/MGTA

Authorized Signatures - This section must be completed for your instructions to be executed.

Please sign exactly as your name(s) appears on your account. If held in joint tenancy, all persons should sign. Trustees, administrators, etc., should include title and authority. Corporations should provide full name of corporation and title of authorized officer signing the Proxy Card.