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CORRESP
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CORRESP

 Goodwin Procter LLP

 Three Embarcadero Center,
28th Floor

 San Francisco, CA 94111

 goodwinlaw.com

+1 (415) 733-6000

 June 22, 2023

 VIA
EDGAR

 Office of Life Sciences

 Division of
Corporation Finance

 U.S. Securities and Exchange Commission

100 F Street NE

 Washington, DC 20549

Attention:

Ms. Doris Stacey Gama

Mr. Jason Drory

Ms. Jenn Do

Mr. Kevin Vaughn

 Re:         Magenta Therapeutics, Inc.

               Registration Statement on Form
S-4

                Filed
May 15, 2023

                File No. 333-271917

Dear. Ms. Gama, Mr. Drory, Ms. Do and Mr. Vaughn:

This letter is submitted on behalf of Magenta Therapeutics, Inc. (“Magenta”) in response to the comments of the staff of the
Division of Corporation Finance (the “Staff”) of the U.S. Securities and Exchange Commission (the “Commission”) with respect to Magenta’s Registration Statement on Form
S-4 (File No: 333-271917), initially filed on May 15, 2023 (the “Registration Statement”), as set forth in the Staff’s letter dated
June 13, 2023 (the “Comment Letter”). Magenta is concurrently submitting Amendment No. 1 to the Registration Statement (“Amendment No. 1”), which includes changes to reflect responses to
the Staff’s comments and other updates.

 For reference purposes, the text of the Comment Letter has been reproduced herein with
responses below each numbered comment. For your convenience, we have italicized the reproduced Staff comments from the Comment Letter. Unless otherwise indicated, page references in the descriptions of the Staff’s comments refer to the
Registration Statement, and page references in the responses refer to Amendment No. 1. All capitalized terms used and not otherwise defined herein shall have the meanings set forth in Amendment No. 1.

Registration Statement on Form S-4

Questions and Answers About the Merger

 Q: What are
contingent value rights (“CVR”)?, page 4

1.
 We note your disclosure that, “[i]n April 2023, Magenta sold certain assets, including intellectual
property, related to its product candidates MGTA-45, MGTA-145 and the CD117 antibodies including the clinical antibody that was used with
MGTA-117, and is continuing to explore strategic alternatives related to its other assets.” Please specify the programs or pre-merger assets held by Magenta the are
covered by the CVR Agreement. We note from your disclosure on pages 253 and 254 that the April 2023 asset sales included certain up-front cash payments as well as future potential milestone payments.
Please clarify whether or not any of the April 2023 asset sales by Magenta, including future milestone payments, are covered by the CVR Agreement.

RESPONSE: Magenta acknowledges the Staff’s comment and has revised the disclosure on pages 4, 23,
258-259, 374, 380 of Amendment No. 1 to reflect the Staff’s comment.

 U.S. Securities and Exchange Commission

June 22, 2023

  Page
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2.
 Please revise your disclosure to clarify the material terms of the CVR Agreement, your intentions with
Magenta’s pre-merger assets and describe any material assets that either have been sold or may be sold by Magenta pursuant to the CVR Agreement or otherwise advise.

RESPONSE: Magenta acknowledges the Staff’s comment and has revised the disclosure on pages 4, 11, 23, 37, 206, 374 and 380 of Amendment No. 1
to reflect the Staff’s comment.

 The Companies Magenta, page 10

3.
 You state here and on page 252 that in April 2023, Magenta sold certain assets, related to Magenta’s
prior product candidates. However, you also state that Magenta is continuing to explore strategic alternatives related to its “other assets.” Given your recent sales in April 2023, please revise your disclosure to clarify what you mean
when you state “other assets” to specifically describe any material assets or otherwise advise.

 RESPONSE: Magenta
acknowledges the Staff’s comment and has revised the disclosure on pages 11 and 256 of Amendment No. 1 to reflect the Staff’s comment. Magenta supplementally advises the Staff that the “other assets” include intellectual
property related to its legacy business that are not currently in development and that Magenta does not consider to be material.

 Prospectus Summary,
page 12

4.
 Please balance your discussion here, and on page 145, to disclose the negative factors or potential risks
associated with your merger agreement that were considered by the boards of directors of Magenta and Dianthus, respectively, when each voted to approve the merger agreement.

RESPONSE: Magenta acknowledges the Staff’s comment and has revised the disclosure on pages 13-16 and 152
of Amendment No. 1 to reflect the Staff’s comment.

 Risk Factors

Risks Related to the Merger

 Some Magenta and Dianthus
directors and executive officers have interests in the merger..., page 28

5.
 We note your disclosure that “certain of Dianthus’ directors are affiliated with investment funds
which hold an interest in Dianthus and are participating in the Dianthus pre- closing financing.” Please update your disclosure here to identify the directors and the fund(s) they are affiliated with that are participating in the pre-closing financing.

 RESPONSE: Magenta acknowledges the Staff’s comment and has
revised the disclosure on page 30 of Amendment No. 1 to reflect the Staff’s comment.

 The Merger

Background of the Merger, page 133

6.
 Please revise your disclosure to identify the individuals who negotiated the material terms of the merger.
For example only, we note your disclosure that “Magenta’s management,” “participants” and certain “financial advisors” were part of the negotiations related to the merger.

RESPONSE: Magenta acknowledges the Staff’s comment and has revised the disclosure on pages 134, and
142-148 of Amendment No. 1 to reflect the Staff’s comment.

 U.S. Securities and Exchange Commission

June 22, 2023

  Page
 3

7.
 We note your disclosure on page 136 discussing certain “Criteria” that would be used to evaluate
any potential indications of interest. Please revise to more specifically describe the criteria proposed to assess potential counterparties. For example, if you were looking for parties with a product candidate that had achieved a specific stage of
development, what stage was that? What were you looking for with respect to the attractiveness of the counterparty’s technology and development pipeline? Additionally, please discuss whether the criteria and/or the prioritization of the
criteria changed over time.

 RESPONSE: Magenta acknowledges the Staff’s comment and has revised the disclosure on pages 138-139 of Amendment No. 1 to reflect the Staff’s comment. Magenta advises the Staff that it has further revised the defined term “Criteria” on
pages 138-139 and 141 of Amendment No. 1 (which was previously included on page 136 of the Registration Statement) to add more specificity in response to the Staff’s comment. Magenta further
advises the Staff (and as disclosed on page 139 of Amendment No. 1), Magenta applied the Criteria to potential counterparties on a holistic basis in considering their relative potential strengths and weaknesses and did not change (nor
reprioritize) the Criteria over time.

8.
 On page 140 you state that on March 21, 2023 representatives of Wedbush communicated to
representatives of Dianthus Magenta’s willingness to agree to a traditional reverse merger in exchange for an increase in the valuation attributed to Magenta. Please include a description of Dianthus’ response to such communication.

 RESPONSE: Magenta acknowledges the Staff’s comment and has revised the disclosure on page 143 of Amendment No. 1 in
response to the Staff’s comment.

9.
 We note your disclosure that “after reviewing all of the submitted indications of interest, the
participants selected 12 indications of interest to prioritize and invite to make management and due diligence presentations.” However, your disclosure appears to only disclose Parties A through D. Please update your disclosure to describe the
seven other parties that were invited to make presentations. In addition, update your existing disclosure where you describe Parties A through D to provide additional details about each party, including a description of the general industry of the
company.

 RESPONSE: Magenta acknowledges the Staff’s comment and has revised the disclosure on pages 139-140 of Amendment No. 1 to reflect the Staff’s comment.

 Opinion of Houlihan Lokey to the Magenta Board,
page 154

10.
 Revise to provide additional information regarding how Houlihan Lokey selected the comparable companies and
whether it excluded any comparable companies that fit those criteria.

 RESPONSE: Magenta acknowledges the Staff’s
comment and has revised the disclosure on page 162 of Amendment No. 1 in response to the Staff’s comment. Magenta further advises the Staff that, as noted in the revised disclosure, Houlihan Lokey may not have included all companies that
might be deemed comparable to Dianthus, but Magenta supplementally advises the Staff that Houlihan Lokey did not exclude any companies that it otherwise deemed relevant.

 U.S. Securities and Exchange Commission

June 22, 2023

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11.
 Please explain the statement “Houlihan Lokey selected an implied enterprise value reference range for
Dianthus of $150.0 million to $200.0 million, which resulted in an aggregate implied equity value reference range for Dianthus of $274.2 million to $324.2 million, and an implied per share
reference range for Dianthus of $4.75 to $5.62.” Please clarify how Houlihan Lokey arrived at the $150.0 million to $200.0 million range. For example, did Houlihan Lokey use the mean, median, high or low value from the calculations of
the comparable companies? Please explain what other considerations Houlihan Lokey deemed relevant and how they impacted Houlihan Lokey’s analysis.

RESPONSE: Magenta acknowledges the Staff’s comment and has revised the disclosure on page 163 of Amendment No. 1 in response to the
Staff’s comment.

12.
 We note your disclosure that “[t]he Magenta Liquidation Analysis and Houlihan Lokey’s selected
companies analysis for Dianthus indicated an implied exchange ratio reference range of 4.42844313 to 5.33756289 shares of Magenta common stock for each share of Dianthus capital stock, as compared to the exchange ratio in the merger pursuant to the
Merger Agreement of 3.88182949 shares of Magenta common stock for each share of Dianthus capital stock.” Please revise to describe the conclusions Houlihan Lokey reached with respect to the implied exchange ratio as a result of such
comparisons.

 RESPONSE: Magenta acknowledges the Staff’s comment and advises the Staff that, as described on page 163 of
Amendment No. 1, “Houlihan Lokey arrived at its opinion based on the results of all analyses undertaken by it and assessed as a whole and did not draw, in isolation, conclusions from or with regard to any individual analysis, methodology
or factor. While the results of each analysis were taken into account in reaching Houlihan Lokey’s overall conclusion with respect to fairness, Houlihan Lokey did not make separate or quantifiable judgments regarding individual analyses.”
Magenta also supplementally advises the Staff that, because Houlihan Lokey’s opinion addressed the fairness, from a financial point of view, to Magenta of the exchange ratio provided for in the merger, the fact that the implied exchange ratio
reference range indicated by Houlihan Lokey’s financial analyses was above the exchange ratio provided for in the Merger supported Houlihan Lokey’s opinion.

The Merger Agreement, page 177 Potential

 Asset Sale,
page 183

13.
 You state hereunder that in April 2023, Magenta entered into asset purchase agreements related to each of
(i) MGTA-145, (ii) MGTA-45 and (iii) the CD117 antibodies, including the clinical antibody that was used with MGTA-117. We note from Magenta’s Form 10-Q for the period then ended that assets held for sale appears to consist of only remaining lab equipment (referring to page 15
therein). Please address the following:

•

 Tell us how you considered the guidance of ASC
205-20-45 in determining whether discontinued operations accounting was appropriate for some or all of the asset purchase agreements for the drug candidates.

•

 Further in this regard, noting the sale of MGTA-45 on
April 7, 2023 (page 143), tell us why you reported the $1.1 million recorded as other income as of March 31, 2023 (referring to page 21 of the March 31, 2023 Form 10-Q), instead of gain from discontinued operations, is appropriate.

 RESPONSE: Magenta
acknowledges the Staff’s comment and advises the Staff that it has considered the provisions of ASC 205-20-45, Discontinued Operations, in concluding that
each of the MGTA-145, MGTA-45, and CD117 antibodies, including the clinical antibody that was used with MGTA-117, asset sales do
not qualify as discontinued operations.

 MGTA-145 and MGTA-45 represent
product candidates that Magenta was advancing through pre-clinical and clinical trials. CD117 antibodies were used with Magenta’s MGTA-117 product candidate, which
Magenta was

 U.S. Securities and Exchange Commission

June 22, 2023

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advancing through clinical trials. The asset sale agreements are comprised of the transfer of intellectual property and related data; contracts and licenses directly related to the assets; and
additional information such as regulatory correspondence and other information, as applicable. Each of the three asset purchase agreements consist of the sale of a single asset that is comprised of intellectual property and associated support
relating to that specific asset.

 Pursuant to ASC
205-20-45-1B, the operations related to a disposal of the MGTA-145, MGTA-45 and CD117 antibodies assets are reported in discontinued operations in the statement of operations if all of the following criteria are met:

•

 The disposed assets (and liabilities) together represent a component of an entity (or a group of components of an
entity).

•

 The component (or group of components) (1) meets the criteria to be classified as held for sale,
(2) has been sold, or (3) has been disposed of other than by sale.

•

 The disposal of the component “represents a strategic shift that has (or will have) a major effect on an
entity’s operations and financial results”.

 In regard to the criteria described above, a component of an entity is defined in
the U.S. GAAP Master Glossary as follows:

 A component of an entity comprises operations and cash flows that can be clearly
distinguished, operationally and for financial reporting purposes, from the rest of the entity. A component of an entity may be a reportable segment or an operating segment, a reporting unit, a subsidiary, or an asset group.

As noted in Magenta’s filings on Forms 10-K and 10-Q, direct research and
development expenses are tracked on a program-by-program basis and consist primarily of external costs, such as fees paid to consultants, central laboratories,
contractors, contract development and manufacturing organizations (”CDMOs”) and contract research organizations (“CROs”) in connection with its preclinical and clinical development activities. Magenta does not allocate employee
costs, costs associated with its platform technology or facility expenses, including depreciation or other indirect costs, to specific product development programs because these costs are deployed across multiple product development programs and, as
such, are not separately classified. MGTA-145 was a product candidate being developed as part of Magenta’s mobilization program. MGTA-45 and MGTA-117, which CD-117 was used with, were product candidates being developed as part of Magenta’s conditioning program.

Neither operations or cash flows for each of the product candidates within these two development programs could be clearly distinguished as internal employee
resources, equipment and facility costs