Dianthus Therapeutics (DNTH) Form 3 Magenta Therapeutics / Stephen F. Mahoney ownership change

                              Power of Attorney

      Know all by these presents, that the undersigned hereby constitutes and
appoints each of Zoran Zdraveski and Cindy Driscoll, signing singly, and with
full power of substitution, as the undersigned's true and lawful
attorney-in-fact to:

      (1) execute for and on behalf of the undersigned, in the undersigned's
      capacity as an officer and/or director of Magenta Therapeutics, Inc., a
      Delaware corporation (the "Company"), from time to time the following
      Securities and Exchange Commission (the "SEC") forms: Forms 3, 4, and 5 in
      accordance with Section 16(a) of the Securities Exchange Act of 1934, as
      amended (the "Exchange Act"), and the rules thereunder;

      (2) do and perform any and all acts for and on behalf of the undersigned
      which may be necessary or desirable to complete and execute any such
      Form 3, 4, or 5, complete and execute any amendment or amendments thereto,
      and timely file such form with the SEC and any stock exchange or similar
      authority; and

      (3) take any other action of any type whatsoever in connection with the
      foregoing which, in the opinion of such attorney-in-fact, may be of
      benefit to, in the best interest of, or legally required by, the
      undersigned, it being understood that the documents executed by such
      attorney-in-fact on  behalf of the undersigned pursuant to this Power of
      Attorney shall be in such form and shall contain such terms and conditions
      as such attorney-in-fact may approve in such attorney-in-fact's
      discretion.

       The undersigned hereby grants to each such attorney-in-fact full power
and authority to do and perform any and every act and thing whatsoever
requisite, necessary, or proper to be done in the exercise of any of the rights
and powers herein granted, as fully to all intents and purposes as the
undersigned might or could do if personally present, with full power of
substitution or revocation, hereby ratifying and confirming all that such
attorney-in-fact, or such attorney-in-fact's substitute or substitutes, shall
lawfully do or cause to be done by virtue of this power of attorney and the
rights and powers herein granted. The undersigned acknowledges that the
foregoing attorneys-in-fact, in serving in such capacity at the request of the
undersigned, is not assuming, nor is the Company assuming, any of the
undersigned's responsibilities to comply with Section 16 of the Exchange Act.

       This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms 3, 4, and 5 with respect to the
undersigned's holdings of and transactions in
securities issued by the Company, unless earlier revoked by the undersigned in a
signed writing delivered to the foregoing attorneys-in-fact. This Power of
Attorney shall expire as to any individual attorney-in-fact if such
attorney-in-fact ceases to be an officer of the Company. This Power of Attorney
may be filed with the SEC as a confirming statement of the authority granted
herein.

       IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of this 3rd day of November, 2020.


Employee:  /s/ Stephen F. Mahoney
         -----------------------

Printed Name: Stephen F. Mahoney