Sec Form 3 Filing - Meng Lei @ Dianthus Therapeutics, Inc. /DE/ - 2023-09-11

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Meng Lei 2. Issuer Name and Ticker or Trading Symbol Dianthus Therapeutics, Inc. /DE/ [ DNTH] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O DIANTHUS THERAPEUTICS, INC., 7 TIMES SQUARE, 43RD FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 09/11/2023 (Street) NEW YORK, NY10036 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 1,217,554 ( 1 ) ( 2 ) I See footnote ( 3 ) ( 4 )

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Meng Lei C/O DIANTHUS THERAPEUTICS, INC. 7 TIMES SQUARE, 43RD FLOOR NEW YORK, NY10036 X Avidity Partners Management LP 2828 N HARWOOD STREET, SUITE 1220 DALLAS, TX75201 X Signatures MENG LEI /s/ Adam Veness, as attorney-in-fact for Lei Meng 09/13/2023 Signature of Reporting Person Date AVIDITY PARTNERS MANAGEMENT LP By: Avidity Partners Management (GP) LLC, its general partner /s/ David Witzke Managing Member /s/ Michael Gregory Managing Member 09/13/2023 Signature of Reporting Person Date AVIDITY PARTNERS MANAGEMENT (GP) LLC /s/ David Witzke Managing Member /s/ Michael Gregory Managing Member 09/13/2023 Signature of Reporting Person Date DAVID WITZKE /s/ David Witzke 09/13/2023 Signature of Reporting Person Date MICHAEL GREGORY /s/ Michael Gregory 09/13/2023 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Effective as of September 11, 2023 (the "Effective Time"), a wholly-owned subsidiary of Magenta Therapeutics, Inc. ("Magenta"), merged (the "Merger") with and into Dianthus Therapeutics, Inc. ("Dianthus") resulting in, among other things, Dianthus becoming a wholly owned subsidiary of Magenta. At the Effective Time, Magenta effected a name change to "Dianthus Therapeutics, Inc." (hereinafter, the "Issuer"). ( 2 )Represents the number of shares of common stock of the Issuer received by the Reporting Person in the Merger in exchange for the shares of Dianthus held by the Reporting Person prior to the Merger. Each share of Dianthus common stock held at the Effective Time was exchanged for 0.2181 shares of the Issuer's common stock, which gives effect to the reverse stock split of common stock effected by the Issuer and the Merger exchange ratio. ( 3 )The reported shares are held by clients of Avidity Partners Management LP and may be deemed to beneficially owned by (i) Avidity Partners Management LP, (ii) Avidity Partners Management (GP) LLC, the general partner of Avidity Partners Management LP and (iii) each of David Witzke and Michael Gregory, the managing members of Avidity Partners Management (GP) LLC. Lei Meng, an employee of Avidity Partners Management LP, is a director of the Issuer. Avidity Partners Management LP, Avidity Partners Management (GP) LLC, Mr. Witzke and Mr. Gregory may be considered directors by deputization due to their affiliation with Ms. Meng. Each Reporting Person disclaims beneficial ownership of these shares except to the extent of its, his or her pecuniary interest, if any, therein, and this report shall not be deemed to be an admission that such Reporting Person is the beneficial owner of such securities for purposes of Section 16 or for any other purpose. ( 4 )As of the date hereof, Avidity Partners Management (GP) LLC, David Witzke and Michael Gregory have not yet received the applicable EDGAR codes required to make filings with the Securities and Exchange Commission; however, such Reporting Persons have applied for the applicable codes and will supplement this Form 3 once such codes are available.

Remarks: Exhibit 24 - Power of Attorney

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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