Sec Form 4 Filing - Bain Capital Life Sciences Investors, LLC @ Solid Biosciences Inc. - 2024-01-11

FORM 4 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

OMB APPROVAL OMB Number: 3235-0287 Expires: November 30, 2011 Estimated average burden hours per response... 0.5

1. Name and Address of Reporting Person Bain Capital Life Sciences Investors, LLC 2. Issuer Name and Ticker or Trading Symbol Solid Biosciences Inc. [ SLDB] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 200 CLARENDON STREET 3. Date of Earliest Transaction (MM/DD/YY) 01/11/2024 (Street) BOSTON, MA02116 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 01/11/2024 A( 1 ) 904,160 A $ 5.53 4,034,582 I See footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) ( 6 ) ( 7 ) ( 8 )

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 Bain Capital Life Sciences Investors, LLC 200 CLARENDON STREET BOSTON, MA02116 X X BCLS SB Investco, LP 200 CLARENDON STREET BOSTON, MA02116 X X Bain Capital Life Sciences Partners, LP 200 CLARENDON STREET BOSTON, MA02116 X X Bain Capital Life Sciences Fund II, L.P. 200 CLARENDON STREET BOSTON, MA02116 X X Bain Capital Life Sciences Investors II, LLC 200 CLARENDON STREET BOSTON, MA02116 X X BCLS II Investco, LP 200 CLARENDON STREET BOSTON, MA02116 X X BCLS II Investco (GP), LLC 200 CLARENDON STREET BOSTON, MA02116 X X BCIP Life Sciences Associates, LP 200 CLARENDON STREET BOSTON, MA02116 X X Signatures See signatures included in Exhibit 99.1 01/12/2024 Signature of Reporting Person Date

Explanation of Responses:

( 1 )On January 8, 2024, BCLS II Equity Opportunities, LP ("BCLS II Equity") entered into a securities purchase agreement with the Issuer pursuant to which the Issuer agreed to issue and sell 904,160 shares of Common Stock to BCLS II Equity at a price of $5.53 per share (the "January 2024 Private Placement"). The January 2024 Private Placement closed on January 11, 2024. BCLS II Equity and BCLS II Equity Opportunities GP, LLC ("BCLS II Equity GP"), its general partner, plan to file a Form 3 with the Securities and Exchange Commission in connection with the acquisition of shares of Common Stock by BCLS II Equity in the January 2024 Private Placement. ( 2 )Represents 528,660 shares of Common Stock held directly by BCLS SB Investco, LP ("BCLS SB"), 267,257 shares of Common Stock held directly by Bain Capital Life Sciences Fund II, L.P. ("BCLS Fund II"), 2,301,955 shares of Common Stock held directly by BCLS II Investco, LP ("BCLS II Investco"), 904,160 shares of Common Stock held directly by BCLS II Equity and 32,550 shares of Common Stock held directly by BCIP Life Sciences Associates, LP ("BCIPLS" and, together with BCLS SB, BCLS Fund II, BCLS II Investco and BCLS II Equity, the "Bain Capital Life Sciences Entities"), after giving effect to the closing of the January 2024 Private Placement. ( 3 )Bain Capital Life Sciences Partners, LP ("BCLSP") is the general partner of BCLS SB. As a result, BCLSP may be deemed to share voting and dispositive power with respect to the securities held by BCLS SB. BCLSP disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 4 )Bain Capital Life Sciences Investors II, LLC ("BCLSI II") is the general partner of BCLS Fund II. As a result, BCLSI II may be deemed to share voting and dispositive power with respect to the securities held by BCLS Fund II. BCLSI II disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 5 )BCLS II Investco (GP), LLC ("BCLS II Investco GP"), whose managing member is BCLS Fund II, is the general partner of BCLS II Investco. As a result, each of BCLSI II, BCLS Fund II and BCLS II Investco GP may be deemed to share voting and dispositive power with respect to the securities held by BCLS II Investco. Each of BCLSI II, BCLS Fund II and BCLS II Investco GP disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 6 )BCLS Fund II is the manager of BCLS II Equity GP. As a result, each of BCLSI II and BCLS Fund II may be deemed to share voting and dispositive power with respect to the securities held by BCLS II Equity. Each of BCLSI II and BCLS Fund II disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 7 )Boylston Coinvestors, LLC is the general partner of BCIPLS. ( 8 )Bain Capital Life Sciences Investors, LLC ("BCLSI") (i) is the general partner of BCLSP, (ii) is the manager of BCLSI II and (iii) governs the investment strategy and decision-making process with respect to investments held by BCIPLS. As a result, BCLSI may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Life Sciences Entities. BCLSI disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein.

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).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.