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 OF SECURITIES
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      
1. Name and Address of Reporting Person * Bain Capital Life Sciences Investors, LLC 2. Issuer Name and Ticker or Trading Symbol Aptinyx Inc. [ APTX ] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable)_____ Director                    __X__ 10% Owner
_____ Officer (give title below)    _____ Other (specify below)
(Last)         (First)         (Middle)
200 CLARENDON STREET, 
3. Date of Earliest Transaction (MM/DD/YYYY)
10/26/2020
(Street)
BOSTON, MA 02116
(City)       (State)       (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)
 
6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person
_ X _ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. 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  10/26/2020    P(1)    3333333  A $3.00  8891758  I  See footnotes (2)(3)(4)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. Trans. 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 7. Title and Amount of Securities Underlying Derivative Security
(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

Explanation of Responses:
(1)  On October 26, 2020, Bain Capital Life Sciences Fund, L.P. ("BCLS") and BCIP Life Sciences Fund, LP ("BCIPLS and, together with BCLS, the "Bain Capital Life Sciences Entities") purchased an aggregate of 3,333,333 shares of Common Stock in an underwritten public offering at a price per share of $3.00. BCLS purchased 3,023,816 of such shares and BCIPLS purchased 309,517 of such shares. Following such purchases, BCLS holds 8,066,113 shares of Common Stock and BCIPLS holds 825,645 shares of Common Stock.
(2)  Bain Capital Life Sciences Partners, LP ("BCLSP") is the general partner of BCLS. As a result, BCLSP may be deemed to share voting and dispositive power with respect to the shares of Common Stock held by BCLS. BCLSP disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein.
(3)  Bain Capital Life Sciences Investors, LLC ("BCLSI"), whose managers are Jeffrey Schwartz and Adam Koppel, is the general partner of BCLSP and governs the investment strategy and decision-making process with respect to investments held by BCIPLS, whose general partner is Boylston Coinvestors, LLC. As a result, each of BCLSI, Mr. Schwartz and Dr. Koppel may be deemed to share voting and dispositive power with respect to the shares of Common Stock held by the Bain Capital Life Sciences Entities. BCLSI, Mr. Schwartz and Dr. Koppel each disclaim beneficial ownership of such securities except to the extent of their pecuniary interest therein.
(4)  Adam Koppel is a director of the Issuer.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
Bain Capital Life Sciences Investors, LLC
200 CLARENDON STREET
BOSTON, MA 02116

X

Bain Capital Life Sciences Partners, LP
200 CLARENDON STREET
BOSTON, MA 02116

X

Bain Capital Life Sciences Fund, L.P.
200 CLARENDON STREET
BOSTON, MA 02116

X

BCIP Life Sciences Associates, LP
200 CLARENDON STREET
BOSTON, MA 02116

X

Schwartz Jeffrey Lawrence
200 CLARENDON STREET
BOSTON, MA 02116

X

Koppel Adam
C/O BAIN CAPITAL LIFE SCIENCES INVESTORS
200 CLARENDON STREET
BOSTON, MA 02116
X X


Signatures
Bain Capital Life Sciences Investors, LLC, By: /s/ Adam Koppel, Title: Managing Director 10/27/2020
**Signature of Reporting Person Date
Bain Capital Life Sciences Partners, LP, By: Bain Capital Life Sciences Investors, LLC, its general partner, By: /s/ Adam Koppel, Title: Managing Director 10/27/2020
**Signature of Reporting Person Date
Bain Capital Life Sciences Fund, L.P., By: Bain Capital Life Sciences Partners, LP, its general partner, By: Bain Capital Life Sciences Investors, LLC, its general partner, By: /s/ Adam Koppel, Title: Managing Director 10/27/2020
**Signature of Reporting Person Date
BCIP Life Sciences Associates, LP, By: Boylston Coinvestors, LLC, its general partner, By: /s/ Adam Koppel, Title: Authorized Signatory 10/27/2020
**Signature of Reporting Person Date
/s/ Jeffrey Schwartz 10/27/2020
**Signature of Reporting Person Date
/s/ Adam Koppel 10/27/2020
**Signature of Reporting Person Date