Sec Form 4 Filing - BAIN CAPITAL VENTURE INVESTORS, LLC @ Quanterix Corp - 2017-12-11

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

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1. Name and Address of Reporting Person BAIN CAPITAL VENTURE INVESTORS, LLC 2. Issuer Name and Ticker or Trading Symbol Quanterix Corp [ QTRX] 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/YY) 12/11/2017 (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 12/11/2017 C 394,273 A 394,273 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) Common Stock 12/11/2017 C 1,034,971 A 1,429,244 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) Common Stock 12/11/2017 C 472,271 A 1,901,515 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) Common Stock 12/11/2017 C 108,670 A 2,010,185 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) Common Stock 12/11/2017 C 125,900 A 2,136,085 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 )

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 Series A-1 Preferred Stock ( 1 ) 12/11/2017 C 1,267,200 ( 6 ) ( 7 ) Common Stock 394,273 ( 1 ) 0 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) Series A-2 Preferred Stock ( 1 ) 12/11/2017 C 3,326,401 ( 6 ) ( 7 ) Common Stock 1,034,971 ( 1 ) 0 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) Series B Preferred Stock ( 1 ) 12/11/2017 C 1,517,880 ( 6 ) ( 7 ) Common Stock 472,271 ( 1 ) 0 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) Series C Preferred Stock ( 1 ) 12/11/2017 C 349,271 ( 6 ) ( 7 ) Common Stock 108,670 ( 1 ) 0 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 ) Series D Preferred Stock ( 1 ) 12/11/2017 C 404,632 ( 6 ) ( 7 ) Common Stock 125,900 ( 1 ) 0 I See Footnotes ( 2 ) ( 3 ) ( 4 ) ( 5 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other BAIN CAPITAL VENTURE INVESTORS, LLC 200 CLARENDON STREET BOSTON, MA02116 X BAIN CAPITAL VENTURE PARTNERS 2005, L.P. 200 CLARENDON STREET BOSTON, MA02116 X BAIN CAPITAL VENTURE FUND 2005, L.P. 200 CLARENDON STREET BOSTON, MA02116 X BCIP Associates III, LLC 200 CLARENDON STREET BOSTON, MA02116 X BCIP Associates III 200 CLARENDON STREET BOSTON, MA02116 X BCIP Associates III-B, LLC 200 CLARENDON STREET BOSTON, MA02116 X BCIP Associates III-B 200 CLARENDON STREET BOSTON, MA02116 X KRUPKA MICHAEL A C/O BAIN CAPITAL VENTURE INVESTORS, LLC 200 CLARENDON STREET BOSTON, MA02116 X Agarwal Ajay C/O BAIN CAPITAL VENTURE INVESTORS, LLC 200 CLARENDON STREET BOSTON, MA02116 X Signatures Bain Capital Venture Investors, LLC, By: /s/ Michael A. Krupka, Name: Michael A. Krupka, Title: Managing Director 12/11/2017 Signature of Reporting Person Date Bain Capital Venture Partners 2005, L.P., By: Bain Capital Venture Investors, LLC, its general partner, By: /s/ Michael A. Krupka, Name: Michael A. Krupka, Title: Managing Director 12/11/2017 Signature of Reporting Person Date Bain Capital Venture Fund 2005, L.P., By: Bain Capital Venture Partners 2005, L.P., its general partner, By: Bain Capital Venture Investors, LLC, its general partner, By: /s/ Michael A. Krupka, Name: Michael A. Krupka, Title: Managing Director 12/11/2017 Signature of Reporting Person Date BCIP Associates III, LLC, By: BCIP Associates III, its manager, By: Boylston Coinvestors, LLC, its managing partner, By: /s/ Michael A. Krupka, Name: Michael A. Krupka, Title: Authorized Signatory 12/11/2017 Signature of Reporting Person Date BCIP Associates III, By: Boylston Coinvestors, LLC, its managing partner, By: /s/ Michael A. Krupka, Name: Michael A. Krupka, Title: Authorized Signatory 12/11/2017 Signature of Reporting Person Date BCIP Associates III-B, LLC, By: BCIP Associates III-B, its manager, By: Boylston Coinvestors, LLC, its managing partner, By: /s/ Michael A. Krupka, Name: Michael A. Krupka, Title: Authorized Signatory 12/11/2017 Signature of Reporting Person Date BCIP Associates III-B, By: Boylston Coinvestors, LLC, its managing partner, By: /s/ Michael A. Krupka, Name: Michael A. Krupka, Title: Authorized Signatory 12/11/2017 Signature of Reporting Person Date /s/ Michael A. Krupka 12/11/2017 Signature of Reporting Person Date /s/ Ajay Agarwal 12/11/2017 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The shares of preferred stock automatically converted into common stock immediately prior to the closing of the Issuer's initial public offering using a calculation defined in the Issuer's Restated Certificate of Incorporation, as amended, based on the initial purchase price and the conversion rate in effect at the time of conversion. The shares of preferred stock automatically converted on a 1-for-3.214 basis and such conversion rate is reflected in the amount of common stock underlying the security. ( 2 )Bain Capital Venture Investors, LLC ("BCVI") is the general partner of Bain Capital Venture Partners 2005, L.P. ("BCVP"), which is the general partner of Bain Capital Venture Fund 2005, L.P. ("Fund 2005"). As a result, BCVP may be deemed to share voting and dispositive power with respect to the securities held by Fund 2005. BCVP disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. Immediately prior to the closing of the Issuer's initial public offering on December 11, 2017, the 1,106,387 shares of the Issuer's Series A-1 Preferred Stock, 2,904,268 shares of the Issuer's Series A-2 Preferred Stock, 1,325,258 shares of the Issuer's Series B Preferred Stock, 304,948 shares of the Issuer's Series C Preferred Stock and 353,283 shares of the Issuer's Series D Preferred Stock held by Fund 2005 automatically converted into 344,239, 903,630, 412,339, 94,881 and 109,921 shares of the Issuer's common stock, respectively. ( 3 )Immediately prior to the closing of the Issuer's initial public offering on December 11, 2017, the 157,639 shares of the Issuer's Series A-1 Preferred Stock, 413,802 shares of the Issuer's Series A-2 Preferred Stock, 188,823 shares of the Issuer's Series B Preferred Stock, 43,449 shares of the Issuer's Series C Preferred Stock and 50,336 shares of the Issuer's Series D Preferred Stock held by BCIP Associates III, LLC ("BCIP III"), whose manager is BCIP Associates III ("BCIPA III"), whose managing partner is Boylston Coinvestors, LLC ("Boylston"), automatically converted into 49,047, 128,749, 58,750, 13,518 and 15,663 shares of the Issuer's common stock, respectively. BCIPA III may be deemed to share voting and dispositive power with respect to the securities held by BCIP III. BCIPA III disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 4 )Immediately prior to the closing of the Issuer's initial public offering on December 11, 2017, the 3,174 shares of the Issuer's Series A-1 Preferred Stock, 8,331 shares of the Issuer's Series A-2 Preferred Stock, 3,799 shares of the Issuer's Series B Preferred Stock, 874 shares of the Issuer's Series C Preferred Stock and 1,013 shares of the Issuer's Series D Preferred Stock held by BCIP Associates III-B, LLC ("BCIP III-B" and together with Fund 2005 and BCIP III, the "Bain Capital Entities"), whose manager is BCIP Associates III-B ("BCIPA III-B"), whose managing partner is Boylston, automatically converted into 987, 2,592, 1,182, 271 and 316 shares of the Issuer's common stock, respectively. BCIPA III-B may be deemed to share voting and dispositive power with respect to the securities held by BCIP III-B. BCIPA III-B disclaims beneficial ownership of such securities except to the extent of its pecuniary interest therein. ( 5 )The governance, investment strategy and decision-making process with respect to the investments held by the Bain Capital Entities is directed by the Executive Committee of BCVI, which consists of Michael A. Krupka and Ajay Agarwal. As a result, BCVI and Messrs. Krupka and Agarwal may be deemed to share voting and dispositive power with respect to the securities held by the Bain Capital Entities. BCVI and Messrs. Krupka and Agarwal disclaim beneficial ownership of such securities except to the extent of their pecuniary interest therein. ( 6 )These shares were convertible into the Issuer's common stock in accordance with the Issuer's Restated Certificate of Incorporation, as amended, at any time after the issuance of such shares, at the holder's election. ( 7 )Not applicable.

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