Sec Form 3 Filing - SVLSF V, LLC @ Arsanis, Inc. - 2017-11-15

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 SVLSF V, LLC 2. Issuer Name and Ticker or Trading Symbol Arsanis, Inc. [ ASNS] 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) ONE BOSTON PLACE, SUITE 3900, 201 WASHINGTON STREET 3. Date of Earliest Transaction (MM/DD/YY) 11/15/2017 (Street) BOSTON, MA02108 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

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 Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 19,128 D ( 6 ) Series A-1 Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 404 D ( 7 ) Series A-2 Convertible Preferred Stock ( 2 ) ( 2 ) ( 2 ) Common Stock 247,010 D ( 6 ) Series A-2 Convertible Preferred Stock ( 2 ) ( 2 ) ( 2 ) Common Stock 5,219 D ( 7 ) Series B Convertible Preferred Stock ( 3 ) ( 3 ) ( 3 ) Common Stock 322,102 D ( 6 ) Series B Convertible Preferred Stock ( 3 ) ( 3 ) ( 3 ) Common Stock 6,806 D ( 7 ) Series C Convertible Preferred Stock ( 4 ) ( 4 ) ( 4 ) Common Stock 111,955 D ( 6 ) Series C Convertible Preferred Stock ( 4 ) ( 4 ) ( 4 ) Common Stock 2,365 D ( 7 ) Series D Convertible Preferred Stock ( 5 ) ( 5 ) ( 5 ) Common Stock 202,915 D ( 6 ) Series D Convertible Preferred Stock ( 5 ) ( 5 ) ( 5 ) Common Stock 4,288 D ( 7 ) Series D Convertible Preferred Stock ( 5 ) ( 5 ) ( 5 ) Common Stock 431,980 D ( 8 ) Series D Convertible Preferred Stock ( 5 ) ( 5 ) ( 5 ) Common Stock 14,789 D ( 9 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other SVLSF V, LLC ONE BOSTON PLACE, SUITE 3900 201 WASHINGTON STREET BOSTON, MA02108 X SVLSF VI, LLC ONE BOSTON PLACE, SUITE 3900 201 WASHINGTON STREET BOSTON, MA02108 X SV Life Sciences Fund VI Strategic Partners, L.P. ONE BOSTON PLACE, SUITE 3900, 201 WASHINGTON STREET BOSTON, MA02108 X SV Life Sciences Fund VI, L.P. ONE BOSTON PLACE, SUITE 3900, 201 WASHINGTON STREET BOSTON, MA02108 X SV Life Sciences Fund V Strategic Partners, L.P. ONE BOSTON PLACE, SUITE 3900, 201 WASHINGTON STREET BOSTON, MA02108 X SV LIFE SCIENCES FUND V LP ONE BOSTON PLACE, SUITE 3900, 201 WASHINGTON STREET BOSTON, MA02108 X Signatures /s/ Mike Gray, as attorney-in-fact on behalf of SVLSF V, LLC 11/15/2017 Signature of Reporting Person Date /s/ Mike Gray, as attorney-in-fact on behalf of SVLSF VI, LLC 11/15/2017 Signature of Reporting Person Date /s/ Mike Gray, as attorney-in-fact on behalf of SV Life Sciences Fund V, L.P. 11/15/2017 Signature of Reporting Person Date /s/ Mike Gray, as attorney-in-fact on behalf of SV Life Sciences Fund V Strategic Partners, L.P. 11/15/2017 Signature of Reporting Person Date /s/ Mike Gray, as attorney-in-fact on behalf of SV Life Sciences Fund VI, L.P. 11/15/2017 Signature of Reporting Person Date /s/ Mike Gray, as attorney-in-fact on behalf of SV Life Sciences Fund VI Strategic Partners, L.P. 11/15/2017 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The Series A-1 Convertible Preferred Stock is convertible into Common Stock on a 0.29300-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 2 )The Series A-2 Convertible Preferred Stock is convertible into Common Stock on a 0.35785-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 3 )The Series B Convertible Preferred Stock is convertible into Common Stock on a 0.44650-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 4 )The Series C Convertible Preferred Stock is convertible into Common Stock on a 0.49832-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 5 )The Series D Convertible Preferred Stock is convertible into Common Stock on a 0.29300-for-one basis into the number of shares of Common Stock shown in column 3 at any time at the holder's election and automatically upon the closing of the Issuer's initial public offering without payment of further consideration. The shares have no expiration date. ( 6 )These shares are owned directly by SV Life Sciences Fund V, L.P. ("SVLS V LP"). SV Life Sciences Fund V (GP), LP ("SVLS V GP") is the general partner of SVLS V LP. The general partner of SVLS V GP is SVLSF V, LLC. Kate Bingham, James Garvey, Eugene D. Hill, III and Michael Ross are members of the investment committee of SVLSF V, LLC. SVLS V GP, SVLSF V, LLC and each of the individuals comprising the SVLSF V, LLC investment committee may be deemed to share voting, dispositive and investment power over the shares held of record by SVLS V LP. Each of SVLS V GP, SVLSF V, LLC and the individual members of the SVLSF V, LLC investment committee disclaims beneficial ownership of these securities and this report shall not be deemed to be an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or any other purpose, except to the extent of their pecuniary interest therein. ( 7 )These shares are owned directly by SV Life Sciences Fund V Strategic Partners, L.P. ("SVLS V SPP"). SVLS V GP is the general partner of SVLS V SPP. The general partner of SVLS V GP is SVLSF V, LLC. Kate Bingham, James Garvey, Eugene D. Hill, III and Michael Ross are members of the investment committee of SVLSF V, LLC. SVLS V GP, SVLSF V, LLC and each of the individuals comprising the SVLSF V, LLC investment committee may be deemed to share voting, dispositive and investment power over the shares held of record by SVLS V SPP. Each of SVLS V GP, SVLSF V, LLC and the individual members of the SVLSF V, LLC investment committee disclaims beneficial ownership of these securities and this report shall not be deemed to be an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or any other purpose, except to the extent of their pecuniary interest therein. ( 8 )These shares are owned directly by SV Life Sciences Fund VI, L.P. ("SVLS VI LP"). SV Life Sciences Fund VI (GP), LP ("SVLS VI GP") is the general partner of SVLS VI LP. The general partner of SVLS VI GP is SVLSF VI, LLC. Kate Bingham, James Garvey, Eugene D. Hill, III, Paul LaViolette, Thomas Flynn and Michael Ross are members of the investment committee of SVLSF VI, LLC. SVLS VI GP, SVLSF VI, LLC and each of the individuals comprising the SVLSF VI, LLC investment committee may be deemed to share voting, dispositive and investment power over the shares held of record by SVLS VI LP. Each of SVLS VI GP, SVLSF VI, LLC and the individual members of the SVLSF VI, LLC investment committee disclaims beneficial ownership of these securities and this report shall not be deemed to be an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or any other purpose, except to the extent of their pecuniary interest therein. ( 9 )These shares are owned directly by SV Life Sciences Fund VI Strategic Partners, L.P. ("SVLS VI SPP"). SVLS VI GP is the general partner of SVLS VI SPP. The general partner of SVLS VI GP is SVLSF VI, LLC. Kate Bingham, James Garvey, Eugene D. Hill, III, Paul LaViolette, Thomas Flynn and Michael Ross are members of the investment committee of SVLSF VI, LLC. SVLS VI GP, SVLSF VI, LLC and each of the individuals comprising the SVLSF VI, LLC investment committee may be deemed to share voting, dispositive and investment power over the shares held of record by SVLS VI SPP. Each of SVLS VI GP, SVLSF VI, LLC and the individual members of the SVLSF VI, LLC investment committee disclaims beneficial ownership of these securities and this report shall not be deemed to be an admission that any one of them is the beneficial owner of such securities for purposes of Section 16 or any other purpose, except to the extent of their pecuniary interest therein.

Remarks: Exhibit Index:24.1 Power of Attorney24.2 Power of Attorney24.3 Power of Attorney24.4 Power of Attorney24.5 Power of Attorney24.6 Power of Attorney

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