SEC Form 3

FORM 3

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

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1. Name and Address of Reporting Person* ORBIMED ADVISORS LLC (Last) (First) (Middle) 601 LEXINGTON AVE., 54TH FLOOR (Street) NEW YORK NY 10022 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 11/15/2017	3. Issuer Name and Ticker or Trading Symbol Arsanis, Inc. [ ASNS ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			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 Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series A-1 Convertible Preferred Stock	(1)	(1)	Common Stock	19,533	(1)	I	See Footnotes(6)(7)
Series A-2 Convertible Preferred Stock	(2)	(2)	Common Stock	252,230	(2)	I	See Footnotes(6)(7)
Series B Convertible Preferred Stock	(3)	(3)	Common Stock	328,909	(3)	I	See Footnotes(6)(7)
Series C Convertible Preferred Stock	(4)	(4)	Common Stock	114,320	(4)	I	See Footnotes(6)(7)
Series D Convertible Preferred Stock	(5)	(5)	Common Stock	653,974	(5)	I	See Footnotes(6)(7)

1. Name and Address of Reporting Person* ORBIMED ADVISORS LLC (Last) (First) (Middle) 601 LEXINGTON AVE., 54TH FLOOR (Street) NEW YORK NY 10022 (City) (State) (Zip)

1. Name and Address of Reporting Person* OrbiMed Capital GP IV LLC (Last) (First) (Middle) 601 LEXINGTON AVE, 54TH FLOOR (Street) NEW YORK NY 10022 (City) (State) (Zip)

1. Name and Address of Reporting Person* ISALY SAMUEL D (Last) (First) (Middle) 601 LEXINGTON AVE, 54TH FLOOR (Street) NEW YORK NY 10022 (City) (State) (Zip)

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. The reported securities are held of record by OrbiMed Private Investments IV, LP ("OPI IV"). OrbiMed Capital GP IV LLC ("GP IV") is the sole general partner of OPI IV, and OrbiMed Advisors LLC ("Advisors"), a registered adviser under the Investment Advisers Act of 1940, as amended, is the sole managing member of GP IV. Samuel D. Isaly ("Isaly"), a natural person, is the managing member of, and owner of a controlling interest in, Advisors. By virtue of such relationships, GP IV, Advisors and Isaly may be deemed to have voting and investment power with respect to the securities held by OPI IV. The Reporting Persons have designated a representative, currently Carl Gordon, a member of Advisors, to serve on the Issuer's board of directors.

7. This report on Form 3 is jointly filed by GP IV, Advisors and Isaly. Each of the reporting persons disclaims beneficial ownership of the securities reported herein for purposes of Rule 16a-1(a) under the Securities Exchange Act of 1934, as amended (the "Exchange Act"), except to the extent of its or his pecuniary interest therein, if any. This report on Form 3 shall not be deemed an admission that any of the reporting persons is a beneficial owner of such securities for the purpose of Section 16 of the Exchange Act, or for any other purpose.

Remarks:

	/s/ Samuel D. Isaly, as managing member of OrbiMed Advisors LLC	11/15/2017
	/s/ Samuel D. Isaly, as managing member of OrbiMed Advisors LLC, the managing member of OrbiMed Capital GP IV LLC	11/15/2017
	/s/ Samuel D. Isaly	11/15/2017
	** Signature of Reporting Person	Date
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