The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

  Names of Reporting Persons.

   D. Victor Perlroth, M.D.

  Check the Appropriate Box if a Member of a Group (See Instructions)

  (a)  ☐        (b)  ☐

  SEC Use Only

  Citizenship or Place of Organization

  United States of America

Number of

Shares

  Beneficially  

Owned by

Each

Reporting

Person

With:

  Sole Voting Power

  5,047,590 shares¹

  Shared Voting Power

  N/A

  Sole Dispositive Power

  5,047,590 shares¹

  Shared Dispositive Power

  N/A

  Aggregate Amount Beneficially Owned by Each Reporting Person

  5,047,590

  Check if the Aggregate Amount in Row (9) Excludes Certain Shares (See Instructions)

  ☐

  Percent of Class Represented by Amount in Row (9)

  13.4%²

  Type of Reporting Person (See Instructions)

  IN

Includes (a) 7,923 unvested shares of common stock subject to a Company right of repurchase as of March 1, 2019; and (b) 936,052 shares of common stock that Dr. Perlroth has the right to acquire from the issuer immediately or within sixty days of December 31, 2018 pursuant to the exercise of option awards, of which 493,750 are unvested, early exercisable and subject to a Company right of repurchase as of March 1, 2019.

Based on 36,829,857 shares of common stock outstanding as of November 14, 2018 as reported on the issuer’s Quarterly Report on Form 10-Q filed on November 16, 2018.

Name of Issuer:

Address of Issuer’s Principal Executive Offices:

Name of Person Filing:

Address of Principal Business Office or, if none, Residence:

Citizenship:

Title of Class of Securities:

CUSIP Number:

☐ Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

☐ Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

☐ Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

☐ Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8).

☐ An investment advisor in accordance with §240.13d-1(b)(1)(ii)(E);

☐ An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

☐ A parent holding company or control person in accordance with §240.13d-1(b)(1)(ii)(G);

☐ A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

☐ A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

☐ A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J); or

☐ Group, in accordance with § 240.13d-1(b)(1)(ii)(K).

Amount beneficially owned

Percent of Class:

Number of shares as to which such person has:

/s/ Victor Perlroth, M.D.