The remainder of this cover page shall be filled out of 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 disclosures provided in a prior cover page.

NAME OF REPORTING PERSON

OPKO Health, Inc.

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a)  ☒        (b)  ☒

SEC USE ONLY

CITIZENSHIP OR PLACE OF ORGANIZATION

Delaware

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH:

SOLE VOTING POWER

488,131 (1)

SHARED VOTING POWER

0

SOLE DISPOSITIVE POWER

488,131 (1)

SHARED DISPOSITIVE POWER

0

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

488,131 (1)

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES ☐

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

4.99% (2)

TYPE OF REPORTING PERSON

CO

Comprised of (i) 135,371 shares of common stock, par value $0.01 (the “Common Stock”), of Mabvax Therapeutics Holdings, Inc. (the “Issuer”) and (ii) 277,778 shares of Common Stock into which shares of Series L Preferred Stock of the Issuer could be converted and 74,982 shares of Common Stock into which Series I Preferred Stock of the Issuer could be converted. Excludes (i) 32,625 shares of Common Stock into which Class I Preferred Stock of the Issuer cannot currently be converted due to a provision that precludes OPKO from converting such preferred stock as applicable, if such conversion would result in OPKO or any of its affiliates beneficially owning in excess of 4.99% of the shares of Common Stock, and (ii) 150,150 shares of Common Stock into which Class E Preferred Stock of the Issuer cannot currently be converted due to a provision that precludes OPKO from converting such preferred stock as applicable, if such conversion would result in OPKO or any of its affiliates beneficially owning in excess of 4.99% of the shares of Common Stock.

Calculated based on (i) 9,429,582 shares of Common Stock outstanding as of April 24, 2019, as reported in the Issuer’s amended quarterly report on Form 10-Q for the fiscal quarter ended September 30, 2018, filed with the Securities and Exchange Commission on April 24, 2019 (the “Quarterly Report”), and (ii) 352,760 shares of Common Stock underlying currently convertible preferred stock.

NAME OF REPORTING PERSON

Phillip Frost, M.D.

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a)  ☒        (b)  ☒

SEC USE ONLY

CITIZENSHIP OR PLACE OF ORGANIZATION

United States

SOLE VOTING POWER

0

SHARED VOTING POWER

487,855 (2)

SOLE DISPOSITIVE POWER

0

SHARED DISPOSITIVE POWER

487,855 (2)

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

487,855 (2)

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES ☒

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

4.99% (1)

TYPE OF REPORTING PERSON

IN

Calculated based on 9,429,582 shares of the Common Stock outstanding as of April 24, 2019, as reported in the Quarterly Report.

Represents (i) 140,778 shares of common stock held by Frost Gamma Investments Trust (“FGIT”), (ii) 69,299 shares of common stock underlying Series D Convertible Preferred Stock and (iii) 277,778 shares of common stock underlying Series L Convertible Preferred Stock. Excludes (i) 129,388 shares of common stock underlying Series D Convertible Preferred Stock which contains a 4.99% beneficial ownership blocker and (ii) 107,607 shares of common stock underlying Series I Convertible Preferred Stock held by FGIT which contains a 4.99% beneficial ownership blocker. Dr. Frost is the trustee of FGIT. Frost Gamma L.P. is the sole and exclusive beneficiary of FGIT. Dr. Frost is one of two limited partners of Frost Gamma L.P. The general partner of Frost Gamma L.P. is Frost Gamma, Inc., and the sole shareholder of

NAME OF REPORTING PERSON

Frost Gamma Investments Trust

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a)  ☒        (b)  ☒

SEC USE ONLY

CITIZENSHIP OR PLACE OF ORGANIZATION

Florida

NUMBER OF

SHARES

BENEFICIALLY

OWNED BY

EACH

REPORTING

PERSON

WITH:

SOLE VOTING POWER

0

SHARED VOTING POWER

487,855 (2)

SOLE DISPOSITIVE POWER

0

SHARED DISPOSITIVE POWER

487,855 (2)

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

487,855 (2)

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES ☒

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9

4.99% (1)

TYPE OF REPORTING PERSON

OO

Calculated based on 9,429,582 shares of the Common Stock outstanding as of April 24, 2019, as reported in the Quarterly Report.

Represents (i) 140,778 shares of common stock held by Frost Gamma Investments Trust (“FGIT”), (ii) 69,299 shares of common stock underlying Series D Convertible Preferred Stock and (iii) 277,778 shares of common stock underlying Series L Convertible Preferred Stock. Excludes (i) 129,388 shares of common stock underlying Series D Convertible Preferred Stock which contains a 4.99% beneficial ownership blocker and (ii) 107,607 shares of common stock underlying Series I Convertible Preferred Stock held by FGIT which contains a 4.99% beneficial ownership blocker. Dr. Frost is the trustee of FGIT. Frost Gamma L.P. is the sole and exclusive beneficiary of FGIT. Dr. Frost is one of two limited partners of Frost Gamma L.P. The general partner of Frost Gamma L.P. is Frost Gamma, Inc., and the sole shareholder of

Name of Issuer:

Address of Issuer’s Principal Executive Offices:

Name of Person Filing:

OPKO Health, Inc., a corporation incorporated under the laws of the State of Delaware;

Phillip Frost, M.D.; and

Frost Gamma Investments Trust, a trust organized under the laws of the State of Florida.

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

Citizenship:

Titles of Classes of Securities:

CUSIP Number:

If This Statement is Filed Pursuant to Rule 13d-1(b), or 13d-2(b) or (c), Check Whether the Person Filing is a(n):

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

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

☐ Insurance company as defined in Section 3(a)(19) of the Exchange 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).

☐ Investment adviser in accordance with §240.13d-1(b)(1)(ii)(E).

☐ Employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F).

☐ Parent holding company or control person in accordance with §240.13d-1(b)(1)(ii)(G).

☐ Savings association as defined in Section 3(b) of the Federal Deposit Insurance Act (13 U.S.C. 1813).

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

☐ Non-U.S. institution in accordance with §240. 13d-1(b)(1)(ii)(J).

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

Ownership

Amount Beneficially Owned:

Percent of Class:

Number of shares as to which such person has:

Sole power to vote or to direct the vote:

Shared power to vote or to direct the vote:

Sole power to dispose or to direct the disposition of:

Shared power to dispose or to direct the disposition of:

Ownership of Five Percent or Less of a Class.

Ownership of More than Five Percent on Behalf of Another Person.

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company.

Identification and Classification of Members of the Group.

Notice of Dissolution of Group.

Certification.