Exhibit 10.28

SORRENTO THERAPEUTICS, INC.

INDEPENDENT DIRECTOR COMPENSATION POLICY

(as amended through December 12, 2012)

Non-employee members of the board of directors (the “Board”) of Sorrento
Therapeutics, Inc. (the “Company”), shall be eligible to receive cash and equity
compensation (e.g., option grants) as set forth in this Independent Director
Compensation Policy effective as of September 6, 2012 (the “Effective Date”) and
amended as of December 12, 2012. The cash compensation and option grants
described in this Independent Director Compensation Policy shall be paid or be
made, as applicable, automatically and without further action of the Board, to
each member of the Board who is not an employee of the Company or any parent or
subsidiary of the Company (each, an “Independent Director”) who may be eligible
to receive such cash compensation or options, unless such Independent Director
declines the receipt of such cash compensation or options by written notice to
the Company. This Independent Director Compensation Policy shall remain in
effect until it is revised or rescinded by further action of the Board.

1. Cash Compensation.

(a) Annual Retainers. Each Independent Director shall be eligible to receive an
annual retainer of $25,000 for service on the Board. In addition, an Independent
Director serving as:

(i) chairman of the Board shall be eligible to receive an additional annual
retainer of $5,000 for such service;

(ii) chairman of the Audit Committee shall be eligible to receive an additional
annual retainer of $5,000 for such service;

(iii) chairman of the Compensation Committee shall be eligible to receive an
additional annual retainer of $5,000 for such service; and

(iv) chairman of the Science Committee shall be eligible to receive an
additional annual retainer of $5,000 for such service.

The annual retainers shall be paid by the Company in quarterly installments or
more frequently as deemed advisable by the officers of the Company for
administrative or other reasons.

(b) Additional Cash Compensation. In the event the Board determines that an
Independent Director’s service to the Company in such capacity at any time
requires extraordinary efforts, such Independent Director shall be eligible to
receive additional compensation as may be approved by the Board in connection
with such additional service.

2. Equity Compensation. The options described below shall be granted under and
shall be subject to the terms and provisions of the Company’s 2009 Stock
Incentive Plan (as amended from time to time, the “2009 Plan”) and shall be
granted subject to the execution and delivery of option agreements, including
attached exhibits, in substantially the same forms previously approved by the
Board, setting forth the vesting schedule applicable to such options and such
other terms as may be required by the 2009 Plan.

(a) Initial Options. A person who is an Independent Director on the Effective
Date, or who is initially elected or appointed to the Board following the
Effective Date, and who is an Independent Director at the time of such initial
election or appointment, shall be eligible to receive a non-

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qualified stock option to purchase 400,000 shares of common stock (subject to
adjustment as provided in the 2009 Plan) (provided that such award shall be
450,000 shares of common stock if the Independent Director is also serving as
the chairman of the Board as of the Effective Date or as of the date of such
initial election or appointment) as soon as practicable following the Effective
Date or on the date of such initial election or appointment, as applicable
(each, an “Initial Option”).

(b) Termination of Employment of Employee Directors. Members of the Board who
are employees of the Company or any parent or subsidiary of the Company who
subsequently terminate their employment with the Company and any parent or
subsidiary of the Company and remain on the Board will not receive an Initial
Option grant pursuant to clause 2(a) above.

(c) Terms of Options Granted to Independent Directors

(i) Exercise Price. The per share exercise price of each option granted to an
Independent Director shall equal 100% of the Fair Market Value (as defined in
the 2009 Plan) of a share of common stock on the date the option is granted.

(ii) Vesting. Unless otherwise determined by the Board, Initial Options granted
to Independent Directors shall become exercisable in forty-eight equal monthly
installments on the last day of each one-month period of service following the
date of the Initial Option grant (or, with respect to the Initial Options
granted to those individuals who were Independent Directors as of the Effective
Date, following September 6, 2012), such that each Initial Option shall be 100%
vested on the fourth anniversary of the date of grant (or, with respect to the
Initial Options granted to those individuals who were Independent Directors as
of the Effective Date, on September 6, 2016), subject to the director’s
continuing service on the Board through such dates. The term of each option
granted to an Independent Director shall be ten years from the date the option
is granted. No portion of an option which is unexercisable at the time of an
Independent Director’s termination of service to the Company shall thereafter
become exercisable. Initial Options shall vest in the event of a Change in
Control (as defined in the 2009 Plan).

 

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