LICENSE AGREEMENT

Exhibit 10.55

***Text Omitted and Filed Separately

with the Securities and Exchange Commission.

Confidential Treatment Requested

Under 17 C.F.R. Sections 200.80(b)(4)

and 240.24b-2.

LICENSE AGREEMENT

THIS AGREEMENT entered into this 29th day of April, 1991 (“Effective Date”) between Life Technologies, Inc., a Delaware corporation having its principal place of business at 8400 Helgerman Court, Gaithersburg, Maryland 20877 (“LTI”) and Vical Incorporated, a Delaware corporation, having its principal place of business at 9373 Towne Center Drive. Suite 100, San Diego, California 92121 (“Vical”).

WHEREAS, LTI is a manufacturer and distributor of a wide range of biological and testing products and is desirous of expanding its product offerings of compounds in the research products market; and

WHEREAS, Vical has developed and has proprietary rights in certain compounds; and

WHEREAS, LTI is desirous of obtaining an exclusive license to make, have made, use, and sell such compounds which Vical has developed or in which it has proprietary rights;

NOW, THEREFORE, in consideration of the mutual covenants herein and for other good and valuable consideration, LTI and Vical agree as follows:

ARTICLE I – DEFINITIONS

As used in this Agreement, the following terms shall have the meaning stated opposite each term:

1.1 “Licensed Patent(s)” shall mean any patent which may issue from Vical’s U.S. patent application Serial No. 07/511,219, filed April 19, 1990 and any divisions, continuations, continuations-in-part, or reissues thereof or any foreign patents deriving priority therefrom.

1.2 “Licensed Product(s)” shall mean any compounds, including, but not limited to, DORI and DORI/CHOL 7/3, covered by the Licensed Technology.

1.3 “The Field” shall mean the research products market, including, but not limited to, protein delivery systems, bulk quantities for industrial use, and all research applications

1.4 “Know-how” shall mean any unpatented Vical knowledge or technology related to the Licensed Patent(s) existing as of the Effective date.

1.5 “Improvements” shall mean any inventions, improvements or discoveries, on or related to the Know-how or the Licensed Patents.

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a) “Vical Improvements” shall mean those Improvements made solely by Vical during the term of this Agreement.

b) “LTI Improvements” shall mean those Improvements made solely by LTI during the term of this Agreement.

c) “Joint Improvements” shall mean those Improvements jointly made by LTI and Vical during the term of this Agreement.

1.6 “Joint Improvement Product(s)” shall mean any compounds covered by the Joint Improvements.

1.7 “Licensed Technology” shall mean the Licensed Patent(s), Know-how, and Vical Improvements.

1.8 “Therapeutic Product(s)” means products which have received, or are intended to receive approval or clearance by the agency or agencies having authority to grant the right to commercialize (sales and promotion) such products for in vitro or in vivo therapeutic use in the United States.

1.9 “LTI” shall include any corporation or other business entity controlled by, controlling, or under common control with LTI. For this purpose, “control” means direct or indirect beneficial ownership of at least fifty percent (50%) interest in the shares of all classes of its voting stock, or possession of the direct power to direct or cause the direction of management and policies of the corporation or other business entity.

1.10 “Net Sales” shall mean the gross invoiced selling price of the Licensed Product(s) in the form in which they are sold, less the following items but only insofar as they actually pertain to the sale of such Licensed Product(s) by LTI and are included in such gross selling price,

a) to the extent such items (except items (i) and (vi)) are separately billed;

i) Usual trade discounts actually allowed (other than advertising allowances, fees, or commissions to any employee);

ii) Packing costs;

iii) Import, export, excise, sales and value-added taxes, and customs duties;

iv) Costs of insurance and transportation from the place of manufacture to the customer’s premises or point of installation;

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v) Costs of installation at the place of use; and

vi) Credit for returns, allowances, or trade discounts; and

b) provided, however, if Licensed Product(s) are sold in combination with other products, Net Sales for computing royalty payments under this Agreement, shall be determined by multiplying the Net Sales of such combination by a fraction, the numerator of which is the selling price of the Licensed Product(s) contained in such combination if the Licensed Product(s) were sold separately and the denominator of which is the selling price of the combination.

1.11 “Sublicense Income” shall mean the gross amount received by LTI, directly or indirectly, from sublicensees for or on account of any of the rights granted hereunder.

ARTICLE II – GRANT

2.1 Vical hereby grants to LTI an exclusive, world-wide right and license to use the Licensed Technology to make, have made, use and sell the Licensed Product(s) in the Field, subject only to Vical’s retained right to:

a) [***];

b) [***]; and

c) [***].

2.2. Each of the parties hereto hereby grants to the other a certain [***], to use its individual interest in the Joint Improvements to [***] in accordance with the limitations set forth below:

a) in the case of LTI, [***]; and

b) in the case of Vical, [***].

2.3 LTI shall have the right to sublicense the rights granted hereunder on terms substantially similar to the terms herein. All sublicenses hereunder granted by LTI shall be coterminable with this Agreement, and this fact shall be stated in any such sublicense agreement. LTI shall have responsibility for the royalty reporting activities of a sublicensee as if the activities were those of LTI. LTI shall promptly provide Vical with a copy of any sublicense issued hereunder.

2.4 Concurrently with the execution of this Agreement, Vical shall hereby assign to LTI all of its right, title, interest, and all goodwill represented therein, in its marks, “Superfectin” and “Turbofectin,” but only insofar as such right, title, interest, and goodwill pertains to use of the Licensed Product(s) in the Field.

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ARTICLE III – DISCLOSURE OF KNOW-HOW

3.1 Within thirty (30) days of execution of this Agreement, Vical will provide LTI with a copy of all Know-how related to production methodologies and protocols in its possession and thereafter during the term of this Agreement will:

a) Advise LTI of any Vical Improvements within thirty (30) days of the recognized discovery thereof;

b) Make available its personnel, upon reasonable request, to assist LTI personnel in understanding and utilizing the Licensed Technology;

c) Allow LTI, upon reasonable notice, during business hours, to enter upon Vical’s premises and observe Vical’s efforts related solely to the Licensed Technology, and, only during business hours for reasonable periods of time, to confer with appropriate Vical research personnel in furtherance of this Agreement; and

d) Provide training to at least [***] of LTI’s employees, but no more than [***], designated by LTI as essential, after consultation with and reasonable agreement by Vical, to LTI’s efforts to utilize the Licensed Technology.

ARTICLE IV – CONSULTING

Vical shall make available to LTI the consulting services of [***] or a mutually agreed-upon substitute, who shall visit LTI’s facilities, no more than four (4) mutually-agreed upon person days per year, upon LTI’s reasonable request and expense, during the term of this Agreement.

ARTICLE V – TERM OF LICENSE

5.1 The term of this Agreement shall commence upon the Effective Date and shall terminate on a country-by-country basis upon:

a) The termination of the life of the Licensed Patent(s) in such country, or the expiration of the term of the pendency of an application for a Licensed Patent(s) in such country, but

b) Should no Licensed Patent(s) issue or no application for a Licensed Patent(s) be filed in any country, the term of the Agreement in that country shall be [***] from the date of first commercial sale.

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ARTICLE VI – PAYMENTS

As consideration for the rights granted by Vical to LTI hereunder:

6.1 LTI shall pay a technology transfer fee of [***] to Vical within thirty (30) days of execution of this Agreement and shall pay Vical an additional fee of [***] on or before [***].

6.2 LTI shall pay earned royalties to Vical based upon LTI’s Net Sales, the amount of which royalties shall be determined in the following manner:

a) If Licensed Product(s) are manufactured or sold in a country:

i) where no Licensed Patent(s) exists; or

ii) where no application(s) for a Licensed Patent(s) is pending after [***] from the Effective Date; or

iii) where a Licensed Patent(s) has been declared invalid in such country by a court of competent jurisdiction through no fault of LTI, then LTI shall pay royalties at the rate of [***] of Net Sales in such country until such time as a competitor enters the market in such country utilizing technology falling within the scope of the Licensed Patent(s) making such payments by LTI commercially unfeasible, then LTI shall serve notice to Vical of such event. Should Vical fail to successfully dispute or disprove such event within thirty (30) days, then no royalty shall be payable by LTI.

b) If Licensed Product(s) are manufactured or sold in a country:

i) where a Licensed Patent(s) exists; or

ii) where an application for a Licensed Patent(s) is pending; or

iii) where less than [***] have passed from Effective Date in any event,

then LTI shall pay royalties at the rate of [***] of Net Sales in such country.

6.3 LTI shall pay to Vical royalties equaling [***] of Sublicense Income.

6.4 LTI shall pay Vical minimum annual royalties in the amount of [***] for each of the [***] of this Agreement upon the [***] of the Effective Date. Amounts paid by LTI under Sections 6.2 and 6.3 shall be credited against the relevant minimum annual royalty due, and any excess amount paid shall be credited against succeeding minimum annual royalty obligations.

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6.5 LTI shall make a bonus payment of [***] to Vical upon the earlier to occur of the following during the term of this Agreement:

a) Vical develops a product which LTI desires to market utilizing the Licensed Technology or technology which is covered by the License Agreement dated and effective as of April 20, 1990 by and between LTI and Vical (the “Prior Agreement Technology”), which product is limited to use in protein delivery systems during the term of this Agreement; or

b) LTI actively promotes the Licensed Product(s) or the Prior Agreement Technology for use in protein delivery systems during the term of this Agreement.

ARTICLE VII – REPORTS

7.1 Within sixty (60) days after the end of each calendar quarter during the term of this Agreement, LTI shall furnish Vical a written report setting forth the Net Sales and royalties payable thereon and the amount of Sublicense Income received, accompanied by payment of such royalties, including royalties payable on Sublicense Income. All royalties shall be paid to Vical in U.S. dollars, and in full. In the event that conversion from foreign currency is required in calculating a royalty payment hereunder, the exchange rate used shall be the rate in effect at the end of the last business day of the month just prior to the date payment is required to be made hereunder as published in the Wall Street Journal.

7.2 LTI shall prepare a final report and payment within sixty (60)&