Securities Purchase Agreement

SECURITIES PURCHASE AGREEMENT

This Securities Purchase Agreement (this "Agreement") is dated as of January 11, 2000 among IGEN International, Inc., a Delaware corporation (the "Company"), and the various purchasers identified and listed on Schedule I hereto (each referred to herein as a "Purchaser" and, collectively, the "Purchasers").

WHEREAS, the Company and the Purchasers are executing and delivering this Agreement in reliance upon the exemption from securities registration afforded by Rule 506 under Regulation D as promulgated by the United States Securities and Exchange Commission (the "Commission") under Section 4(2) of the Securities Act of 1933, as amended (the "Securities Act");

WHEREAS, subject to the terms and conditions set forth in this Agreement, the Company desires to issue and sell to the Purchasers, and the Purchasers desire to acquire from the Company, an aggregate principal amount of $35,000,000 of 5% Subordinated Convertible Debentures due January 11, 2005 (the "Debentures"), in the form of Exhibit A annexed hereto and warrants (the "Warrants") to purchase 282,258 shares of the Company's common stock, par value $0.001 per share (the "Common Stock"), in the form of Exhibit B annexed hereto; and

WHEREAS, contemporaneously with the execution and delivery of this Agreement, the parties hereto are executing and delivering a Registration Rights Agreement in the form of Exhibit C annexed hereto (the "Registration Rights Agreement") pursuant to which the Company has agreed to provide certain registration rights under the Securities Act and the rules and regulations promulgated thereunder, and applicable state securities laws.

NOW THEREFORE, in consideration of the promises and mutual covenants and agreements hereinafter, the Company and the Purchasers hereby agree as follows:

ARTICLE I. PURCHASE AND SALE OF THE DEBENTURES AND WARRANTS

1.1 PURCHASE AND SALE.

Subject to the terms and conditions set forth herein, the Company shall issue and sell to each Purchaser, and each Purchaser, severally and not jointly, shall purchase from the Company on the Closing Date (as defined below), the principal amount of Debentures as set forth for such Purchaser on Schedule I.

1.2 CLOSING.

a. The Closing. The closing of the purchase and sale of the Debentures and the issuance of the Warrants (the "Closing") shall take place at the offices of Akin, Gump, Strauss, Hauer & Feld, L.L.P., 590 Madison Avenue, New York, New York 10022, or by transmission by facsimile and overnight courier, immediately following the execution hereof, or such later date or different location as the parties shall agree, but not prior to the date that the conditions set forth in Section 4.1 have been satisfied or waived by the appropriate party (the "Closing Date").

At the Closing:

• Each Purchaser shall deliver, as directed by the Company, its portion of the purchase price as set forth next to its name on Schedule I in United States dollars in immediately available funds to an account or accounts designated in writing by the Company;

• The Company shall deliver to each Purchaser a Debenture(s) in the form of Exhibit A hereto representing the principal amount of Debentures purchased by such Purchaser as set forth on Schedule I hereto;

• The Company shall deliver to each Purchaser a Warrant, in the form of Exhibit B hereto, representing the right to acquire the number of shares of Common Stock as set forth on Schedule I hereto; and

• The parties shall execute and deliver each of the documents referred to in Section 4.1 hereof.

ARTICLE II. REPRESENTATIONS AND WARRANTIES

2.1 REPRESENTATIONS, WARRANTIES AND AGREEMENTS OF THE COMPANY.

The Company hereby makes the following representations and warranties to each of the Purchasers. Any information disclosed in any Schedule hereto shall be deemed to have been disclosed in all Schedules hereto.

2.2 REPRESENTATIONS AND WARRANTIES OF THE PURCHASERS.

Each of the Purchasers, severally and not jointly, hereby represents and warrants to the Company as follows:

ARTICLE III. OTHER AGREEMENTS

3.1 TRANSFER RESTRICTIONS.

Any transfer of the Debentures, the Warrants, the Debenture Shares or the Warrant Shares is subject to the restrictions set forth herein and applicable securities laws.

3.2 STOP TRANSFER INSTRUCTION.

The Company may not make any notation on its records or give instructions to any transfer agent of the Company which enlarge the restrictions on transfer set forth in Section 3.1.

3.3 FURNISHING OF INFORMATION.

As long as any Purchaser owns the Debentures, the Warrants, the Debenture Shares or the Warrant Shares, the Company will continue to furnish required reports and information.

3.4 BLUE SKY LAWS.

The Company shall qualify the Debenture Shares and the Warrant Shares under applicable state securities laws as requested by the Purchasers.

3.5 INTEGRATION.

The Company shall not sell, offer for sale or solicit offers to buy any security that would be integrated with the offer or sale of the Debentures or Warrants in a manner requiring registration under the Securities Act.

3.6 LISTING, REGISTRATION AND RESERVATION OF DEBENTURE SHARES AND WARRANT SHARES.

The Company shall take all steps necessary to list and reserve the Required Minimum Shares and maintain such listing.

3.7 NOTICE OF BREACHES.

The Company and each Purchaser shall give prompt written notice of any breach or event likely to cause a breach of any representation, warranty or covenant.

3.8 FORM D.

The Company agrees to file a Form D with respect to the Debentures and Warrants as required by Rule 506 under Regulation D.

3.9 FUTURE FINANCINGS.

If the Company offers New Securities while any Debentures are outstanding, the Purchasers shall have a pro rata right to purchase such securities on the terms described herein.

3.10 USE OF PROCEEDS.

The Company shall use the proceeds from the sale of the Debentures and the exercise of the Warrants for capital expenditures, research and development, expansion of sales, customer support and marketing functions, working capital and possible strategic acquisitions.

3.11 TRANSACTIONS WITH AFFILIATES.

So long as any Debentures or Warrants are outstanding, the Company shall not enter into certain related party transactions except as permitted herein.

3.12 TRANSFER AGENT INSTRUCTIONS.

At the Closing the Company shall issue irrevocable instructions to its transfer agent to issue certificates for the Debenture Shares and/or the Warrant Shares as specified by each Purchaser.

3.13 ORDINARY COURSE BROKERAGE AND TRADING.

Subject to compliance with applicable securities laws and Nasdaq regulations, the Purchasers may engage in ordinary course brokerage and trading activities in respect of the Company's Common Stock.

3.14 COMMERCIALLY REASONABLE EFFORTS.

Each of the parties hereto shall use all commercially reasonable efforts to satisfy each of the conditions to be satisfied by it.

3.15 NO VIOLATION OF APPLICABLE LAW.

If any redemption required under this Agreement is prohibited by Delaware law, it shall be effected as soon as permitted under such law.

3.16 MATERIAL INFORMATION.

Any material non-public information provided by the Company to the Purchasers shall cease to be material non-public information by the date the Initial Registration Statement is declared effective.

ARTICLE IV. CONDITIONS

4.1 CLOSING CONDITIONS.

The Closing is subject to the satisfaction or waiver of the conditions set forth herein.

ARTICLE V. INDEMNIFICATION

5.1 INDEMNIFICATION.

The Company shall defend, protect, indemnify and hold harmless each Purchaser and the Indemnitees as described herein.

ARTICLE VI. MISCELLANEOUS

This Agreement contains the entire understanding of the parties with respect to the subject matter hereof and supersedes all prior agreements and understandings.