Enzon and Micromet Announce Strategic Collaboration for Novel Single-Chain Antibody Therapeutics.

Business Editors and Medical/Health Writers

PISCATAWAY, N.J. and MUNICH, Germany--(BUSINESS WIRE)--April 10, 2002

- Partnership Creates the Leading Platform for Next Generation

of Antibody Therapeutics -

Enzon, Inc. (NASDAQ:ENZN) and Micromet AG (private) announced today a multi-year strategic collaboration to identify and develop the next generation of antibody-based therapeutics.

Under the terms of the agreement, Enzon and Micromet will combine their significant patent estates and complementary expertise in single-chain antibody (SCA) technology to create a leading platform of therapeutic products based on antibody fragments. The collaboration will also benefit from a non-exclusive, royalty-bearing license from Enzon for PEGylated SCA products. The companies will establish a new R&D Unit located at Micromet's research facility in Germany. The Unit will be staffed initially with 25 scientists and plans to be fully operational by the end of 2002. During the first phase of the collaboration, covering a 30-month period beginning in the third quarter of calendar year 2002, the new R&D Unit will focus on the generation of at least two clinical product candidates in therapeutic areas of common strategic interest. The Partners will share equally the costs of research and development, and plan to share the revenues generated from technology licenses and from future commercialization of any developed products. In addition to the R&D collaboration, Enzon will make a US $8 million investment into Micromet.

"Our collaboration with Micromet underscores Enzon's commitment to leverage our leadership position in SCA technology and to expand our pipeline with innovative new products," said Arthur J. Higgins, Enzon's chairman and chief executive officer. "Through this product development collaboration we have now brought together the necessary breadth of scientific expertise, broad intellectual property position, and capabilities in PEG and inhalation technologies that are necessary for SCAs to become a new frontier of antibody-based therapeutics."

SCAs combine the antigen binding regions of antibodies on a single polypeptide chain. They are considerably smaller in size than conventional antibodies, and can be produced conveniently on a commercial scale in microbial protein expression systems, providing significant cost-savings when compared to monoclonal antibodies. SCAs are highly versatile and can readily be genetically engineered to work in a variety of formats. These formats include SCAs specific for cell-surface receptors for application as biological antagonists and agonists; SCAs designed to block the activity of cytokines and other soluble biological mediators; and SCA-fusion proteins, where cell-specific SCAs are "armed" with toxins, radionuclides, enzymes, or cytotoxic drugs for selective elimination of particular cell types, for example in cancer. The variety of SCA formats make them attractive products potentially suitable for a broad range of therapeutic applications, beyond the reach of conventional monoclonal antibodies in areas such as cancer, central nervous system disorders, transplantation, inflammation and autoimmunity. The ability to deliver SCAs by alternative routes of administration, e.g. by pulmonary delivery, and to predictably extend the biological half-life of SCAs by PEGylation, further expands the clinical utility of SCA products beyond the range of monoclonal antibodies.

"We are delighted to drive this major initiative, together with Enzon, to develop novel SCA therapeutics with tailor-made clinical profiles contributing significantly to our respective product pipelines," commented Erich Felber, MD, PhD, CEO of Micromet. "This initiative will build on our combined strengths and experience in SCA technology and Enzon's commercially successful PEG technology." Christian Itin, Ph.D., Vice President of Business and Corporate Development of Micromet added, "We have already demonstrated with our BiTE(TM) format the unique advantages of single-chain antibodies, and will now extend this experience to the development of SCA therapeutics with agonistic, antagonistic and modulatory properties for the treatment of a wide range of human diseases."

Enzon holds core intellectual property in SCAs. These fundamental patents, combined with Micromet's key patents in SCA linkers and fusion protein technology, generate a compelling technology platform for SCA product development. The companies have renewed their cross-license agreement to their respective SCA IP and have decided to jointly market their combined SCA IP to third parties. Micromet will be the exclusive marketing partner and will institute a comprehensive licensing program on behalf of the partnership, for which the parties will share equally in the costs and revenues. Current licensees to Enzon and Micromet IP include Alexion, Bristol-Myers Squibb, Cambridge Antibody Technologies, Cell Genesys, Celltech, Crucell, Eli Lilly, Seattle Genetics and Xoma. Several SCA molecules are in clinical trials. Alexion Pharmaceuticals, Inc. (NASDAQ:ALXN) are currently in Phase III clinical studies in cardiopulmonary bypass surgery.

About Antibodies

Antibodies are proteins produced naturally by the body's immune system, in response to infection, and specifically recognize target molecules known as antigens, present on virus-infected cells or located on the surface of microbial pathogens. Hybridoma technology has enabled the generation of specific monoclonal antibodies (antibodies derived from a single clone of cells) directed to a range of biological targets of therapeutic interest. Subsequent technical advances have also addressed issues such as commercial-scale manufacturing, and the production of "humanized" mouse monoclonal antibodies, and totally human monoclonal antibodies, to overcome immunogenicity problems associated with first-generation products. Several monoclonal antibodies have been approved and commercialized for human therapeutic use, creating a multi-billion-dollar market that is expected to grow significantly in the next several years. Monoclonal antibodies generally have a long circulating half-life, making them suitable for particular types of therapy.

Enzon Conference Call and Management Availability

Company management of Enzon will be making a live webcast presentation on Thursday, April 11, 2002 at 8:30AM EST regarding the formation of this strategic collaboration. All interested parties can access the call and slide presentation via the internet at www.enzon.com or www.vcall.com. Additionally, interested parties can listen to the presentation using the following information:

          Domestic dial-in number:      800-288-8961
          International dial-in number: 612-332-0819
          Access Code:                  634961

For those parties unable to listen at the time of Enzon's presentation, an audio rebroadcast will be available following the call from April 11, 2002 at approximately 3:15PM. This rebroadcast will end on April 18, 2002 at 11:59PM. The rebroadcast may be accessed using the following information:

          Domestic Dial-In Number:      800-475-6701
          International Dial-In Number: 320-365-3844
          Access Code:                  634961

About Enzon

Enzon is a biopharmaceutical company that develops and commercializes enhanced therapeutics for life-threatening diseases through the application of its proprietary platform technologies: PEG Modification and single-chain antibodies (SCA(R)). Three products are currently marketed which utilize Enzon's technology: PEG-INTRON marketed by Schering-Plough for hepatitis C, ONCASPAR(R) for Acute Lymphoblastic Leukemia (ALL), and ADAGEN(R) a treatment for a form of Severe Combined Immunodeficiency Disease (SCID), commonly known as the "Bubble Boy Disease." In addition to three approved products, Enzon has several products in various stages of clinical development by itself and with partners, including additional indications for PEG-INTRON with Schering-Plough. A Phase III clinical trial is being conducted for PEG-INTRON for the treatment of malignant melanoma. Enzon develops and markets products on its own and through strategic alliances, which in addition to Schering-Plough Corporation, include Alexion Pharmaceuticals, Inc., Baxter Healthcare Corporation, Bristol-Myers Squibb Company, Eli Lilly & Company, and Aventis.

About Micromet

Micromet AG, a privately held, Munich-based biotechnology company, designs and develops innovative antibody-based drugs for the treatment of cancer, autoimmune and inflammatory diseases. The Company is building a broad pipeline of drug candidates on the basis of proprietary technologies with two candidates being in Phase I clinical trials. Fundamental to Micromet's therapeutic strategy is the elimination of cells playing a pivotal role in the pathogenesis of human diseases by recruiting and activating immune effector cells. The Company has established the BiTE(TM) technology ("Bispecific T cell engagers"), a unique drug format that leverages the outstanding cytotoxic potential of T cells, the most powerful `killer cells' of the human immune system. Micromet has integrated expertise and infrastructure in key drug development disciplines. The Company has investments from leading international life science investors with a cumulative financing volume of 68.2 million euros.

Except for the historical information herein, the matters discussed in this news release include forward-looking statements that may involve a number of risks and uncertainties. Actual results may vary significantly based upon a number of factors, which are described in the Enzon's Form 10-K, Form 10-Q's and Form 8-K's on file with the SEC, including without limitation, risks in obtaining and maintaining regulatory approval for indications and expanded indications, market acceptance of and continuing demand for Enzon's products and the impact of competitive products and pricing.

This release is also available at http://www.enzon.com and http://www.micromet.de