Potential SARS Treatment to be Developed by Medarex and Massachusetts Biologic Laboratories

April 25, 2003

PRINCETON, N.J. and JAMAICA PLAIN, Mass.—Medarex, Inc. (Nasdaq: MEDX ) and the Massachusetts Biologic Laboratories (MBL) of the University of Massachusetts Medical School today announced that they have entered into an agreement by which they intend to co-develop fully human antibodies to severe acute respiratory syndrome (SARS). The parties plan to use Medarex’s UltiMAb(TM) technology to generate fully human antibodies to SARS. Under the terms of the agreement, Medarex and MBL expect to share equally the development costs of any antibody products as well as any future revenues arising from these products.

“We are delighted to partner with Medarex to develop a monoclonal antibody to combat SARS,” says Donna Ambrosino, M.D., Director of MBL and Professor of Pediatrics at the University of Massachusetts Medical School (UMMS). “A collaborative effort using appropriate technologies and experience will be necessary to successfully respond to this urgent public health need. The U.S. Centers for Disease Control (CDC) has led this spirit of collaboration by isolating the SARS agent and then making information rapidly available to all sources. Dr. Larry Anderson at CDC has provided the isolate to the University of Massachusetts Medical School so that the special containment facilities and expertise at UMass Medical School could be tapped to rapidly create targets for monoclonal antibody development by MBL and Medarex. John Sullivan, M.D., and Katherine Ruiz de Luzuriaga, M.D., will lead a team of scientists at the UMMS Worcester campus who will closely work with the UMMS scientists at MBL.”

“MBL is well suited to address the critical need for effective SARS agent, as we are experienced at developing and manufacturing monoclonal antibodies for clinical use,” says Dr. Ambrosino. “Our mission is to develop biologics to meet the health needs of the public, and MBL is committed to rapidly respond to SARS using the available resources and expertise to contribute to the success of this important collaborative effort with Medarex.”

“We believe that MBL’s experience in the development of vaccines and biologic products as well as their strong working relationship with public agencies provides us the opportunity to further expand our product development efforts in the area of infectious disease,” said Donald L. Drakeman, President and CEO of Medarex.

“We believe that development of a fully human neutralizing antibody to the SARS virus may be a relatively rapid approach to obtain an agent that can limit the disease in infected and exposed individuals,” said Israel Lowy, M.D., Ph.D., Director of Infectious Diseases at Medarex. “We expect to work closely with our collaborators at MBL to identify an efficacious antibody that blocks infection.”

About SARS

According to the CDC, severe acute respiratory syndrome (SARS) is a respiratory illness that has recently been reported in Asia, North America, and Europe. Scientists at CDC and other laboratories have detected a previously unrecognized coronavirus in patients with SARS. Cases of SARS continue to be reported mainly among people who have had direct close contact with an infected person, such as those sharing a household with a SARS patient and health-care workers. As of today, over 4,400 cases of SARS have been reported in a total of 22 countries.

About MBL

MBL is the only non-profit FDA-licensed manufacturer of vaccines and other biologic products in the United States. The laboratory was established in 1894 by the Massachusetts Board of Health to produce diphtheria antitoxin, and since then MBL’s singular focus has been to improve public health through applied research, development and production of biologic products. In 1997 the State Legislature transferred MBL operations to UMass Medical School to “maintain their public purpose, preserving their ability to compete in an increasingly competitive marketplace and maximize their value to the Commonwealth.”

The University of Massachusetts Medical School is one of the fastest growing academic health centers in the country, has built a reputation as a world-class research institution, consistently producing noteworthy advances in clinical and basic research. The Medical School attracts more than $143 million in research funding annually, 80 percent of which comes from federal funding sources. Research funding enables UMMS scientists to explore human disease from the molecular level to large-scale clinical trials. Basic and clinical research leads to new approaches for diagnosis, treatment and prevention of disease. Visit www.umassmed.edu for additional information.

About Medarex

Medarex is a biopharmaceutical company focused on the discovery and development of therapeutics to treat life-threatening and debilitating diseases. Medarex’s UltiMAb Human Antibody Development System(SM) is a unique combination of human antibody technologies that Medarex believes enables the rapid creation and development of fully human antibodies for a wide range of potential disease targets for therapeutic antibody products, including products for the treatment of cancer, inflammation, autoimmune and infectious diseases. Medarex’s product pipeline is based on a variety of therapeutic antibody products developed through the use of its UltiMAb(TM) technology. Medarex creates and develops fully human antibodies for itself and others, offering a full range of antibody related capabilities, including pre-clinical and clinical development supported by cGMP manufacturing services. For more information about Medarex, visit its Web site at www.medarex.com .

For Medarex: Except for the historical information presented herein, matters discussed herein may constitute forward-looking statements that are subject to certain risks and uncertainties that could cause actual results to differ materially from any future results, performance or achievements expressed or implied by such statements. Statements that are not historical facts, including statements preceded by, followed by, or that include the words “potential,”  “believes,” “anticipates,”  “intends,”  “plans,”  “expects,”  “estimates,”  “could,” or similar statements are forward-looking statements. Medarex disclaims, however, any intent or obligation to update these forward-looking statements. Risks and uncertainties include risks associated with product discovery and development as well as risks detailed from time to time in Medarex’s public disclosure filings with the U.S. Securities and Exchange Commission (SEC), including its Annual Report on Form 10-K for the fiscal year ended December 31, 2002 and subsequent Quarterly Reports on Form 10-Q. There can be no assurance that such development efforts will succeed, that such products will receive required regulatory clearance or that, even if such regulatory clearance were received, such products would ultimately achieve commercial success. Copies of Medarex’s public disclosure filings are available from its investor relations department.

Medarex®, the Medarex logo, UltiMAb(TM), and UltiMAb Human Antibody Development System(SM) are trademarks and service marks of Medarex, Inc. All rights are reserved.


Contact:

Mark L. Shelton, UMMS/MBL (508) 856-2000

Laura S. Choi, Medarex Investor Relations (609) 430-2880 x 2216

Jean Mantuano, Medarex Corporate Communications (609) 430-2880 x 2221