Researchers Announce Phase 1 Clinical Trial of a Novel Fully Human Antibody for the Treatment of Hospital Acquired Diarrhea

September 29, 2004

Jamaica Plain, Mass. and Princeton, N.J. — The Massachusetts Biologic Laboratories (MBL) of the University of Massachusetts Medical School (UMMS) and Medarex, Inc. (Nasdaq: MEDX) today announced the allowance of an Investigational New Drug (IND) application filed with the U.S. Food and Drug Administration (FDA) to initiate a Phase 1 clinical trial of CDA-1 (also referred to as MDX-066), a novel fully human monoclonal antibody designed to treat a serious and sometimes deadly form of diarrhea called Clostridium difficile associated diarrhea (CDAD), which can complicate the stays of hospitalized patients and residents of long-term care facilities.

The dose-escalation Phase 1 trial of CDA-1, planned to begin shortly, is expected to enroll up to 30 healthy volunteers. The participants will be monitored for any adverse side effects, and their blood will be tested to measure the concentration of the antibody in their systems.

“CDAD may not often grab headlines, but in its most serious form it is a significant and costly public health problem that affects approximately 300,000 Americans each year,” said Donna Ambrosino, MD, director of the MBL and a professor of pediatrics at the medical school. “Given the recognition of the impact of this disease, we felt it important to attempt to develop a better therapy.”

Donald L. Drakeman, president and CEO of Medarex, Inc. noted, “We are pleased with our continued collaboration with MBL and the research that has been conducted in order to advance this antibody into clinical trials.”

CDAD is typically treated with antibiotics alone; however approximately 20 percent of those affected by CDAD suffer a relapse of the disease after treatment, and approximately two percent of those afflicted with CDAD die of the disease.  CDA-1, which would be used in conjunction with antibiotic treatment, is believed to work by binding to a toxin released by C. difficile, thereby forestalling the disease state that arises from the toxin’s effect on the intestinal tract.

“Based on what we’ve seen so far, we hope this antibody will help shorten the duration of disease in people, reduce their length of stay in the hospital, and/or prevent recurrence,” said Deborah Molrine, MD, director of clinical affairs at MBL and associate professor of pediatrics at UMMS.

Israel Lowy, MD, PhD, director of clinical science and infectious diseases at Medarex, agrees. “Antibiotic treatment alone may prolong the disruption in the normal balance of flora in the intestinal tract and thereby maintain the opportunity for CDAD to relapse when the antibiotics are stopped. By providing the neutralizing anti-toxin antibody in conjunction with antibiotics, we believe that patients will both resolve their illness faster, as well as remain protected from relapse after the antibiotics are completed while the normal floral balance returns,” he said.

CDA-1 (MDX-066) is a novel, fully human antibodythat is believed to target and neutralize the effects of Toxin A, a toxin produced by the bacterium Clostridium difficile (C. difficile), which is associated with a serious and sometimes deadly form of diarrhea called C. difficile associated diarrhea (CDAD). Published epidemiologic studies of hospitalized patients at risk for CDAD have shown a positive correlation between detectable levels of antibody in the blood to Toxin A and protection from disease or relapse. Preclinical studies suggest that CDA-1 neutralizes the effects of Toxin A, the toxin associated with CDAD.

About MBL

The Massachusetts Biologic Laboratories is the only non-profit FDA-licensed manufacturer of vaccines and other biologic products in the

United States  . The laboratory was established in 1894 and since then the MBL's mission has been to improve public health through applied research, development and production of biologic products. MBL has been a part of the UMass Medical School since1997.

About

UMass    Medical    School

The University of Massachusetts Medical School is one of the fastest growing academic health centers in the country and 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 $148 million in extramural research funding annually. Research dollars enable UMMS scientists to explore human disease from the molecular level to large-scale clinical trials. Basic and clinical research has led 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 fully human antibody-based therapeutics to treat life-threatening and debilitating  diseases, including cancer, inflammation, autoimmune and infectious diseases.  Medarexapplies its UltiMAb™ technology and product development and clinical manufacturing experience to generate, support and potentially commercialize a broad range of fully human antibody products for itself and its partners.  Twenty of these therapeutic products derived from Medarex technology are currently in human clinical testing, with the most advanced currently in a Phase III clinical trial.  Medarex is committed to building value by developing a diverse pipeline of antibody products to address the world’s unmet healthcare needs.  For information about Medarex, visit its website 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”; “believe”; “anticipate”; “intend”; “plan”; “expect”; “estimate”; “could”; “may”; 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, uncertainties related to the outcome of clinical trials, slower than expected rates of patient recruitment, unforeseen safety issues resulting from the administration of CDA-1 products in patients, uncertainties related to product manufacturing 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, 2003 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 and UltiMAb Human Antibody Development System® are registered trademarks of Medarex, Inc. UltiMAbTM is a trademark of Medarex, Inc. All rights are reserved.

Contacts:UMMS/MBL -- Michael Cohen, (508) 856-2000, michael.cohen@umassmed.edu  

Investor Relations, Medarex, Inc. -- Laura S. Choi, (609) 430-2880 x 2216; Media, Medarex, Inc. -- Jean Mantuano, (609) 430-2880 x 2221