( Pilot Study Demonstrates 50% Survival ...)Anthrax Monoclonal Antibody Valortim(tm) Demonstrates Therapeutic,Effect in New Primate Model of Established Anthrax Infection,Health

Pilot Study Demonstrates 50% Survival in Valortim-Treated Animals

PRINCETON, N.J. and ANNAPOLIS, MD., March 29, 2007 - Medarex, Inc. (Nasdaq: MEDX), a leading monoclonal antibody company, and PharmAthene, Inc., a privately held biotechnology company dedicated to the development of biodefense countermeasures, today announced that Valortim, a fully human monoclonal antibody product candidate being developed for the prevention and treatment of anthrax infection, has been shown to have a therapeutic effect in a new primate model of established inhalation anthrax infection.

The new model, which is being developed at the United States Army Medical Research Institute of Infectious Diseases (USAMRIID), seeks to improve on existing therapeutic models for anthrax by closely monitoring the disease process to establish the presence of anthrax bacteremia and determine the optimal window for therapeutic intervention. In addition, the new model uses the African Green monkey, which, based on research data, USAMRIID believes follows a similar disease course as is expected in humans exposed to aerosolized Bacillus anthracis spores. B. anthracis is the bacterium responsible for anthrax infection. This new animal model has not yet been validated under the U.S. Food and Drug Administration Animal Effectiveness Rule.

In the pilot study conducted at USAMRIID, adult African Green monkeys were exposed to aerosolized anthrax spores and blood samples were collected at regular intervals beginning 24 hours post-exposure. The samples were closely monitored for evidence of bacteremia both by culture and by use of a rapid assay designed to detect protective antigen. Protective antigen is one of the toxins produced by B. anthracis and its presence in the blood is being evaluated as a surrogate marker for symptomatic anthrax disease. Once bacteremia was detected by the rapid assay, animals were administered either Valortim
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