Anthrax Vaccine Clinical Trials

Anthrax is rarely encountered in the U.S. since the introduction of attenuated vaccines for cattle in the 1930's. A vaccine for humans, composed of a cell-free preparation absorbed onto alum, was licensed in 1970 after successful clinical trials. Vaccination against anthrax in the U.S. was confined to individuals at risk such as wool sorters and some veterinarians until the prospects were raised of B. anthracis being used as a weapon after the Iraq war. Now anthrax vaccine is administered routinely to the armed forces. Interest in improving this vaccine was stimulated by the use of B. anthracis spores for bioterrorism. The active component of the investigational vaccine is called the protective antigen. When B. anthracis invades the host tissues, the protective antigen activates two other proteins to form anthrax toxin. The symptoms of anthrax are caused by this toxin. Alone, the protective antigen has no known toxicity. The gene for this protein has been isolated and changed specifically to improve its properties as a vaccine-this recombinant protective antigen (rPA) elicits antibodies that neutralize the anthrax toxin and, thereby, can be predicted to confer protection. This is the first study of our investigational rPA vaccine in humans. The broad objectives are to characterize the safety and serum antibody levels of different doses and formulations of rPA in comparison to the licensed anthrax vaccine, AVA.