Positive Anthrax result

San-Diego, US-based Vical has shown that its novel DNA-based anthrax vaccine generated anti-bodies against specific anthrax proteins and provided complete protection of rabbits against aerosolised inhalation spore challenge more than seven months after vaccination.

Rabbits are likely to be accepted by the FDA as an animal model for anthrax under the Animal Rule, which allows marketing approval based on proof of protective efficacy in two animal models and both safety and immunogenicity in humans.

Vical's investigational DNA vaccine for anthrax, formulated with cationic lipids, encodes detoxified forms of both the Protective Antigen (PA) and Lethal Factor (LF) anthrax proteins, which in their natural forms combine to form lethal toxin (Letx). This bivalent vaccine is designed to provide broader protection than other anthrax vaccines, which target PA alone, in-cluding the vaccine currently licensed in the US and others under development.

Significant levels of anti-PA, anti-LF and Letx-neutralising antibodies were achieved in the rabbit study. In addition, post-challenge immune response data from the rabbit study suggest that the vaccine-generated antibodies may inhibit germination of anthrax spores, potentially providing sterile immunity.

Dr David Kaslow, Vical's cso said: 'The successful testing of our anthrax vaccine in rabbits is an important milestone in our ongoing progress toward developing a safe and effective vaccine against weaponised forms of anthrax. With appropriate guidance from the FDA on the new Animal Rule, an application for marketing approval could be based on effectiveness testing in accepted animal challenge models such as the rabbit, coupled with clinical safety and immunogenicity trials in humans, without the need for conventional clinical efficacy trials.'

About Anthrax

Anthrax is a serious infectious disease most frequently occurring in hoofed mammals, but also affecting humans exposed to the spore-forming Bacillus anthracis. Bacterial spores can survive for extended periods and become active upon gaining access to a host. Human infection with anthrax spores can occur after exposure through a cut or abrasion on the skin or through ingestion of contaminated meat, but the most serious risk is through inhalation. Inhalation anthrax results in death for 90-100% of those exposed, if not treated promptly. Symptoms typically appear within a week of exposure, and may be misdiagnosed as a common cold or flu. Bacterial spores travel from the lungs to the lymph nodes, where they begin to grow. Eventually, they spread into the circulatory system and throughout the body, causing widespread internal bleeding and organ failure. People who work with animals or process animal products are at greatest risk of naturally acquired infection. The greatest potential threat for most people is the inhalation of anthrax spores used in biological warfare or in a bioterrorist attack. The toxic effects of anthrax infection are the result of three proteins produced by the bacteria: edema factor (EF), lethal factor and protective antigen. PA couples with either EF or LF and allows these toxins to penetrate and kill host cells, releasing large numbers of bacteria into circulation. Treatment for proven or suspected anthrax infection involves a long course of antibiotic therapy beginning as soon as possible after diagnosis or suspected exposure. Antibiotics used against anthrax work by killing the bacteria to prevent further production of the toxic proteins. They do not eliminate proteins that accumulate before treatment, and do not offer residual protection against infection after the treatment course has been completed.