Vical Incorporated announced that peer-reviewed data from the company's anthrax vaccine challenge study in rabbits were published recently.
The novel DNA-based vaccine being developed by Vical generated antibodies against specific anthrax proteins and provided complete protection of rabbits against aerosolized inhalation spore challenge more than seven months after vaccination. Rabbits will likely be accepted by the US 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, including the vaccine currently licensed in the United States and others under development. Significant levels of anti-PA, anti-LF and Letx-neutralizing 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, a company release said.
David C 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 weaponized 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."
"Based on the successful demonstration in rabbits that our state-of-the-art DNA vaccine has been optimized for eliciting antibodies, we have now initiated proof-of-concept testing in man," added Dr. Kaslow.
The rabbit study was supported by a Small Business Technology Transfer Research (STTR) grant from the US National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health (NIH). The company also received a three-year, $5.9 million Phase II Small Business Innovation Research (SBIR) grant from the NIAID for additional non-clinical development. The vaccine is now being tested for safety and immune responses in a phase 1 clinical trial in healthy human volunteers at two NIAID-funded Vaccine and Treatment Evaluation Units (VTEUs). The company intends to seek additional government funding to support further development, the release added.
The data was published in the September 14 issue of the Proceedings of the National Academy of Sciences (PNAS).