West Nile virus DNA vaccine shows promise in phase 1 trial

Vical Incorporated has announced that in a Phase 1 clinical trial, a West Nile virus (WNV) vaccine candidate administered using Vical's proprietary DNA delivery technology was safe and well tolerated, and produced neutralizing antibody WNV-specific responses in all 11 healthy volunteers who returned for follow-up testing after completing the three-dose vaccination schedule.

The Phase 1, open-label clinical trial study was sponsored by the National Institute of Allergy and Infectious Diseases (NIAID), National Institutes of Health (NIH), and conducted at the NIH Clinical Center. The data were presented at the American Society of Gene Therapy (ASGT) 2006 Annual Meeting in Baltimore, MD, by Julie E. Martin, D.O., a trial investigator and research scientist at NIAID's Dale and Betty Bumpers Vaccine Research Center (VRC), which developed the vaccine. The DNA vaccine used in the Phase 1 trial incorporates genetic material encoding precursor membrane (prM) and envelope (E) proteins from the West Nile virus. Vical has secured a license from the U.S. Centers for Disease Control and Prevention for technology used in the vaccine. This WNV vaccine candidate was jointly developed by the VRC, NIAID, NIH and Vical under a Cooperative Research and Development Agreement (CRADA), and Vical has an option to secure exclusive commercialization rights from the NIH under the CRADA.

"This vaccine was previously shown to be highly immunogenic in animal studies, and the high rate of seroconversion in humans, as measured in this study by neutralizing antibody titers, adds to the growing body of evidence demonstrating immunogenicity with DNA vaccines in humans as well," said David C. Kaslow, M.D., Vical's Chief Scientific Officer. "Furthermore, the data encourage investigation of vaccines against diseases caused by other flaviviruses such as yellow fever, Japanese encephalitis, and dengue, as well as other diseases for which antibody responses may be protective."

The vaccine used in the Phase 1 trial contained a single plasmid (closed loop of DNA) encoding precursor membrane (prM) and envelope (E) proteins from the West Nile virus. Fifteen subjects were enrolled and 12 completed the vaccination schedule, which consisted of three 4 mg doses of vaccine at one-month intervals via intramuscular needle-free injection. The vaccine was well tolerated, and there were no severe adverse reactions to the vaccine. Among the 12 volunteers who completed the 3-dose vaccination schedule, 11 returned for follow-up testing. WNV-specific neutralizing antibody responses were detected in all 11, as well as in some subjects following just 2 doses.