Vical's prophylactic Vaxfectin-formulated pDNA vaccine effective against HSV-2 in animal model

Jul 26 2010

Vical Incorporated (Nasdaq:VICL) today announced that its prophylactic Vaxfectin^®-formulated plasmid DNA (pDNA) vaccine against herpes simplex virus type 2 (HSV-2) protected mice against lethal challenge, provided sterilizing immunity and inhibited viral counts at both the primary and latent infection sites. The Vaxfectin^® adjuvant substantially improved vaccine effectiveness. A related vaccine significantly reduced the recurrence of HSV-2 lesions in a therapeutic model using guinea pigs with latent infection. HSV-2 is a sexually transmitted virus which is the leading cause of genital herpes. Approximately one out of every six individuals in the United States and an estimated one out of every four worldwide is infected by HSV-2 before age 50. HSV-2 infection also significantly increases the risk of acquiring HIV-1.

David Koelle, M.D., professor of medicine in the Division of Allergy and Infectious Diseases at the University of Washington School of Medicine, who led this research, said, "The complete protection and high rate of sterilizing immunity observed in our initial mouse studies are quite impressive with such a safe and practical vaccine platform. We are particularly encouraged by the ability of this novel vaccine to address both primary and latent infection sites."

Initial results presented Saturday at the International Herpes Workshop (Salt Lake City, July 24 – 30) demonstrated that an appropriate dose of the prophylactic Vaxfectin^®-formulated vaccine, which encoded the HSV-2 glycoprotein D (gD2) antigen:

• Elicited antibody responses in 100% of mice against the encoded antigen;
• Protected 100% of mice against subsequent challenge with a lethal dose of live virus;
• Reduced viral shedding in mice at both the primary and latent infection sites; and
• Elicited sterilizing immunity in 80% of mice as evidenced by no detectable virus after challenge at either the primary (vagina) or latent (dorsal root ganglia) infection sites.

A therapeutic version of the vaccine, which encoded the gD2 antigen as well as the tegument proteins UL46/UL47, significantly reduced recurrence of HSV-2 lesions in guinea pigs with latent infection (p<0.05). Three doses of Vaxfectin^®-formulated vaccine were administered after resolution of the primary infection.

The preclinical development is being funded under a two-year, $2.0 million Phase II Small Business Technology Transfer (STTR) grant awarded in 2008 by the U.S. National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health (NIH), an agency of the U.S. Department of Health and Human Services. The grant period was recently extended to allow preclinical development to continue for a third year. The $2.0 million Phase II STTR grant supplements the $0.3 million awarded to Vical in 2005 for the HSV-2 vaccine program under a Phase I STTR grant from the NIAID, which partially funded Vical's initial development of the HSV-2 vaccine.

The initial preclinical development activities covered by the $2.0 million grant are being conducted at the University of Washington School of Medicine and the Sealy Center for Vaccine Development, both centers of excellence in herpes virus research. The vaccine is being designed primarily for use in people already infected with HSV-2, with the goal of reducing or eliminating periodic viral flare-ups and the associated viral shedding and transmission.

SOURCE Vical Incorporated