Over the past few years, we completed human trials of recombinant glycoprotein vaccines for treatment and prevention of genital herpes. The vaccines proved inadequate. We turned, therefore, to animal model studies using new classes of HSV vaccines to define ones that appear to be more immunogenic and potentially more effective. We have compared a recombinant glycoprotein vaccine which expresses glycoprotein D (recombinant gD2), a DNA-based plasmid vector that expresses gD2, and a live, genetically-engineered replication defective vaccine for genital herpes. The engineered virus vaccine termed dl5/29 was made by David Knipe at Harvard and consists of HSV-2 deleted for genes 5 and 29, impairing replication and establishment of latency. We compared the three vaccines in mouse and guinea pig models of HSV-2. In mice and guinea pigs dl5-29 is as protective as recombinant gD2 against acute disease, latency and recurrence rates. Both of these vaccines were superior to the DNA-based plasmid vaccine. In guinea pigs, dl5-29 was more immunotherapeutic, i.e. able to treat an established HSV-2 infection, than recombinant protein in adjuvant. Latent viral DNA could not be detected in nervous tissue after inoculation with dl5-29. dl5-29 induced higher levels of virus neutralizing antibody than recombinant gD2. We have developed techniques to recover and quantify CD8+ T cells that express interferon gamma upon exposure to HSV infected cells from the spleen and regional sensory nerve ganglia. We found that the dl5-29 vaccine induces significantly stronger virus-specific T cell responses in the spleen and such cells traffic to and accumulate more rapidly and to higher total numbers in regional ganglia. Over the coming year we intend to characterize these T cells more fully and better define the roles they play in controlling primary and reactivation infections.
