Herpes simplex virus 2 (HSV-2) causes genital herpes and increases the risk of transmission and infection with HIV. Thus a vaccine for HSV-2 would not only reduce the rate of genital herpes, but also might reduce spread of HIV. Several HSV-2 vaccines have been tested in humans for prevention or reduction of genital herpes disease. A vaccine containing a single viral protein (HSV-2 glycoprotein D) recently showed no evidence for protection against genital herpes in a large international, phase three, randomized controlled trial in HSV-2 seronegative women. We postulate that the limited efficacy of the HSV-2 glycoprotein D vaccine is likely due to inadequate induction of broadly neutralizing antibody and cellular immune responses. Last year we reported that we cloned the entire HSV-2 genome into a plasmid containing a bacterial artificial chromosome (BAC). We showed that virus derived from the HSV-2 BAC replicated in cell culture at the same rate as wild-type virus and that mice infected with the HSV-2 BAC developed disease as well as latent HSV-2 infection at a similar rate as animals infected with wild-type virus. This year, we engineered mutations in the HSV-2 BAC and obtained HSV-2 with mutations in the viral glycoprotein D (gD) that are critical for the ability of gD to interact with one of its receptors, nectin-1, but not with another receptor, HVEM. Since HVEM is expressed on epithelial cells and lymphocytes, while nectin-1 is expressed on neurons and epithelial cells, the HSV-2 gD mutant would be predicted to be impaired for infecting neurons, but not epithelial cells and therefore might induce a potent immune response, but not cause neurologic disease in animals. The HSV-2 mutant was able to infect cells expressing HVEM (epithelial cells), but not cells only expressing nectin-1 (neuroblastoma cells). The mutant did not productively infect ganglia in the nervous system of mice. The inability of the HSV mutant to productively infect neuronal cells in culture or ganglia in mice after intramuscular inoculation suggests that the HSV-2 mutant might be an attractive candidate as a live attenuated HSV-2 vaccine. We are also planning to initiate a phase 1 clinical trial to test the safety and immunogenicity of a different vaccine- a replication-defective HSV-2 vaccine in humans. This vaccine was developed by Dr. David Knipe at Harvard, and our lab performed much of the preclinical work in mice and guinea pigs. The clinical protocol has been approved by our IRB and we are currently screening patients to identify those who will be eligible to enroll in the vaccine trial.
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