Most cases of genital herpes are due to herpes simplex virus (HSV)-2. The rate of HSV-2 infections increased by 30% from 1988 to 1994. In addition to genital herpes, transmission of HSV-2 to neonates causes severe life-threatening infections. Recent studies demonstrate a link between genital herpes and increased rates of transmission of HIV. Therefore, an effective HSV-2 vaccine is needed. 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 an large international, phase three, randomized controlled trial in HSV-2 seronegative women. We postulated 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. We have been evaluating a candidate HSV-2 vaccine deleted for two essential genes, termed HSV-2 dl5-29, which was developed by David Knipe at Harvard University. In order to construct additional vaccine candidates, 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. We have begun to engineer mutations in the HSV-2 BAC and to obtain mutated HSV-2. We are currently attempting to create a candidate HSV-2 vaccine that can replicate in the skin and induce a potent immune response, but not infect the nervous system and therefore not undergo latent infection and virus reactivation.
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