Herpes keratitis is the most common non-traumatic cause of blindness in young adults. The major morbidity comes not from the primary infection but from the recurrent disease: i.e., after reactivation of latent herpes simplex virus (HSV) is trigeminal ganglia. The goals of anti-HSV vaccines are to block the establishment of the latent infection or, failing this, to alter latency so that reactivation is less frequent or recurrences less severe. For reasons of safety, subunit vaccines free of HSV DNA are preferable. But trials in animal models have shown that these vaccines are less effective in blocking latency than immunization with live virus. The hypothesis in this proposal is that cell-mediated immunity is important in protection and that subunit vaccines may be limited by their failure to induce histocompatibility-restricted cytotoxic T lymphocytes. To test this hypothesis, model vaccines will be constructed by cloning two major HSV glycoproteins gB and gD into a plasmid vector. This vector will then be used to transfect murine cell lines so that the transformed cells each express a single surface HSV antigen. These cell lines will be used to immunize syngeneic and allogeneic mice. Anti-HSV antibody and cytotoxic T lymphocytes will be determined and the optimal immunization procedure established. Then the immunized mice will be challenged with live HSV inoculated by the corneal route. Immunization groups will be monitored for corneal disease, mortality/encephalitis, percentage ganglionic infection, and amount of HSV DNA in ganglia. In those immunization groups where the latent ganglionic infection is not blocked, experiments will be done to determine the capacity of latent virus to reactivate. The reactivation assay will involve epinephrine iontophoresis across the cornea with detection of HSV shedding in the tear film. This experimental approach uses well-defined model vaccines to determine the importance of cytotoxic T lymphocytes in HSV immunization.
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