Therapeutic Ocular HSV Vaccine in HLA Transgenic Rabbits

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Herpes simplex virus 1 (HSV-1) infects the cornea and then establishes latency in sensory neurons of the trigeminal ganglia (TG). Sporadic spontaneous reactivation of HSV-1 causes shedding of virus in tears leading to spread of virus to other individuals, and can also cause recurrent Herpes Stromal Keratitis (HSK), a blinding ocular disease. A major gap in our current knowledge is: "How can we prevent or significantly reduce virus shedding in tears and HSV-induced ocular disease due to spontaneous reactivation of latent virus in the TG?" HSV-specific CD8+ T-cells appear to decrease in vitro induced HSV-1 reactivation in explanted mouse TG. Unfortunately, spontaneous reactivation of HSV-1 in mice is extremely rare so the relevance of these findings to in vivo HSV-1 spontaneous reactivation cannot be determined in mice. We now have a "humanized" HLA transgenic rabbit model of ocular HSV-1 that mounts "human-like" CD8 T-cell immune responses (HLA Tg rabbits). In a Preliminary Study we found that therapeutic immunization of latently infected HLA Tg rabbits with 3 human CD8 T-cell epitopes from HSV-1 gD decreased spontaneous reactivation 4-fold. This novel animal model will now allow us for the first time to test the hypothesis that a therapeutic vaccine that induces appropriate human T-cell responses to HSV-1 can decrease the effects of spontaneous reactivation (virus shedding in eyes and HSV-induced ocular disease). Our specific Aims include: (1). Test the hypothesis that therapeutic immunization with HSV-1 human CD8+ T-cell epitopes can decrease spontaneous reactivation in latently infected HLA Transgenic rabbits. CD4-CD8 lipopeptide vaccines, bearing different combinations of human CD4+ and CD8+ T cell epitopes from glycoprotein B and D (gB & gD), will be used to immunize latently infected HLA Tg rabbits. Protection against virus shedding in eyes (due to spontaneous reactivation) and HSV-induced ocular disease will be determined. (2). Test the hypothesis that the protective immunity induced by the therapeutic vaccination of HLA Transgenic rabbits in Aim 1 correlates with the presence of effector and memory CD8+ T-cells in the TG, conjunctiva, and/or draining lymph nodes. We will assess whether the number/function of HSV- and epitope- specific CD8+ T cells induced in vivo correlates with protection from spontaneous virus shedding in tears and ocular disease. We will assess the CD8+ T cell mechanism that correlates with protection. (3). Test the hypothesis that decreasing CD8+ T cells in latently infected HLA Tg rabbits will abrogate vaccine efficacy and also increase spontaneous reactivation in unvaccinated rabbits. These studies will provide important new information regarding the role of CD8+ T cells specific to human epitopes in immune control of HSV-1 spontaneous reactivation. This may lead to the development of new paradigms for immunotherapeutic strategies against ocular herpes.