Varicella zoster virus (VZV) is a neurotropic alpha-herpesvirus that causes varicella (chickenpox) and establishes latency in the sensory ganglia. Reactivation of VZV leads to herpes zoster (shingles), a painful and debilitating disease that is associated with post-herpetic neuralgia. Most cases of herpes zoster occur in persons over 50 years of age, with immunosuppression being an additional risk factor. Two approved VZV vaccines are available, both based on a live-attenuated strain of VZV. The high-dose version is recommended for adults to reduce the incidence of shingles; this reduction is on the order of 50%. However, the long-term efficacy of these live-attenuated vaccines is inadequate, and improved vaccines are desirable. Reactivation of VZV, with the attendant consequences of herpes zoster, is thought to be due to inefficient T- cell immunity. Because VZV-specific antibody titers do not significantly decline with age, the increased risk of VZV reactivation among older individuals is likely due to an age-associated decrease in T-cell immunity. Improved vaccines should therefore be efficient at inducing a robust cellular immune response. The only animal model that recapitulates the human VZV-induced disease is intrabronchial infection of young rhesus macaques with simian varicella virus (SVV). SVV and VZV are evolutionarily related and are co-linear with respect to genome organization. Immunization of patas monkeys with VZV can protect the animals from SVV challenge, demonstrating substantial antigenic relatedness of the two viruses. Recent studies by Dr. Messaoudi, the Co-PI of this Proposal, have examined the T-cell responses given by each of the nearly 70 open reading frames (ORFs) of SVV in infected macaques. ORFs have been identified that are responsible for strong T-cell responses during acute infection but are only weakly immunogenic in latent infection. We hypothesize that these ORFs are candidates for an effective vaccine to prevent reactivation and thus herpes zoster. In this Proposal, we will create DNA vaccines expressing nine ORFs that are strongly immunogenic in acute infection but weakly so in latency. Initial studies with mice will allow identification of those ORFs that are potent inducers of T-cel responses. We will select three ORFs for immunization of rhesus macaques with DNA vaccines delivered by electroporation. Electroporation can increase the potency of DNA vaccines and is efficacious, safe, and well tolerated in human clinical trials; it represents a realistic product modality for a VZV/HZ vaccine destined for adults. After several immunizations, macaques will be challenged with live SVV and the viral titers evaluated. Immune responses will also be measured after immunization and challenge in peripheral blood cells and bronchial lavage to characterize the kinetics and magnitude of T- and B-cell proliferation, the frequency of antigen-specific T cells, and antigen-specific antibody titer. The immunization protocol will be considered a success if the vaccine produces a significant and large reduction of viral loads.
Previous infections by varicella-zoster virus can lead to herpes zoster, commonly known as shingles. A complication of shingles is post-herpetic neuralgia, which is a severe, disabling, and persistent pain that can last for months or years. Most cases of shingles occur in persons 50 years of age or older. Although vaccines are available for this age group, they are of limited efficacy. Thus, the development of more effective vaccines would be highly desirable and is the objective of this Proposal.
