Recurrent viral diseases often occur after the viruses evade the hosts' immune system, by inducing exhaustion of antiviral T cells. In the present study, we found that functionally exhausted herpes simplex virus type 1 (HSV-1) -specific CD8⁺ T cells, with elevated expression of lymphocyte activation gene-3 (LAG-3), an immune checkpoint receptor that promotes T cell exhaustion, were frequent in symptomatic (SYMP) patients with a history of numerous episodes of recurrent corneal herpetic disease. Similarly, following UV-B induced virus reactivation from latency the symptomatic wild-type (WT) B6 mice that developed increase virus shedding and severe recurrent corneal herpetic disease had more exhausted HSV-specific LAG-3⁺CD8⁺ T cells in both trigeminal ganglia (TG) and cornea. Moreover, a therapeutic blockade of LAG-3 immune checkpoint with antagonist antibodies combined with a therapeutic immunization with gB_498-505 peptide immunodominant epitope of latently infected B6 mice significantly restored the quality and quantity of functional HSV-1 gB_498-505 specific CD8⁺ T cells in both TG and cornea and protected against UV-B induced recurrent corneal herpes infection and disease. In contrast to dysfunctional HSV-specific CD8⁺ T cells from WT B6 mice, more functional HSV-specific CD8⁺ T cells were detected in LAG-3^-/- deficient mice and were associated with less UV-B induced recurrent corneal herpetic disease. Thus, the LAG-3 pathway plays a fundamental role in ocular herpes T cell immunopathology and provides an important immune checkpoint target that can synergizes with T cell-based therapeutic vaccines against symptomatic recurrent ocular herpes.

Herpes simplex virus 1 (HSV-1) is a prevalent human pathogen that infects the cornea, causing potentially blinding herpetic disease. A clinical herpes vaccine is still lacking. In the present study, a novel prime/pull vaccine was tested in a human leukocyte antigen (HLA) transgenic rabbit model of ocular herpes (HLA Tg rabbits). Three peptide epitopes were selected, from the HSV-1 membrane glycoprotein C (UL44_400-408), the DNA replication binding helicase (UL9_196-204), and the tegument protein (UL25_572-580), all preferentially recognized by CD8⁺ T cells from "naturally protected" HSV-1-seropositive healthy asymptomatic (ASYMP) individuals (who never had recurrent corneal herpetic disease). HLA Tg rabbits were immunized with a mixture of these three ASYMP CD8⁺ T cell peptide epitopes (UL44_400-408, UL9_196-204, and UL25_572-580), which were delivered subcutaneously with CpG₂₀₀₇ adjuvant (prime). Fifteen days later, half of the rabbits received a topical ocular treatment with a recombinant neurotropic adeno-associated virus type 8 (AAV8) vector expressing the T cell-attracting CXCL10 chemokine (pull). The frequency and function of HSV-specific CD8⁺ T cells induced by the prime/pull vaccine were assessed in the peripheral blood, cornea, and trigeminal ganglion (TG). Compared to the cells generated in response to peptide immunization alone, the peptide/CXCL10 prime/pull vaccine generated frequent polyfunctional gamma interferon-positive (IFN-γ⁺) CD107⁺ CD8⁺ T cells that infiltrated both the cornea and TG. CD8⁺ T cell mobilization into the cornea and TG of prime/pull-vaccinated rabbits was associated with a significant reduction in corneal herpesvirus infection and disease following an ocular HSV-1 (strain McKrae) challenge. These findings draw attention to the novel prime/pull vaccine strategy for mobilizing antiviral CD8⁺ T cells into tissues to protect against herpesvirus infection and disease.IMPORTANCE There is an urgent need for a vaccine against widespread herpes simplex virus infections. The present study demonstrates that immunization of HLA transgenic rabbits with a peptide/CXCL10 prime/pull vaccine triggered mobilization of HSV-specific CD8⁺ T cells locally into the cornea and TG, the sites of acute and latent herpesvirus infections, respectively. Mobilization of antiviral CD8⁺ T cells into the cornea and TG of rabbits that received the prime/pull vaccine was associated with protection against ocular herpesvirus infection and disease following an ocular HSV-1 challenge. These results highlight the importance of the prime/pull vaccine strategy to bolster the number and function of protective CD8⁺ T cells within infected tissues.