Human Epitopes Identified from Herpes Simplex Virus Tegument Protein VP11/12 (UL46) Recall Multifunctional Effector Memory CD4 T Cells in Asymptomatic Individuals and Protect from Ocular Herpes Infection and Disease in "Humanized" HLA-DR Transgenic...

While the role of CD8 T cells in the control of herpes simplex virus 1 (HSV-1) infection and disease is gaining wider acceptance, a direct involvement of effector CD4 T cells in this protection and the phenotype and function of HSV-specific human CD4 T cell epitopes remain to be fully elucidated. In the present study, we report that several epitopes from the HSV-1 virion tegument protein (VP11/12) encoded by UL46 are targeted by CD4 T cells from HSV-seropositive asymptomatic individuals (who, despite being infected, never develop any recurrent herpetic disease). Among these, we identified two immunodominant effector memory CD4 T cell epitopes, amino acids (aa) 129 to 143 of VP11/12 (VP11/12) and VP11/12, using , , and approaches based on the following: (i) a combination of the TEPITOPE algorithm and PepScan library scanning of the entire 718 aa of HSV-1 VP11/12 sequence; (ii) an peptide-protein docking analysis and binding assay that identify epitopes with high affinity to soluble HLA-DRB1 molecules; and (iii) an ELISpot assay and intracellular detection of gamma interferon (IFN-γ), CD107 degranulation, and CD4 T cell carboxyfluorescein succinimidyl ester (CFSE) proliferation assays. We demonstrated that native VP11/12 and VP11/12 epitopes presented by HSV-1-infected HLA-DR-positive target cells were recognized mainly by effector memory CD4 T cells while being less targeted by FOXP3 CD4 CD25 regulatory T cells. Furthermore, immunization of HLA-DR transgenic mice with a mixture of the two immunodominant human VP11/12 CD4 T cell epitopes, but not with cryptic epitopes, induced HSV-specific polyfunctional IFN-γ-producing CD107 CD4 T cells associated with protective immunity against ocular herpes infection and disease. We report that naturally protected HSV-1-seropositive asymptomatic individuals develop a higher frequency of antiviral effector memory CD4 T cells specific to two immunodominant epitopes derived from the HSV-1 tegument protein VP11/12. Immunization of HLA-DR transgenic mice with a mixture of these two immunodominant CD4 T cell epitopes induced a robust antiviral CD4 T cell response in the cornea that was associated with protective immunity against ocular herpes. The emerging concept of developing an asymptomatic herpes vaccine that would boost effector memory CD4 and CD8 T cell responses is discussed.