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

ABSTRACT

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_EM cell epitopes, amino acids (aa) 129 to 143 of VP11/12 (VP11/12_129–143) and VP11/12_483–497, using in silico, in vitro, and in vivo 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 in silico peptide-protein docking analysis and in vitro 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^a/b degranulation, and CD4⁺ T cell carboxyfluorescein succinimidyl ester (CFSE) proliferation assays. We demonstrated that native VP11/12_129–143 and VP11/12_483–497 epitopes presented by HSV-1-infected HLA-DR-positive target cells were recognized mainly by effector memory CD4⁺ T_EM 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_EM cell epitopes, but not with cryptic epitopes, induced HSV-specific polyfunctional IFN-γ-producing CD107^ab+ CD4⁺ T cells associated with protective immunity against ocular herpes infection and disease.

IMPORTANCE We report that naturally protected HSV-1-seropositive asymptomatic individuals develop a higher frequency of antiviral effector memory CD4⁺ T_EM 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_EM cell responses is discussed.