Systemic Immunodominant CD8 Responses With an Effector-Like Phenotype Are Induced by Intravaginal Immunization With Attenuated HSV Vectors Expressing HIV Tat and Mediate Protection Against HSV Infection

Abstract

Mucosal HSV infection remains a public health issue in developing and developed world. However, an effective vaccine is still missing, partly because of the incomplete knowledge of correlates of protection. In this study we have investigated the kinetics and quality of immunity elicited by an attenuated HSV1 vector expressing the immunomodulatory Tat protein of HIV-1 (HSV1-Tat). Animals were immunized by intravaginal (IVag) or intradermal (ID) route with HSV1-Tat or with a control HSV1 vector expressing the LacZ gene (HSV1-LacZ) and immune responses were characterized in different anatomical districts.

IVag immunization with HSV1-Tat enhanced both expansion and memory phases of HSV-specific immunodominant CD8 responses at systemic, but not local, level and induced short- and long-term protection against mucosal challenge. Conversely, ID immunization with HSV1-Tat favored HSV-subdominant CD8 responses, which protected mice only at early time points after immunization.

IVag immunization, in particular with HSV1-Tat, compared to ID immunization, induced the differentiation of CD8⁺ T lymphocytes into short-lived effector (SLEC) and effector memory (Tem) cells, generating more robust recall responses associated with increased control of virus replication. Notably, systemic SLEC and Tem contributed to generate protective local secondary responses, demonstrating their importance for mucosal control of HSV. Finally, IgG responses were observed mostly in IVag HSV1-Tat immunized animals, although seemed dispensable for protection, which occurred even in few IgG negative mice. Thus, HSV1 vectors expressing Tat induce protective anti-HSV1 immune responses.