T cell-mediated protection and epitope mapping with a trivalent alphavirus-like replicon particle vaccine (VIR2P.1167)

Abstract

Abstract Venezuelan (VEEV), eastern (EEEV) and western (WEEV) equine encephalitis viruses cause debilitating and sometimes fatal illness. These pathogens are highly infectious when aerosolized, and thus favorable candidates for weaponization, yet no licensed vaccines exist. In a subcutaneous model of infection protection correlates with neutralizing antibody response, but studies suggest that protection from aerosol challenge is partially mediated by cellular immunity. We have previously shown that a trivalent (VEEV/EEEV/WEEV) virus-like replicon particle (triVRP) vaccine protected mice against lethal aerosol challenge. To investigate the cell-mediated response, splenocytes from triVRP- and mock-vaccinated mice were cultured for 6 days ex vivo in the presence of VEEV, EEEV or WEEV peptides. Fifteen-mer peptide pool libraries against E1 and E2 glycoproteins were used for T cell epitope mapping. Splenocytes were analyzed via flow cytometry for T cell-specific markers and cytokine production. Restimulation with specific regions of the VEEV E2 protein induced a memory CD8+CD44+ T cell response, as well as an increase in proliferating, non-cytokine producing CD8+CD44+ T cells. Thus, triVRP-vaccinated mice developed a cell-mediated, peptide-specific memory response. Studies are ongoing to precisely map T cell epitopes within VEEV, EEEV and WEEV glycoproteins. Future studies will evaluate the importance of these responses to protection from lethal aerosol alphavirus challenge.