Recombinant Japanese Encephalitis Virus Envelope Antigen Presented on CoPoP Liposomes Elicits Cellular Immunity and Protects Mice From Lethal Challenge.

Japanese encephalitis virus (JEV) causes severe encephalitis in endemic regions, and vaccination remains the primary preventive measure. To develop subunit vaccines that enhance cellular immunity, we produced a soluble His-tagged recombinant JEV envelope (rJEV-E) ectodomain and particularized it on cobalt porphyrin-phospholipid (CoPoP) immunogenic liposomes containing an monophosphoryl lipid A-related TLR4 agonist, with or without Quillaja saponaria saponin fraction 21 (QS-21). CoPoP-mediated particleization enabled stable antigen display and, when combined with QS-21 (rJEV-E/ECLSQ), elicited Th1-biased CD4+ and CD8+ T-cell IFN-γ responses alongside functional neutralizing Abs. In a stringent intracerebral lethal challenge model, rJEV-E/ECLSQ conferred robust protection despite moderate 50% plaque reduction neutralization test titers. JEV-specific IgG responses were sustained for at least one year, with recallable cellular immunity upon late boosting. These findings demonstrate that CoPoP-based particleization enables qualitative modulation of vaccine-induced immunity while maintaining effective protection in a stringent challenge setting.