A single intramuscular injection of recombinant plasmid DNA induces protective immunity and prevents Japanese encephalitis in mice

Plasmid vectors containing Japanese encephalitis virus (JEV) premembrane (p rM) and envelope (E) genes were constructed that expressed prM and E protei ns under the control of a cytomegalovirus immediate-early gene promoter. CO S-1 cells transformed with this plasmid vector (JE-4B clone) secreted JEV-s pecific extracellular particles (EPs) into the culture media. Groups of out bred ICR mice were given one or two doses of recombinant plasmid DNA or two doses of the commercial vaccine JEVAX, All mice that received one or two d oses of DNA vaccine maintained JEV-specific antibodies 18 months after init ial immunization. JEVAX induced 100% seroconversion in 3-week-old mice; how ever, none of the 3-day-old mice had enzyme-linked immunosorbent assay tite rs higher than 1:400. Female mice immunized with this DNA vaccine developed plaque reduction neutralization antibody titers of between 1:20 and 1:160 and provided 45 to 100% passive protection to their progeny following intra peritoneal challenge with 5,000 PFU of virulent JEV strain SA14. Seven-week -old adult mice that had received a single dose of JEV DNA vaccine when 3 d ays of age were completely protected from a 50,000-PFU JEV intraperitoneal challenge. These results demonstrate that a recombinant plasmid DNA which p roduced JEV EPs in vitro is an effective vaccine.