Chang GJ, Hunt AR, Davis B
           Division of Vector-Borne Infectious Diseases, Centers for Disease
           Control and Prevention, Public Health Service, U.S. Department of Health
           and Human Services, Fort Collins, Colorado 80522, USA. [email protected]
           Virol 2000 May;74(9):4244-52

        Plasmid vectors containing Japanese encephalitis virus (JEV) premembrane
        (prM) and envelope (E) genes were constructed that expressed prM and E
        proteins under the control of a cytomegalovirus immediate-early gene
        promoter. COS-1 cells transformed with this plasmid vector (JE-4B clone)
        secreted JEV-specific extracellular particles (EPs) into the culture
        media. Groups of outbred 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 doses of DNA vaccine maintained
        JEV-specific antibodies 18 months after initial immunization. JEVAX
        induced 100% seroconversion in 3-week-old mice; however, none of the
        3-day-old mice had enzyme-linked immunosorbent assay titers 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
        intraperitoneal 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 days of age were completely protected from a 50, 000-PFU
        JEV intraperitoneal challenge. These results demonstrate that a
        recombinant plasmid DNA which produced JEV EPs in vitro is an effective
        vaccine.