Konishi E, Yamaoka M, Khin-Sane-Win, Kurane I, Takada K, Mason PW
           Department of Health Sciences, Kobe University School of Medicine, Kobe
           654-0142, Japan. [email protected]
           Virol 1999 Jul;73(7):5527-34

        For Japanese encephalitis (JE), we previously reported that recombinant
        vaccine-induced protection from disease does not prevent challenge virus
        replication in mice. Moreover, DNA vaccines for JE can provide
        protection from high challenge doses in the absence of detectable
        prechallenge neutralizing antibodies. In the present study, we evaluated
        the role of postchallenge immune responses in determining the outcome of
        JE virus infection, using mice immunized with a plasmid, pcDNA3JEME,
        encoding the JE virus premembrane (prM) and envelope (E) coding regions.
        In the first experiment, 10 mice were vaccinated once (five animals) or
        twice (remainder) with 100 micrograms of pcDNA3JEME. All of these mice
        showed low (6 of 10) or undetectable (4 of 10) levels of neutralizing
        antibodies. Interestingly, eight of these animals showed a rapid rise in
        neutralizing antibody following challenge with 10,000 50% lethal doses
        of JE virus and survived for 21 days, whereas only one of the two
        remaining animals survived. No unimmunized animals exhibited a rise of
        neutralizing antibody or survived challenge. Levels of JE virus-specific
        immunoglobulin M class antibodies were elevated following challenge in
        half of the unimmunized mice and in the single pcDNA3JEME-immunized
        mouse that died. In the second experiment, JE virus-specific primary
        cytotoxic T-lymphocyte (CTL) activity was detected in BALB/c mice
        immunized once with 100 micrograms of pcDNA3JEME 4 days after challenge,
        indicating a strong postchallenge recall of CTLs. In the third
        experiment, evaluation of induction of CTLs and antibody activity by
        plasmids containing portions of the prM/E cassette demonstrated that
        induction of CTL responses alone were not sufficient to prevent death.
        Finally, we showed that antibody obtained from pcDNA3JEME-immunized mice
        4 days following challenge could partially protect recipient mice from
        lethal challenge. Taken together, these results indicate that
        neutralizing antibody produced following challenge provides the critical
        protective component in pcDNA3JEME-vaccinated mice.