INDUCTION OF PROTECTIVE IMMUNITY AGAINST JAPANESE ENCEPHALITIS IN MICE BY IMMUNIZATION WITH A PLASMID ENCODING JAPANESE ENCEPHALITIS-VIRUS PREMEMBRANE AND ENVELOPE GENES

A DNA vaccine plasmid containing the Japanese encephalitis (JE) virus premembrane (prM) and envelope (E) genes (designated pcDNA3JEME) was e valuated for immunogenicity and protective efficacy in mice. Two immun izations of 4-week-old female ICR mice with pcDNA3JEME by intramuscula r or intradermal injections at a dose of 10 or 100 mu g per mouse elic ited neutralizing (NEUT) antibodies at titers of 1:10 to 1:20 (90% pla que reduction), and all immunized mice survived a challenge with 10,00 0 50% lethal doses of the P3 strain of JE virus. A single immunization with 100 mu g of pcDNA3JEME did not elicit detectable NEUT antibodies but induced protective immunity. Spleen cells obtained from BALB/c mi ce immunized once with 10 or 100 mu g of pcDNA3JEME contained JE virus -specific memory cytotoxic T lymphocytes (CTLs). BALB/c mice maintaine d detectable levels of memory B cells and CTLs for at least 6 months a fter one immunization with pcDNA3JEME at a dose of 100 mu g. The CTLs induced in BALB/c mice immunized twice with 100 mu g of pcDNA3JEME wer e CD8 positive and recognized mainly the envelope protein. These resul ts indicate that pcDNA3JEME has the ability to induce a protective imm une response which includes JE virus-specific antibodies and CTLs.