NAKED DNA VACCINES EXPRESSING THE PRM AND E-GENE OF RUSSIAN SPRING-SUMMER ENCEPHALITIS-VIRUS AND CENTRAL-EUROPEAN ENCEPHALITIS-VIRUS PROTECT MICE FROM HOMOLOGOUS AND HETEROLOGOUS CHALLENGE

Naked DNA vaccines expressing the prM and E genes of two tick-borne fl aviviruses, Russian spring summer encephalitis (RSSE) virus and Centra l European encephalitis (CEE) virus were evaluated in mice. The vaccin es were administered by particle bombardment of DNA-coated gold beads by Accell gene gun inoculation. Two immunizations of 0.5 to 1 mu g of RSSE or CEE constructs/dose, delivered at 4-week intervals, elicited c ross-reactive antibodies detectable by enzyme-linked immunosorbent ass ay and high-titer neutralizing antibodies to CEE virus. Cross-challeng e experiments demonstrated that either vaccine induced protective immu nity to homologous or heterologous RSSE or CEE virus challenge. The ab sence of antibody titer increases after challenge and the presence of antibodies to E and prM, but not NS1, both before and after challenge suggest that the vaccines prevented productive replication of the chal lenge virus. One vaccination with 0.5 mu g of CEE virus DNA provided p rotective immunity for at least 2 months, and two vaccinations protect ed mice from challenge with CEE virus for at least 6 months.