Co-immunization with West Nile DNA and inactivated vaccines provides synergistic increases in their immunogenicities in mice

West Nile virus is now distributed throughout many temperate, subtropical and tropical areas: vaccines need to be developed that are affordable for developed and developing countries. Here, we constructed and evaluated a DNA vaccine expressing the premembrane and envelope proteins of West Nile virus (pcWNME). Mice immunized twice with 100 or 10 μg of pcWNME developed high or moderate levels of neutralizing antibodies, respectively. These mice were protected from viremia and death after lethal challenge. Mice immunized with a mixture of 1 μg of pcWNME and a small amount (1/10 dose) of a commercial inactivated vaccine developed moderate levels of neutralizing antibodies, whereas immunization with pcWNME or the inactivated vaccine alone induced only low or undetectable levels: co-immunization with the DNA and protein vaccines synergistically increased their own immunogenicities. The synergism reduced the amount of DNA sufficient to induce neutralizing antibodies: a single immunization with doses as low as 0.1 μg induced a titer of 1:40 at a 90% plaque reduction 6 or 9 weeks after immunization. Both IgG1 and IgG2a antibodies were induced in mice by co-immunization with the DNA and protein vaccines.