Evaluation of the Kinetic Change of the Immunogenicity of Dengue-2 DNA Vaccine in Mice Administered by Different Administration Routes

A plasmid DNA vaccine is able to induce both humoral and cellular immune responses; however, the kinetic change of the Th1/Th2 response, antibody avidity, cytokine secretion, and neutralization activity after different priming and boosting strategies have not been evaluated. A plasmid DNA, designated pCBD2 and previously shown to efficiently induce an immune response very similar to that by a wild type virus, was evaluated kinetically in this study. Our results suggest that a DNA vaccine delivered by the gene gun (gg) route produced higher and longer DENV-2-specific antibody titers than those induced through the intramuscular (im) route. Although the gg group induced a Th2 response and im delivery induced a Th1 response, priming by gg delivery, followed by a boosting by im delivery, did not shift the immune response from a Th2 to Th1 response. Furthermore, the antibody avidity (AI) measured by ELISA demonstrated a gradual increase of AI from low (AI range from 6.8% - 9.6%) on day 42 to high (AI value > 30) on day 119 in all but the gene-gun immunization group, in which an AI value of 23 was observed. Although there was lower avidity in the gg group, the mice sera from all three groups of mice demonstrated significant neutralization activity. This is the first report about the kinetics of immunogenicity of a DNA vaccine through different administration strategies, which suggests that gene gun delivery of a DNA vaccine can induce an immune response containing both neutralizing and nonneutralizing antibodies at high titers important for neutralization.