Characterization and modulation of immune responses in mice to a DNA-based vaccine

DNA-based vaccines represent a novel method of immunization that has been demonstrated to induce immune responses in animals against a variety of plasmid encoded antigens and following a number of different methods of vaccine delivery. We characterized the immune response to DNA-based vaccines encoding intracellular, membrane anchored (cell associated) and extracellular (secreted) forms of glycoprotein D (gD), an antigen from the viral envelope of the bovine herpesvirus-1 (BHV-1). Intramuscular injection of mice with plasmids encoding secreted or cell associated forms of this antigen led to seroconversion and a predominance of splenic IFN γ. Mice receiving plasmids encoding cell associated or secreted antigens displayed a predominance of IgG₂ₐ and IgG₁, respectively. The predominant serum isotype correlated with the cytokine and antibody isotype profiles within the draining lymph node. We demonstrated modulation of immune responses in mice following co-delivery of plasmids encoding a secreted form of gD and each of eight different murine cytokines (IL-1α, IL-12, IL-4, IL-6, IL-10, GM-CSF, IFN γ, TNF α). Plasmids encoding GM-CSF, TNF α, IL-4 and IL-6 demonstrated the capacity to enhance serum IgG titers and seroconversion efficiency. Plasmids encoding IFN γ and TNF α increased levels of serum IgG₂ₐ in mice. Varying the dose of plasmids encoding GM-CSF enhanced (10 μg) or suppressed (50 μg) serum antibody levels and induced significant increases in IL-4 levels in the spleen and draining lymph nodes. High doses of GM-CSF (50 μg) increased the levels of serum IgG₂ₐ after boosting. Co-administration of plasmids encoding IFN γ either reduced (10 μg) or enhanced (50 μg) serum antibody levels and elevated mean serum IgG₂ₐ levels. Finally, we investigated the potential for plasmids encoding the secreted form of gD to elicit immune responses in passively immune mice. We demonstrated that a single intramuscular immunization of passively immune C3H.HeN or C57BL/6 mice with plasmids encoding the secreted form of BHV-1 gD resulted in the development of both cell-mediated and humoral immunity