Modulation of the immune response to DNA vaccine by co-delivery ofcostimulatory molecules

We have investigated methods for modulating immune responses, against herpe s simplex virus (HSV), generated from DNA vaccination by co-delivery of gen es encoding costimulatory molecules. A strong delayed-type hypersensitivity (DTH) reaction was induced in mice co-injected via the intradermal (i.d.) route with a eukaryotic expression plasmid encoding the CD80 molecule (pCD8 0) and a plasmid encoding the glycoprotein D of the HSV-2 (pgD). Furthermor e, when spleen cells from these mice were cultured in the presence of inact ivated HSV, a significant increase in the expression of interleukin-2 recep tor (IL-2R) was observed in the CD4 subset compared with mice immunized onl y with pgD. Analysis of cytokine synthesis at the single-cell level indicat ed that CD80 genes induce a significant increase in the number of interfero n-gamma (IFN-gamma)-, IL-2- and IL-4-secreting cells in the spleen. On the other hand, co-administration of the CD80 gene via the intramuscular (i.m.) route did not induce an increase in the cell-mediated immune response. Whe n a plasmid carrying the CD86 gene (pCD86) was co-injected via the i.m. rou te with the pgD plasmid, a small decrease in the number of IFN-gamma-secret ing cells was observed. This down-regulation of the immune response was als o observed when eukaryotic expression cassettes for CD80 and for CD86 were coadministered with the pgD plasmid via the i.d. route. However, co-injecti on of pCD86 via the i.m. route produced a small increase in the number of I L-4-secreting cells. When immunized mice were challenged intravaginally wit h 100 plaque-forming units of virus, only co-injection of the CD80 gene by the i.d. route provoked an adjuvant effect compared with mice immunized wit h pgD alone. A reduction in the titres of HSV in vaginal washings was obser ved together with a decrease in the lesion score.