Plasmids encoding granulocyte-macrophage colony-stimulating factor and CD154 enhance the immune response to genetic vaccines.

We examined whether plasmids encoding granulocyte-macrophage colony-stimulating factor (pGM-CSF) or CD40-ligand (pCD40L) could modify the immune response to antigen encoded by co-injected plasmid DNA. For this we used as antigen Escherichia coli beta galactosidase (beta-gal), encoded by the plasmid pLacZ. We found that intradermal co-injection of pLacZ with both pGM-CSF and pCD40L enhanced the anti-beta-gal IgG response by approximately two orders of magnitude compared to injections of pLacZ alone. Co-injection of both pGM-CSF and pCD40L with pLacZ significantly enhanced antigen-specific IgG, and in particular IgG(2a), over that of animals co-injected with pLacZ and either pGM-CSF or pCD40L. We found that co-injection of pGM-CSF and pCD40L with pLacZ enhanced the generation of beta-gal-specific cytotoxic T cells, and allowed for a significant expansion of CD8(+) T cells from splenocytes co-cultured with beta-gal expressing stimulator cells. The immunostimulatory effects induced by pGM-CSF or pCD40L required injection of these plasmids to the same site that received pLacZ. 'Priming' experiments, where the site of injection was pre-injected with either plasmid adjuvant, showed that pGM-CSF, but not pCD40L, could enhance the anti-beta-gal immune response induced by subsequently administered plasmid antigen. We conclude that plasmids encoding GM-CSF and CD154 are particularly effective genetic adjuvants when used together to enhance the humoral and cellular immune response to a plasmid-encoded antigen.