ELISPOT analysis of a new CTL based DNA vaccine for HIV-1 using GM-CSF in DNA prime/peptide boost strategy: GM-CSF induced long-lived memory responses.

Genetic adjuvants have potential role in improvement of immune responses against DNA vaccines. GM-CSF as a genetic adjuvant can recruit and augment dendritic cell numbers in the site of immune responses and thereby induce cellular and humoral immune responses. Here we show that co-immunization of a DNA vaccine from HIV-1P24-Nef with GM-CSF in DNA priming and peptide boost strategy increases the immunogenicity of our candidate vaccine. Analysis of immune response shows that co-immunization with GM-CSF boosts cellular immune responses through increasing proliferation activity and CTL function. Results of cytokine profile studies show that both IL-4 and IFN-γ levels were augmented. Also, co-immunization with GM-CSF resulted in a higher level of total IgG, comprising approximately equal levels of both specific IgG1 and IgG2a subtypes. Monitoring of cellular and humoral immune responses for 20 weeks after final immunization revealed the aptitude of GM-CSF for inducing long-lived humoral and cell mediated immune responses. Overall, our results suggest that GM-CSF is able to induce long term memory for the HIV-1 P24-Nef vaccine candidate while the exact mechanisms involved remained to be clarified.