Use of DNA priming and vaccinia virus boosting to trigger an efficient immune response to HIV-1 gp120

To enhance the ef f ic iency of DNA vaccines to HIV-1, we immunized BALB/c mice sequential ly with a gp120 DNA vector and a recombinant vaccinia virus (VV). We have also evaluated the effect of granulocyte macrophage colony st imulation factor (GM-CSF) expression by a DNA vector on both cellular and humoral immune responses when coadministered with the gp120-encoding DNA at priming. Our results show a significant enhancement of both arms of the immune system when the DNA prime/VV boost regime i s used, as compared with the immunization protocol based on priming and boosting with vector DNA. A 100-fold increase in the number of antigen-specific IFN-secreting CD8 T cel ls was observed in splenocyte cultures from mice immunized with the combined vector DNA/VV protocol . The humoral immune response is also improved in animals receiving the vector DNA/VV combined vaccine , as shown by the increase in both env-speci f ic antibody titers and HIV-1 neutralizing activity in sera. IgG1 was the predominant isotype detected in sera from the immunized animals. This , together with the IL-4 and IFNproduction in splenocyte cultures from these animals, indicated that both Th1 and Th2 responses are induced by the combined immunization approach. Coadministration of a GM-CSF-expressing DNA vector in the priming step resulted in enhanced T cell proliferation rates, irrespective of whether the booster was g iven with vector DNA or recombinant VV. In addit ion, a s l ight increase in the humoral immune response was also observed in animals primed with gp120 and GM-CSF-expressing plasmid and boosted with recombinant VV. These findings describe a combinatorial priming/booster immunization approach that may be effective in the control of HIV-1 infection and of other pathogens.