Dendritic cells enhance detection of antigen-specific cellular immune responses by lymphocytes from rhesus macaques immunized with an HIV envelope peptide cocktail vaccine

Detection and enumeration of functional antigen-specific T cells is important for understanding the breadth of cell-mediated immunity to infections and experimental vaccines. We tested the utility of dendritic cells (DC), the professional antigen presenting cells, in the enzyme-linked immunosorbent spot-forming cell assay (ELISPOT) for efficient monitoring of antigen-specific immunity in rhesus macaques vaccinated with an HIV envelope peptide-cocktail. Compared with direct antigen-specific stimulation of peripheral blood mononuclear cells, the DC-ELISPOT protocol involving co-culturing of macaque T cells with autologous DC pulsed with the various peptides from the vaccine cocktail yielded up to 18-fold higher numbers of interferon-gamma producing cells without increasing the background. Importantly, use of DC in the analyses revealed immune responses in vaccinated macaques that were otherwise undetectable. Similar data were obtained when recall responses to purified protein derivative were analyzed by the DC-ELISPOT method using blood samples from human volunteers. These data establish the importance of DC in improving detection sensitivity and eliminating false negative results, both essential for efficient monitoring of antigen-specific cellular immune responses.