In vivo targeting of an HIV synthetic peptide cocktail vaccine to dendritic cells in rhesus macaques to prime antigen-specific cell-mediated immunity

Dendritic cells (DC) serve as the professional antigen presenting cells for initiating strong antigen-specific cellular immune responses. We reported earlier protection of rhesus macaques from chronic infection and AIDS by immunizing with DC pulsed ex vivo with a conserved HIV envelope peptide-cocktail vaccine for efficient priming of cellular immune responses. In the present study, we attempted to target DC in vivo by combining subcutaneous administration of fins-like tyrosine 3 kinase ligand (FL) and immunization with the envelope peptide-cocktail and synthetic oligodeoxynucleotide containing unmethylated CpG motifs as adjuvant. The vaccinated animals exhibited transient mobilization of DC into peripheral blood and priming of T cells with antigen specific proliferation, IFN-γ production as well as cytolytic activity. Polychromatic flow cytometry analyses revealed the presence of antigen-specific CD4 memory T cells producing cytokines in the vaccinated animals, but not the mock-vaccinated controls. Pathogenic SHIV challenge provided marginal protective efficacy suggesting the need for further improvements to realize the full potential of the in vivo DC-targeting strategy for delivering HIV candidate vaccines.