DEC-205 receptor on dendritic cells mediates presentation of HIV gag protein to CD8⁺ T cells in a spectrum of human MHC I haplotypes

Optimal HIV vaccines should elicit CD8⁺ T cells specific for HIV proteins presented on MHC class I products, because these T cells contribute to host resistance to viruses. We had previously found that the targeting of antigen to dendritic cells (DCs) in mice efficiently induces CD8⁺ T cell responses. To extend this finding to humans, we introduced the HIV p24 gag protein into a mAb that targets DEC-205/CD205, an endocytic receptor of DCs. We then assessed cross-presentation, which is the processing of nonreplicating internalized antigen onto MHC class I for recognition by CD8⁺ T cells. Low doses of αDEC-gag, but not control Ig-gag, stimulated proliferation and IFN-γ production by CD8⁺ T cells isolated from the blood of HIV-infected donors. αCD205 fusion mAb was more effective for cross-presentation than αD209/DC-SIGN, another abundant DC uptake receptor. Presentation was diverse, because we identified eight different gag peptides that were recognized via DEC-205 in 11 individuals studied consecutively. Our results, based on humans with highly polymorphic MHC products, reveal that DCs and DEC-205 can cross-present several different peptides from a single protein. Because of the consistency in eliciting CD8 ⁺ T cell responses, these data support the testing of αDEC-205 fusion mAb as a protein-based vaccine.