Purpose: Our goal was to target melanoma antigens to the dendritic cell-specific receptor DEC-205. DEC-205 is an antigen receptor expressed on dendritic cells and has been shown to guide antigens to MHC class I and II compartments for processing and presentation to T cells.
Experimental design: The melanoma tumor-associated antigen (TAA), gp100, was fused to the single-chain fragment variable (scFv) specific for DEC-205. The binding capacity of the scFv was tested on lymph node-isolated CD11c+ cells. Mixed lymphocyte reactions were carried out to show an increased proliferative capacity of gp100 antigen-specific CD4 and CD8 T cells. Furthermore the scFv-TAA was used in a therapeutic setting using two different melanoma mouse models.
Results: C57Bl/6 mice were injected with scFv-DEC-205-gp100, monoclonal antibody anti-DEC-205, or PBS. Using fluorescence-activated cell sorting, we showed that lymph node CD11c+ dendritic cells stained positive for the binding of the scFv-mDEC-205-gp100 and the anti-DEC-205 monoclonal antibody, whereas the PBS-injected animals were negative. In mixed lymphocyte reactions, bone marrow-derived dendritic cells pulsed with scFv-mDEC-205-gp100 significantly increased proliferation of gp100-specific CD8+ and CD4+ T cells beyond gp100 peptide-pulsed or nonpulsed bone marrow-derived dendritic cells. Finally, in B16/F10 and RET models, a concentration-dependent suppression of tumor growth using scFv-mDEC-205-gp100 (66% reduction of tumor volume), in comparison with gp100 peptide vaccination, was observed.
Conclusions: Our results indicate that the scFv-mDEC-205-gp100 targets TAA to dendritic cells in vivo for presentation on both MHC class I and II molecules. In vivo, this leads to an improved immune response and a decrease in tumor growth rate.