Enhancing DC cancer vaccine by allogeneic MHC class II expression and Treg depletion

We assessed the therapeutic efficacy of a semiallogeneic dendritic cell (DC) vaccine in comparison to a syngeneic one for suppression of B16-F10 and TC-1 tumors. Syngeneic bone marrow-derived DCs (BMDCs) were generated from C57BL/6J mice and semiallogeneic BMDCs with a mutation in either MHC class I or II were generated from B6.C-H2-Kbm1/ByJ or B6(C)-H2-Ab1bm12/KhEgJ mice, respectively. We demonstrated in vivo and in vitro that the MHC class II semiallogeneic BMDC vaccine had superior efficacy over the syngeneic and the MHC class I semiallogeneic BMDC vaccine, providing allogeneic CD4+ T cell help to enhance the antitumor CD8+ T cell response through allogeneic stimulation by the mutant MHC class II molecules. We discovered that this help was induced only at an early stage of tumor growth and at a later stage of tumor growth; combining our BMDC vaccine with Treg depletion enhanced tumor suppression. We demonstrated the improved efficacy of a semiallogeneic BMDC vaccine that kept tumor-peptide presentation intact on syngeneic MHC class I molecules so that mutant MHC class II could provide allogeneic help. This strategy should enable promising new DC-based cancer immunotherapies, offering an alternative to autologous DC vaccines by incorporating allogenicity as an adjuvant.