Redefining Dendritic Cell Vaccines: Synergistically Co‐priming DC and B Cells With Nanoparticles Loading Whole Cell Antigens Maximizes the Efficacy of DC Vaccines

ABSTRACT Dendritic cells (DC) play core roles in inducing antigen‐specific T cells. However, limited effectiveness hinders their applications as vaccines. To improve the efficacy of traditional DC vaccines, this study optimized three aspects: tumor antigens, cell sources and co‐incubating molecules, and thus proposed a new DC‐BC vaccine: co‐priming B cells and DC at a precise ratio. The therapeutic efficacy was significantly improved by co‐incubating DC and B cells. Regarding tumor antigens, utilizing nanoparticles loading whole‐tumor lysates performed better than utilizing nanoparticles loading multiple neo‐antigens, or nanoparticles loading only water‐soluble lysates, or free whole‐tumor lysates. Moreover, adding IL‐15 and αPD‐L1 antibody further bettered DC‐BC vaccines. The optimal DC‐BC vaccines showed excellent therapeutic efficacy with a 100% response rate and could cure most tumor‐bearing mice on several different cancer models, including melanoma, lung cancer and orthotopic pancreatic cancer. The mechanism investigation demonstrated that several molecules, including Ticam1 (TRIF), Traf3, Mavs, and Ifnar2, were involved in promoting APC maturation and improving therapeutic efficacy of vaccines by activating innate immune pathways (TLR/NLR/RLR). In summary, this study provides a new DC‐BC vaccine that has much better therapeutic efficacy and explores the underlying mechanism of why co‐incubating DC and B cells improved the therapeutic efficacy.