In vivo depletion of DC impairs the anti‐tumor effect of agonistic anti‐CD137 mAb

Anti‐CD137 mAb are capable of inducing tumor rejection in several syngeneic murine tumor models and are undergoing clinical trials for cancer. The anti‐tumor effect involves co‐stimulation of tumor‐specific CD8⁺ T cells. Whether antigen cross‐presenting DC are required for the efficacy of anti‐CD137 mAb treatment has never been examined. Here we show that the administration of anti‐CD137 mAb eradicates EG7‐OVA tumors by a strictly CD8β⁺ T‐cell‐dependent mechanism that correlates with increased CTL activity. Ex vivo analyses to determine the identity of the draining lymph node cell type responsible for tumor antigen cross‐presentation revealed that CD11c⁺ cells, most likely DC, are the main players in this tumor model. A minute number of tumor cells, revealed by the presence of OVA cDNA, reach tumor‐draining lymph nodes. Direct antigen presentation by tumor cells themselves also participates in anti‐OVA CTL induction. Using CD11c diphtheria toxin receptor‐green fluorescent protein→C57BL/6 BM chimeric mice, which allow for sustained ablation of DC with diphtheria toxin, we confirmed the involvement of DC in tumor antigen cross‐presentation in CTL induction against OVA_257–264 epitope and in the antitumor efficacy induced by anti‐CD137 mAb.