Amato J. Giaccia

Pancreatic cancer is one of the deadliest cancers, against which current immunotherapy strategies are not effective. Herein, we analyzed the immune cell composition of the tumor microenvironment of pancreatic cancer samples in The Cancer Genome Atlas and found that the presence of intratumoral natural killer (NK) cells correlates with survival. Subsequent analysis also indicated that NK cell exclusion from the microenvironment is found in a high percentage of clinical pancreatic cancers and in preclinical models of pancreatic cancer. Mechanistically, NK cell exclusion is regulated in part by complement C3a and its receptor signaling. Inhibition of the C3a receptor enhances NK cell infiltration in syngeneic mouse models of pancreatic cancer resulting in tumor growth delay. However, tumor growth inhibition mediated by NK cells is not sufficient alone for complete tumor regression, but is potentiated when combined with radiotherapy. Our findings indicate that although C3a inhibition is a promising approach to enhance NK cell–based immunotherapy against pancreatic cancer, its combination with radiotherapy holds greater therapeutic benefit. Significance: Immunotherapeutic agents are not effective against pancreatic cancer. We show that the inhibition of complement C3a enhances NK cell infiltration in preclinical models of pancreatic cancer, resulting in tumor growth delay. This effect is further potentiated by radiotherapy, thereby leading to significant antitumor activity compared with either therapy alone.