Novel combination immunotherapy for pancreatic cancer: potent anti-tumor effects with CD40 agonist and interleukin-15 treatment.

OBJECTIVES: With the poorest 5-year survival of all cancers, improving treatment for pancreatic cancer is one of the biggest challenges in cancer research. We sought to explore the potential of combining both priming and activation of the immune system. To achieve this, we combined a CD40 agonist with interleukin-15 and tested its potential in pancreatic cancer. METHODS: Response to this combination regimen was assessed in pancreatic ductal adenocarcinoma mouse models, and a thorough analysis of the tumor microenvironment was performed. RESULTS: We demonstrated profound reduction in tumor growth and increased survival of mice with the majority of mice being cured when both agents were combined, including an unprecedented 8-fold dose reduction of CD40 agonist without losing any efficacy. RNAseq analysis showed involvement of natural killer (NK) cell- and T-cell-mediated anti-tumor responses and the importance of antigen-presenting cell pathways. This combination resulted in enhanced infiltration of tumors by both T cells and NK cells, as well as a striking increase in the ratio of CD8+ T cells over Tregs. We also observed a significant increase in numbers of dendritic cells (DCs) in tumor-draining lymph nodes, particularly CD103+ DCs with cross-presentation potential. A critical role for CD8+ T cells and involvement of NK cells in the anti-tumor effect was highlighted. Importantly, strong immune memory was established, with an increase in memory CD8+ T cells only when both interleukin-15 and the CD40 agonist were combined. CONCLUSION: These novel preclinical data support initiation of a first-in-human clinical trial with this combination immunotherapy strategy in pancreatic cancer.