Oncolytic vaccinia virus armed with 4-1BBL elicits potent and safe antitumor immunity and enhances the therapeutic efficiency of PD-1/PD-L1 blockade in a pancreatic cancer model.

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal disease with a poor prognosis. Mono-immunotherapy, such as blockade of the PD-1/PD-L1 pathway, for PDAC has proven to be less effective. The systemic exertion of 4-1BB signaling enhanced antitumor immunity accompanied by hepatotoxicity, which is an obstacle for its clinical application. Our study exploits an oncolytic virus armed with 4-1BBL (VV-ΔTK-4L) to locally express 4-1BBL in the tumor microenvironment (TME), thus avoiding hepatotoxicity. VV-ΔTK-4L prolonged the survival time of a pancreatic tumor mouse model and modified the immune status of the TME and spleen. In the TME, the quantities of CD45 cells, NK1.1 cells, CD11c DCs, CD3T, CD4T, and CD8T cells increased. Compared to VV-ΔTK treatment, VV-ΔTK-4L further increases the number of CD8T cells with effector phenotypes, and downregulates exhaustion-related molecules on CD8T cells, and does not increase the proportion of Foxp3T cells. Thus, the TME of pancreatic cancer was converted from "cold" to "hot" by VV-ΔTK-4L. Blockade of the PD-1/PD-L1 pathway combined with VV-ΔTK-4L further significantly improves the survival ratio of a tumor-bearing mouse model. This study provides a systemic therapeutic strategy and approach for PDAC immunotherapy.