Oncolytic vaccinia virus acts synergistically with anti-PD-L1 antibody to enhance the killing of colon cancer cells by CD8+ T cells

Both oncolytic vaccinia virus (OVV) and anti-PD-L1 antibody hold promise in cancer immunotherapy. Herein, we aimed to explore the possible synergistic effects of OVV and anti-PD-L1 on the growth and metastasis of colon cancer (CC) in mouse models. Microarray profiling of CC-related genes was first conducted. Expression of PD-L1 in CC tissues was predicted by TCGA and verified by flow cytometry and RT-qPCR. Then, mouse CC cell lines stably carrying luciferase MC38-luc and CT26-luc were infected with recombinant double-deleted vaccinia virus (vvDD) to evaluate the effect of vvDD on cell viability. The data indicated that PD-L1 was highly expressed in CC tissues and cells following vvDD infection. MC38-luc cells were inoculated into mice to construct CC-bearing mouse models, which were treated with vvDD or combined with anti-PD-L1, with tumor growth, metastasis, survival, and the immune environment analyzed. It was found that OVV combined with anti-PD-L1 antibody led to lower tumor burden and growth and higher survival rates than individual treatment in CC-bearing mice. In addition, this combination exerted a remote effect on the untreated subcutaneous tumors in the lateral abdomen, thus suppressing the tumor metastasis. Furthermore, combined therapy of OVV with anti-PD-L1 antibody activated CD8+ T cells, reduced exhaustion of CD8+ T cells, and enhanced their immune response, strengthening the killing of CC cells and inhibiting tumor growth and metastasis. In conclusion, our findings provide mechanistic insights into the action and efficacy of OVV as an immunomodulatory agent combined with the anti-PD-L1 antibody for the treatment of CC.