Enhanced anti-tumor immunity of vaccine combined with anti-PD-1 antibody in a murine bladder cancer model

PURPOSE: Programmed cell death protein 1 (PD-1) and ligand programmed death ligand 1 (PD-L1) are important immune-suppressive regulators in the tumor microenvironment. A vaccine-induced immune effect on tumor cells is blunted by the immunosuppressive tumor microenvironment. Therefore, we hypothesized that a dendritic cell (DC) vaccine combined with anti-PD-1 (αPD-1) antibodies could elicit a synergistic anti-tumor immunity in bladder cancer. MATERIALS AND METHODS: We produced a model of subcutaneous transplantation in C3H/HeJ mice by transplanting murine MBT-2 bladder cancer cells. DCs were isolated from normal C3H/HeJ mice, followed by stimulation against MBT-2 lysate before injection. Two weeks later of MBT-2 inoculation, αPD-1 and stimulated DCs were injected two times at one-week interval intraperitoneally and intravenously, respectively. Tumor-infiltrating immune cells and splenocytes were analyzed using flow cytometry. T-cell-mediated anti-tumor responses were measured by interferon (IFN)-γ ELISPOT and lactate dehydrogenase assays. RESULTS: The mice treated with DC+αPD-1 showed a significant decrease in tumor volume compared to the DC-treated mice and IgG-treated group. Survival of the DC+αPD-1–treated group was improved compared with that of the IgG-treated mice. IFN-γ secretion from splenocytes against tumor cells was significantly increased in the DC+αPD-1 group compared with that of αPD-1–treated mice. The frequency of CD8(+) and CD4(+) T-cells in spleens was statistically increased in the DC+αPD-1–treated mice compared to those receiving monotherapy (DC- or αPD-1–treated group). CONCLUSIONS: Our results support the hypothesis that the combination therapy of a DC vaccine and αPD-1 antibodies could enhance the anti-tumor immune response against bladder cancer.