Intravesical oncolytic virotherapy and immunotherapy for non‐muscle‐invasive bladder cancer mouse model.

Objectives: To test if intravesical instillation of both an anti‐programmed cell death protein 1 (PD‐1) inhibitor and an oncolytic reovirus would demonstrate a greater effect than either treatment alone, as non‐muscle‐invasive bladder cancer that is refractory to intravesical bacillus Calmette–Guérin can be treated by systemic anti‐PD‐1 immunotherapy and we previously demonstrated improved overall survival (OS) with six once‐weekly instillations of intravesical anti‐PD‐1 in a murine model. Materials and Methods: Using an orthotopic syngeneic C3H murine model of MBT2 urothelial bladder cancer, groups of 10 mice were compared between no treatment, intravesical anti‐PD‐1, intravesical oncolytic reovirus, or intravesical reovirus + anti‐PD‐1. A single intravesical treatment session was given. The primary outcome was OS, and the secondary outcomes included long‐term immunity and tumour–immune profile. Results: With a median follow‐up of 9 months, all mice that received no treatment died with a median survival of 41 days, while the comparison median OS was not reached for reovirus (hazard ratio [HR] 14.4, 95% confidence interval [CI] 3.9–32.6; P < 0.001), anti‐PD‐1 (HR 28.4, 95% CI 7.0–115.9; P < 0.001), and reovirus + anti‐PD‐1 (HR 28.4, 95% CI 7.0–115.9; P < 0.001). Monotherapy with anti‐PD‐1 or reovirus demonstrated no significant differences in survival (P = 0.067). Mass cytometry showed that reovirus + anti‐PD‐1 treatment enriched monocytes and decreased myeloid‐derived suppressor cells, generating an immuno‐responsive tumour microenvironment. Depletion of CD8+ T cells eliminated the survival advantage provided by the intravesical treatment. Conclusions: Treatment of murine orthotopic bladder tumours with a single instillation of intravesical reovirus, anti‐PD‐1 antibody, or the combination confers superior survival compared to controls. Tumour–immune microenvironment differences indicated myeloid‐derived suppressor cells and CD8+ T cells mediate the treatment response. [ABSTRACT FROM AUTHOR]