Intravesical chemotherapy enhances anti-tumor immunity in bladder cancer by modulating CD8+ T cell activation and Treg populations

Bladder cancer is one of the most common malignancies of the urinary system, with standard treatments including surgery, radiotherapy, and chemotherapy. However, these conventional approaches often yield suboptimal outcomes, necessitating exploring alternative therapeutic strategies. This study evaluated the efficacy of intravesical chemotherapy, both alone and in combination with immunotherapy, using an orthotopic mouse model of bladder cancer. To establish the model, luciferase-expressing bladder cancer cells were orthotopically implanted into immunocompetent mice. Treatment efficacy was assessed by monitoring changes in bioluminescence imaging (BLI) signal intensity, indicative of tumor burden, and by measuring tumor weights post-mortem. Mice were divided into four groups: G1: untreated control; G2: intravesical chemotherapy with 40 mph Doxorubicin (0.05 ml per mouse, bladder instillation); G3intraperitoneal (i.p.) chemotherapy with 10 mph Doxorubicin; G4: immune combination therapy with 10 mph Doxorubicin (i.p.) plus 10 mph PD-L1 inhibitor (i.p.). Results demonstrated that intravesical chemotherapy significantly reduced tumor burden compared to both conventional systemic chemotherapy and immune combination therapy (p-value <0.05). Flow cytometry analysis revealed a notable decrease in CD8⁺ T cell expression in both the intravesical and conventional chemotherapy groups (p value < 0.01). Additionally, Treg cell expression was moderately reduced in the conventional and immune combination therapy groups (p value < 0.05). Notably, intravesical chemotherapy led to a significant increase in CD69 activation on CD8⁺ T cells (p value < 0.05), suggesting enhanced T cell activation, while also moderately reducing PD-1 expression, a marker of T cell exhaustion (p value < 0.05).Histological analysis, including hematoxylin and eosin (HE) staining and Ki-67 immunohistochemistry, further confirmed significant differences in tumor morphology and proliferation among the treatment groups (p value < 0.05). These findings suggest that intravesical chemotherapy not only exerts a direct anti-tumor effect but also modulates the immune response by activating CD8⁺ T cells and mitigating T cell exhaustion. To conclusion, this study highlights the potential of intravesical chemotherapy as a promising and clinically feasible approach for bladder cancer treatment, warranting further investigation in translational and clinical practice.