Intravesical BCG induces CD4+ T Cell Expansion in a Clinically Relevant Immune Competent Model of Bladder Cancer

Intravesical BCG Immunotherapy is the standard of care in treating non-muscle invasive bladder cancer, yet its mechanism of action remains elusive. Both innate and adaptive immune responses have been implicated in BCG activity. While prior research has indirectly demonstrated the importance of T cells and shown a rise in CD4+ T cells in bladder tissue after BCG, T cell subpopulations have not been fully characterized. We investigated the relationship between effector and regulatory T cells in an immune competent, clinically relevant rodent model of bladder cancer. Our data demonstrate that cancer progression in the MNU rat model of bladder cancer is characterized by a decline in the CD8/FoxP3 ratio, consistent with decreased adaptive immunity. By contrast, treatment with intravesical BCG leads to a large, transient rise in the CD4+ T cell population in the urothelium, and is both more effective and immunogenic compared to intravesical chemotherapy. Interestingly, whole transcriptome expression profiling of post-treatment intravesical CD4+ and CD8+ T cells revealed minimal differences in gene expression after BCG treatment. Together, our results suggest that while BCG induces T cell recruitment to the bladder, the T cell phenotype does not markedly change, implying that combining T cell activating agents with BCG might improve clinical activity. Digested Rat bladders, sorted for CD8 and CD4 T cells. Biologic groups are two replicates each of: control bladders, untreated bladders with bladder cancer, and bladders with bladder cancer treated with intravesical BCG