Divergent Macrophage-Regulated T cell States Determine Response to Bacillus Calmette-Guérin vaccine in High-Risk Bladder Cancer

BACKGROUND: Primary therapy for high-risk bladder cancer (BCa) is repeated instillations of the tuberculosis vaccine Bacillus Calmette-Guerin (BCG). Although BCG reduces the risk of recurrence by more than half, the mechanisms underlying its immune-activating effects remain unknown. Our objective was to investigate how the immune response differs between BCG responders and non-responders and to compare systemic and local immune responses. METHODS: We performed single-cell RNA sequencing (scRNA-seq) of isolated immune cells adjacent to high-risk bladders in BCG responders and non-responders before and after BCG. We also compared concurrent scRNA-seq profiles of circulating immune cell populations with those of bladder immune cells. RESULTS: We identify an increase in Th17-like Th1 cells in BCG responders, characterized by greater expression of pro-inflammatory cytokines. Alternatively, non-responders show increased CD8+ T-cell exhaustion and T regulatory cells. We identify that the primary mechanism driving divergent T-cell activity is altered polarization and immunosuppressive signaling with myeloid cells. Using a machine-learning-based approach, we identify that Th17-like Th1 cytokines, such as IL-17, IL-21, and IL-26, are predictive of response, which is subsequently validated in a separate BCG-treated BCa cohort. CONCLUSION: Together, these findings suggest that dynamic regulation of myeloid-T cell interactions can be critical for outcomes of BCG treated bladder cancer.