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

The primary therapy for high-risk bladder cancer (BCa) is repeated instillations of the tuberculosis vaccine, Bacillus Calmette-Guerin (BCG). While BCG decreases the risk of recurrence by more than half, the concerted mechanisms of immune activation from BCG are unknown. Our objective was to investigate how the immune response differs between responders and non-responders to BCG therapy. We performed single-cell RNA-sequencing of isolated immune cells adjacent to high-risk bladders before and after BCG in BCG responders and non-responders. We identify an increase in Th17-like Th1 cells in BCG responders, characterized by greater expression of pro-inflammatory cytokines. Alternatively, non-responders had increased CD8+ T-cell exhaustion and T-regulatory cells. We identify that the primary mechanism of divergent T cell activity is driven by altered polarization and immunosuppressive signaling with myeloid cells. Through a machine-learning-based approach, we identified a Th17-like Th1 cytokines, such as IL17, IL21, and IL26, were predictive of a response, which were then validated in a separate BCG-treated BCa cohort. Together, this suggests that dynamic regulation of myeloid-T cell interactions can be targeted to improve BCG activity.