Abstract Bacillus Calmette-Guérin (BCG) is recommended as intravesical immunotherapy to reduce the risk of tumor recurrence in patients with non-muscle invasive bladder cancer (NMIBC). Currently, it is unknown whether intravesical BCG application induces trained immunity. Here, we found that intravesical BCG does induce trained immunity based on an increased production of TNF and IL-1β after heterologous ex-vivo stimulation of circulating monocytes 6- 12 weeks after intravesical BCG treatment; and a 37% decreased risk (OR 0.63 (95% CI 0.40- 1.01)) for respiratory infections in BCG-treated versus non-BCG-treated NMIBC patients. An epigenomics approach combining ChIP-sequencing and RNA-sequencing with in-vitro trained immunity experiments identified enhanced inflammasome activity in BCG-treated individuals. Finally, germline variation in genes that affect trained immunity was associated with recurrence and progression after BCG therapy in NMIBC, suggesting a link between trained immunity and oncological outcome.

Intravesical BCG in patients with non-muscle invasive bladder cancer induces trained immunity and decreases respiratory infections