Microbial cancer immunotherapy reprograms hematopoiesis to enhance myeloid-driven anti-tumor immunity

Mycobacterium bovis Bacillus Calmette-Guérin (BCG) is the vaccine against tuberculosis and an immunotherapy for bladder cancer. When administered intravenously, BCG reprograms bone marrow hematopoietic stem and progenitor cells (HSPCs), leading to heterologous protection against infections. Whether HSPC reprogramming contributes to the anti-tumor effects of BCG administered into the bladder is unknown. We demonstrate that BCG administered in the bladder colonizes the bone marrow and, in both mice and humans, reprograms HSPCs to alter and amplify myelopoiesis. BCG-reprogrammed HSPCs are sufficient to confer augmented anti-tumor immunity through production of neutrophils, monocytes, and dendritic cells that broadly remodel the tumor microenvironment, drive T cell-dependent anti-tumor responses, and synergize with checkpoint blockade. We conclude that bladder BCG acts systemically through hematopoiesis, highlighting the broad potential of HSPC reprogramming to enhance the innate drivers of T cell-dependent tumor immunity.