Summary
Animals have coevolved with complex communities of microorganisms living on barrier tissues, referred to as the microbiota or commensals. The microbiota controls immune function not only locally within barrier tissues but also systemically, modulating functions such as hematopoiesis, immune system development, and responses to vaccines (1). The role of the microbiota in enhancing responses to cancer immunotherapy has represented a major focus of research (2–7), although the mechanisms have remained largely unclear. On page 1040 of this issue, Griffin et al. (8) show that members of the Enterococcus genus promote immunotherapy responses in mice through immunostimulatory muropeptides, which are structural units of bacterial cell walls.