Translocating Lactobacillus torments tumors via tryptophan catabolism

Variability in the efficacy of immune checkpoint inhibitors in cancer patients is associated with the human gut microbiota. However, detailed mechanisms are unclear. In this issue of Cell, Bender et al. uncovered that a probiotic Lactobacillus strain translocates into murine tumors to enhance immunotherapy via the tryptophan metabolite indole-3-aldehyde (I3A).