Study Reveals Cancer-Fighting Role for Probiotic Bacteria

Probiotic bacteria can help the immune system attack cancer cells, enhancing the effect of immunotherapy, according to an animal study appearing in Cell. The findings may help in the design of novel dietary and probiotic combinational therapeutic strategies for cancer. Increasingly, cancer patients are using probiotics to improve their health, with a recent report finding that nearly half of its cohort of advanced melanoma patients beginning immunotherapy take them. However, the impact of probiotics on cancer immunotherapy is not well understood. In their new study, a team led by University of Pittsburgh scientists examined the effects of feeding Lactobacillus reuteri — a bacteria naturally present in the human intestines and found in many commercial probiotics — to mice with melanoma. They find that L. reuteri traveled from the animals' guts and stably colonized their tumors, where it stimulated the production of cancer-killing CD8 T cells through the secretion of tryptophan catabolite I3A, thereby bolstering immune checkpoint inhibitor (ICI) treatment. The researchers also show that feeding the mice a diet enriched with the amino acid tryptophan, which the bacteria convert to I3A, increased the therapeutic benefits of ICI. The work, the study's authors state, not only points to the potential of I3A in promoting ICI responses in melanoma patients but suggests it could potentially be used as a biomarker for ICI sensitivity.