Fong discovered that in CRC tumors, the metabolite indole‐3‐carboxylic acid (ICA) from Lactobacillus gallinarum competes with Kyn for binding to the aryl hydrocarbon receptor (AhR), counteracting Kyn's interaction with AhR on CD4+ T cells and inhibiting Treg differentiation in vitro [210]. This evidence concerns the gene AHR and colorectal carcinoma.