In the tumor microenvironment, tumor cells can induce IDO1 over expression, which causes the depletion of local tryptophan and the accumulation of metabolites such as kynurenine, thereby activating GCN2 and AHR signaling pathways, inhibiting T cell proliferation, and inducing apoptosis (Muller et al., 2005). The gene discussed is AHR; the disease is neoplasm.