It is also known that the uptake of kynurenine, the tryptophan metabolite produced by indoleamine 2,3-dioxygenase or tryptophan-2,3-dioxygenase, by natural killer (NK) cells or T cells within the tumor microenvironment is mediated by LAT1, which leads to the suppression of their proliferation and effector functions [31]. The gene discussed is TDO2; the disease is neoplasm.