During metabolic reprogramming, while cancer cells can express more nutrients import molecules (e.g., GLUT1, MCTs, ASCT2, LATs) to obtain fuel sources for survival, effector T cell proliferation and activation are restricted due to the crucial lack of tryptophan and arginine, caused by elevated indoleamine-2,3 dioxygenase 1 (IDO1) and arginase (ARG1, ARG2) in metabolically altered stromal cells. This evidence concerns the gene IDO1 and cancer.