Fig. 6.

Inhibition of T effector cells and activation of Treg cells by the tumor microenvironment. Nutrient deprivation-induced AMPK activation, depletion of extracellular amino acids, and lactate accumulation inhibit TCR signaling and downstream glycolysis that inhibits T effector cells. Inhibition of glycolysis, activation of OXPHOS, fatty-acid oxidation (FAO), and tumor microenvironment-related factors (e.g., hypoxia, Kynurenine (Kyn), TGF-b, and IL-10) instead activate Treg cells, which causes immune evasion and tumor growth (Biswas 2015). Arg, Arginine; Orn, Ornithine; Trp, tryptophan; Gln, glutamine; NO, nitric oxide; FAS, Fatty acid synthase