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. Author manuscript; available in PMC: 2021 Nov 5.
Published in final edited form as: Mol Cell. 2020 Sep 29;80(3):384–395. doi: 10.1016/j.molcel.2020.09.006

Figure 3. Role of arginine and Try-Kyn metabolisms in tumor immune evasion.

Figure 3.

Arginine (Arg) is transported by SLC7A2. Intracellular Arg metabolism results in extracellular Arg depletion and NO production. Arg deficiency impairs and NO inhibits T cell function.

Trp is transported by SLC3A2 and SLC7A5 or SLC7A8. Trp is catalyzed by indoleamine-2,3-dioxygenase (IDO) or tryptophan-2,3-dioxygenase (TDO) to become kynurenine (Kyn). Trp-Kyn metabolism results in extracellular Trp depletion and Kyn accumulation, subsequently causing T cell inhibition.

Arginine deiminase (ADI-PEG20) degrades arginine. PEG-KYNase degrades Kyn. Small inhibitors that target key enzymes in Arg and Trp-Kyn metabolic pathways are listed in red.

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