Arginase 1 (ARG1) is a metabolic enzyme that breaks down the amino acid L-arginine to urea and ornithine; several reports detail how arginine is necessary for the activation and proliferation of CD8+ T cells, and some tumor cells can secret arginase to deplete arginine, an amino acid necessary for T cell proliferation and activation [27]. The gene discussed is ARG1; the disease is neoplasm.