The lower availability of arginine in the microenvironment that results from upregulated arginine metabolism in tumor cells, in M2 macrophages, and in myeloid-derived suppressor cells (MDSCs), exerts a regulatory effect in lymphocyte activation through downregulation of the TCR CD3ζ chain, central for signaling and responsiveness in activated T cells [71]. The gene discussed is CD247; the disease is neoplasm.