Within the tumor environment, ARG1 can cooperate with NOS2 to produce high levels of superoxide anion (O2-) that can react with either nitric oxide (NO) or H2O generating reactive–nitrogen species (RNS), such as peroxinitrites (ONOO−), which damage both the function and migration of T cells to tumor site (60), and reactive-oxygen species (ROS), such as H2O2 which decreases T cellular CD3ζ expression limiting the activation of T cells, respectively (61). The gene discussed is ARG1; the disease is neoplasm.