ARG1 and neoplasm: In particular, MDSCs that have accumulated in the pre-metastatic niche also inhibit anti-tumor T cells through arginase 1 (ARG1), resulting in a decrease in CD3 on T cells, cyclin D3 and cyclin-dependent kinase-4 (CDK4) on lymphocytes and reactive oxygen species (ROS) production, through mechanisms involving the inhibition of Janus kinase 3 (JAK3) and signal transducer and activator of transcription 5 (STAT5), a decrease in major histocompatibility complex 2 (MHC II) molecules and induction of apoptosis due to the suppression of the functions of T cells [142].