ARG1 and neoplasm: Finally, as MDSC immunosuppressive potential in tumors mainly rely on the expression and activity of two key enzymes, Arginase 1 (ARG1) and Nitric Oxide Synthase 2 (NOS2), we checked by Real time-PCR the transcription level of these enzymes in CD11b+ cells isolated from the spleens of tumor-bearing mice.