The presence in CLL patients of a higher percentage of MDSCs characterized by immunosuppressive features and expressing IDO together with others immunoregulatory molecules/cytokines, such as arginase 1 (ARG1), nitric oxide synthase (NOS2), TGF-β and IL-10, was also described by Zarobkiewicz M and co-author [60]. The gene discussed is IDO1; the disease is B-cell chronic lymphocytic leukemia.