IDO1 and B-cell chronic lymphocytic leukemia: Jitschin R. and collaborators [59] further reported that untreated CLL patients show a significantly increased frequency of monocytes CD14 + DRlow, which are defined as myeloid-derived suppressor cells (MDSCs) and characterized by high IDO levels expression, that induced the suppression of T cell activation while expanding T regulatory cells (Tregs); the MDSC-mediated modulation of T cells was attributed to their increased IDO activity.