In 79 consecutive untreated patients affected by chronic lymphocytic leukemia (CLL) mo-MDSCs were increased with suppressing activity against T-cells due to increased indoleamine 2,3-dioxygenase (IDO) activity associated to T-regs expansion, a reduction of chronically activated CD45RA+ effector memory (TEMRA, CCR7− CD45RA+) cells resulting in impaired immune responses. This evidence concerns the gene IDO1 and B-cell chronic lymphocytic leukemia.