CD38 and B-cell chronic lymphocytic leukemia: The fact that CD38 is expressed in a high percentage of leukemic cells in IgHV-unmutated (U-CLL) patients indicates that CD38+ leukemic cells constitute a heterogeneous population including a small fraction of cells with an increased proliferative potential, ranging from 0.08 to 1.7% (143), suggesting that not all CD38+ cells are actively proliferating.