Expression of CD38 and High Levels of CD5 Identifies Members of CLL Clones That Have Progressed beyond G1 and Proliferated.

Abstract Chronic lymphocytic leukemia (CLL) is characterized by the monoclonal expansion of CD5+ B cells with the morphology of small mature lymphocytes. Although the great majority of circulating CLL B cells appears as quiescent/non-proliferating lymphocytes, a small percentage of cells in peripheral blood appear to be cycling. Furthermore, within these clones, the CD38+ subset is enriched in those cells that entered G1, as evidenced by a larger number of Ki67-expressing cells. In an attempt to further identify submembers of CLL clones with different proliferative capacities, we measured, by flow cytometry, expression of Ki67 along with mcm6 and Cyclin D1, expressed from G1 to M, and Cyclin B1, expressed in G2-M. Since the expression of CD5 is characteristic of CLL cells and increases in vitro upon cellular activation, the intensity of CD5 expression was used to further divide CD38+ and CD38− cells into CD5bright and CD5dim fractions. The leukemic clones of eighteen IgVH unmutated CLL (U-CLL) and 16 IgVH mutated CLL (M-CLL) patients were analyzed. A similar pattern of expression for each cell cycle related marker studied was found. The presence of CD38 and high expression of CD5 was correlated with increased percent of cells expressing the various cell cycle markers (CD38−CD5dim