Function of CD39 (NTPDase-1) in Chronic Lymphocytic Leukemia.

Chronic lymphocytic leukemia (CLL) is characterized by accumulation of large numbers of mature lymphocytes. However, thrombotic events in CLL are relatively rare. CD39, the main control system for blood fluidity, was identified on the surface of CLL cells in about 80% of patients in two recent studies. This suggests that CD39 could play a role in prevention of thrombotic events in CLL. Lymphocytes were prepared from peripheral blood of an initial 13 patients with CLL by histopaque isolation and purified to at least 95%. The ADPase and ATPase activities in these lymphocytes was measured by our radio-thin-layer chromatographic assay. Additionally, cells were stained with antibodies to CD3, CD19, and CD39, and analyzed by FACS. Remaining lymphocytes were pelleted and frozen for semi-quantitative RT-PCR analysis of the CD39 transcipt. Lymphocytes from patients with CLL showed increased ATPase and ADPase activities compared with lymphocytes from normal donors. Average ADPase activity per 50,000 cells from CLL patients was 57pmol/min, compared with 14pmol/min in lymphocytes from normal donors. Average ATPase activity was 43.6pmol/min in CLL patients, and 10.6 pmol/min in normal lymphocytes. Semi-quantitative RT-PCR of CLL lymphocytes showed upregulation of CD39 RNA compared with normal lymphocytes. FACS data showed that the percentage of cells expressing CD39 was greater in CLL cells (62.5%) than in normal lymphocytes (11%). Additionally, some CLL cells appear to express CD39 at higher densities than normal lymphocytes. Interestingly, one patient in whom lymphocytes were isolated before and during an accelerated phase of the disease showed a decrease in CD39 expression on his lymphocytes as the disease progressed. Two other patients with advanced disease, requiring chemotherapy, showed relatively low CD39 levels as well. We conclude that CD39 is present and functions as an ecto-nucleotidase on the surface of most malignant lymphocytes in CLL. The quantities are much higher than observed in normal lymphocytes. CD39 may be protective from thrombotic events in patients with CLL. In addition, lymphocyte CLL may be a marker of earlier or less aggressive disease and a decrease of CD39 on the cell surface may signify a worsening of the disease.