Proliferative index and expression of CD38, Zap-70, and CD25 in different lymphoid compartments of chronic lymphocytic leukemia patients

Recent studies of chronic lymphocytic leukemia (CLL) show that malignant B cells proliferate at a rate similar to normal B lymphocytes. This is in apparent contradiction to the very low proliferation rate found in blood specimens from CLL patients. To address this problem, we studied the expression of Ki-67, CD38, CD25, and Zap-70 in different compartments of CLL patients. Using triple-color flow cytometry, we examined the expression of CD38, CD25, Zap-70, and Ki-67 antigens in the peripheral blood, bone marrow, spleen, and lymph nodes biopsies of patients with CLL, splenic marginal zone lymphoma (SMZL), and nonmalignant diseases. In parallel probes of lymph node/spleen biopsies and blood taken from one and the same patient, Ki-67 expression was 17 times higher. Among the whole cohort, we also found significantly higher Ki-67 expression in biopsies from lymph nodes and spleen (4.95% π 0.55%), compared with bone marrow (1.88% π 0.32%) and peripheral blood (0.45% π 0.03%, P 0.01). In CLL patients, there are statistically significant correlations between the expression of CD38 and Ki-67 in bone marrow (P 0.01), Zap-70 and Ki-67 in blood (P 0.01), and Zap-70 and CD38 in blood (P 0.01). Patients with SMZL also showed a significant correlation between Ki-67 and CD38 expression (P 0.01) and between Ki-67 and Zap-70 expression (P 0.01). We show for the first time that proliferation of B lymphocytes in CLL patients is associated primarily with lymph nodes/spleen. Malignant cells in the blood represent only a subpopulation of nonproliferating and less-activated B cells in this disease.