Flow Cytometric Detection and Phenotype of Circulating CD34+ Cells in Patients Affected by Chronic Lymphocytic Leukemia.

Flow cytometric determination of peripheral blood CD34+ cells provides reliable measurements of circulating hemopoietic progenitors. Since the detection of the absolute number of circulating CD34+ cells has been found of clinical utility in the setting of chronic myeloproliferative disorders, we investigated whether peripheral CD34+ cells could play any role in the clinical work-up of B-cell chronic lymphocytic leukemia (B-CLL). In this view, we determined by flow cytometry the absolute number of circulating CD34+ cells in the peripheral blood of 28 patients (16 males and 12 females, median age 67 years) affected by typical B-CLL (Matutes score 5,4,3) and in different Rai stages of the disease (19 early stage: Rai 0, I, II; 9 advanced stage: Rai III, IV). Conventional and multiparameter flow cytometric analysis was performed utilizing a FACSCalibur cytometer (Becton Dickinson). Our data showed a significant increase in the number of circulating CD34+ cells in the peripheral blood of patients with B-CLL (median CD34+ cells:7.8mL) as compared to controls (median CD34+ cells 0.1mL) (p=0.008). No statistical difference between B-CLL patients in early versus advanced stage (p=0.5) and between untreated versus treated (p=0.7) was found, as well as there was no correlation with some of the clinical characteristics of B-CLL (WBC-count, LDH levels, Beta-2M). In 10 out of 28 B-CLL affected patients, circulating CD34+ cells were correlated with ZAP-70 and CD38 antigen but no correlation was found. In addition, we detected in the peripheral blood of 22 out of 28 patients small numbers of circulating CD34+ cells displaying the CD19+/CD5+ phenotype (median CD34+/CD19+/CD5+ cells:5.7mL) whereas these cells were absent in normal controls. This unexpected finding, whose significance remains to be clarified and still restricted to a small number of cases, could be directly correlated to the underlying lymphproliferative disease and might represent a pool of leukemic stem cells. However, further studies are warranted.