Circulating endothelial cells in patients with chronic lymphocytic leukemia

Angiogenesis is increased in B-cell chronic lymphocytic leukemia (B-CLL). We wanted to quantify and characterize the circulating endothelial cells (CECs) in patients with B-CLL and correlate with plasma angiogenesis-related factors. Using a four-color flow cytometry, we prospectively analyzed the CEC in the whole blood of 20 healthy controls and 20 patients with B-CLL. We quantified (CD45-/CD31+/CD146+) and characterized the CECs according to whether they were apoptotic (annexin stain) or activated (CD106+). We also measured plasma levels of vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF-2), and thrombospondin-1 (TSP-1). Most patients (90%) had Rai stages 0-2 at the time of diagnosis. As a group, B-CLL patients had higher number of CECs (median of 26.5 cells/ml) compared (P = 0.04) to healthy controls (18.5 cells/ml). However, only four (20%) patients had elevated CEC counts, defined as ≥2 SD of the control mean (≥53 cells/ml). The proportions of apoptotic (P = 0.83) and activated (P = 0.12) CECs were similar in both groups. B-CLL patients had higher FGF-2 (P < 0.001), lower TSP-1 (P = 0.004), and similar VEGF (P = 0.27) plasma levels. The number of CECs was not associated with Rai stage, absolute lymphocyte count, or levels of angiogenesis-related factors. CECs are increased in only a small fraction of B-CLL patients in our cohort with low rates of apoptosis and activation. While no correlation was found between CECs and clinical features, more studies in a larger patient sample size and advanced disease are necessary.