A new approach for rapid and reliable enumeration of circulating endothelial cells in patients

. Background broken vertical bar Mature circulating endothelial cells (CECs) are surrogate markers of endothelial damage/dysfunction. A lack of standardized assays and consensus on CEC phenotype has resulted in a wide variation of reported CEC numbers (41300 per mL). Objectives broken vertical bar Given the need for a quick, reliable, robust and validated CEC assay at an affordable price, we present a novel approach to enumerate CECs using a multi-parameter flow cytometric (FCM) method without immunological pre-enrichment. Methods broken vertical bar CECs were defined as CD34+, CD45neg, CD146+ and DNA+ events based on the immunophenotype of endothelial cells from vein-wall dissections. As CECs express high levels of CD34, we based our assay on absolute CD34 counts after analyzing all CD34 positive events in a total blood volume of 4 mL needed for a precise enumeration of CECs at a frequency of < 1 cell mu L-1. Results broken vertical bar The endothelial origin of CECs was confirmed by morphology, immunohistochemistry and gene expression. The new FCM assay was tested in parallel with a validated assay (i.e. CellSearch (R)). CEC levels ranged from 4 to 79 CEC mL-1 in healthy individuals and were significantly higher in patients with advanced solid malignancies (P = 0.0008) and in patients with hematological malignancies (P < 0.0001). Conclusions broken vertical bar This flow cytometric method should be useful as a fast and economical assay to enumerate and characterize CECs.