Flow cytometric detection of circulating endothelial cells and endothelial progenitor cells in healthy subjects

Circulating endothelial cells (CEC) and endothelial progenitor cells (CEP) play an important role in tissue neovascularization. In human tumours, these cells may have clinical implications as prognostic/predictive factors during antiangiogenic therapy. The lack of a standardized assay for the quantification of these rare events has lead to a wide variation in the reported ranges of CEC and CEP. This study aimed to develop a flow cytometric (FCM) method for the immunophenotipic detection and enumeration of these cells in a healthy population. Peripheral blood samples from 32 subjects were analysed. Multiparameter FCM analysis was used to quantify resting and activated CEC and CEP. The mean values of the percentage and of the absolute number were: 0.005 +/- 0.004% and 306 +/- 243 cells/ml for CEC; 0.002 +/- 0.001% and 130 +/- 110 cells/ml for rCEC; 0.003 +/- 0.002% and 176 +/- 150 cells/ml for aCEC; 0.0001 +/- 0.00005% and 6 +/- 2 for CEP. We confirmed that FCM is an accurate and sensitive method for the quantitative analysis of CEC and CEP. The determination of normal ranges of CEC and CEP is helpful in defining their role as surrogate biomarkers of antiangiogenic treatment efficacy during clinical trials in oncology.