Abstract
Background Circulating endothelial cells (CECs) are a potential biomarker of angiogenesis. CECs
increase in numbers after vessel injury. Higher CEC numbers are reported in cancer
patients. Most methods for CEC detection and enumeration rely on flow cytometry (FCM);
however, there is no agreement on CEC phenotype and the detection method to be used.
This leads to uncertainty about the clinical applicability and variation between studies
on CEC numbers reported.
Objective To develop a selective and accurate method for CEC enumeration in peripheral blood
by enrichment, followed by FCM in healthy volunteers (HV) and cancer patients.
Methods Samples were enriched using CD34 microbeads, stained with nuclear dye and anti-CD14,
CD15, CD45, CD34 and CD146 antibodies. Putative CECs were examined for Weibel–Palade
bodies (WPBs) using anti–von Willebrand factor (vWF) antibody and fluorescence microscopy.
Linear range of detection (R
2), recovery and precision (coefficient of variation percentage [CV%]) were defined
in three experiments by spiking a known number (range 12–12,800 CECs/4 mL) of surrogate
endothelial cells in peripheral blood. Sample storage was determined at –80°C for
up to 2 months.
Results Sorted CECs showed vWF in the WPBs. The relationship between spiked and detected
surrogate cells was R
2 = 1.0, recovery of 94.0 to 101.4% and CV% of 1.0 to 18.4%. Recovery ± standard deviation
(within-run days 1, 2 and 3) were, respectively, 102.5% ± 8.2, 97.8% ± 4.6, 99.1% ± 7.7,
and after 2 months 94.3% ± 15.3. The median CECs/mL in patients was 24.1 versus 14.4
in HVs.
Conclusion This method for selective, sensitive and reliable CEC analysis by FCM allows for
investigation of CECs as a biomarker in clinical research.
Keywords
circulating endothelial cells - enrichment - CD34 magnetic microbeads - flow cytometry
- angiogenesis
