Circulating Endothelial Cells Background Circulating endothelial cells (CECs) have been proven and shown to be biomarkers of vascular damage in a number of diseases. These diseases include, but are not limited to: myocardial infarction, transplantation, and vasculitis. Immunomagnetic isolation is currently the most widely used technique to detect CECs for identification of disease progression (Woywodt, Blann, & Kirsch, 2006). However, this technique is restricted by large aggregates of cells as well as smaller particles that are difficult to distinguish from artifacts. In addition, interactions with other cells are common which can interfere with the collection and enumeration of CECs. Damage to endothelial cells is a critical step during the disease progression of vascular disorders. Therefore, reliable biomarkers of vascular and endothelial damage are necessary to measure the extent of such diseases marked by the presence of circulating endothelial cells. Since CECs are specifically distinguished by morphological features that differentiate themselves, they remain a key marker for vascular and endothelial disorders (Woywodt, Blann, & Kirsch, 2006).

Applications of Circulating Endothelial Cells (CECs) Circulating endothelial cells are cells that release from the walls of blood vessels during the natural process of endothelial turnover. As previously mentioned, researchers identified CECs present in a number of diseases including cancer. In regards to cancer and oncology research, the measured levels of circulating endothelial cells have been identified as a biomarker correlating with tumor regrowth (angiogenic activity), chemotherapy resistance, and metastasis. If circulating endothelial cells can be identified and enumerated, they can be very valuable to researchers. In healthy individuals CECs are present in very low quantities: 0.01% to 0.0001% of all peripheral blood cells (Khan, Solomon, McCoy, 2005). One of the main applications of CECs are that these cells can be used to predict catastrophic cardiovascular events. It has been shown that reduced levels of CECs independently predict atherosclerotic disease progression, thus supporting an important role for endogenous vascular repair to modulate the clinical course of coronary artery disease. There is growing evidence that CECs are a novel biomarker to predict vascular abnormalities.
Current Methods
One of the current methods used to detect circulating endothelial cells is by flow cytometry. Flow cytometry is well suited for the detection and enumeration of circulating endothelial cells. However, the development of flow cytometry assays is restricted by the lack of reasonably specific monoclonal antibodies designed for this task. Background noise is a major issue when using flow cytometry to separate CECs. Since the volume of CECs are extremely minimal in peripheral blood, the cytometric assay would need to be greater than 99.999% free of background noise for accurate detection (Khan, Solomon, McCoy, 2005). The other main method used to detect circulating endothelial cells is immunomagnetic bead separation. This technique has gained widespread use but is restricted by the lack of definition of CECs and the lack of a consensus for their enumeration. Table 1.
Comparison of CEC counts/ml by flow cytometry vs. immuno bead method among study participants with acute coronary syndrome, breast cancer and healthy control subjects.
Patient group
CEC count immunobead
CEC count flow cytometry
P value between methods
Breast cancer (n=60)
08.0 (6.0 – 12.75)
08.0 (6.0 –16.0)
0.92
Acute coronary syndrome (n=34)
10.0 (7.0 –18.0)
14.0 (8.0 – 20.0)
0.35
Healthy controls (n=30)
04.5 (3.0 – 8.0)
08.0 6.0 – 10.0)
0.055
(Goon, et al., 2006) Table 2.
Studies reporting CECs in disease states, either by immunomagnetic bead or flow cytometry.
Study
Condition
Method
Primary markers2
Beerepoot et al. (7)
Cancer3