Circulating Stem Cells and Aneurysmal Disease

Background

Endothelial progenitor cells (EPCs) are circulating stems cells important in modulating vascular repair. Vascular injury stimulates bone marrow mobilisation of EPCs into the circulation. Animal studies have demonstrated incorporation into areas of vascular injury including aneurysms, with subsequent differentiation to endothelial cells. In addition, EPC infusion in animals with atherosclerosis has been shown to be beneficial. The aim of this study was to investigate EPC numbers in patients with AAA.

Methods

Whole blood was taken from 22 patients with AAA and 14 age-matched controls. Peripheral blood mononuclear cells (PBMNs) were prepared using density gradient centrifugation. The combination of the endothelial cell surface marker CD34 combined with the more specific progenitor marker CD133 were used to represent a population of EPCs. Due to the rarity of EPCs, PBMNs were enriched utilising immunomagnetic cell seperation to positively select CD133⁺ cells. These cells were then incubated with CD133-PE and CD34-FITC conjugated fluorochromes and subjected to flow cytometric analysis. Gates were set on the forward and side scatter plot corresponding to known morphology of progenitor cells. Positive cells were compared to negative isotype controls.

Results

Figure 1

Cytometric data demonstrating

dual-stained CD133⁺/CD34⁺cells

Table 1 — Cell numbers expressed as % of total events (mean + S.E)

Cell Surface Marker	AAA	Controls	P-value
CD 133+	2.38+0.39	1.33+0.24	0.052
CD 34+	2.18+0.39	1.48+0.24	0.038
CD 133+ / CD 34+	2.33+0.37	1.30+0.23	0.049

Cell purities were similar in both groups following magnetic separation. There were more CD34⁺ cells in the AAA group than controls, and more dual stained CD133⁺/CD34⁺ cells in the AAA group compared to controls (P=0.0488, Students t-test).

Conclusions

These data suggest that EPCs are mobilised in patients with AAA, as an ongoing attempt at repair of a chronic disease. EPCs may well represent a novel method of disease modification and warrant further study.