Are circulating CD133+ cells biomarkers of vascular disease?

Single cell bone marrow transplantation leaves no doubt as to the ability of bone marrow cells to differentiate and integrate into the endothelium, though the physiological significance of this remains controversial. Reported rates of bone marrow cell integration into the endothelium after injury vary widely, ranging from almost no cells to large percentages. Bone marrow cell maintenance of the quiescent (ie, nongrowing) vasculature has been less well studied, but at least one mouse study suggests it could be significant.1 Whether or not large numbers of circulating cells integrate into the vessel wall, a consensus seems to be emerging that circulating bone marrow–derived cells can promote vascular growth. Exactly how this is accomplished is not clear, though it is presumably due to release of proangiogenic factors.