96). The second method uses
specific antibodies labeled with different fluorescent dyes directed
against specific cell surface marker. For subsequent quantification
the cells are analyzed by flow cytometry. In most cases a combination
of a hematopoietic stem cell marker, like CD34, CD117
(cKit), or CD133, with a marker for endothelial cells, like vascular
endothelial growth factor receptor 2 (KDR) or Ve-cadherin, are
used to identify EPCs (summarized in Refs. 1, 28, 81). The
combination of CD34/KDR is the most often used set for
quantification of EPCs in the current literature. Nevertheless,
whether cells identified in this way are true EPCs has to be
questioned, since it could recently be demonstrated that
CD34CD133VEGFR-2 cells were devoid of vessel forming
activity (10).