Blood circulating endothelial cells (CECs) and circulating hematopoietic progenitor cells (CPCs) represent two cell populations that are thought to play important roles in tissue vascularization. CECs and CPCs are currently studied as surrogate markers in patients for more than a dozen pathologies, including heart disease and cancer. However, data interpretation has often been difficult because of multiple definitions, methods and protocols used to evaluate and count these cells by different laboratories. Here, we propose a cytometry protocol for phenotypic identification and enumeration of CECs and CPCs in human blood using four surface markers: CD31, CD34, CD133 and CD45. This method allows further phenotypic analyses to explore the biology of these cells. In addition, it offers a platform for longitudinal studies of these cells in patients with different pathologies. The protocol is relatively simple, inexpensive and can be adapted for multiple flow cytometer types or software. The procedure should take 2-2.5 h, and is expected to detect 0.1-6.0% viable CECs and 0.01-0.20% CPCs within blood mononuclear cell population.
