In Reply

Abstract

George et al regarding our article on the differential expression between tissue endothelial cells and viable blood circulating endothelial cells (CECs) in rectal cancer patients, published in the March 20 issue of the Journal of Clinical Oncology. 1 We had considered and addressed most of the issues raised by these authors in the Discussion section of our article. For the most part, we subscribe to their conclusions and consider our findings and conclusions to be in good agreement.We commend the authors and their collaborators for establishing a unified immunoseparation protocol with CD146 magnetic beads. Using the criteria of positive Europaeus Lectin-1 (UEA-1) expression, number of immunomagnetic beads attached, and cell size larger than 10 m, they have cultured, identified, and counted using fluorescence microscopy an extremely rare population of viable CD146 ϩ lectin ϩ CECs. As we discussed in our article, culture-based assay may enrich for viable CD146 ϩ cells with the loss of leukocytes and nonviable CECs, and may induce CD146 upregulation in CECs, particularly in the CECs with progenitor capacity. 2 Interestingly, the authors detected CD34 ϩ CD146 ϩ CD45 -CECs using flow cytometry,

Defining human endothelial progenitor cells

“…Duda et al. [34] responded to this correspondence by pointing out that the differences in the number of CEC measured in the blood of human subjects could be due to the immunomagnetic separation technique and the FACS protocol identifying CD31 bright CD45 − CD34 dim CD133 − cells may represent two different populations. Indeed the CD31 bright CD45 − CD34 dim CD133 − events did not show evidence of CD146 expression.…”

“…While Duda et al. [34] have not yet sorted cells from the CD31 bright CD45 − CD34 dim CD133 − events to examine the cell size and morphology for evidence that these events are indeed CEC, the fact that this population diminishes in the blood of cancer patients receiving an antiangiogenic agent, suggests that these cells are playing an important role in the disease pathogenesis [35].…”