Differential circulation kinetics during antiangiogenic therapy of four distinct blood cell populations expressing endothelial markers

Abstract

3038 Background: Circulating endothelial cells (CECs) are evaluated as potential biomarker of antiangiogenic therapy. CD146 is an endothelial marker, but its use as a single marker to detect CECs is questionable. In addition, several sub-populations of CECs are thought to exist. Methods: We analyzed the expression of CD31, CD34, CD45, CD133 and CD146 on mononuclear blood cells and primary tissue endothelial cells by flow cytometric and immunohistochemical analyses. Furthermore, we investigated by flow cytometry the phenotype of blood cells expressing endothelial markers and evaluated their changes VEGF blockade by bevacizumab in ten rectal cancer patients enrolled in a Phase I trial. Percent values obtained at days 3 and 12 after bevacizumab infusion were compared with pre-treatment values in individual patients using the Wilcoxon signed-rank test. Results: In the blood, CD146 primarily marked cells with lymphoid markers (CD3 and CD4). CD146 was largely undetectable on blood CD31+CD45- CECs or CD34+CD133+ progenitor cells. In contradistinction, CD146 was detectable in tissues on both cellular components of the vessel wall: CD31brightCD45- endothelial cells and CD31-CD45- pericytes. The CD31+CD45- CEC population contained two distinct populations: CD31brightCD34+CD45- (viable CECs) and CD31dimCD45- (mostly non-viable CECs). Unlike CD31brightCD45- CECs and CD34+CD133+ progenitor cells, CD146+ and CD31dimCD45- cell concentration in the peripheral blood of cancer patients did not decrease during VEGF blockade. Conclusions: In the blood of cancer patients, we identified 4 distinct populations using endothelial markers. CD146 identified T lymphocytes. Within the CD31+CD45- CEC population, there were 2 distinct subpopulations, while the rare progenitor populations localized primarily within the CD45+ hematopoietic cell pool. The changes in blood concentration of these 4 cell types during anti-VEGF therapy were distinct in individual patients. These results underscore the need for further characterization and identification of new markers for CEC subpopulations for their development as biomarkers of antiangiogenic therapy. [Table: see text]