Coexpression of endothelial markers and CD14 by cytokine mobilized CD34+ cells under angiogenic stimulation

Abstract

Objective: A subset of adult peripheral blood leukocytes functions as endothelial progenitor cells that incorporate into the vasculature in animal models of neovascularization. The basic mechanisms by which differentiation proceeds are still unclear. This study analyses the in vitro differentiation of cytokine mobilized, human CD34⁺ cells. Methods: Granulocyte-monocyte colony stimulating factor mobilized human CD34⁺ cells were isolated and grown in culture in the presence of vascular endothelial growth factor (50 ng/ml) and basic fibroblast growth factor (10 ng/ml). Their differentiation was followed using cytological and immunohistochemical techniques. Fibronectin-coated culture dishes or three-dimensional cultures were used. Results: CD34⁺ cells grown on fibronectin-coated dishes differentiated along the granulocytic and monocytic/macrophage lineages with no evidence for an endothelial cell differentiation. CD14⁺ macrophages appeared in long-term culture and then acquired endothelial cell markers such as VE-cadherin, the endothelial form of NO synthase and the von Willebrand factor. Yet they were unable to form tubular structures in Matrigel^®. Only typical macrophages were observed in Matrigel^®. Conclusion: Angiogenic stimulation of CD34⁺ precursor cells leads to cells that expressed mixed macrophage and endothelial cell properties. They could represent an intermediate phenotype in the pathway that leads to mature endothelial cells.