Background-Two types of cells are cultured from the human peripheral blood, early endothelial progenitor cells (EPCs) and outgrowth endothelial cells (OECs), as previously reported. Here, we further characterize these cells, especially with respect to their different origins and functions both in vitro and in vivo. We also investigated whether the combination of these different cell types shows synergism during neovascularization. Methods and Results-Early EPCs were heterogeneously made up of both CD14ϩ monocyte-derived cells, which secrete cytokines, and CD14Ϫ -derived cells, which contain high levels of CD34 ϩ KDR ϩ cells. OECs were cultured almost exclusively from CD14 Ϫ cells, not CD14 ϩ cells, and were distinct from mature endothelial cells in terms of proliferation potential, KDR ϩ expression level, and telomerase activity. A portion of cells from CD14 Ϫ cells and early EPCs produced rapidly proliferating, capillary-forming cells in both the Matrigel plug and the ischemic hind limb similar to OECs. Early EPCs and OECs expressed receptors for vascular endothelial growth factor and interleukin-8, cytokines secreted by early EPCs. There was a differential increase in matrix metalloproteinases (MMPs): MMP-9 in early EPCs and MMP-2 in OECs. In vitro, the angiogenic capability of the 2 cell types was augmented by mutual interaction through cytokines and MMPs. Injection of a mixture of the 2 cells resulted in superior neovascularization in vivo to any single-cell-type transplantation. Conclusions-Distinct origins of the different types of EPCs exist that have different functions in neovascularization.Mixed transplantation of these cells results in synergistic neovascularization through cytokines and MMPs.

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Background-The colony number of early endothelial progenitor cells (EPCs) has been used as a quantitative indicator of the number of EPCs in the blood or as a biological marker of cardiovascular diseases. In the present study, we found a subset of T cells that were localized at the center of the EPC colony and played a pivotal role in colony formation and differentiation of early EPCs. Methods and Results-We found that CD3ϩ CD31 ϩ CXCR4 ϩ T cells (referred to as angiogenic T cells in the present study) constituted the center of EPC colonies during cultures of human peripheral blood mononuclear cells. These angiogenic T cells were required for colony formation and differentiation of early EPCs. They secreted high levels of angiogenic cytokines such as vascular endothelial growth factor, interleukin-8, and matrix metalloproteinases. Angiogenic T cells showed superior angiogenic potential to the other subset of T cells in the experiments with regard to Matrigel tube formation, adhesion, transendothelial migration, and collagen invasion assay, mainly through the stromal cell-derived factor 1/CXCR-4 axis. Furthermore, angiogenic T cells enhanced endothelial cell proliferation and function. In vivo study showed that angiogenic T cells play an important role in the process of vessel formation. Clinical study showed that the level of angiogenic T cells in the peripheral blood was well correlated with EPC colony numbers and had inverse relationships with age and the number of risk factors for coronary artery disease. Conclusions-These findings suggest that angiogenic T cells could be a potential therapeutic target for ischemic cardiovascular diseases.