Background— Transplantation of ex vivo expanded circulating endothelial progenitor cells (EPCs) from peripheral blood mononuclear cells improves the neovascularization after critical ischemia. However, the origin of the endothelial progenitor lineage and its characteristics have not yet been clearly defined. Therefore, we investigated whether the phenotype and functional capacity of EPCs to improve neovascularization depend on their monocytic origin.

Methods and Results— Monocytic CD14⁺ cells were isolated from mononuclear cells and incubated on fibronectin-coated dishes in endothelial medium in the presence of vascular endothelial growth factor. After 4 days of cultivation, adherent cells deriving from CD14⁺ or CD14⁻ mononuclear cells showed equal expression of endothelial marker proteins and capacity for clonal expansion as determined by measuring endothelial colony-forming units. In addition, transplanted EPCs (5×10⁵ cells) deriving from CD14⁺ or CD14⁻ cells were incorporated into vascular structures of nude mice after hind-limb ischemia and significantly improved neovascularization from 0.27±0.12 (no cells) to 0.66±0.12 and 0.65±0.17, respectively (P<0.001; laser Doppler-derived relative blood flow). In contrast, no functional improvement of neovascularization was detected when freshly isolated CD14⁺ mononuclear cells without ex vivo expansion were used (0.33±0.17). Moreover, macrophages or dendritic cells differentiated from isolated CD14⁺ cells were significantly less effective in improving neovascularization than EPCs cultivated from the same starting population (P<0.01).

Conclusions— These data demonstrate that EPCs can be generated from nonmonocytic CD14⁻ peripheral blood mononuclear cells and exhibit a unique functional activity to improve neovascularization after hind-limb ischemia.