PURPOSE. Recent evidence suggests that vasculogenesis as well as angiogenesis occurs throughout the body during neovascularization. The recruitment of circulating stem cells is a key feature of vasculogenesis. The purpose of the present study was to determine whether markers of endothelial progenitor cells (EPCs) are present in choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD). METHODS. Surgically excised CNV (n ϭ 9) membranes from patients with AMD were

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... ed with immunohistochemical techniques using the following monoclonal antibodies: AC133 a putative marker of EPCs and hematopoietic stem cells (HSCs); the endothelial cells markers CD31, CD34, and von Willebrand factor (vWF); and cytokeratins and CD68, markers for retinal pigment epithelium (RPE) and macrophages, respectively. After secondary antibody amplification, reactions were visualized with fast red substrate. RESULTS. Six of nine specimens demonstrated cells positive for AC133 that were all found within predominantly cellular regions of the specimens. In the avascular fibrous stromal core of all specimens, the predominant cells were RPE cells and macrophages. The peripheral component of all CNV membranes was highly vascular and showed varying immunoreactivity for all endothelial markers. The greatest immunoreactivity for endothelial markers was observed with CD34 and vWF and least for CD31. CONCLUSIONS. These findings support animal studies that vasculogenesis, in addition to angiogenesis, may contribute to the neovascularization that occurs in AMD. (Invest Ophthalmol Vis Sci.