Background: A major limitation of intracoronary infusion of stem cells is the poor engraftment rate to ischemic tissue(less than 5%). We hypothesized that COMP-Angiopoietin 1 would enhance the adhesion of the mobilized peripheral blood stem cells(PBSCs) to extracellular matrix(ECM) and to endothelial cells (ECs), leading to increased engraftment to ischemic tissue and enhancement of angiogenesis ultimately. Methods and Results: (1)PBSCs mobilized by G-CSF and non-mobilized peripheral blood mononuclear cells(PBMC) were exposed to recombinant human angiopoietin-1(COMP-Ang1) for 3 hours and evaluated the change of their adhesive capacity on mature EC monolayer and on an ECM, fibronectin. COMP-Ang1-stimulated PBSCs showed increased adhesion to ECs and to fibronectin, however no significant changes were observed in PBMCs. (2)COMP-Ang1-stimulated PBSCs expressed more adhesion molecules(ICAM-1, 慣v棺5, and 棺2-integrin) in their surface in FACS analysis, whereas no significant changes occurred in PBMCs. (3)The portions of Tie-2+ cells among in PBSCs and in PBMCs were assayed by FACS analysis. Then, to evaluate whether Tie-2 receptor mediated pathway contributes COMP-Ang1-enhanced adhesion of PBSCs, Tie-2 proportion in adherent cells versus in total PBSCs were compared after COMP-Ang1 treatment. The result was that adherent population contained twice as much Tie-2+ cells as total PBSCs(p<0.05). (4)In an athymic hind limb ischemia model, transplantation of the COMP-Ang1-stimulated PBSCs showed improved neovascularization at day 21(perfusion ratio: 0.65짹0.09 in COMP-Ang1-treated PBSCs, 0.27짹0.12 in control PBSCs, n=8, p<0.05). The engraftment of cells into the ischemic tissue was assessed using CFSE-tagged mobilized PBSCs at day 7. The result showed that significantly more PBSCs were engrafted into vascular structures in COMP-Ang1-stimulated group than in control group(n=8, p<0.05). Conclusion: COMP-Angiopoietin 1 pretreatment increased adhesion molecules of PBSCs, leading to higher efficiency of engraftment rate into ischemic limb. The results of our study suggest that 'priming��� of the mobilized PBSCs with COMP-Ang1 would be a promising strategy enhancing the efficacy of stem cell therapy.