Background-We investigated whether catheter-based, intramyocardial transplantation of autologous endothelial progenitor cells can enhance neovascularization in myocardial ischemia. Methods and Results-Myocardial ischemia was induced by placement of an ameroid constrictor around swine left circumflex artery. Four weeks after constrictor placement, CD31ϩ mononuclear cells (MNCs) were freshly isolated from the peripheral blood of each animal. After overnight incubation of CD31ϩ MNCs in noncoated plates, nonadhesive cells (NA/CD31ϩ MNCs) were harvested as the endothelial progenitor cell-enriched fraction. Nonadhesive CD31Ϫ cells (NA/CD31Ϫ MNCs) were also prepared. Autologous transplantation of 10 7 NA/CD31ϩ MNCs, 10

Background-We hypothesized that estrogen-induced acceleration of reendothelialization might be mediated in part by effects involving mobilization and incorporation of bone marrow-derived endothelial progenitor cells (EPCs). Methods and Results-Carotid injury was induced in ovariectomized wild-type mice receiving either 17␤-estradiol or placebo. Estradiol treatment significantly accelerated reendothelialization of injured arterial segments within 7 days and resulted in a significant reduction of medial thickness 14 and 21 days after the injury. Significant increases in circulating EPCs 3 days after the injury were observed in the estradiol group compared with placebo-treated mice. These data were further supported by fluorescence-activated cell sorting analysis, which disclosed a significant increase in Sca-1/Flk-1-positive cells in estradiol versus control mice. To evaluate the effects of estradiol on bone marrow-derived EPC incorporation at sites of reendothelialization, carotid injury was established in ovariectomized wild-type mice transplanted with bone marrow from transgenic donors expressing ␤-galactosidase transcriptionally regulated by the Tie-2 promoter. Significantly greater numbers of X-gal-positive cells were observed at reendothelialized areas in the estradiol group 3 days after injury as compared with placebo. Fluorescent immunohistochemistry 14 days after the injury documented a marked increase in cells expressing both ␤-gal, indicating bone marrow origin and Tie-2 expression, and isolectin B4, also indicating endothelial lineage, in the estradiol group compared with control. In contrast, estradiol did not accelerate reendothelialization or augment EPC mobilization into the peripheral circulation after injury in endothelial nitric oxide synthase-deficient mice (eNOS Ϫ/Ϫ ). Furthermore, estradiol exhibited direct stimulatory effects on EPC mitogenic and migration activity and inhibited EPC apoptosis. Conclusions-Estradiol

We have identified a subpopulation of stem cells within adult human BM, isolated at the single-cell level, that self-renew without loss of multipotency for more than 140 population doublings and exhibit the capacity for differentiation into cells of all 3 germ layers. Based on surface marker expression, these clonally expanded human BM-derived multipotent stem cells (hBMSCs) do not appear to belong to any previously described BM-derived stem cell population. Intramyocardial transplantation of hBMSCs after myocardial infarction resulted in robust engraftment of transplanted cells, which exhibited colocalization with markers of cardiomyocyte (CMC), EC, and smooth muscle cell (SMC) identity, consistent with differentiation of hBMSCs into multiple lineages in vivo. Furthermore, upregulation of paracrine factors including angiogenic cytokines and antiapoptotic factors, and proliferation of host ECs and CMCs, were observed in the hBMSC-transplanted hearts. Coculture of hBMSCs with CMCs, ECs, or SMCs revealed that phenotypic changes of hBMSCs result from both differentiation and fusion. Collectively, the favorable effect of hBMSC transplantation after myocardial infarction appears to be due to augmentation of proliferation and preservation of host myocardial tissues as well as differentiation of hBMSCs for tissue regeneration and repair. To our knowledge, this is the first demonstration that a specific population of multipotent human BM-derived stem cells can induce both therapeutic neovascularization and endogenous and exogenous cardiomyogenesis.

Background-We compared the therapeutic potential of purified mobilized human CD34ϩ cells with that of mobilized total mononuclear cells (tMNCs) for the preservation/recovery of myocardial tissue integrity and function after myocardial infarction (MI). Methods and Results-CD34ϩ cells were purified from peripheral blood tMNCs of healthy volunteers by magnetic cell sorting after a 5-day administration of granulocyte colony-stimulating factor. Phosphate-buffered saline (PBS), 5ϫ10 5 CD34