The identification of cardiac progenitor cells in mammals raises the possibility that the human heart contains a population of stem cells capable of generating cardiomyocytes and coronary vessels. The characterization of human cardiac stem cells (hCSCs) would have important clinical implications for the management of the failing heart. We have established the conditions for the isolation and expansion of c-kit-positive hCSCs from small samples of myocardium. Additionally, we have tested whether these cells have the ability to form functionally competent human myocardium after infarction in immunocompromised animals. Here, we report the identification in vitro of a class of human c-kit-positive cardiac cells that possess the fundamental properties of stem cells: they are self-renewing, clonogenic, and multipotent. hCSCs differentiate predominantly into cardiomyocytes and, to a lesser extent, into smooth muscle cells and endothelial cells. When locally injected in the infarcted myocardium of immunodeficient mice and immunosuppressed rats, hCSCs generate a chimeric heart, which contains human myocardium composed of myocytes, coronary resistance arterioles, and capillaries. The human myocardium is structurally and functionally integrated with the rodent myocardium and contributes to the performance of the infarcted heart. Differentiated human cardiac cells possess only one set of human sex chromosomes excluding cell fusion. The lack of cell fusion was confirmed by the Cre-lox strategy. Thus, hCSCs can be isolated and expanded in vitro for subsequent autologous regeneration of dead myocardium in patients affected by heart failure of ischemic and nonischemic origin.generation of human myocardium ͉ progenitor cells ͉ stem cell niches

Coronary artery disease is the most common cause of cardiac failure in the Western world, and to date there is no alternative to bypass surgery for severe coronary atherosclerosis. We report that c-kitpositive cardiac progenitor cells (CPCs) activated with insulin-like growth factor 1 and hepatocyte growth factor before their injection in proximity of the site of occlusion of the left coronary artery in rats, engrafted within the host myocardium forming temporary niches. Subsequently, CPCs divided and differentiated into endothelial cells and smooth muscle cells and, to a lesser extent, into cardiomyocytes. The acquisition of vascular lineages appeared to be mediated by the up-regulation of hypoxia-inducible factor 1␣, which promoted the synthesis and secretion of stromal-derived factor 1 from hypoxic coronary vessels. Stromal-derived factor 1 was critical in the conversion of CPCs to the vascular fate. CPCs formed conductive and intermediate-sized coronary arteries together with resistance arterioles and capillaries. The new vessels were connected with the primary coronary circulation, and this increase in vascularization more than doubled myocardial blood flow in the infarcted myocardium. This beneficial effect, together with myocardial regeneration attenuated postinfarction dilated myopathy, reduced infarct size and improved function. In conclusion, locally delivered activated CPCs generate de novo coronary vasculature and may be implemented clinically for restoration of blood supply to the ischemic myocardium.coronary blood flow ͉ infarct size ͉ myocardial regeneration ͉ stem cells ͉ vasculogenesis

During bacterial infection, the bone marrow hematopoietic activity shifts toward granulocyte production, which is critical for host defenses. Along with this enhancement of granulopoiesis, the bone marrow also increases its release of hematopoi-

Alcohol abuse predisposes the host to bacterial infections. In response to bacterial infection, the bone marrow hematopoietic activity shifts toward granulocyte production, which is critical for enhancing host defense. This study investigated the hematopoietic precursor cell response to bacteremia and how alcohol affects this response. Acute alcohol intoxication was induced in BALB/c mice 30 min before initiation of Escherichia coli bacteremia. Bacteremia caused a significant increase in the number of bone marrow lineage (lin−)-c-kit+Sca-1+ cells. Marrow lin−c-kit+Sca-1+ cells isolated from bacteremic mice showed an increase in CFU-granulocyte/macrophage activity compared with controls. In addition to enhanced proliferation of lin−c-kit+Sca-1+ cells as reflected by BrdU incorporation, phenotypic inversion of lin−c-kit+Sca-1+Sca-1− cells primarily accounted for the rapid increase in marrow lin−c-kit+Sca-1+ cells following bacteremia. Bacteremia increased plasma concentration of TNF-α. Culture of marrow lin−c-kit+Sca-1+Sca-1− cells with murine rTNF-α for 24 h caused a dose-dependent increase in conversion of these cells to lin−c-kit+Sca-1+ cells. Sca-1 mRNA expression by the cultured cells was also up-regulated following TNF-α stimulation. Acute alcohol intoxication inhibited the increase in the number of lin−c-kit+Sca-1+ cells in the bone marrow after E. coli infection. Alcohol impeded the increase in BrdU incorporation into marrow lin−c-kit+Sca-1+ cells in response to bacteremia. Alcohol also suppressed the plasma TNF-α response to bacteremia and inhibited TNF-α-induced phenotypic inversion of lin−c-kit+Sca-1+Sca-1− cells in vitro. These data show that alcohol inhibits the hematopoietic precursor cell response to bacteremia, which may serve as one mechanism underlying the impaired host defense in alcohol abusers with severe bacterial infections.