Rationale The regenerative potential of the heart is insufficient to fully restore functioning myocardium after injury, motivating the quest for a cell-based replacement strategy. Bone marrow derived mesenchymal stem cells (MSC) have the capacity for cardiac repair that appears to exceed their capacity for differentiation into cardiac myocytes. Objective Here we test the hypothesis that bone marrow derived MSCs stimulate the proliferation and differentiation of endogenous cardiac stem cells (CSCs) as part of their regenerative repertoire. Methods And Results Female Yorkshire pigs (n=31) underwent experimental myocardial Infarction (MI); and 3 days later received transendocardial injections of allogeneic male bone marrow-derived MSCs, MSC concentrated conditioned medium (CCM), or placebo (Plasmalyte). A no-injection control group was also studied. MSCs engrafted and differentiated into cardiomyocytes and vascular structures. In addition, endogenous c-kit+ CSCs increased 20-fold in MSC treated animals vs. controls (p<0.001), there was a 6-fold increase in GATA-4+ CSCs in MSC vs. control (p<0.001), and mitotic myocytes increased 4-fold. Porcine endomyocardial biopsies were harvested and plated as organotypic cultures in the presence or absence of MSC feeder layers. In vitro, MSCs stimulated c-kit+ CSCs proliferation into enriched populations of adult cardioblasts that expressed Nkx2-5 and troponin I. Conclusions MSCs stimulate host CSCs, a new mechanism of action underlying successful cell-based therapeutics.

The mechanism(s) underlying cardiac reparative effects of bone marrow-derived mesenchymal stem cells (MSC) remain highly controversial. Here we tested the hypothesis that MSCs regenerate chronically infarcted myocardium through mechanisms comprising long-term engraftment and trilineage differentiation. Twelve weeks after myocardial infarction, female swine received catheterbased transendocardial injections of either placebo (n ‫؍‬ 4) or male allogeneic MSCs (200 million; n ‫؍‬ 6). Animals underwent serial cardiac magnetic resonance imaging, and in vivo cell fate was determined by co-localization of Y-chromosome (Y pos ) cells with markers of cardiac, vascular muscle, and endothelial lineages. MSCs engrafted in infarct and border zones and differentiated into cardiomyocytes as ascertained by co-localization with GATA-4, Nkx2.5, and ␣-sarcomeric actin. In addition, Y pos MSCs exhibited vascular smooth muscle and endothelial cell differentiation, contributing to large and small vessel formation. Infarct size was reduced from 19.3 ؎ 1.7% to 13.9 ؎ 2.0% (P < 0.001), and ejection fraction (EF) increased from 35.0 ؎ 1.7% to 41.3 ؎ 2.7% (P < 0.05) in MSC but not placebo pigs over 12 weeks. This was accompanied by increases in regional contractility and myocardial blood flow (MBF), particularly in the infarct border zone. Importantly, MSC engraftment correlated with functional recovery in contractility (R ‫؍‬ 0.85, P < 0.05) and MBF (R ‫؍‬ 0.76, P < 0.01). Together these findings demonstrate long-term MSC survival, engraftment, and trilineage differentiation following transplantation into chronically scarred myocardium. MSCs are an adult stem cell with the capacity for cardiomyogenesis and vasculogenesis which contribute, at least in part, to their ability to repair chronically scarred myocardium.cardiac chimerism ͉ cellular cardiomyoplasty ͉ heart failure ͉ catheter delivery

To demonstrate the safety of transendocardial stem cell injection (TESI) with autologous MSCs and BMCs in patients with ICM.• To assess prespecified outcomes of efficacy.

Rationale While accumulating data support the efficacy of intramyocardial cell-based therapy to improve LV function in patients with chronic ischemic cardiomyopathy undergoing CABG, the underlying mechanism and impact of cell injection site remain controversial.Mesenchymal stem cells (MSCs) improve LV structure and function through several effects including: reducing fibrosis, neoangiogenesis and neomyogenesis. Objective To test the hypothesis that the impact on cardiac structure and function following intramyocardial injections of autologous MSCs results from a concordance of pro-recovery phenotypic effects. Methods and Results Six patients were injected with autologous MSCs into akinetic/hypokinetic myocardial territories not receiving bypass graft for clinical reasons. MRI was used to measure scar, perfusion, wall thickness and contractility at baseline, 3, 6 and 18 months and to compare structural and functional recovery in regions that received MSC injections alone, revascularization alone, or neither. A composite score of MRI variables was used to assess concordance of antifibrotic effects, perfusion, and contraction at different regions. After 18 months, subjects receiving MSCs exhibited increased LVEF (+9.4±1.7%, p=0.0002) and decreased scar mass (-47.5±8.1%; p<0.0001) compared to baseline. MSC-injected segments had concordant reduction in scar size, perfusion and contractile improvement (concordant score: 2.93±0.07), whereas revascularized (0.5±0.21) and non-treated segments (-0.07±0.34) demonstrated non-concordant changes (p<0.0001 vs. injected segments). Conclusions Intramyocardial injection of autologous MSCs into akinetic yet non-revascularized segments produces comprehensive regional functional restitution, which in turn drives improvement in global LV function. These findings, although inconclusive due to lack of placebo group, have important therapeutic and mechanistic hypothesis-generating implications.

Together these data demonstrate that autologous MSCs can be safely delivered in an adult heart failure model, producing substantial structural and functional reverse remodelling. These findings demonstrate the safety and efficacy of autologous MSC therapy and support clinical trials of MSC therapy in patients with chronic ischaemic cardiomyopathy.

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