Composite cell sheets: a further step toward safe and effective myocardial regeneration by cardiac progenitors derived from embryonic stem cells.

BACKGROUND: The safety and efficacy of myocardial regeneration using embryonic stem cells are limited by the risk of teratoma and the high rate of cell death. METHODS AND RESULTS: To address these issues, we developed a composite construct made of a sheet of adipose tissue-derived stroma cells and embryonic stem cell-derived cardiac progenitors. Ten Rhesus monkeys underwent a transient coronary artery occlusion followed, 2 weeks later, by the open-chest delivery of the composite cell sheet over the infarcted area or a sham operation. The sheet was made of adipose tissue-derived stroma cells grown from a biopsy of autologous adipose tissue and cultured onto temperature-responsive dishes. Allogeneic Rhesus embryonic stem cells were committed to a cardiac lineage and immunomagnetically sorted to yield SSEA-1(+) cardiac progenitors, which were then deposited onto the cell sheet. Cyclosporine was given for 2 months until the animals were euthanized. Preimplantation studies showed that the SSEA-1(+) progenitors expressed cardiac markers and had lost pluripotency. After 2 months, there was no teratoma in any of the 5 cell-treated monkeys. Analysis of >1500 histological sections showed that the SSEA-1(+) cardiac progenitors had differentiated into cardiomyocytes, as evidenced by immunofluorescence and real-time polymerase chain reaction. There were also a robust engraftment of autologous adipose tissue-derived stroma cells and increased angiogenesis compared with the sham animals. CONCLUSIONS: These data collected in a clinically relevant nonhuman primate model show that developmentally restricted SSEA-1(+) cardiac progenitors appear to be safe and highlight the benefit of the epicardial delivery of a construct harboring cells with a cardiomyogenic differentiation potential and cells providing them the necessary trophic support.

Is xenotransplantation of embryonic stem cells a realistic option?

To test the purported immune privilege of embryonic stem cells (ESC) in the challenging setting of xenotransplantation, 14 immunocompetent baboons were subjected to a coronary artery occlusion-reperfusion sequence and, two weeks later, randomized to receive in-scar injections of culture medium or cardiac-committed mouse ESC engineered to express fluorescent reporter genes driven by cardiac-specific promoters. Two months after transplantation, left ventricular function, as assessed by echocardiography, deteriorated to a similar extent in control and treated baboons. This correlated with failure to identify the grafted cells by X-gal histology and immunofluorescence. Rejection did not seem to be mediated by xenoantibodies, but rather by T lymphocytes and natural killer cells as suggested by positive immunostaining for CD3 and CD56 early after transplantation. There was no increase in circulating levels of regulatory T cells. These data raise a cautionary note about the immune privilege of ESC and suggest that from a mere immunologic standpoint, ESC xenotransplantation is likely to be an unrealistic challenge.

Psychostimulants and G tolerance in rhesus monkeys: effects of oral modafinil and injected caffeine.

INTRODUCTION: Caffeine and modafinil are psychostimulants that may be taken by fighter aircraft pilots to reduce fatigue. Fighter pilots are subjected to high positive G loads that reduce cerebral blood flow and consequently may induce G-LOC. The aim of the experiment was to determine whether these drugs may reduce tolerance to G stress. METHODS: Seven adult male rhesus monkeys participated in the experiment. Five were equipped with ECoG and ECG wires and underwent two G tests (A and B). Each experiment consisted of five centrifuge runs. Before the runs, the monkeys received no drug (control) or were given either 7.5 mg x kg(-1) caffeine IM or 64 mg x kg(-1) modafinil PO or the corresponding vehicles. The runs were performed up to +13 Gz with an onset rate of 0.1 G x s(-1) (test A) or 3 G x s(-1) (test B). The run was ended when the electrical activity of one ECoG channel had disappeared (i.e., G-LOC). RESULTS: In experiment A, drug administration had no significant effect. In experiment B, the injection of the caffeine-free solvent caused a delay in G-LOC compared with the control condition (no administration). Caffeine solvent also induced an increase in plasma osmolality. DISCUSSION: Modafinil administration has no significant effect on the G tolerance of rhesus monkeys. Regarding caffeine, the drug seems to have caused the reverse effect compared with the solvent. CONCLUSIONS: Caffeine and modafinil administration had no significant effect on the G-tolerance of rhesus monkeys when compared with controls. This result needs to be confirmed in humans.

Influence of mobilized stem cells on myocardial infarct repair in a nonhuman primate model.

Although previous findings have suggested that some adult stem cells are pluripotent and could differentiate in an appropriate microenvironment, the fate conversion of adult stem cells is currently being debated. Here, we studied the ability of mobilized stem cells to repair cardiac tissue injury in a nonhuman primate model of acute myocardial infarction. Mobilization was carried out with stem cell factor, 25 mcg/Kg/d (D), and granulocyte-colony-stimulating factor, 100 mcg/Kg/D administered 5 days before (D - 5 group; n = 3) or 4 hours after (H + 4 group; n = 4) circumflex coronary artery ligation; no growth factor was administered to 3 baboons of the control group. No adverse effect relating to growth factor administration was observed. Flk-1 and transcription factors of cardiac lineages could be detected in peripheral blood only by reverse transcriptase-polymerase chain reaction. When comparing positron emission tomography (PET) with [11C]-acetate between examinations from D2 and D30, a relative increase (perfusion ratio between infarct and noninfarct regions) of 26% (P =.01) in myocardial blood flow was found in the H + 4 group; the relative rate of oxidative metabolism remained unaltered in the 3 groups. No change was observed in the echographic indices of the left ventricular enlargement or systolic function in the 3 animal groups during the 2-month follow-up. The PET findings concurred with the immunohistochemistry analysis of left ventricular myocardial sections with evidence of endothelial cells but no myocyte differentiation; few cycling cells were observed at this time. Thus, the present data suggest that, in nonhuman primates submitted to coronary artery ligation, mobilization by hematopoietic growth factors could promote angiogenesis in the infarcted myocardium, without detectable myocardial repair.