Autologous bone marrow-derived stem-cell transfer in patients with ST-segment elevation myocardial infarction: double-blind, randomised controlled trial

Inflammatory responses after intracoronary injection of autologous mononuclear bone marrow cells in patients with acute myocardial infarction

BACKGROUND

Inflammatory responses after intracoronary injection of autologous mononuclear bone marrow cells (mBMC) are not clarified. The aim of this study was to investigate the influence of intracoronary injection of mBMC on inflammatory mediators in patients with acute myocardial infarction (AMI).

METHODS

Patients with AMI in the ASTAMI trial (N = 100) treated with percutaneous coronary intervention were randomized to intracoronary injections of mBMC or control. Fasting blood samples were drawn the day before stem cell transplantation (baseline 4-5 days after AMI) and 1 day, 3 days, 2 to 3 weeks, and 3 months after transplantation for determination of circulating levels of selected inflammatory markers and mRNA levels in whole blood samples.

RESULTS

From baseline to day 1, the levels of interleukin 6 and the expression of tumor necrosis factor alpha mRNA increased significantly in the mBMC group compared to the control group (P < .05 for both). The decrease in interleukin 6 levels from baseline to 2 to 3 weeks in the mBMC group was less pronounced than in the controls (P < .05), as was also the decrease in C-reactive protein levels from baseline to day 1 and day 3 in the mBMC group (P < .05). However, from baseline to 3 months the levels of tumor necrosis factor alpha and monocyte chemoattractant protein 1 increased less in the mBMC group (P < .05 for both).

CONCLUSION

Intracoronary injection of mBMC in patients with AMI induces a marked short-term inflammatory response, but a slightly reduced inflammation after 3 months which may have implications for the timing of stem cell transplantation in AMI.

The Long-term Effect of Autologous Endothelial Progenitor Cells from Peripheral Blood Implantation on Infarcted Myocardial Contractile Force

This study was designed to evaluate the long-term effect of endothelial progenitor cell (EPC) implantation in acute myocardial infarction in Sprague-Dawley rats after ligation of the left anterior descending coronary artery. Autologous EPCs from peripheral blood were purified and implanted into an acute myocardial infarct site. Specimens and muscle strip were harvested at 3 and 6 weeks, and at 6, 8 and 12 months for contractile force assessment and, by immunohistology, for expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF) and factor VIII. Expression of VEGF and bFGF, and microvessel counts and contractile force in the cell implantation group were significantly higher than in the control group up to 8 months after implantation. Beyond 8 months following implantation, however, no further improvement occurred. The EPCs showed an ability to improve contractile performance in infarcted myocardium by means of angiogenesis and vasculogenesis, and the results seemed to persist long-term.

Contrast-enhanced magnetic resonance imaging in the assessment of myocardial infarction and viability

Contrast-enhanced magnetic resonance imaging (MRI) can be used to visualize the transmural extent of myocardial infarction with high spatial resolution. The aim of this review is to provide an overview of the use of contrast-enhanced MRI for characterization of ischemic myocardial injury in comparison to other imaging methods and its relevance in clinical syndromes related to coronary artery disease. Infarcted myocardium appears hyperenhanced compared with normal myocardium when imaged by a delayed-enhancement MRI technique with the use of an inversion-prepared T(1)-weighted sequence after injection of gadolinium chelates, such as gadolinium-diethylenetriamine pentaacetic acid. Experimental and clinical studies indicate that the extent of delayed enhancement is reproducible and closely correlates with the size of myocardial necrosis or infarct scar as determined by established in vitro and in vivo methods. Furthermore, MRI appears to be more sensitive than other imaging methods in detecting small subendocardial infarctions. The transmural extent of delayed enhancement potentially predicts functional outcome after revascularization in acute myocardial infarction and chronic ischemic heart disease, indicating that it can accurately discriminate between infarction and dysfunctional but viable myocardium. Further experience from clinical trials is needed to understand the association of delayed enhancement with clinical outcomes.

Stem cell differentiation: cardiac repair

Cellular transplantation has been employed for several years to deliver donor cardiomyocytes to normal and injured hearts. Recent reports of a variety of stem cells with apparent cardiomyogenic potential have raised the possibility of cell transplantation-based therapeutic interventions for heart disease. Here we review the preclinical studies demonstrating that intracardiac transplantation of skeletal myoblasts, cardiomyocytes and cardiomyogenic stem cells is feasible. In addition, recent clinical studies of skeletal myoblast and adult stem cell transplantation for heart disease are discussed.

Cell therapy in congestive heart failure

Congestive heart failure (CHF) has emerged as a major worldwide epidemic and its main causes seem to be the aging of the population and the survival of patients with post-myocardial infarction. Cardiomyocyte dropout (necrosis and apoptosis) plays a critical role in the progress of CHF; thus treatment of CHF by exogenous cell implantation will be a promising medical approach. In the acute phase of cardiac damage cardiac stem cells (CSCs) within the heart divide symmetrically and/or asymmetrically in response to the change of heart homeostasis, and at the same time homing of bone marrow stem cells (BMCs) to injured area is thought to occur, which not only reconstitutes CSC population to normal levels but also repairs the heart by differentiation into cardiac tissue. So far, basic studies by using potential sources such as BMCs and CSCs to treat animal CHF have shown improved ventricular remodelling and heart function. Recently, however, a few of randomized, double-blind, placebo-controlled clinical trials demonstrated mixed results in heart failure with BMC therapy during acute myocardial infarction.

Bone marrow subpopulations contain distinct types of endothelial progenitor cells and angiogenic cytokine-producing cells

Therapeutic angiogenesis can be induced by the implantation of bone marrow cells (BMCs). However, the mechanism of BMC-mediated neovascularization remains to be clarified. We investigated the differential activities of bone marrow subpopulations in angiogenesis and cytokine production. BMCs were separated into positive and negative fractions by surface expression of Mac-1, Gr-1, CD19, and c-kit, respectively. After 7 days of culture in the presence of vascular endothelial growth factor (VEGF), the cells produced adherent cells which incorporate acetylated low-density lipoprotein (acLDL). Mac-1(+) and Mac-1(-) cells produced almost equal numbers of acLDL(+) cells, but only Mac-1(-) cells expressed endothelial markers, including Flk-1, vWF, and CD31. Similarly, the expression of endothelial markers was detected in Gr-1(-), CD19(-), and c-kit(+) BMC fractions at 7-day cultures, but not in Gr-1(+), CD19(+), or c-kit(-) cells. In contrast, freshly isolated Mac-1(+) and Gr-1(+) BMCs expressed higher levels of mRNAs for angiogenic cytokines (including VEGF-A, FGF-2, and HGF) than Mac-1(-) and Gr-1(-) cells, respectively. Moreover, Mac-1(+)/c-kit(+) BMC subpopulation expressed higher levels of VEGF-A and SDF-1 mRNAs than other subpopulations. These data demonstrate that a relatively small proportion of VEGF-cultured adherent cells are true endothelial cells with a Flk-1(+)/vWF(+)/CD31(+) phenotype. Moreover, endothelial stem/progenitor cells (EPCs) are limited primarily to Mac-1(-), Gr-1(-), and c-kit(+) BMC populations. In contrast, angiogenic cytokine mRNAs were also produced by Mac-1(+), Gr-1(+), and c-kit(-) BMCs, suggesting the heterogeneity of effector cell types for neovasculatization therapy.

Similarities and differences in design considerations for cell therapy and pharmacologic cardiovascular clinical trials

Cell therapies hold the potential for suppression, modification, or cure of disease. Several unique challenges have been recognized as this field has developed. Many of these involve considerations of trial design. This paper summarizes the discussion and suggestions constructed during the 8th Cardiovascular Clinical Trialists Workshop, a meeting involving cardiovascular clinical trialists, biostatisticians, National Institutes of Health scientists, European and United States regulators, and pharmaceutical industry scientists. Investigators must adapt research methods to accommodate the scientific advances associated with cell therapy. Safety and efficacy of cell therapy for cardiovascular indications should be evaluated with the same degree of scientific rigor required of pharmacologic agents, and the same fundamental regulatory requirements and scientific processes apply to both. Clinical trials for these indications should also meet standards similar to those set for drug therapies. Safety should be determined throughout development, dose responsiveness should be established and, while surrogate endpoints are important development tools, the ultimate demonstration of efficacy must rely on clinical benefit. The establishment of a global safety database for cell therapy would significantly advance the field. Efforts to discover innovative therapies must be balanced by a commitment to comprehensively evaluate the safety and efficacy of the new treatments.

Cell-based therapy of myocardial infarction

Cell-based therapy is a promising option for treatment of ischemic diseases. Several cell types have experimentally been shown to increase the functional recovery of the heart after ischemia by physically forming new blood vessels, differentiating to cardiac myocytes and--additionally or alternatively--by providing proangiogenic and antiapoptotic factors promoting tissue repair in a paracrine manner. Clinical studies preferentially used adult bone marrow-derived cells for the treatment of patients with acute myocardial infarction. Most of the studies suggested that cell therapy reduced the infarct size and improved cardiac contractile function. However, cell therapy is in its early stages, and various questions remain. For example, the identification of those patients who benefit most from cell therapy, the optimal cell type and number for patient with acute and chronic diseases, the best time and way of cell delivery, and the mechanisms of action by which cells exhibit beneficial effects, need to be further evaluated. Although no major safety concerns were raised during the initial clinical trials, several potential side effects need to be carefully monitored. The present review article summarizes the results of the clinical studies and discusses the open issues.

Use of stem cells for the treatment of multiple sclerosis

The reported evidence of neurodegeneration in multiple sclerosis (MS) may explain the lack of efficacy of the currently used immunomodulating modalities and the irreversible axonal damage, which results in accumulating disability. To date, efforts for neuroprotective treatments have not been successful in clinical studies in other CNS diseases. Therefore, for MS, the use of stem cells may provide a logical solution, since these cells can migrate locally into the areas of white-matter lesions (plaques) and have the potential to support local neurogenesis and rebuilding of the affected myelin. This is achieved both by support of the resident CNS stem cell repertoire and by differentiation of the transplanted cells into neurons and myelin-producing cells (oligodendrocytes). Stem cells were also shown to possess immunomodulating properties, inducing systemic and local suppression of the myelin-targeting autoimmune lymphocytes. Several types of stem cells (embryonic and adult) have been described and extensively studied in animal models of CNS diseases and the various models of MS (experimental autoimmune encephalomyelitis [EAE]). In this review, we summarize the experience with the use of different types of stem cells in CNS disease models, focusing on the models of EAE and describe the advantages and disadvantages of each stem cell type for future clinical applications in MS.

Evidence that intracoronary-injected CD133+ peripheral blood progenitor cells home to the myocardium in chronic postinfarction heart failure

OBJECTIVE

To study the biodistribution of purified CD133(+) cells after intracoronary injection in patients with stable chronic postinfarction heart failure.

PATIENTS AND METHODS

Patients with longstanding myocardial infarction (>12 months prior to inclusion) and with an accessible left coronary artery were eligible. CD133(+) cells were mobilized with granulocyte colony-stimulating factor and purified with a CliniMACS device. Cells were labeled with (111)Indium and injected through a balloon catheter in a coronary artery feeding the necrotic or viable infarct-related region of the left ventricle during a standard coronary catheterization procedure. The total body biodistribution of (111)Indium was studied with a dual-head gamma camera in combination with (99m)Technetium-sestaMIBI cardiac distribution analysis.

RESULTS

The number of CD133(+) cells injected ranged between 5 and 10 x 10(6) cells (low dose, three patients) or between 18.5 and 50 x 10(6) cells (high dose, five patients). In the five patients receiving the higher cell doses, a clear residual radioactivity was observed at the level of the chronic injury at 2, 12, and up to 36 hours after injection. A detailed analysis in two patients showed 6.9% to 8.0% (after 2 hours) and 2.3% to 3.2% (after 12 hours) residual radioactivity at the heart. No adverse events were observed during the procedure and up to 3 months follow-up.

CONCLUSIONS

We demonstrate that CD133(+) progenitor cells are capable of homing to the postinfarction remodeling myocardium after intracoronary injections in patients with chronic postinfarction heart failure.

T2-weighted cardiovascular magnetic resonance imaging

Technical advances in T2-weighted cardiovascular MR (CMR) imaging allow for accurate identification and quantification of tissue injuries that alter myocardial T2 relaxation. Of these, myocardial edema is of special relevance. Increased myocardial water content is an important feature of ischemic as well as nonischemic cardiomyopathies, which are often associated with acute myocardial inflammation. In this article, we review technical considerations and discuss clinical indications of myocardial T2-weighted imaging.

Impact of intracoronary cell therapy on left ventricular function in the setting of acute myocardial infarction: a collaborative systematic review and meta-analysis of controlled clinical trials

OBJECTIVES

We aimed to perform a meta-analysis of clinical trials on intracoronary cell therapy after acute myocardial infarction (AMI).

BACKGROUND

Intracoronary cell therapy continues to be evaluated in the setting of AMI with variable impact on left ventricular ejection fraction (LVEF).

METHODS

We searched the CENTRAL, mRCT, and PubMed databases for controlled trials reporting on intracoronary cell therapy performed in patients with a recent AMI (< or =14 days), revascularized percutaneously, with follow-up of > or =3 months. The primary end point was change in LVEF, and secondary end points were changes in infarct size, cardiac dimensions, and dichotomous clinical outcomes.

RESULTS

Ten studies were retrieved (698 patients, median follow-up 6 months), and pooling was performed with random effect. Subjects that received intracoronary cell therapy had a significant improvement in LVEF (3.0% increase [95% confidence interval (CI) 1.9 to 4.1]; p < 0.001), as well as a reduction in infarct size (-5.6% [95% CI -8.7 to -2.5]; p < 0.001) and end-systolic volume (-7.4 ml [95% CI -12.2 to -2.7]; p = 0.002), and a trend toward reduced end-diastolic volume (-4.6 ml [95% CI -10.4 to 1.1]; p = 0.11). Intracoronary cell therapy was also associated with a nominally significant reduction in recurrent AMI (p = 0.04) and with trends toward reduced death, rehospitalization for heart failure, and repeat revascularization. Meta-regression suggested the existence of a dose-response association between injected cell volume and LVEF change (p = 0.066).

CONCLUSIONS

Intracoronary cell therapy following percutaneous coronary intervention for AMI appears to provide statistically and clinically relevant benefits on cardiac function and remodeling. These data confirm the beneficial impact of this novel therapy and support further multicenter randomized trials targeted to address the impact of intracoronary cell therapy on overall and event-free long-term survival.

Bone marrow derived mesenchymal cell mobilization by granulocyte-colony stimulating factor after acute myocardial infarction: results from the Stem Cells in Myocardial Infarction (STEMMI) trial

BACKGROUND

Granulocyte-colony stimulating factor (G-CSF) after myocardial infarction does not affect systolic function when compared with placebo. In contrast, intracoronary infusion of bone marrow cells appears to improve ejection fraction. We aimed to evaluate the G-CSF mobilization of subsets of stem cells.

METHODS AND RESULTS

We included 78 patients (62 men; 56+/-8 years) with ST-elevation myocardial infarction treated with primary percutaneous intervention <12 hours after symptom onset. Patients were randomized to double-blind G-CSF (10 microg/kg/d) or placebo. Over 7 days, the myocardium was exposed to 25x10(9) G-CSF mobilized CD34+ cells, compared with 3x10(9) cells in placebo patients (P<0.001); and to 4.9x10(11) mesenchymal stem cells, compared with 2.0x10(11) in the placebo group (P<0.001). The fraction of CD34+ cells/leukocyte increased during G-CSF treatment (from 0.3+/-0.2 to 1.1+/-0.9 x10(-3), P<0.001 when compared with placebo), whereas the fraction of putative mesenchymal stem cells/leukocyte decreased (from 22+/-17 to 14+/-11 x10(-3), P=0.01 when compared with placebo). An inverse association between number of circulating mesenchymal stem cells and change in ejection fraction was found (regression coefficient -6.8, P=0.004), however none of the mesenchymal cell subtypes analyzed, were independent predictors of systolic recovery.

CONCLUSIONS

The dissociated pattern for circulating CD34+ and mesenchymal stem cells could be attributable to reduced mesenchymal stem cell mobilization from the bone marrow by G-CSF, or increased homing of mesenchymal stem cells to the infarcted myocardium. The inverse association between circulating mesenchymal stem cells and systolic recovery may be of clinical importance and should be explored further.

Comparison of intracoronary and transendocardial delivery of allogeneic mesenchymal cells in a canine model of acute myocardial infarction

This study assessed safety of transendocardial (TE) electromechanical-guided delivery of bone marrow mesenchymal stem cells (MSCs) after acute myocardial infarction (AMI) and compared intracoronary (IC) delivery with TE delivery. In a canine acute myocardial ischemia model, 100 x 10(6) MSCs were delivered 7 days after AMI via IC and TE routes. Functional assessment was performed by 2D echocardiogram, and detailed histopathologic analyses were performed to assess the impact of cell therapy in vascular density and fibrosis. Patterns of cell distribution in both delivery methods were also compared. There was a statistically significant reduction in the amount of myocardial ischemia in the TE group (P=0.007). Left ventricular ejection fraction (LVEF) increased 13% (mean) in the TE group (21-day follow-up) and was significantly better than that of the controls (P=0.01), but did not improve in the IC-delivery group. Dissimilar patterns of cell distribution were noted between the IC and TE groups. This study suggests that MSC treatment is probably safe and effective after AMI. In the comparison of TE and IC delivery, the TE group showed higher cell retention (clusters even in the injury center of the infarct) with an increased vascularity and greater functional improvement than did the IC group (no clusters; cells at the border of the infarct). The higher local cell density in the TE group may be important for therapeutic effectiveness.

The art of cobbling a running pump--will human embryonic stem cells mend broken hearts?

The heart is one of the least regenerative organs in the body, and highly vulnerable to the increasing incidence of cardiovascular diseases in an aging world population. Cell-based approaches aimed at cardiac repair have recently caused great public excitement. But clinical trials of patients' own skeletal myoblasts or bone marrow cells for transplantation have been disappointing. Human embryonic stem cells (hESCs) form bona fide cardiomyocytes in vitro which are readily generated in mass culture and are being tested in animal models of heart damage. The early results, while encouraging, underscore that much remains to be done. This review focuses on the many challenges that remain before hESCs-mediated repair of the human heart becomes a reality.

Injection of Adeno-associated Viral Vector–Encoding Vascular Endothelial Growth Factor Gene in Infarcted Swine Myocardium: MR Measurements of Left Ventricular Function and Strain

PURPOSE

To prospectively investigate the long-term effect of adeno-associated viral (AAV) vector-encoding vascular endothelial growth factor gene (VEGF) (AAV-VEGF) on left ventricular (LV) mass and volumes, as well as on regional contractility and circumferential strain, in a swine model of reperfused myocardial infarction.

MATERIALS AND METHODS

All experimental procedures received approval from the institutional committee on animal research. Of 16 pigs subjected to reperfused myocardial infarction, six were treated, six were controls, and four died during the ischemic intervention. In six animals, cardiac-specific AAV-VEGF was injected into the periinfarcted and infarcted myocardium 1 hour after reperfusion. Magnetic resonance (MR) imaging was performed at 3 days and 8 weeks after infarction by using cine, tagged, and delayed enhancement (with gadoterate meglumine) sequences to measure global and regional LV function and infarct size. At postmortem examination, tissue samples stained with isolectin B4, Masson trichrome, and hematoxylin-eosin were used to characterize injured myocardium. Two-tailed Student t test was used for statistical analysis.

RESULTS

Six treated animals showed no change in mean LV ejection fraction after 8 weeks (40.3%+/-0.9 [standard error of the mean] vs 41.0%+/-0.7) in contrast to a decrease measured in six control animals (41.4%+/-0.7 vs 36.1%+/-0.6, P<.001). AAV-VEGF improved wall thickening and circumferential strain in periinfarcted and remote myocardium. A greater reduction in gadoterate meglumine-enhanced infarct area was measured in treated animals (18.6%+/-1.5 of the LV mass at 3 days vs 9.8%+/-1.0 of the LV mass at 8 weeks, P<.001) compared with control animals (17.7%+/-2.0 vs 14.8%+/-1.0, P=.008). Findings at histopathologic evaluation indicated an increase in vascular density and a decrease in myocyte diameter in the periinfarcted myocardium of treated, compared with control, animals.

CONCLUSION

Angiogenesis and arteriogenesis induced by VEGF genes improved regional myocardial strain and wall thickening and preserved ejection fraction after infarction.

Exercise capacity and quality of life after intracoronary injection of autologous mononuclear bone marrow cells in acute myocardial infarction: results from the Autologous Stem cell Transplantation in Acute Myocardial Infarction (ASTAMI) randomized controlled trial

BACKGROUND

The effects on left ventricular function of intracoronary injection of bone marrow cells in acute myocardial infarction (AMI) have been studied with conflicting results. The aim of this substudy of the ASTAMI trial was to examine the effects of this novel treatment on exercise capacity and quality of life.

METHODS

We studied 100 patients with anterior wall ST-elevation AMI. All had percutaneous coronary intervention with stent in the proximal or mid left anterior descending coronary artery 2 to 12 hours after start of symptoms. Patients were randomized to intracoronary injection of mononuclear bone marrow cells (mBMCs) in left anterior descending coronary artery 6 +/- 1.3 days after AMI (n = 50) or control (n = 50). Assessment of physical capacity by maximal symptom-limited bicycle ergometer exercise tests and quality of life by the Short Form 36 health survey was performed 2 to 3 weeks and 6 months after the AMI.

RESULTS

There was a significantly greater improvement in exercise time in the mBMC group than in the control group (treatment effect 0.9 minute, 95% CI 0.3-1.6, P < .01), and a similar improvement in peak oxygen consumption in the groups (2.8 +/- 3.9 mL/[kg min] in the mBMC group vs 2.4 +/- 3.5 mL/[kg min] in controls, P = .62). Peak heart rate and percentage of heart rate reserve increased significantly more in the treatment group than in the control group. Treatment with mBMCs did not influence quality of life.

CONCLUSIONS

In this randomized open-labeled study, the mBMC group significantly improved exercise time and heart rate responses to exercise compared with the control group. There was no treatment effect on peak oxygen consumption.

Arteriogenesis: basic mechanisms and therapeutic stimulation

Pharmacological attempts to stimulate the growth of collateral arteries (arteriogenesis) are evolving towards a new treatment option for patients with vascular occlusive diseases. This enlargement of small pre-existing anastomoses towards large conductance arteries takes place independent of local oxygen tension and is driven by changes in luminal shear stress and infiltration of circulating cells. With the increasing knowledge regarding the distinct differences between capillary sprouting (angiogenesis) and arteriogenesis, several cytokines and growth factors have been demonstrated to stimulate the growth of arterial blood vessels in preclinical models of vascular disease. However, the translation towards clinical practice remains difficult and first in-man trials show limited success. Intensive research especially regarding new drug delivery platforms and the potentially serious side effects of pro-arteriogenic therapeutics is warranted before stimulation of arteriogenesis could become a significant treatment option for vascular occlusive diseases. This review focuses on the recent advances in the field of collateral artery growth. In addition, possible means to overcome the hurdles that have hampered the clinical implementation of pro-arteriogenic therapies will be discussed.

STEM CELL MECHANISMS AND PARACRINE EFFECTS

Heart disease remains the leading cause of death in the industrialized world. Stem cell therapy is a promising treatment modality for injured cardiac tissue. A novel mechanism for this cardioprotection may include paracrine actions. Cardiac surgery represents the unique situation where preischemia and postischemia treatment modalities exist that may use stem cell paracrine protection. This review (1) recalls the history of stem cells in cardiac disease and the unraveling of its mechanistic basis for protection, (2) outlines the pathways for stem cell-mediated paracrine protection, (3) highlights the signaling factors expressed, (4) explores the potential of using stem cells clinically in cardiac surgery, and (5) summarizes all human stem cell studies in cardiac disease to date.

Do stem cells in the heart truly differentiate into cardiomyocytes?

Chronic congestive heart failure (CHF) is a common consequence of heart muscle or valve damage and remains a major cause of morbidity and mortality worldwide. There are increasing interests to treat cardiac failure by stem cell-based therapy. Many types of stem cells or progenitor cells have been suggested for cellular therapy of heart failure. While stem cell-based therapy was initially thought to be achieved by transdifferentiation of stem cells into myocardial cells including cardiomyocytes it has become clear that this may be rather an infrequent event. Instead cardiac regeneration may result from vascular differentiation of stem cells or even from stem cell-mediated reverse remodelling. Thus the term stem cell-mediated cardiac regeneration covers the spectrum from stem cell transdifferentiation into cardiomyocytes to cell-mediated pharmacotherapy. In this review we revise stem cell-based cardiac regeneration both in experimental models and in clinical application. We have limited our discussion on some selected types of stem cells, with particular emphasis on their differentiation potential, current status and perspectives on their future applications.

Can we pass from the experimental to the clinical phase in MS stem cell research?

A crucial point in development of new treatments is the step from the experimental level to the first clinical trials. For stem cell treatments in general, but for stem cell treatment in Multiple Sclerosis specifically, this is the question for the moment. To answer this question a rational analysis of the hypotheses and the suppositions behind the application of stem cells is necessary, as well as a review of the present knowledge, the risks and the gains to be expected. This is a personal analysis of 32 oral presentation and discussions of the European Charcot Foundation Symposium, Taormina 2006. It is the application of the Kenter and Cohen [Kenter MJH, Cohen AF. Establishing risk of human experimentation with drugs: lessons from TGN 1412. Lancet 2006; 368:1387-91] approach, adapted for stem cell treatment in MS. About half of the pertinent issues plead for the start of clinical experiments now. However, the absence of knowledge on deleterious effects and their predictability heavily weights against it. Organisational and funding aspects were discussed to prevent uncritical, uncontrolled clinical approaches.

Intracoronary transplantation of non-expanded peripheral blood-derived mononuclear cells promotes improvement of cardiac function in patients with acute myocardial infarction

BACKGROUND

Transplantation of non-expanded peripheral blood mononuclear cells (PBMNCs) enhances neovessel formation in ischemic myocardium and limbs by releasing angiogenic factors. This study was designed to examine whether intracoronary transplantation of PBMNCs improves cardiac function after acute myocardial infarction (AMI).

METHODS AND RESULTS

After successful percutaneous coronary intervention (PCI) for a ST-elevation AMI with occlusion of proximal left anterior descending coronary artery within 24 h, patients received an intracoronary infusion of PBMNCs within 5 days after PCI (PBMNC group). PBMNCs were obtained from patients by COBE spectra-apheresis and concentrated to 10 ml, 3.3 ml of which was infused via over-the-wire catheter. The global left ventricular ejection fraction (LVEF) change from baseline to 6 months followup in th ePBMNC group that underwent standard PCI for similar AMI [corrected]. The primary endpoint was the global left ventricular ejection fraction (LVEF) change from baseline to 6 months' follow-up. The data showed that the absolute increase in LVEF was 7.4% in the control group and 13.4% (p=0.037 vs control) in the PBMNC group. Cell therapy resulted in a greater tendency of DeltaRegional ejection fraction (EF) or significant improvement in the wall motion score index and Tc-99m-tetrofosmin perfusion defect score associated with the infarct area, compared with controls. Moreover, intracoronary administration of PBMNCs did not exacerbate either left ventricular (LV) end-diastolic and end-systolic volume expansion or high-risk arrhythmia, without any adverse clinical events.

CONCLUSION

Intracoronary infusion of non-expanded PBMNCs promotes improvement of LV systolic function. This less invasive and more feasible approach to collecting endothelial progenitor cells may provide a novel therapeutic option for improving cardiac function after AMI.

Therapeutic myocardial angiogenesis

Armed with an improved understanding of the mediators of angiogenesis, physicians and scientists have made significant efforts at harnessing this naturally occurring process in order to treat patients with a variety of peripheral vascular and coronary ischemic syndromes. There is a growing population of patients with end-stage coronary artery disease (CAD) who are no longer candidates for mechanical revascularization, yet suffer from chronic myocardial ischemia who may benefit from regeneration of the depleted microvasculature.

Stem cells and cardiac regeneration

Despite many advances in cardiovascular medicine, heart failure (HF) remains the leading cause of death in developed countries affecting at least 10 million people in Western Europe alone. The poor long-term prognosis of HF patients, and immense public health implications has fuelled interest in finding new therapeutic modalities. Recent observations of the beneficial effect of stem cells on the damaged heart in animal experiments have generated tremendous excitement and stimulated clinical studies suggesting that this approach is feasible, safe, and potentially effective in humans. Cell-based myocardial regeneration is currently explored for a wide range of cardiac disease states, including acute and chronic ischemic myocardial damage, cardiomyopathy and as biological heart pacemakers. The aim of the present manuscript is to review the work that has been done to establish the role of stem cells in cardiac repair, give an update on the clinical trials performed so far, as well as to discuss critically the controversies, challenges and future surrounding this novel therapeutic concept.

Stem cell therapy in acute myocardial infarction

Despite state-of-the-art therapy, clinical outcome remains poor in myocardial infarction (MI) patients with reduced left ventricular (LV) function with yearly mortality rates of approximately 15% and rehospitalization rates for heart failure or recurrent infarction within the first year exceeding 20%. Progenitor cell-mediated repair of the damaged heart is a promising new development in cardiovascular medicine. Progenitor cells residing in bone marrow and presumably also in the heart are capable of improving LV function in preclinical MI models but underlying mechanisms remain incompletely understood. Recent placebo-controlled, randomized bone marrow cell transfer trials in MI patients have shown augmented recovery of global LV function of variable magnitude. The observed changes were associated with a favourable effect on myocardial perfusion, with greater infarct size reduction, or with enhanced regional contraction in the infarct border zones. There is now growing consensus that these beneficial effects of bone marrow-derived progenitor cell transfer, as applied in post-MI patients thus far, occur independent of cardiomyocyte formation. At the same time, we have recognized that insufficient homing and survival of transplanted cells into the ischaemic milieu limits the full potential of cell-based cardiac repair. A better understanding of underlying molecular mechanisms of these critical steps in cell-based repair will, however, facilitate the development of improved clinical strategies to enhance functional recovery after myocardial infarction in the years to come.

Bringing cardiac cell therapy with bone marrow stem cells to the clinic: where are we now?

Stem cell therapy is emerging as a potential therapeutic option for cell death-related heart diseases. Preclinical as well as early-phase human studies have demonstrated the ability for cell therapy to augment perfusion and increase myocardial contractility. In addition, recent intermediate-size randomized trials suggested the potential of bone marrow stem cells to augment left ventricular recovery after a recent myocardial infarction. In general, the effects are modest and often similar despite differences in the study design, cell number or type. Therefore, a number of issues should be addressed before stem cell therapy will become standard clinical practice. They are related to the selection of the optimal cell type, standardization of the cell processing and release criteria. Other issues include timing of the cells injections and cell homing and retention. Further research is needed to understand the mechanisms underlying observed functional and beneficial effects including optimization of myocardial biological effects. Finally, despite overall enthusiasm, safety of the cardiac stem cell therapy should remain under scrutiny. The safety profile needs to be established in the large clinical trials and in a close interaction between translational and clinical research to address conceptual or procedural issues.

Three-, 6-, and 12-month results of autologous transplantation of mononuclear bone marrow cells in patients with acute myocardial infarction

BACKGROUND

There are only few data on long-term effectiveness of the stem cell therapy.

AIM

We studied the time course of global and regional left ventricular function in patients with acute myocardial infarction within 1 year after the autologous mononuclear bone marrow cell transplantation.

METHODS

Sixty patients with a first acute myocardial infarction, who had been randomized into 3 groups, completed a 12-month protocol. Two groups were intracoronarily given bone marrow cells in either higher (10(8) cells, HD group, n=20) or lower (10(7) cells, LD group, n=20) doses. Twenty patients without cell transplantation served as a control (C) group. Doppler tissue imaging and the gated technetium-99m sestamibi single photon emission computed tomography were performed before cell transplantation and at 3, 6, and 12 months later.

RESULTS

The baseline peak systolic velocities of longitudinal contraction of the infarcted wall (S(infarct)) of 5.2 cm/s, 4.6 cm/s, and 4.4 cm/s in C, LD, and HD groups increased by 0.0 cm/s, 0.3 cm/s (p=NS vs. C group), and by 0.7 cm/s (p<0.05 vs. C group), respectively, at 3 months. At 12 months, however, the corresponding changes from baseline values of 0.1 cm/s, 0.2 cm/s, and 0.6 cm/s did not differ significantly (all p=NS). In contrast, the post-transplant improvements in the left ventricular ejection fraction by 6%, 7%, and 7% at months 3, 6, and 12, respectively, were preserved in HD group patients during the whole 12-month follow-up and remained significantly better as compared to controls.

CONCLUSIONS

In our study, the autologous mononuclear bone marrow cell transplantation provided sustained improvement in global left ventricular systolic function in patients with acute myocardial infarction. However, when evaluating regional systolic function of the infarcted wall, the short-term benefit was partially lost during the 12-month follow-up.

The bone marrow--cardiac axis of myocardial regeneration

Congestive heart failure remains the leading cause of morbidity and mortality in the developed world. Current therapies do not address the underlying pathophysiology of this disease, namely, the progressive loss of functional cardiomyocytes. The notion of repairing or regenerating lost myocardium via cell-based therapies remains highly appealing. The recent identification of adult stem cells, including both cardiac stem/progenitor cells and bone marrow stem cells, has triggered an explosive interest in using these cells for physiologically relevant cardiomyogenesis. Enthusiasm for cardiac regeneration via cell therapy has further been fueled by the many encouraging reports in both animals and human studies. Further intensive research in basic science and clinical arenas are needed to make this next great frontier in cardiovascular regenerative medicine a reality. In this review, we focus on the role of bone marrow-derived stem cells and cardiac stem/progenitor cells in cardiomyocyte homeostasis and myocardial repair and regeneration, as well as provide a brief overview of current clinical trials using cell-based therapeutic approaches in patients with heart disease.

Xenotransplantation: current status and a perspective on the future

Xenotransplantation using pigs as the transplant source has the potential to resolve the severe shortage of human organ donors. Although the development of relatively non-toxic immunosuppressive or tolerance-inducing regimens will be required to justify clinical trials using pig organs, recent advances in our understanding of the biology of xenograft rejection and zoonotic infections, and the generation of alpha1,3-galactosyltransferase-deficient pigs have moved this approach closer to clinical application. This Review highlights the major obstacles impeding the translation of xenotransplantation into clinical therapies and the potential solutions, providing a perspective on the future of clinical xenotransplantation.

Potential risks of bone marrow cell transplantation into infarcted hearts

Cellular replacement therapy has emerged as a novel strategy for the treatment of heart failure. The aim of our study was to determine the fate of injected mesenchymal stem cells (MSCs) and whole bone marrow (BM) cells in the infarcted heart. MSCs were purified from BM of transgenic mice and characterized using flow cytometry and in vitro differentiation assays. Myocardial infarctions were generated in mice and different cell populations including transgenic MSCs, unfractionated BM cells, or purified hematopoietic progenitors were injected. Encapsulated structures were found in the infarcted areas of a large fraction of hearts after injecting MSCs (22 of 43, 51.2%) and unfractionated BM cells (6 of 46, 13.0%). These formations contained calcifications and/or ossifications. In contrast, no pathological abnormalities were found after injection of purified hematopoietic progenitors (0 of 5, 0.0%), fibroblasts (0 of 5, 0.0%), vehicle only (0 of 30, 0.0%), or cytokine-induced mobilization of BM cells (0 of 35, 0.0%). We conclude that the developmental fate of BM-derived cells is not restricted by the surrounding tissue after myocardial infarction and that the MSC fraction underlies the extended bone formation in the infarcted myocardium. These findings seriously question the biologic basis and clinical safety of using whole BM and in particular MSCs to treat nonhematopoietic disorders.

Therapeutic potential of adult progenitor cells in cardiovascular disease

Cardiovascular diseases are responsible for high morbidity/mortality rates worldwide. Advances in patient care have significantly reduced deaths from acute myocardial infarction. However, the cardiac remodeling processes induced after ischaemia are responsible for a worsening in the heart condition, which in many cases ends up in failure. In the last decade, a novel therapy based on stem cell transplantation is being intensively studied in animal models and some stem cell types (i.e., skeletal myoblasts and bone marrow-derived cells) are already being tested in clinical trials. A novel stem cell population isolated from the bone marrow, termed multipotent adult progenitor cells was characterised a few years ago by its ability to differentiate, at the single cell level, towards cells derived from the three embryonic germ layers. Later on, other pluripotent cell populations have been also derived from the bone marrow. In this overview, the authors outline different stem cell sources that have been tested for their cardiovascular potential and put the regenerative potential of multipotent adult progenitor cells in animal models of acute and chronic myocardial infarction into perspective.

Paracrine effects of direct intramyocardial implantation of bone marrow derived cells to enhance neovascularization in chronic ischaemic myocardium

OBJECTIVE

To determine the optimal bone marrow (BM) cell types, and their potential mechanisms of action for neovascularization in chronic ischaemic myocardium.

METHODS AND RESULTS

The functional effects, angiogenic potential and cytokine expression of direct intramyocardial implantation of autologous BM CD31-positive endothelial progenitor cells (EPC, n=9), BM mononuclear cells (MNCs, n=9), and saline (n=9) were compared in a swine model of chronic ischaemic myocardium. Autologous BM cells were harvested and catheter-based electromechanical mapping-guided direct intramyocardial injection was performed to target ischaemic myocardium. After 12 weeks, injection of BM-MNC resulted in significant improvements in left ventricular dP/dt (+21+/-8%, P=0.032), left ventricular pressure (+17+/-4%, P=0.048) and regional microsphere myocardial perfusion over ischaemic endocardium (+74+/-28%, P<0.05) and epicardium (+73+/-29%, P<0.05). No significant effects were observed following injection of BM-EPC or saline. Capillary density (1132+/-69 versus 903+/-44 per mm(2), P=0.047) and expression of mRNA of vascular endothelial growth factor (VEGF, 32.3+/-5.6 versus 13.1+/-3.7, P<0.05,) and angiopoietin-2 (23.9+/-3.6 versus 13.7+/-3.1, P<0.05) in ischaemic myocardium was significantly greater in the BM-MNC group than the saline group. The capillary density in ischaemic myocardium demonstrated a significant positive correlation with VEGF expression (r=0.61, P<0.001).

CONCLUSION

Catheter-based direct intramyocardial injection of BM-MNC enhanced angiogenesis more effectively than BM-EPC or saline, possibly via a paracrine effect, with increased expression of VEGF that subsequently improved cardiac performance of ischaemic myocardium.

Stem cells: a revolution in therapeutics-recent advances in stem cell biology and their therapeutic applications in regenerative medicine and cancer therapies

Basic and clinical research accomplished during the last few years on embryonic, fetal, amniotic, umbilical cord blood, and adult stem cells has constituted a revolution in regenerative medicine and cancer therapies by providing the possibility of generating multiple therapeutically useful cell types. These new cells could be used for treating numerous genetic and degenerative disorders. Among them, age-related functional defects, hematopoietic and immune system disorders, heart failures, chronic liver injuries, diabetes, Parkinson's and Alzheimer's diseases, arthritis, and muscular, skin, lung, eye, and digestive disorders as well as aggressive and recurrent cancers could be successfully treated by stem cell-based therapies. This review focuses on the recent advancements in adult stem cell biology in normal and pathological conditions. We describe how these results have improved our understanding on critical and unique functions of these rare sub-populations of multipotent and undifferentiated cells with an unlimited self-renewal capacity and high plasticity. Finally, we discuss some major advances to translate the experimental models on ex vivo and in vivo expanded and/or differentiated stem cells into clinical applications for the development of novel cellular therapies aimed at repairing genetically altered or damaged tissues/organs in humans. A particular emphasis is made on the therapeutic potential of different tissue-resident adult stem cell types and their in vivo modulation for treating and curing specific pathological disorders.

Stem Cell Therapy: A Hope for Dying Hearts

The restoration of functional myocardium following heart failure still remains a formidable challenge among researchers. Irreversible damage caused by myocardial infarction is followed by left ventricular remodeling. The current pharmacologic and interventional strategies fail to regenerate dead myocardium and are usually insufficient to meet the challenge caused by necrotic cardiac myocytes. There is growing evidence, suggesting that the heart has the ability to regenerate through the activation of resident cardiac stem cells or through the recruitment of a stem cell population from other tissues such as bone marrow. These new findings belie the earlier conception about the poor regenerating ability of myocardial tissue. Stem cell therapy is a promising new approach for myocardial repair. However, it has been limited by the paucity of cell sources for functional human cardiomyocytes. Moreover, cells isolated from different sources exhibit idiosyncratic characteristics including modes of isolation, ease of expansion in culture, proliferative ability, characteristic markers, etc., which are the basis for several technical manipulations to achieve successful engraftment. Clinical trials show some evidence for the successful integration of stem cells of extracardiac origin in adult human heart with an improved functional outcome. This may be attributed to the discrepancies in the methods of detection, study subject selection (early or late post transplantation), presence of inflammation, and false identification of infiltrating leukocytes. This review discusses these issues in a comprehensive manner so that their physiological significance in animal as well as in human studies can be better understood.

Biologic properties of endothelial progenitor cells and their potential for cell therapy

Recent studies indicate that portions of ischemic and tumor neovasculature are derived by neovasculogenesis, whereby bone marrow (BM)-derived circulating endothelial progenitor cells (EPCs) home to sites of regenerative or malignant growth and contribute to blood vessel formation. Recent data from animal models suggest that a variety of cell types, including unfractionated BM mononuclear cells and those obtained by ex vivo expansion of human peripheral blood or enriched progenitors, can function as EPCs to promote tissue vasculogenesis, regeneration, and repair when introduced in vivo. The promising preclinical results have led to several human clinical trials using BM as a potential source of EPCs in cardiac repair as well as ongoing basic research on using EPCs in tissue engineering or as cell therapy to target tumor growth.

Restoration of microvascular function in the infarct-related artery by intracoronary transplantation of bone marrow progenitor cells in patients with acute myocardial infarction: the Doppler Substudy of the Reinfusion of Enriched Progenitor Cells and Infarct Remodeling in Acute Myocardial Infarction (REPAIR-AMI) trial

BACKGROUND

The Doppler Substudy of the randomized, double-blind, placebo-controlled Reinfusion of Enriched Progenitor Cells and Infarct Remodeling in Acute Myocardial Infarction (REPAIR-AMI) trial aimed to investigate the effects of intracoronary infusion of bone marrow-derived progenitor cells (BMCs) on coronary blood flow regulation in patients with reperfused acute myocardial infarction.

METHODS AND RESULTS

In a total of 58 patients (BMC group, n=30; placebo group, n=28), coronary flow reserve (CFR) in the infarct artery and a reference vessel was assessed by intracoronary Doppler at the time of study therapy (4.2+/-0.1 days after acute myocardial infarction) and at the 4-month follow-up. Initial CFR was reduced in the infarct artery compared with the reference vessel in both groups (BMC: 2.0+/-0.1 versus 2.9+/-0.2, P<0.05; placebo: 1.9+/-0.1 versus 2.8+/-0.2; P<0.05). At the 4-month follow-up, CFR in the infarct artery had slightly improved in the placebo group (+0.88+/-0.18; P<0.001 versus initial) but was markedly increased by 90% (+1.80+/-0.25; P=0.005 versus placebo) in BMC-treated patients, resulting in a normalization of CFR (3.8+/-0.2; P<0.001 versus initial and placebo at 4 months). In the infarct vessel, adenosine-induced minimal vascular resistance index declined slightly in the placebo group (from 1.77+/-0.12 to 1.52+/-0.15 mm Hg x s/cm; P<0.05) but considerably decreased by -29+/-6% in the BMC group (from 1.86+/-0.19 to 1.20+/-0.12 mm Hg x s/cm; P<0.05 versus initial and placebo at 4 months).

CONCLUSIONS

Intracoronary BMC therapy after acute myocardial infarction restores microvascular function of the infarct-related artery, which is associated with a significant improvement in maximal vascular conductance capacity. These data provide clinical proof of concept that progenitor cell transplantation promotes vascular repair.

Peripheral infusion of rat bone marrow derived endothelial progenitor cells leads to homing in acute lung injury

BACKGROUND

Bone marrow-derived progenitors for both epithelial and endothelial cells have been observed in the lung. Besides mature endothelial cells (EC) that compose the adult vasculature, endothelial progenitor cells (EPC) are supposed to be released from the bone marrow into the peripheral blood after stimulation by distinct inflammatory injuries. Homing of ex vivo generated bone marrow-derived EPC into the injured lung has not been investigated so far. We therefore tested the hypothesis whether homing of EPC in damaged lung tissue occurs after intravenous administration.

METHODS

Ex vivo generated, characterized and cultivated rat bone marrow-derived EPC were investigated for proliferation and vasculogenic properties in vitro. EPC were tested for their homing in a left-sided rat lung transplant model mimicking a severe acute lung injury. EPC were transplanted into the host animal by peripheral administration into the femoral vein (10(6) cells). Rats were sacrificed 1, 4 or 9 days after lung transplantation and homing of EPC was evaluated by fluorescence microscopy. EPC were tested further for their involvement in vasculogenesis processes occurring in subcutaneously applied Matrigel in transplanted animals.

RESULTS

We demonstrate the integration of intravenously injected EPC into the tissue of the transplanted left lung suffering from acute lung injury. EPC were localized in vessel walls as well as in destructed lung tissue. Virtually no cells were found in the right lung or in other organs. However, few EPC were found in subcutaneous Matrigel in transplanted rats.

CONCLUSION

Transplanted EPC may play an important role in reestablishing the endothelial integrity in vessels after severe injury or at inflammatory sites and might further contribute to vascular repair or wound healing processes in severely damaged tissue. Therapeutic applications of EPC transplantation may ensue.

Cardiac tissue engineering: a clinical perspective

Engineered myocardium may be used to repair myocardial defects. Although not clinically applicable yet, initial studies in rodents have demonstrated the feasibility of tissue engineering based myocardial repair in vivo. In order for restorative treatment to evolve into a functional treatment modality, tissue engineers have to generate human myocardium of sufficient size and with relevant contractile function to replace/repair myocardial defects. This requires the identification of a scalable and ideally autologous cardiomyocyte source as well as the development of strategies to overcome size limitations. We will further address pivotal issues pertaining to the allocation of suitable human cells for myocardial tissue engineering and discuss the translation of present myocardial tissue engineering concepts into preclinical, as well as clinical, trials.