Transcatheter Transplantation of Autologous Skeletal Myoblasts in Postinfarction Patients With Severe Left Ventricular Dysfunction

Role of prostaglandin E2 in allogeneic mesenchymal stem cell therapy for cardiac repair

Ischemic heart disease is among the primary causes of cardiovascular-related deaths worldwide. Conventional treatments including surgical interventions and medical therapies aid in preventing further damage to heart muscle but are unable to provide a permanent solution. In recent years, stem cell therapy has emerged as an attractive alternative to restore damaged myocardium after myocardial injury. Allogeneic (donor-derived) mesenchymal stem cells (MSCs) have shown great promise in preclinical and clinical studies, making them the most widely accepted candidates for cardiac cell therapy. MSCs promote cardiac repair by modulating host immune system and secreting various soluble factors, of which prostaglandin E2 (PGE2) is an important one. PGE2 plays a significant role in regulating cardiac remodeling following myocardial injury. In this review, we provide an overview of allogeneic MSCs as candidates for myocardial regeneration with a focus on the role of the PGE2/cyclooxygenase-2 (COX2) pathway in mediating these effects.

Clinical Safety Profile of Transendocardial Catheter Injection Systems: A Plea for Uniform Reporting

OBJECTIVES

The aim of this study was to characterize the clinical safety profile of transendocardial injection catheters (TIC) reported in the published literature.

BACKGROUND

Transendocardial delivery is a minimally invasive approach to deliver potential therapeutic agents directly into the myocardium. The rate of adverse events across TIC is uncertain.

METHODS

A systematic search was performed for trial publications using TIC. Procedure-associated adverse event data were abstracted, pooled and compared across catheters for active treatment and placebo injected patients. The transendocardial injection associated serious adverse events (TEI-SAE) was defined as the composite of death, myocardial infarction, stroke or transient ischemic attack within 30 days and cardiac perforation causing death or requiring evacuation, serious intraprocedural arrhythmias and serious coronary artery or peripheral vascular complications.

RESULTS

The search identified 4 TIC systems: a helical needle (HN), an electro-anatomically tracked straight needle (EAM-SN), a straight needle without tracking elements (SN), and a curved needle (CN). Of 1799 patients who underwent transendocardial injections, the combined TEI-SAE was 3.4% across all catheters, and 1.1%, 3.3%, 7.1%, and 8.3% for HN, EAM-SN, SN and CN, respectively. However, TIC procedure duration and post procedural cardiac biomarker levels were reported in only 24% and 36% of published trials, respectively.

CONCLUSIONS

Transendocardial injection is associated with varied TEI-SAE but the data are very limited. The HN catheter appeared to be associated with lower TEI-SAE, versus other catheters. Procedure duration and post procedure cardiac biomarker levels were under-reported. Clearly, standardized, procedure-related event reporting for trials involving transcatheter delivery would improve our understanding of complications across different systems.

Stem Cells in Cardiovascular Medicine: Historical Overview and Future Prospects

Cardiovascular diseases remain the leading cause of death in the developed world, accounting for more than 30% of all deaths. In a large proportion of these patients, acute myocardial infarction is usually the first manifestation, which might further progress to heart failure. In addition, the human heart displays a low regenerative capacity, leading to a loss of cardiomyocytes and persistent tissue scaring, which entails a morbid pathologic sequela. Novel therapeutic approaches are urgently needed. Stem cells, such as induced pluripotent stem cells or embryonic stem cells, exhibit great potential for cell-replacement therapy and an excellent tool for disease modeling, as well as pharmaceutical screening of novel drugs and their cardiac side effects. This review article covers not only the origin of stem cells but tries to summarize their translational potential, as well as potential risks and clinical translation.

Safety, feasibility and effectiveness of first in-human administration of muscle-derived stem/progenitor cells modified with connexin-43 gene for treatment of advanced chronic heart failure

AIMS

To assess the safety and efficacy of transendocardial delivery of muscle-derived stem/progenitor cells with connexin-43 overexpression (Cx-43-MDS/PC) in advanced heart failure (HF).

METHODS AND RESULTS

Thirteen subjects with advanced HF, New York Heart Association (NYHA) class II-III were enrolled and treated with targeted injection of Cx-43-MDS/PCs and then monitored for at least 6 months. Overexpression of Cx43 (Cx43+) was significantly higher in all but one subject (Cx43-). Injection of MDS/PCs was associated with significant improvement of exercise capacity: NYHA (3 ± 0 vs. 1.8 ± 0.7, P = 0.003), exercise duration (388.69 ± 141.83 s vs. 462.08 ± 176.69 s, P = 0.025), peak oxygen consumption (14.38 ± 3.97 vs. 15.83 ± 3.74 ml/kg.min, P = 0.022) and oxygen pulse (10.58 ± 2.89 vs. 18.88 ± 22.63 mLO₂ /heart rate, P = 0.012). Levels of BNP, left ventricular (LV) ejection fraction and LV end-diastolic volumes tended to improve. There was a significant improvement of the mean unipolar voltage amplitudes measured for the injected segments and the entire left ventricle (9.62 ± 2.64 vs. 11.62 ± 3.50 mV, P = 0.014 and 8.83 ± 2.80 vs. 10.22 ± 3.41 mV, P = 0.041, respectively). No deaths were documented, Cx43+ (n = 12) subjects presented no significant ventricular arrhythmia; one Cx43- subject suffered from ventricular tachycardia (successfully treated with amiodarone).

CONCLUSIONS

Injection of Cx-43-MDS/PCs in patients with severe HF led to significant improvement in exercise capacity and myocardial viability of the injected segments while inducing no significant ventricular arrhythmia. This may arise from improved electrical coupling of the injected cells and injured myocardium and thus better in-situ mechanical cooperation of both cell types. Therefore, further clinical studies with Cx43+ MDS/PCs are warranted.

Effects of the intramyocardial implantation of stromal vascular fraction in patients with chronic ischemic cardiomyopathy

BACKGROUND

Stromal vascular fraction (SVF) can easily be obtained from a mini-lipoaspirate procedure of fat tissue. The SVF contains a mixture of cells including ADSCs and growth factors and has been depleted of the adipocyte (fat cell) population. We evaluated the safety and efficacy of administering SVF intra-myocardially into patients with chronic ischemic cardiomyopathy.

METHODS

A total of 28 patients underwent a local tumescent liposuction procedure to remove approximately 60 ml of fat tissue. The fat was separated to isolate the SVF and the cells were delivered into the akinetic myocardial scar region using a transendocardial delivery system (MyoCath(®)) in patients who had experienced a previous myocardial infarct. The subjects were then monitored for adverse events, ejection fraction via echocardiogram and six-minute walk test (6MWT) over a period of 6 months.

RESULTS

The average EF was 29 % at baseline and significantly increased to 35 % at both 3 and 6 months. Patients walked an average of 349 m at baseline and demonstrated a statistically significant improvement at 3 and 6 months' post treatment of more than 80 m.

CONCLUSIONS

Overall, patients were pleased with the treatment results. More importantly, the procedure demonstrated a strong safety profile with no severe adverse events or complications linked to the therapy. Trial registration NCT01502514 Name of registry: http://www.clinicaltrials.gov URL: https://www.clinicaltrials.gov/ct2/show/NCT01502514?term=adipose+cells+heart&rank=4 Date of registration: December 27, 2011 Date of enrollment: January 2012.

Correlation of the New York Heart Association Classification and the 6-Minute Walk Distance: A Systematic Review

BACKGROUND

Functional status assessment is the cornerstone of heart failure management and trials. The New York Heart Association (NYHA) classification and 6-minute walk distance (6MWD) are commonly used tools; however, the correlation between them is not well understood.

HYPOTHESIS

We hypothesised that the relationship between the NYHA classification and 6MWD might vary across studies.

METHODS

A systematic literature search was performed to identify all studies reporting both NYHA class and 6MWD. Two reviewers independently assessed study eligibility and extracted data. Thirty-seven studies involving 5678 patients were included.

RESULTS

There was significant heterogeneity across studies in 6MWD within all NYHA classes: I (n = 16, Q = 934.2; P < 0.001), II (n = 25, Q = 1658.3; P < 0.001), III (n = 30, Q = 1020.1; P < 0.001), and IV (n = 6, Q = 335.5; P < 0.001). There was no significant difference in average 6MWD between NYHA I and II (420 m vs 393 m; P = 0.416). There was a significant difference in average 6MWD between NYHA II and III (393 m vs 321 m; P = 0.014) and III and IV (321 m vs 224 m; P = 0.027). This remained significant after adjusting for region of study, age, and sex.

CONCLUSIONS

Although there is an inverse correlation between NYHA II-IV and 6MWD, there is significant heterogeneity across studies in 6MWD within each NYHA class and overlap in 6MWD between NYHA I and II. The NYHA classification performs well in more symptomatic patients (NYHA III/IV) but less so in asymptomatic/mildly symptomatic patients (NYHA I/II). Nonetheless, the NYHA classification is an easily applied first-line tool in everyday clinical practice, but its potential subjectivity should be considered when performing comparisons across studies.

Drug and cell delivery for cardiac regeneration

The spectrum of ischaemic cardiomyopathy, encompassing acute myocardial infarction to congestive heart failure is a significant clinical issue in the modern era. This group of diseases is an enormous source of morbidity and mortality and underlies significant healthcare costs worldwide. Cardiac regenerative therapy, whereby pro-regenerative cells, drugs or growth factors are administered to damaged and ischaemic myocardium has demonstrated significant potential, especially preclinically. While some of these strategies have demonstrated a measure of success in clinical trials, tangible clinical translation has been slow. To date, the majority of clinical studies and a significant number of preclinical studies have utilised relatively simple delivery methods for regenerative therapeutics, such as simple systemic administration or local injection in saline carrier vehicles. Here, we review cardiac regenerative strategies with a particular focus on advanced delivery concepts as a potential means to enhance treatment efficacy and tolerability and ultimately, clinical translation. These include (i) delivery of therapeutic agents in biomaterial carriers, (ii) nanoparticulate encapsulation, (iii) multimodal therapeutic strategies and (iv) localised, minimally invasive delivery via percutaneous transcatheter systems.

Tracking of stem cells in vivo for cardiovascular applications

In the past ten years, the concept of injecting stem and progenitor cells to assist with rebuilding damaged blood vessels and myocardial tissue after injury in the heart and peripheral vasculature has moved from bench to bedside. Non-invasive imaging can not only provide a means to assess cardiac repair and, thereby, cellular therapy efficacy but also a means to confirm cell delivery and engraftment after administration. In this first of a two-part review, we will review the different types of cellular labeling techniques and the application of these techniques in cardiovascular magnetic resonance and ultrasound. In addition, we provide a synopsis of the cardiac cellular clinical trials that have been performed to-date.

Optimized delivery system achieves enhanced endomyocardial stem cell retention

BACKGROUND

Regenerative cell-based therapies are associated with limited myocardial retention of delivered stem cells. The objective of this study is to develop an endocardial delivery system for enhanced cell retention.

METHODS AND RESULTS

Stem cell retention was simulated in silico using 1- and 3-dimensional models of tissue distortion and compliance associated with delivery. Needle designs, predicted to be optimal, were accordingly engineered using nitinol, a nickel and titanium alloy displaying shape memory and superelasticity. Biocompatibility was tested with human mesenchymal stem cells. Experimental validation was performed with species-matched cells directly delivered into Langendorff-perfused porcine hearts or administered percutaneously into the endocardium of infarcted pigs. Cell retention was quantified by flow cytometry and real-time quantitative polymerase chain reaction methodology. Models, computing optimal distribution of distortion calibrated to favor tissue compliance, predicted that a 75°-curved needle featuring small-to-large graded side holes would ensure the highest cell retention profile. In isolated hearts, the nitinol curved needle catheter (C-Cath) design ensured 3-fold superior stem cell retention compared with a standard needle. In the setting of chronic infarction, percutaneous delivery of stem cells with C-Cath yielded a 37.7±7.1% versus 10.0±2.8% retention achieved with a traditional needle without effect on biocompatibility or safety.

CONCLUSIONS

Modeling-guided development of a nitinol-based curved needle delivery system with incremental side holes achieved enhanced myocardial stem cell retention.

Cell therapy for heart failure: a comprehensive overview of experimental and clinical studies, current challenges, and future directions

Despite significant therapeutic advances, the prognosis of patients with heart failure (HF) remains poor, and current therapeutic approaches are palliative in the sense that they do not address the underlying problem of the loss of cardiac tissue. Stem cell-based therapies have the potential to fundamentally transform the treatment of HF by achieving what would have been unthinkable only a few years ago-myocardial regeneration. For the first time since cardiac transplantation, a therapy is being developed to eliminate the underlying cause of HF, not just to achieve damage control. Since the initial report of cell therapy (skeletal myoblasts) in HF in 1998, research has proceeded at lightning speed, and numerous preclinical and clinical studies have been performed that support the ability of various stem cell populations to improve cardiac function and reduce infarct size in both ischemic and nonischemic cardiomyopathy. Nevertheless, we are still at the dawn of this therapeutic revolution. Many important issues (eg, mechanism(s) of action of stem cells, long-term engraftment, optimal cell type(s), and dose, route, and frequency of cell administration) remain to be resolved, and no cell therapy has been conclusively shown to be effective. The purpose of this article is to critically review the large body of work performed with respect to the use of stem/progenitor cells in HF, both at the experimental and clinical levels, and to discuss current controversies, unresolved issues, challenges, and future directions. The review focuses specifically on chronic HF; other settings (eg, acute myocardial infarction, refractory angina) are not discussed.

Periprocedural adverse events in cell therapy trials in myocardial infarction and cardiomyopathy: a systematic review

BACKGROUND

Cell therapy (CTh) is a promising novel therapy for myocardial infarction (MI) and ischemic cardiomyopathy (iCMP). Recognizing adverse events (AE) is important for safety evaluation, harm prevention and may aid in the design of future trials.

OBJECTIVE

To define the prevalence of periprocedural AE in CTh trials in MI and iCMP.

METHODS

A literature search was conducted using the MEDLINE database from January 1990 to October 2010. Controlled clinical trials that compared CTh with standard treatment in the setting of MI and/or iCMP were selected. AE related to CTh were analyzed.

RESULTS

A total of 2,472 patients from 35 trials were included. There were 26 trials including 1,796 patients that used CTh in MI and 9 trials including 676 patients that used CTh in iCMP. Periprocedural arrhythmia monitoring protocols were heterogeneous and follow-up was short in most of the trials. In MI trials, the incidence of periprocedural adverse events (AE) related to intracoronary cell transplantation was 7.5 % (95 % CI 6.04-8.96 %). AE related to granulocyte colony-stimulating factor (GCS-F) used for cell mobilization for peripheral apheresis was 16 % (95 % CI 9.44-22.56 %). During intracoronary transplantation in iCMP, the incidence of periprocedural AE incidence was 2.6 % (95 % CI 0.53-4.67 %). There were no AE reported during transepicardial transplantation and AE were rare during transendocardial transplantation.

CONCLUSIONS

The majority of periprocedural AE in CTh trials in MI occurred during intracoronary transplantation and GCS-F administration. In iCMP, periprocedural AE were uncommon. Avoiding intracoronary route for CTh implantation may decrease the burden of periprocedural AE. Standardization of AE definition in CTh trials is needed.

Emerging roles for integrated imaging modalities in cardiovascular cell-based therapeutics: a clinical perspective

Despite preclinical promise, the progress of cell-based therapy to clinical cardiovascular practice has been slowed by several challenges and uncertainties that have been highlighted by the conflicting results of human trials. Most telling has been the revelation that current strategies fall short of achieving sufficient retention and engraftment of cells to meet the ambitious objective of myocardial regeneration. This has sparked novel research into the refinement of cell biology and delivery to overcome these shortcomings. Within this context, molecular imaging has emerged as a valuable tool for providing noninvasive surveillance of cell fate in vivo. Direct and indirect labelling of cells can be coupled with clinically relevant imaging modalities, such as radionuclide single photon emission computed tomography and positron emission tomography, and magnetic resonance imaging, to assess their short- and long-term distributions, along with their viability, proliferation and functional interaction with the host myocardium. This review details the strengths and limitations of the different cell labelling and imaging techniques and their potential application to the clinical realm. We also consider the broader, multifaceted utility of imaging throughout the cell therapy process, providing a discussion of its considerable value during cell delivery and its importance during the evaluation of cardiac outcomes in clinical studies.

Tracking stem cells for cardiovascular applications in vivo: focus on imaging techniques

Despite rapid translation of stem cell therapy into clinical practice, the treatment of cardiovascular disease using embryonic stem cells, adult stem and progenitor cells or induced pluripotent stem cells has not yielded satisfactory results to date. Noninvasive stem cell imaging techniques could provide greater insight into not only the therapeutic benefit, but also the fundamental mechanisms underlying stem cell fate, migration, survival and engraftment in vivo. This information could also assist in the appropriate choice of stem cell type(s), delivery routes and dosing regimes in clinical cardiovascular stem cell trials. Multiple imaging modalities, such as MRI, PET, SPECT and CT, have emerged, offering the ability to localize, monitor and track stem cells in vivo. This article discusses stem cell labeling approaches and highlights the latest cardiac stem cell imaging techniques that may help clinicians, research scientists or other healthcare professionals select the best cellular therapeutics for cardiovascular disease management.

Cellular cardiomyoplasty and cardiac regeneration

Despite of vast improvements in treatment, myocardial infarction often leads to heart failure (HF) which remains the leading cause of death in developed countries. Other than heart transplantation, therapeutic options have a limited role in improving out comes in patients with severe HF. It is therefore no surprise that cardiac cell therapy has raised many hopes as a novel therapeutic approach aimed at cardiac myocyte replacement/regeneration termed "cellular cardiomyoplasty". However, the ideal source, cell type, critical cell number, and mode of application for optimal therapeutic effect have not been defined thus far. Recent observations of the beneficial effect of cell transplantation 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 being explored for a wide range of cardiac disease states, including acute and chronic ischemic myocardial damage, cardiomyopathy and as biological heart pacemakers. The main purpose of this article is to review recent literature on the use of various cells for the examination of their in vitro cardiogenic potential and their in vivo capacity to engraft and improve the functional properties of the infarcted heart.

The use of stem cells for the repair of cardiac tissue in ischemic heart disease

Ischemic heart diseases are the leading cause of death in the Western world. With increasing numbers of patients surviving their acute myocardial infarction owing to effective heart catheter techniques and intensive care treatment, congestive heart failure has become an increasing health concern. With therapeutic options for the prevention and treatment of ischemic heart disease being limited at present, huge efforts have been made in the field of stem cell research to try to establish new approaches for myocardial tissue regeneration. Owing to their pronounced differentiation potential, pluripotent stem cells seem to represent the most promising cell source for future engineering of myocardial replacement tissue. However, several crucial hurdles regarding cell yield and purity of the cultured cardiovascular progenitor cells have still not been overcome to facilitate a clinical application today. By contrast, plenty of adult stem and progenitor cells have already been well characterized and investigated in human disease. However, all of these heterogeneous cell lines primarily seem to work in a paracrine manner on ischemic myocardial tissue, rather than transdifferentiating into contractile cardiomyocytes. This article will focus on the production, application and present limitations of stem cells potentially applicable for myocardial repair.

Final results of a phase IIa, randomised, open-label trial to evaluate the percutaneous intramyocardial transplantation of autologous skeletal myoblasts in congestive heart failure patients: the SEISMIC trial

AIMS

The SEISMIC study was an open-label, prospective, randomised study to assess the safety and feasibility of percutaneous myoblast implantation in heart failure patients with implanted cardioverter-defibrillators (ICD).

METHODS AND RESULTS

Patients were randomised 2:1 to autologous skeletal myoblast therapy vs. optimal medical treatment. The primary safety end-point was defined as the incidence of procedural and device related serious adverse events, whereas the efficacy endpoints were defined as the change in global LVEF by MUGA scan, change in NYHA classification of heart failure and in the distance achieved during a six-minute walk test (6MW) at 6-month follow-up. Forty subjects were randomised to the treatment arm (n=26), or to the control arm (n=14). There were 12 sustained arrhythmic events and one death after episodes of ventricular tachycardia (VT) in the treatment group and 14 events in the control group (P=ns). At 6-month follow-up, 6MW distance improved by 60.3±54.1?meters in the treated group as compared to no improvement in the control group (0.4±185.7?meters; P=ns). In the control group, 28.6% experienced worsening of heart failure status (4/14), while 14.3% experienced an improvement in NYHA classification (2/14). In the myoblast-treatment arm, one patient experienced a deterioration in NYHA classification (8.0%), whereas five patients improved one or two classes (20.0%; P=0.06). However, therapy did not improve global LVEF measured by MUGA at 6-month follow-up.

CONCLUSIONS

These data indicate that implantation of myoblasts in patients with HF is feasible, appears to be safe and may provide symptomatic relief, though no significant effect was detected on global LVEF.

Cell therapy for heart failure: the need for a new therapeutic strategy

Improvements in the treatment of ischemic heart disease have led to a significant growth in the numbers of patients with systolic heart failure secondary to myocardial injury. Current therapies fail to address the loss of contractile tissue due to myocardial injury. Cell therapy is singular in its promise of primarily treating this underlying issue through salvage of viable myocardium or generation of new contractile tissue. Multiple cell types have been used to target acute myocardial infarction, chronic ischemic heart disease and heart failure due to infarction. Bone marrow mononuclear cells have been used to increase myocardial salvage after acute infarction. Randomized trials of over 800 patients have demonstrated no safety issues, and meta-analyses have suggested an improvement in left ventricular function in treated patients with trends toward improvements in hard cardiac end points. Cell therapy for chronic ischemic heart disease with bone marrow angiogenic progenitors has shown similar safety and trends toward improvement in function. While these therapies have targeted patients with viable myocardium, myoblasts have been used to treat patients with left ventricular dysfunction secondary to transmural infarction. Cell types with cardiomyogenic potential, including induced pluripotent stem cells and cardiac progenitor cells, offer the promise of true myocardial regeneration. Future studies with these cells may open the door for true myocardial regeneration.

Skeletal myoblasts for cardiac repair

Stem cells provide an alternative curative intervention for the infarcted heart by compensating for the cardiomyocyte loss subsequent to myocardial injury. The presence of resident stem and progenitor cell populations in the heart, and nuclear reprogramming of somatic cells with genetic induction of pluripotency markers are the emerging new developments in stem cell-based regenerative medicine. However, until safety and feasibility of these cells are established by extensive experimentation in in vitro and in vivo experimental models, skeletal muscle-derived myoblasts, and bone marrow cells remain the most well-studied donor cell types for myocardial regeneration and repair. This article provides a critical review of skeletal myoblasts as donor cells for transplantation in the light of published experimental and clinical data, and indepth discussion of the advantages and disadvantages of skeletal myoblast-based therapeutic intervention for augmentation of myocardial function in the infarcted heart. Furthermore, strategies to overcome the problems of arrhythmogenicity and failure of the transplanted skeletal myoblasts to integrate with the host cardiomyocytes are discussed.

Review: The New Concept of ‘‘Interventional Heart Failure Therapy’’: Part 2—Inotropes, Valvular Disease, Pumps, and Transplantation

Recent advances in heart failure therapy include a variety of mechanical and device-based technologies that target structural aspects of heart failure that cannot be treated with drug therapy alone; these newer therapies can collectively be described as interventional heart failure therapy. This article is the second in a 2-part series reviewing interventional heart failure therapy. Interventions included in this discussion include those indicated for the treatment of end-stage refractory heart failure, including interventional medical therapy, interventional treatment of valvular disease, mechanical assist devices, and heart transplantation. Also included is a review of the currently available catheter-based pumps, which are intended to provide temporary support in patients with acute hemodynamic compromise. The use of cellular or stem cell therapy for the treatment of heart failure is an emerging interventional therapy and data supporting its use for the treatment heart failure will also be presented, as will a discussion of the role of palliative care and self-care in heart failure therapy.

Stem cell therapy for heart failure

Heart failure (HF) is a chronic disease and a significant global public health concern. Current medical treatment for HF can reduce symptoms but does little to decrease mortality and the need for cardiac transplantation. Novel therapies are needed to further decrease mortality and limit or eliminate the need for cardiac transplantation. Recently, several basic science and clinical trials have suggested that enhancing endogenous regeneration (repair) and exogenous cell therapy might be an approach to improve the function of the failing heart. This article reviews cell therapy clinical trials in patients with chronic HF. The three major subgroups of cells being studied in phase 1 and beginning phase 2 trials are skeletal myoblasts, bone marrow-derived mononuclear cells, and enriched subpopulations of bone marrow and cardiac stem cells. Techniques for stimulating upregulation of endogenous bone marrow progenitor cells in the circulating blood have raised serious safety issues and need to be carefully evaluated. Intracoronary infusion and both transepicardial and transendocardial direct injection of stem cells have been tested clinically and shown to be safe. Skeletal myoblast implantation has led to improved cardiac function, but studies show formation of skeletal muscle in the heart and a lack of electrical integration with surrounding myocardium, a cause for concern. Bone marrow-derived mononuclear cells and enriched subpopulations of cardiac and bone marrow stem cells have been studied extensively in animals and in recent clinical trials, with both controversy and success. There is still much room for improvement, but animal and human studies of enriched subpopulations of cardiac and bone marrow stem cells have shown that these cells are safe, have significant capability for cardiac repair, and offer the best chance for legitimate medical therapy for patients with chronic HF.

Cardiac repair and regeneration: the Rubik's cube of cell therapy for heart disease

Acute ischemic injury and chronic cardiomyopathies damage healthy heart tissue. Dead cells are gradually replaced by a fibrotic scar, which disrupts the normal electromechanical continuum of the ventricular muscle and compromises its pumping capacity. Recent studies in animal models of ischemic cardiomyopathy suggest that transplantation of various stem cell preparations can improve heart recovery after injury. The first clinical trials in patients produced some encouraging results, showing modest benefits. Most of the positive effects are probably because of a favorable paracrine influence of stem cells on the disease microenvironment. Stem cell therapy attenuates inflammation, reduces apoptosis of surrounding cells, induces angiogenesis, and lessens the extent of fibrosis. However, little new heart tissue is formed. The current challenge is to find ways to improve the engraftment, long-term survival and appropriate differentiation of transplanted stem cells within the cardiovascular tissue. Hence, there has been a surge of interest in pluripotent stem cells with robust cardiogenic potential, as well as in the inherent repair and regenerative mechanisms of the heart. Recent discoveries on the biology of adult stem cells could have relevance for cardiac regeneration. Here, we discuss current developments in the field of cardiac repair and regeneration, and present our ideas about the future of stem cell therapy.

Role of nuclear imaging in regenerative cardiology

Advances in noninvasive imaging techniques may aid in the understanding of cardiac stem cell therapy. Nuclear imaging enables in vivo evaluation of myocardial perfusion, metabolism, and function, in addition to the stem cell fate. This article summarizes recent clinical and experimental nuclear imaging studies in cardiac stem cell therapy.

Cell-based therapy for heart disease: a clinically oriented perspective

Over the past decade, cell therapy has emerged as a potential new treatment of a variety of cardiac diseases, including acute myocardial infarction, refractory angina, and chronic heart failure. A myriad of cell types have been tested experimentally, each of them being usually credited by its advocates of a high "regeneration" potential. This has led to a flurry of clinical trials entailing the use of skeletal myoblasts or bone marrow-derived cells either unfractionated or enriched in progenitor subpopulations. As often in medicine, the hype generated by the early uncontrolled and small-sized studies has been dampened by the marginally successful outcomes of the subsequent, more rigorously conducted randomized trials. Although they may have failed to achieve their primary end points, these trials have been positive in the sense that they have allowed to identify some key issues and it is reasonable to speculate that if these issues can now be addressed by appropriately focused benchwork, the outcomes of the second generation of cell-transplantation studies would likely be upgraded. It, thus, appears that not "one cell fits all" but that the selection of the cell type should be tailored to the primary clinical indication. On the one hand, it does not make sense to develop an "ideal" cell in a culture dish, if we remain unable to deliver it appropriately and to keep it alive, at least for a while, which requires to improve on the delivery techniques and to provide cells along with the vascular and extracellular matrix type of support necessary for their survival and patterning. On the other hand, the persisting mechanistic uncertainties about cell therapy should not preclude continuing clinical trials, which often provide the unique opportunity of identifying issues missed by our suboptimal preclinical models. Finally, regardless of whether cells are expected to act paracrinally or by physically replacing lost cardiomyocytes and, thus, effecting a true myocardial regeneration, safety remains a primary concern. It is, thus, important that clinical development programs be shaped in a way that allows the final cell-therapy product to be manufactured from fully traceable materials, phenotypically well characterized, consistent, scalable, sterile, and genetically stable as these characteristics are those that will be required by the ultimate gatekeeper, i.e., the regulator, and are thus unbypassable prerequisites for an effective and streamlined leap from bench to bedside.

Isolation of a slowly adhering cell fraction containing stem cells from murine skeletal muscle by the preplate technique

This protocol details a procedure, known as the modified preplate technique, which is currently used in our laboratory to isolate muscle cells on the basis of selective adhesion to collagen-coated tissue culture plates. By employing this technique to murine skeletal muscle, we have been able to isolate a rapidly adhering cell (RAC) fraction within the earlier stages of the process, whereas a slowly adhering cell (SAC) fraction containing muscle-derived stem cells is obtained from the later stages of the process. This protocol outlines the methods and materials needed to isolate RAC and SAC populations from murine skeletal muscle. The procedure involves mechanical and enzymatic digestion of skeletal muscle tissue with collagenase XI, dispase and trypsin followed by plating the resultant muscle slurry on collagen type I-coated flasks where the cells adhere at different rates. The entire preplate technique requires 5 d to obtain the final preplate SAC population. Two to three additional days are usually required before this population is properly established. We also detail additional methodologies designed to further enrich the resultant cell population by continuing the modified preplating process on the SAC population. This process is known as replating and requires further time.

Adult stem cells and their trans-differentiation potential--perspectives and therapeutic applications

Stem cells are self-renewing multipotent progenitors with the broadest developmental potential in a given tissue at a given time. Normal stem cells in the adult organism are responsible for renewal and repair of aged or damaged tissue. Adult stem cells are present in virtually all tissues and during most stages of development. In this review, we introduce the reader to the basic information about the field. We describe selected stem cell isolation techniques and stem cell markers for various stem cell populations. These include makers for endothelial progenitor cells (CD146/MCAM/MUC18/S-endo-1, CD34, CD133/prominin, Tie-2, Flk1/KD/VEGFR2), hematopoietic stem cells (CD34, CD117/c-Kit, Sca1), mesenchymal stem cells (CD146/MCAM/MUC18/S-endo-1, STRO-1, Thy-1), neural stem cells (CD133/prominin, nestin, NCAM), mammary stem cells (CD24, CD29, Sca1), and intestinal stem cells (NCAM, CD34, Thy-1, CD117/c-Kit, Flt-3). Separate section provides a concise summary of recent clinical trials involving stem cells directed towards improvement of a damaged myocardium. In the last part of the review, we reflect on the field and on future developments.

Current status and future prospects for cell transplantation to prevent congestive heart failure

Although most cardiac cell therapy trials have focused on patients with acute myocardial infarction, attempts at "regenerating" chronically failing hearts have also been performed. These studies have entailed use of skeletal myoblasts and bone marrow-derived cells. In the case of skeletal myoblasts, the randomized placebo-controlled myoblast autologous grafting in ischemic cardiomyopathy (MAGIC) trial has failed to show that myoblast injections increased ejection fraction beyond that seen in controls but the finding that the highest dose of myoblasts resulted in a significant antiremodeling effect compared with the placebo group provides an encouraging signal. In the case of bone marrow cells, surgical injections of the mononuclear fraction combined with coronary artery bypass surgery have not shown a substantial benefit but positive results have been reported with intraoperative epicardial injections of CD133(+) progenitors. There are three possible reasons for these mixed results. The first is the marked heterogeneity of cell functionality (particularly in the case of bone marrow), which would expectedly translate into variable clinical outcomes. The second reason is the low rate of sustained engraftment. The third possible explanation is a mismatch between the choice of end points and the presumed mechanism of action of the cells. The initial assumption that adult stem cells could effect myocardial tissue regeneration has led to usual focus on ejection fraction as the major surrogate endpoint. It is now increasingly recognized that adult stem cells, in contrast to their embryonic counterparts, have little if any regenerative capacity and that their presumed beneficial effects more likely involve paracrine signaling, in which case infarct size, perfusion, or left ventricular volumes might be more appropriate markers. Altogether, these observations provide a framework for future research, the results of which will then have to be integrated in the protocol design of second-generation clinical trials.

Drawbacks to stem cell therapy in cardiovascular diseases

Stem cells seem to have unlimited potential for repairing injured tissues derived from cardiovascular diseases. Much as the initial euphoria over preclinical models has ushered in some skepticism, several reports have advised caution against over exuberance, as cellular therapy has both theoretical and reported safety concerns. Embryonic stem cells, skeletal myoblasts, bone marrow-derived stem cells and mesenchymal stem cells are current candidates for cell therapy in end-stage cardiovascular diseases. However, before large-scale clinical trials can take place, a few safety concerns have to be clarified, such as atherogenesis, postangioplasty or stenting restenosis, tumorigenesis, stem cell metastasis, stem cell-mobilized cytokine-related complications and arrhythmogenesis. In this review, potential ways to overcome these issues are discussed, including medical and gene manipulations, dedicated cell-purification techniques, antiarrhythmic cell therapy design, and new concepts such as using natural constructs. With these safety issues under control, stem cell therapy still has a promising future in the next decade.

Cellular replacement therapy for arrhythmia treatment: early clinical experience

Clinical and experimental studies have demonstrated the proarrhythmic potential of skeletal myoblast transplantation for repair of infarcted myocardium. The evidence on proarrhythmia following bone marrow-derived stem cells, and particular msenchymal stem cells, transplantation is inconclusive. There are experimental and preliminary clinical data supporting the possibility that mesenchymal stem cell transplantation might exert an anti-arrhythmic action by intervening with myocardial scar remodeling. However, clinical experience is limited.

The Myoblast Autologous Grafting in Ischemic Cardiomyopathy (MAGIC) Trial

Background— Phase I clinical studies have demonstrated the feasibility of implanting autologous skeletal myoblasts in postinfarction scars. However, they have failed to determine whether this procedure was functionally effective and arrhythmogenic.

Methods and Results— This multicenter, randomized, placebo-controlled, double-blind study included patients with left ventricular (LV) dysfunction (ejection fraction ≤35%), myocardial infarction, and indication for coronary surgery. Each patient received either cells grown from a skeletal muscle biopsy or a placebo solution injected in and around the scar. All patients received an implantable cardioverter-defibrillator. The primary efficacy end points were the 6-month changes in global and regional LV function assessed by echocardiography. The safety end points comprised a composite index of major cardiac adverse events and ventricular arrhythmias. Ninety-seven patients received myoblasts (400 or 800 million; n=33 and n=34, respectively) or the placebo (n=30). Myoblast transfer did not improve regional or global LV function beyond that seen in control patients. The absolute change in ejection fraction (median [interquartile range]) between 6 months and baseline was 4.4% (0.2; 7.3), 3.4% (−0.3; 12.4), and 5.2% (−4.4; 11.0) in the placebo, low-dose, and high-dose groups, respectively ( P =0.95). However, the high-dose cell group demonstrated a significant decrease in LV volumes compared with the placebo group. Despite a higher number of arrhythmic events in the myoblast-treated patients, the 6-month rates of major cardiac adverse events and of ventricular arrhythmias did not differ significantly between the pooled treatment and placebo groups.

Conclusions— Myoblast injections combined with coronary surgery in patients with depressed LV function failed to improve echocardiographic heart function. The increased number of early postoperative arrhythmic events after myoblast transplantation, as well as the capability of high-dose injections to revert LV remodeling, warrants further investigation.

Cell therapy for left ventricular remodeling

The increasing longevity of patients with heart failure (HF) and the rise in the incidence of HF has created an urgent need to effectively treat and prevent left ventricular remodeling. Within the past 6 years, skeletal myoblast and bone marrow mononuclear cell transplantation have been undertaken in over 200 patients with HF, geared to the underlying injury, not just its mechanisms. Early safety/feasibility studies showed promising but somewhat conflicting secondary symptomatic and functional improvements, and safety concerns have arisen. However, the patient population, cell type, dose, time, mode of delivery, and outcome measures differed-making comparisons problematic. It is now time to: 1) create a central registry of all patients treated with cells; 2) perform side-by-side comparisons of different types of cells in patients with similar HF states; 3) agree on standardized trial designs; and 4) define acceptable and unacceptable outcomes (and measures) compared with both standard of care and to other emerging therapies. By doing so, we can avoid the pitfalls that previous biologics (eg, angiogenic gene therapy) have suffered, increase the likelihood of success, shorten the time-to-presentation of cell-based algorithms to clinicians, and deliver these therapies to patients who await new ways of reduction of symptoms and improvement of quality of life.

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.

[Cellular therapy in cardiology]

Cardiac cell therapy has been initially designed to regenerate the infarcted myocardium through its repopulation by new cells able to restore function of scar areas. Six years after the first human application of this novel approach, it is timely appropriate to review the results of the first randomised trials in the three major indications, i.e., acute myocardial infarction, heart failure, and refractory angina. It should be recognized that the results are mixed, with benefits ranging from absent to transient and, at most, marginal. However, lessons drawn from this first wave of clinical series and the experimental data that have been concomitantly collected are multiple and highly informative. They indicate that adult stem cells, whether muscular or bone marrow-derived, fail to generate new cardiomyocytes. They suggest that the potential benefits of cardiac cell therapy are thus mediated by alternate mechanisms such as limitation of left ventricular remodelling or paracrine activation of signalling pathways involved in angiogenesis. They highlight the fact that the therapeutic benefits of grafted cells will not be fully exploited until issues of cell transfer and postengraftment survival have not been adequately addressed. These observations thus allow us to better fine-tune upcoming research, which should specifically concentrate on the development of cells featuring a true regeneration potential. In this setting, the greatest promises are currently held by embryonic stem cells.

Comparison of intracardiac cell transplantation: autologous skeletal myoblasts versus bone marrow cells

An increasing number of patients living with cardiovascular disease (CVD) and still unacceptably high mortality created an urgent need to effectively treat and prevent disease-related events. Within the past 5 years, skeletal myoblasts (SKMBs) and bone marrow (or blood)-derived mononuclear cells (BMNCs) have demonstrated preclinical efficacy in reducing ischemia and salvaging already injured myocardium, and in preventing left ventricular (LV) remodeling, respectively. These findings have been translated into clinical trials, so far totaling over 200 patients for SKMBs and over 800 patients for BMNCs. These safety/feasibility and early phase II studies showed promising but somewhat conflicting symptomatic and functional improvements, and some safety concerns have arisen. However, the patient population, cell type, dose, time and mode of delivery, and outcome measures differed, making comparisons problematic. In addition, the mechanisms through which cells engraft and deliver their beneficial effects remain to be fully elucidated. It is now time to critically evaluate progress made and challenges encountered in order to select not only the most suitable cells for cardiac repair but also to define appropriate patient populations and outcome measures. Reiterations between bench and bedside will increase the likelihood of cell therapy success, reduce the time to development of combined of drug- and cell-based disease management algorithms, and offer these therapies to patients to achieve a greater reduction of symptoms and allow for a sustained improvement of quality of life.

Present and future of stem cells for cardiovascular therapy

In this review we summarize the available evidence regarding the application of stem cell therapy for human cardiovascular repair, going over the principal concepts that will help us understand the present and future of this therapy: first the different types of cells available in clinical practice, second the delivery approaches, and third highlighting the most important clinical studies and their efficacy and safety results. In addition, we also speculate on the value of current clinical data to gain an insight into the mechanism of stem cell-based cardiac repair and to design clinical trials in the future.

Postinfarction heart failure: surgical and trans-coronary-venous transplantation of autologous myoblasts

Increasing experimental evidence indicates that skeletal myoblasts can be considered as a possible source of cells for regeneration of contractile performance in chronic postinfarction myocardial injury. In experimental models, the observed functional benefit of transplanting skeletal myoblasts into an area of chronic fibrotic myocardial scar has led to the development of clinical trials to evaluate the potential use of autologous skeletal myoblasts for myocardial regeneration in patients with postinfarction heart failure. We conducted an independent, phase I clinical trial to evaluate myoblast transplantation during coronary artery bypass grafting. In addition, to test whether the effect of transplanted cells on myocardial contractility was independent of revascularization, we performed a clinical study of percutaneous transvenous myoblast transplantation-the POZNAN trial. These trials have shown the feasibility of myoblast transplantation during cardiac surgery and via a percutaneous route, as well as the safety of both procedures when performed with concurrent prophylactic administration of amiodarone. Here, we review the details of our observations from both of these phase I clinical trials in the context of the clinical work in cardiovascular cell transplantation performed by others.