Autologous Myoblast Transplantation Research Articles

Our journey with François Gros.

Gillian Butler-Browne began working on muscle at the Institut Pasteur in the laboratory of François Gros in 1978. She characterized the expression profile of different myosin isoforms during both human and rodent development. Vincent Mouly joined this laboratory for his PhD in 1982, and defined the different populations of myoblasts appearing during development in birds and then in humans. Together, they demonstrated the impact of the limit in proliferation of the precursor cells on the regenerative capacity of human skeletal muscle, and their group developed models to evaluate the regenerative potential of skeletal muscle in vitro, measuring the telomeric erosion, and identified the involvement of a stress pathway in the proliferative arrest of muscle progenitors. A platform to produce human immortalized muscle cell lines was the successful result of this research, initiated with François Gros and W. E. Wright. The in vivo regenerative potential of human muscle cells was evaluated by injection into muscles of immunodeficient mice. Their group in collaboration with the clinical team of Professor Jean Lacau St-Guily and Professor Sophie Perié completed a successful autologous myoblast transplantation clinical trial for Oculo-pharyngeal muscular dystrophy. This common scientific career was made possible thanks to the precious and always benevolent support of François Gros.

Recent Progress in Oculopharyngeal Muscular Dystrophy.

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset intractable myopathy, characterized by slowly progressive ptosis, dysphagia, and proximal limb weakness. It is caused by the abnormal expansion of the alanine-encoding (GCN)n trinucleotide repeat in the exon 1 of the polyadenosine (poly[A]) binding protein nuclear 1 gene (11–18 repeats in OPMD instead of the normal 10 repeats). As the disease progresses, the patients gradually develop a feeling of suffocation, regurgitation of food, and aspiration pneumonia, although the initial symptoms and the progression patterns vary among the patients. Autologous myoblast transplantation may provide therapeutic benefits by reducing swallowing problems in these patients. Therefore, it is important to assemble information on such patients for the introduction of effective treatments in nonendemic areas. Herein, we present a concise review of recent progress in clinical and pathological studies of OPMD and introduce an idea for setting up a nation-wide OPMD disease registry in Japan. Since it is important to understand patients’ unmet medical needs, realize therapeutically targetable symptoms, and identify indices of therapeutic efficacy, our attempt to establish a unique patient registry of OPMD will be a helpful tool to address these urgent issues.

Extending Flaps Lifts an Infarcted Heart Toward Repair

Normal hearts comprise 2 × 109 myocytes, but this number may be doubled in excessively hypertrophied hearts. After a heart attack caused by blockage of one of the arteries that supply the heart, approximately 20% or more of cardiomyocytes are acutely and irreversibly lost in the ischemic area. However, the damage is not limited to the acute interruption of blood flow. Reperfusion of the ischemic territory can cause additional damage due to a burst of toxic reactive oxygen species. Moreover, additional cardiomyocytes are lost in the peri-infarct area during the subacute phase, leading to extension of the infarcted area. The ensuing remodeling response, which consists of cardiomyocyte hypertrophy and collagen accumulation, is insufficient to compensate for the massive cell loss, thus leading to scar expansion, ventricular chamber dilation, and failure.

Clarifying Misconceptions About Myoblast Transplantation in Myology

Clarifying Misconceptions About Myoblast Transplantation in Myology

Autologous Muscle Derived Cells for Treatment of Stress Urinary Incontinence in Women

We assess the 12-month safety and potential efficacy of autologous muscle derived cells for urinary sphincter repair (Cook MyoSite Incorporated, Pittsburgh, Pennsylvania) in women with stress urinary incontinence. Pooled data from 2 phase I/II studies with identical patient selection criteria and outcome measures were analyzed. Enrolled patients had stress urinary incontinence refractory to prior treatment and no symptom improvement during the last 6 months. Patients received intrasphincter injection of 10 (16), 50 (16), 100 (24) or 200×10(6) (24) autologous muscle derived cells for urinary sphincter repair, derived from biopsies of each patient's quadriceps femoris. The primary outcome measure was safety, determined by incidence and severity of adverse events. Potential efficacy was measured by changes in 3-day voiding diaries, 24-hour pad tests, and UDI-6 and IIQ-7 scores. A total of 80 patients underwent injection of autologous muscle derived cells for urinary sphincter repair, and 72 completed diaries and pad tests at 12-month followup. No adverse events attributed to autologous muscle derived cells for urinary sphincter repair were reported. Higher dose groups tended to have greater percentages of patients with at least a 50% reduction in stress leaks and pad weight at 12-month followup. All dose groups had statistically significant improvement in UDI-6 and IIQ-7 scores at 12-month followup compared to baseline. Autologous muscle derived cells for urinary sphincter repair at doses of 10, 50, 100 and 200×10(6) cells appears safe. Efficacy data suggest a potential dose response with a greater percentage of patients responsive to higher doses.

Autologous Myoblast Transplantation for Oculopharyngeal Muscular Dystrophy: a Phase I/Iia Clinical Study

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset autosomal dominant genetic disease mainly characterized by ptosis and dysphagia. We conducted a phase I/IIa clinical study (ClinicalTrials.gov NCT00773227) using autologous myoblast transplantation following myotomy in adult OPMD patients. This study included 12 patients with clinical diagnosis of OPMD, indication for cricopharyngeal myotomy, and confirmed genetic diagnosis. The feasibility and safety end points of both autologous myoblast transplantation and the surgical procedure were assessed by videoendoscopy in addition to physical examinations. Potential therapeutic benefit was also assessed through videoendoscopy and videofluoroscopy of swallowing, quality of life score, dysphagia grade, and a drink test. Patients were injected with a median of 178 million myoblasts following myotomy. Short and long-term (2 years) safety and tolerability were observed in all the patients, with no adverse effects. There was an improvement in the quality of life score for all 12 patients, and no functional degradation in swallowing was observed for 10 patients. A cell dose-dependant improvement in swallowing was even observed in this study. This trial supports the hypothesis that a local injection of autologous myoblasts in the pharyngeal muscles is a safe and efficient procedure for OPMD patients.

Role of autologous myoblast transplantation in endplate regeneration and neuromuscular function restoration after direct nerve implantation in rats

Objective To observe the effects of autologous myoblast transplantation on endplate regeneration and neuromuscular function restoration following direct nerve implantation （DNI） in rats so as to offer experimental basis for the use of myoblasts in neural regeneration area and further lay founda- tion for the research using myohlasts as transgenic carriers. Methods A total of 20 male SD rats were randomly divided into experimental group and control group, with 10 rats in each group. Models of DNI in rat gastrocnemius were established. The experimental group was injected with primarily cultured autolo- gous myoblasts to the DNI location, while the control group was injected with isometric medium without autologous myoblasts. The effects of myoblasts on the neuromuscular function recovery following DNI were studied by detecting the tibial functional index （FFI）, neuro-electrophysiology and pathohistology. Results The experimental group displayed faster tibial nerve function recovery than the control group （P 〈 0.01 ）. The peak to peak value （PPV） of gastrocnemius neuro-electrophysiology, area under the curve and regenerated endplate number of the experimental group had statistical significances as compared with the control group （P 〈 0.01 ）. Conclusion Myoblast autotransplantation accelerates the recovery of neuromuscular function after rat DNI and increases the number of the regenerated endplates. Key words: Myoblasts ; Transplantation; Neuromuscular function repairation

Transplantation of autologous myoblasts transfected with VEGF165 improves heart function after myocardial infarction in rabbits

To determine the improvements of post-infarction heart function after transplantation of autologous skeletal myoblasts transfected with VEGF165 in rabbits. Myocardium infarction was induced in rabbits by left anterior descending coronary artery ligation. At 2 weeks, 1.75×10(7) autologous skeletal myoblasts transfected with pcDNA3.1-VEGF165 were infused into the region of MI via direct intramuscular injection; pcDNA3.1 served as a control. The DAPI-labeled and Desmin-positive immunostained skeletal myofibers were found throughout the infracted areas and border zones, and the density of blood capillary in the MI region transplanted by myoblasts with VEGF165 was increased (measured 4 weeks later and compared with controls). Heart function was examined by the Buxco system and demonstrated that maximum dp/dt [(1607.23±102.67) mmHg/s vs (1217.77±89.91) mmHg/s] and minimum dp/dt [(-1535.09 ± 81.34) mmHg/s vs (1174.58 ± 91.5) mmHg/s] were improved in the heart transplanted with the transfected myoblasts(P<0.05). Autologous skeletal myoblasts transfected with VEGF165 could ameliorate the blood supply in the MI region, and aid recovery of heart function more quickly in post-infarction hearts. This suggests an effective treatment for myocardium infarction.

Safety, Efficacy and Health Related Quality of Life of Autologous Myoblast Transplantation for Treatment of Urinary Incontinence in Children With Bladder Exstrophy-Epispadias Complex

Children with bladder exstrophy-epispadias complex undergoing endourethral autologous myoblast transplantation to treat urinary incontinence were evaluated at 4 years of followup regarding the safety, efficacy and durability of the procedure, and health related quality of life. Seven boys underwent autologous myoblast transplantation between May and December 2006. All patients had persistent urinary incontinence after bladder neck reconstruction and bulking agent injection. Patients were followed for 4 years after autologous myoblast transplantation regarding clinical outcomes and cystometric, urodynamic, uroflowmetric and urethrocystoscopic evaluations. Health related quality of life was also measured before treatment and at final followup. No evidence of urinary obstruction was observed. Five children (71%) were completely continent and 2 (29%) were socially dry with complete daytime dryness at final followup. Health related quality of life was improved significantly. Urodynamic studies revealed a progressive increase in bladder capacity (p <0.001). Mean detrusor leak point pressure showed a 27 cm H(2)O (158%) increase during 4-year followup. Uroflowmetry parameters of voided volume and average maximum flow rate were improved significantly (p <0.001). The 4-year outcomes demonstrate that autologous myoblast transplantation for urinary incontinence in children with bladder exstrophy-epispadias complex is relatively reliable, reproducible, safe and effective with minimal morbidity. This novel treatment represents a promising therapeutic approach in patients with urinary incontinence. Further randomized trials with larger numbers of patients and longer followup are needed.

Transcription Factor Rational Design Improves Directed Differentiation of Human Mesenchymal Stem Cells Into Skeletal Myocytes

There is great interest in transdifferentiating cells from one lineage into those of another and in dedifferentiating mature cells back into a stem/progenitor cell state by deploying naturally occurring transcription factors (TFs). Often, however, steering cellular differentiation pathways in a predictable and efficient manner remains challenging. Here, we investigated the principle of combining domains from different lineage-specific TFs to improve directed cellular differentiation. As proof-of-concept, we engineered the whole-human TF MyoDCD, which has the NH(2)-terminal transcription activation domain (TAD) and adjacent DNA-binding motif of MyoD COOH-terminally fused to the TAD of myocardin (MyoCD). We found via reporter gene and marker protein assays as well as by a cell fusion readout system that, targeting the TAD of MyoCD to genes normally responsive to the skeletal muscle-specific TF MyoD enforces more robust myogenic reprogramming of nonmuscle cells than that achieved by the parental, prototypic master TF, MyoD. Human mesenchymal stem cells (hMSCs) transduced with a codon-optimized microdystrophin gene linked to a synthetic striated muscle-specific promoter and/or with MyoD or MyoDCD were evaluated for complementing the genetic defect in Duchenne muscular dystrophy (DMD) myocytes through heterotypic cell fusion. Cotransduction of hMSCs with MyoDCD and microdystrophin led to chimeric myotubes containing the highest dystrophin levels.

Percutaneous versus surgical delivery of autologous myoblasts after chronic myocardial infarction: An in vivo cardiovascular magnetic resonance study

Stem cell transplantation for chronic myocardial infarction (MI) provides variable benefits. Most clinical trials have relied on surgical delivery, where results are biased by simultaneous coronary bypass. When bypass is not indicated, percutaneous delivery may provide comparable efficacy with reduced risk. We evaluated in vivo by cardiovascular magnetic resonance (CMR) the effects of autologous myoblast (AM) transplantation on myocardial morphology, function, perfusion and scar, and compared percutaneous versus surgical delivery. Chronic MI was completed in 10 Yucatan mini-pigs. Three months later, AM were injected in half by percutaneous NOGA(R) system and in the other half by surgical mini-thoracotomy. CMR was performed at baseline and 6 months after transplantation. Six months after injection, AM transplantation led to a 26.3% decrease in indexed left ventricular end-diastolic volume (95% CI: 20.1-29.7%; P = 0.02), 25.5% thickening of the infarct-related segment (IRS) wall (95% CI: 19.6-33.2%; P = 0.03), and 20.9% increase in left ventricle (LV) ejection fraction (95% CI: 15.8-28.4%; P = 0.03). Scar tissue within IRS decreased by 29.4% (95% CI: 19.2-37.0%; P = 0.03), whereas the number of nonviable segments decreased by 25.0% (95% CI: 16.4-32.6%; P = 0.04). Myocardial perfusion of IRS improved by 29.1% (95% CI: 19.7-36.1%; P = 0.04). The arrhythmogenic peri-infarct zone increased by 33.2% (95% CI: 21.4-44.1%; P = 0.01) after AM transplantation. Benefits were similar by percutaneous or by surgical delivery. Comprehensive in vivo CMR reveals reversed remodeling and improved systolic function, perfusion, and scar characteristics after AM transplantation. A relative increase in the arrhythmogenic peri-infarct border zone may explain previously reported arrhythmia. Percutaneous and surgical transplantation of AM both lead to comparable improvements in chronic MI.

Polymer transfected primary myoblasts mediated efficient gene expression and angiogenic proliferation

This study was designed to assess the in vitro gene expression efficiency and therapeutic effectiveness of polymer mediated transfection of primary myoblasts. Autologous primary myoblast transplantation may improve the function of infarcted myocardium via myogenesis. In addition, primary myoblasts can carry exogenous angiogenic genes that encode angiogenic factors to promote therapeutic angiogenesis. Viral vectors have limited clinical application due to the induction of inflammatory reactions, tumorigenic mutations and genome integration. To overcome these problems, two new biodegradable poly(disulfide amine)s, poly(cystaminebisacryamide-diaminohexane) [poly(CBA-DAH)] and poly(cystaminebisacryamide-diaminohexane-arginine) [poly(CBA-DAH-R)], were synthesized as polymer carriers for gene delivery. In this study, primary myoblasts were isolated and purified from rat skeletal muscles. Based on an optimized polymer mediated transfection procedure using a luciferase assay and confocal microscopy, these two poly(disulfide amine)s induced up to 16-fold higher luciferase expression and much higher green fluorescence protein expression than branched poy(ethylenimine) (bPEI, 25 kDa) in primary myoblasts. By flow cytometry, poly(CBA-DAH) and poly(CBA-DAH-R) promote rates of cellular uptake of florescence-labeled polymer/pDNA complexes of 97% and 99%, respectively, which are rates higher than that of bPEI 25 kDa (87%). Both poly(disulfide amine)s were much less cytotoxic than bPEI 25 kDa. The in vitro time-course and co-culture experiments verified that polymer engineered primary myoblasts have the ability to stimulate endothelial proliferation. These data confirmed that poly(disulfide amine)s are the safe and feasible polymeric gene carriers to transfect VEGF 165 into primary myoblasts. Polymer engineered primary myoblasts have potential for therapeutic application in the treatment of ischemic heart diseases.

Cardiac cell therapy: overexpression of connexin43 in skeletal myoblasts and prevention of ventricular arrhythmias

Cell-based therapies have great potential for the treatment of cardiovascular diseases. Recently, using a transgenic mouse model Roell et al. reported that cardiac engraftment of connexin43 (Cx43)-overexpressing myoblasts in vivo prevents post-infarct arrhythmia, a common cause of death in patients following heart attack. We carried out a similar study but in a clinically relevant context via transplantation of autologous connexin43-overexpressing myoblasts in infarcted rats. Seven days after coronary ligation, rats were randomized into three groups: a control group injected with myoblasts, a null group injected with myoblasts transduced with an empty lentivirus vector (null) and a Cx43 group injected with myoblasts transduced with a lentivirus vector encoding connexin43. In contrast to Roell’s report, arrhythmia occurrence was not statistically different between groups (58%, 64% and 48% for the control (n= 12), null (n= 14) and Cx43 (n= 23) groups, respectively, P= 0.92). Using ex vivo intramural monophasic action potential recordings synchronous electrical activity was observed between connexin43-overexpressing myoblasts and host cardiomyocytes, whereas such synchrony did not occur in the null-transduced group. This suggests that ex vivo connexin43 gene transfer and expression in myoblasts improved intercellular electrical coupling between myoblasts and cardiomyocytes. However, in our model such electrical coupling was not sufficient to decrease arrhythmia induction. Therefore, we would suggest a note of caution on the use of combined Cx43 gene and cell therapy to prevent post-infarct arrhythmias in heart failure patients.

Improved diastolic function after myoblast transplantation in a model of ischemia-infarction

Objectives. The aim of this study was to evaluate the effect of myoblast transplantation on left ventricular function, perfusion, and scar formation after compromised coronary flow. Design. A coronary vessel with Ameroid-induced stenosis was ligated and skeletal muscle was biopsied for isolation and cultivation of myoblasts. Two weeks after ligation, animals were randomly selected to receive intramyocardial injections of 2×106 myoblasts or vehicle. Fifteen animals survived the whole study period (n=9 and n=6, respectively). All animals underwent cardiac magnetic resonance imaging (MRI) and angiography pretreatment and four weeks posttreatment. Results. Peak filling rate of the left ventricle improved in the myoblast group (p=0.0048), but not in the control group. Peak ejection rate and duration of diastole improved only in the myoblast group (p=0.049 and p=0.0039, respectively). Ejection fraction or local thickening did not change. Fibrosis and perfusion were similar in both groups, but more microvessels were present histologically in the myoblast group. Conclusions. In this preclinical study, autologous myoblast transplantation improved ischemic heart function via enhanced diastolic filling of the left ventricle.

Myoblast Transplantation for Cardiac Repair: From Automyoblast to Allomyoblast Transplantation

We sought to compare host immune cell kinetics, survival profile of donor skeletal myoblasts, and skeletal myoblast graft efficacy after autologous and allogeneic skeletal myoblast transplantation into a rat model of myocardial infarction. One week after myocardial infarction, 128 animals were divided into four groups: group 1 (n = 24, receiving medium only), group 2 (n = 24, receiving medium and cyclosporine), group 3 (n = 40, autologous skeletal myoblast transplantation), and group 4 (n = 40, allogeneic skeletal myoblast transplantation with cyclosporine treatment). Rats were euthanized 10 minutes, 1 day, and 4, 7, and 28 days later. Host immune cell kinetics were assessed by immunohistochemical studies for macrophages, and CD4+ and CD8+ lymphocytes. Donor skeletal myoblast survival was confirmed by tracking prelabeled signals, and quantified by beta-gal assay. Heart function was evaluated by echocardiography. A transient immune cell infiltration was demonstrated in group 3, with macrophage infiltration on day 1 and day 4, CD8+ cell infiltration on day 4 and day 7, and CD4+ cell infiltration on day 4. In group 4, immunocyte infiltration was slightly more severe than that in group 3. Automyoblasts and allomyoblasts showed no significant difference of survival from day 1 to day 7 (p > 0.10); however, on day 28, automyoblasts showed better survival than allomyoblasts (p < 0.05). Transplantation of allomyoblasts increased systolic heart function and limited heart dilation after myocardial injury to a similar degree as automyoblasts (p > 0.10). The use of allomyoblasts is feasible and effective for cardiac repair with immunosuppressive treatment as compared with automyoblasts.

Colony-stimulating factor-1 transfection of myoblasts improves the repair of failing myocardium following autologous myoblast transplantation

Skeletal myoblasts are used in repair of ischaemic myocardium. However, a large fraction of grafted myoblasts degenerate upon engraftment. Colony-stimulating factor-1 (CSF-1) accelerates myoblast proliferation and angiogenesis. We hypothesized that CSF-1 overexpression improves myoblast survival and cardiac function in ischaemia-induced heart failure. Three weeks following myocardial infarction, rats developed heart failure and received intramyocardial injections of mouse CSF-1-transfected or untransfected primary autologous rat myoblasts, recombinant human CSF-1, mouse CSF-1 expressing plasmids, or culture medium. Tissue gene and protein expression was measured by quantitative RT-PCR (reverse transcription-polymerase chain reaction) and western blotting. Fluorescence imaging and immunocytochemistry were used to analyse myoblasts, endothelial cells, macrophages, and infarct wall thickening. Electrocardiograms were recorded online using a telemetry system. Left ventricular function was assessed by echocardiography over time, and improved significantly only in the CSF-1-overexpressing myoblast group. CSF-1-overexpression enhanced myoblast numbers and was associated with an increased infarct wall thickness, enhanced angiogenesis, increased macrophage recruitment and upregulated matrix metalloproteases (MMP)-2 and -12 in the zone bordering the infarction. Transplantation of CSF-1-overexpressing myoblasts did not result in major arrhythmias. Autologous intramyocardial transplantation of CSF-1 overexpressing myoblasts might be a novel strategy in the treatment of ischaemia-induced heart failure.

Autologous muscle precursor cell Transplantation for the treatment of Urinary Incontinence in Children with Classic Bladder Extrophy: One year follow up

PURPOSE The application of muscle derived stem cells is an area of active research that may represent an improved alternative for the treatment of urinary incontinence. We investigated the effectiveness of autologous muscle precursor cell transplantation as a treatment option for urinary incontinence due to sphincter incompetence in children with the bladder exstrophy/epispadias complex (BEEC). MATERIAL AND METHODS Twelve patients with BEEC (11 boys and 1 girl) with persistent urinary incontinence entered the study. All patients had undergone staged bladder repair and bladder neck reconstruction and all of them (except 1) had received 1-3 transurethral injections of bulking agents with minimal effects. Muscle precursor cells were isolated from each patient's abdominal skeletal muscle, and cultured before endourethral injection. The effectiveness of treatment was evaluated with particular emphasis on clinical outcome (based on a 24-hour voiding diary), cystometric and urodynamic studies. RESULTS Eight Patients had a mean follow-up of 11.3 (from 8 to 14 months), The remaining 4 cases with less than 6 months follow-up are not presented in this data. There was a significant time-dependent improvement in patients' urinary continence. At the final follow-up, all 7 (88%) boys were socially dry (day-time dryness >3 hours) – including 3 (38%) completely dry. Urodynamic studies revealed an increase in mean bladder capacity (p < 0.001) and leak point pressure (p < 0.001). Six months after injection, all 7 boys (versus 2 cases preoperatively) had normal micturition with demonstrable voiding detrusor contraction in presence of compliant, stable bladders (p < 0.05). These changes were accompanied by an increment in the average maximum urinary flow (p < 0.01). CONCLUSIONS Autologous myoblast transplantation may be a safe, effective and attractive alternative treatment option for structural urinary incontinence, with possible ability for functional regeneration of urethral sphincter.

MAGIC (Myoblast Autologous Grafting in Ischaemic Cardiomyopathy) phase II study: The Hamburg experience

Objective: Autologous myoblast transplantation (AMT) is an innovative technique for the treatment of ischaemic cardiomyopathy (ICM). This study evaluates the safety and efficacy of AMT and coronary artery bypass grafting (CABG) for the treatment of ICM (MAGIC Phase II Study, MG Biotherapeutics Inc.).

Autologous myoblast transplantation in an animal model applicable as a potential bulking agent at the ureterovesical junction?

Purpose Myoblast transplantation has been shown to augment damaged tissue. Moreover it could be used as an autologous bulking agent in refluxing vesicoureteral junctions in order to restore the damaged muscular integrity. But graft viability and the behaviour of the donor myoblasts at the ureterovesical junction have not been demonstrated yet. Material and methods Muscle biopsies from the back muscles of 5 pigs were obtained. Quality of the cells was evaluated by electrophysiological and immunohistochemical tests. Additionally they were labelled with a PKH fluorescent membrane dye to provide fluorescent marking of live cells. 5 weeks after muscle biopsies all animals underwent cell transplantation with 300 × 106 cells suspended in transplantation medium loaded into five 1-cc tuberculin syringes and injected into the ureterovesical junction. Animals were sacrificed 8 weeks later, the donor cells were identified using PKH26 labelling and fluorescence-activated cell-sorter analysis. Moreover histopathology and evaluation concerning tissue reaction at the donor site was also carried out. Results 2-3 intact autologous skeletal myoblast–derived skeletal muscle cells/visual field were found in all injected animals. However, immunohistochemistry demonstrated viability of transplanted myoblasts only at the borders of the bulking area wheras central widespread necrosis with red fluorescent cell detritus could be observed. We did not observe marked signs of an inflammatory response, even though a fibrotic scar was found at the site of injection. Conclusions These results highlight the inability of the vast majority of transplanted myoblasts to survive. Only a small portion of the cells survive when transplanted into a well vascularized area which is in favour of the assumption of an indirect impairment such as paracrine effects. Failure of myoblast transplantation in this animal study does not prove that the procedure itself is ineffective, but these results do caution against the application of in vivo myoblasts as a bulking agent.

Cardiac Stem Cell Therapy

Cardiovascular disease remains the number one cause of morbidity and mortality in the United States and Europe. In the United States alone, ≈1 million patients suffer a myocardial infarction every year, with an associated mortality of 25% at 3 years.1 A more sobering statistic is the fact that there are ≈5 million Americans with congestive heart failure, with an associated 20% mortality per year. This remains the case despite advances in pharmacotherapy, cardiac resynchronization therapies, and the use of implantable cardioverter-defibrillators.2 Some patients with end-stage congestive heart failure are considered for cardiac transplantation, but the demand for this therapeutic approach greatly outweighs the availability of donor hearts. Over the past few years, several animal studies and a few clinical trials have supported the use of stem cells as a potential therapeutic modality to address this unmet clinical need. Response by Boyle et al p 358 Several different types of cells have been used in both animal studies and patients to promote the repair of damaged myocardium. The 2 main sources of stem cells are adult stem and embryonic stem (ES) cells. ### ES Cells ES cells are derived from the inner mass of developing embryos during the blastocyst stage. Characteristic features of ES cells include their proliferative and self-renewing properties and their ability to differentiate into a wide variety of cell types, including cardiac myocytes.3 The major concerns with their use in human trials include the formation of teratomas when ES cells are injected into immunocompromised animals. This is particularly important because the ES cells currently available for use in humans would be of allogeneic origin and therefore would require immunosuppression. As nuclear transfer techniques improve, they will provide a way of generating an unlimited supply of histocompatible ES cells using the nuclei of cells obtained directly from the recipient …