Quality Control Optimization for Minimizing Security Risks Associated with Mesenchymal Stromal Cell-Based Product Development

Mesenchymal stromal cells (MSCs) have been considered a therapeutic strategy in regenerative medicine because of their regenerative and immunomodulatory properties. The translation of MSC-based products has some challenges, such as regulatory and scientific issues. Quality control should be standardized and optimized to guarantee the reproducibility, safety, and efficacy of MSC-based products to be administered to patients. The aim of this study was to develop MSC-based products for use in clinical practice. Quality control assays include cell characterization, cell viability, immunogenicity, and cell differentiation; safety tests such as procoagulant tissue factor (TF), microbiological, mycoplasma, endotoxin, genomic stability, and tumorigenicity tests; and potency tests. The results confirm that the cells express MSC markers; an average cell viability of 96.9%; a low expression of HLA-DR and costimulatory molecules; differentiation potential; a high expression of TF/CD142; an absence of pathogenic microorganisms; negative endotoxins; an absence of chromosomal abnormalities; an absence of genotoxicity and tumorigenicity; and T-lymphocyte proliferation inhibition potential. This study shows the relevance of standardizing the manufacturing process and quality controls to reduce variability due to the heterogeneity between donors. The results might also be useful for the implementation and optimization of new analytical techniques and automated methods to improve safety, which are the major concerns related to MSC-based therapy.

Human Adipose-Derived Stem Cells Reduce Cellular Damage after Experimental Spinal Cord Injury in Rats

Traumatic spinal cord injury (SCI) is a devastating condition without an effective therapy. Cellular therapies are among the promising treatment strategies. Adult stem cells, such as mesenchymal stem cells, are often used clinical research for their immunomodulatory and regenerative potential. This study aimed to evaluate the effect of human adipose tissue-derived stem cells (ADSC) infusion through the cauda equina in rats with SCI. The human ADSC from bariatric surgery was isolated, expanded, and characterized. Wistar rats were subjected to blunt SCI and were divided into four groups. Two experimental groups (EG): EG1 received one ADSC infusion after SCI, and EG2 received two infusions, the first one after SCI and the second infusion seven days after the injury. Control groups (CG1 and CG2) received infusion with a culture medium. In vivo, cell tracking was performed 48 h and seven days after ADSC infusion. The animals were followed up for 40 days after SCI, and immunohistochemical quantification of myelin, neurons, and astrocytes was performed. Cellular tracking showed cell migration towards the injury site. ADSC infusion significantly reduced neuronal loss, although it did not prevent the myelin loss or enhance the area occupied by astrocytes compared to the control group. The results were similar when comparing one or two cell infusions. The injection of ADSC distal to the injured area was shown to be a safe and effective method for cellular administration in spinal cord injury.

Somatic mosaicism in patients with Fanconi anaemia: Proposal of alternative tissue for inconclusive diagnoses

INTRODUCTION

Fanconi anaemia (FA) is a rare genetic disorder marked by progressive bone marrow failure, chromosomal fragility, and increased cancer susceptibility. Laboratory diagnosis includes chromosomal instability test and mutation investigation. A total of 15%-25% of all patients may have somatic mosaicism, characterized by two distinct haematopoietic cell populations, one resistant and one sensitive to agents that induce chromosomal breakage, which complicates the diagnosis by a high incidence of reverted cells leading to inconclusive or false-negative results. The study aimed to evaluate the use of bone marrow stromal mesenchymal cells (BM-MSCs) as an alternative, non-haematopoietic tissue for diagnosis.

METHODS

Bone marrow mesenchymal stromal cells from 12 patients with positive diepoxybutane (DEB) tests were cultivated and analysed by cytogenetics and mutation investigation.

RESULTS

The DEB test was performed at 0.1 and 0.01 μg/ml concentrations, with an index ranging from 0.24 to 1.00. At higher concentration, the metaphases number was lower, probably due to toxicity. Regarding the molecular investigation, all the mutations previously found in peripheral blood were identified on BM-MSC.

CONCLUSION

This study demonstrated the possibility of using BM-MSCs as an alternative tissue for cytogenetic and molecular investigation. Future tests using an intermediate DEB concentration may lead to an optimal protocol that could be non-toxic to cells but provides conclusive results.

Chromosomal aberrations after induced pluripotent stem cells reprogramming

Induced pluripotent stem cells (iPSCs) are generated from adult cells that have been reprogrammed to pluripotency. However, in vitro cultivation and genetic reprogramming increase genetic instability, which could result in chromosomal abnormalities. Maintenance of genetic stability after reprogramming is required for possible experimental and clinical applications. The aim of this study was to analyze chromosomal alterations by using the G-banding karyotyping method applied to 97 samples from 38 iPSC cell lines generated from peripheral blood or Wharton’s jelly. Samples from patients with long QT syndrome, Jervell and Lange-Nielsen syndrome and amyotrophic lateral sclerosis and from normal individuals revealed the following chromosomal alterations: acentric fragments, chromosomal fusions, premature centromere divisions, double minutes, radial figures, ring chromosomes, polyploidies, inversions and trisomies. An analysis of two samples generated from Wharton’s jelly before and after reprogramming showed that abnormal clones can emerge or be selected and generate an altered lineage. IPSC lines may show clonal and nonclonal chromosomal aberrations in several passages (from P6 to P34), but these aberrations are more common in later passages. Many important chromosomal aberrations were detected, showing that G-banding is very useful for evaluating genetic instability with important repercussions for the application of iPSC lines.

Combined Use of Tocilizumab and Mesenchymal Stromal Cells in the Treatment of Severe Covid-19: Case Report

The coronavirus pandemic is one of the most significant public health events in recent history. Currently, no specific treatment is available. Some drugs and cell-based therapy have been tested as alternatives to decrease the disease's symptoms, length of hospital stay, and mortality. We reported the case of a patient with a severe manifestation of COVID-19 in critical condition who did not respond to the standard procedures used, including six liters of O₂ supplementation under a nasal catheter and treatment with dexamethasone and enoxaparin in prophylactic dose. The patient was treated with tocilizumab and an advanced therapy product based on umbilical cord-derived mesenchymal stromal cells (UC-MSC). The combination of tocilizumab and UC-MSC proved to be safe, with no adverse effects, and the results of this case report prove to be a promising alternative in the treatment of patients with severe acute respiratory syndrome due to SARS-CoV-2.

Adipose tissue-derived stromal/stem cells + cholecalciferol: a pilot study in recent-onset type 1 diabetes patients

Objective

Adipose tissue-derived stromal/stem cells (ASCs) and vitamin D have immunomodulatory actions that could be useful for type 1 diabetes (T1D). We aimed in this study to investigate the safety and efficacy of ASCs + daily cholecalciferol (VIT D) for 6 months in patients with recent-onset T1D.

Methods

In this prospective, dual-center, open trial, patients with recent onset T1D received one dose of allogenic ASC (1 × 10⁶ cells/kg) and cholecalciferol 2,000 UI/day for 6 months (group 1). They were compared to patients who received chol-ecalciferol (group 2) and standard treatment (group 3). Adverse events were recorded; C-peptide (CP), insulin dose and HbA1c were measured at baseline (T0), after 3 (T3) and 6 months (T6).

Results

In group 1 (n = 7), adverse events included transient headache (all), mild local reactions (all), tachycardia (n = 4), abdominal cramps (n = 1), thrombophlebitis (n = 4), scotomas (n = 2), and central retinal vein occlusion at T3 (n = 1, resolution at T6). Group 1 had an increase in basal CP (p = 0.018; mean: 40.41+/-40.79 %), without changes in stimulated CP after mixed meal (p = 0.62), from T0 to T6. Basal CP remained stable in groups 2 and 3 (p = 0.58 and p = 0.116, respectively). Group 1 had small insulin requirements (0.31+/- 0.26 UI/kg) without changes at T6 (p = 0.44) and HbA1c decline (p = 0.01). At T6, all patients (100%; n = 7) in group 1 were in honeymoon vs 75% (n = 3/4) and 50% (n = 3/6) in groups 2 and 3, p = 0.01.

Conclusion

Allogenic ASC + VIT D without immunosuppression was safe and might have a role in the preservation of β-cells in patients with recent-onset T1D. ClinicalTrials.gov: NCT03920397.

USE OF TOCILIZUMAB AND MESENCHYMAL STROMAL CELLS IN THE TREATMENT OF SEVERE COVID-19 - A CASE REPORT

Background

Currently, there is no specific treatment for coronavirus disease, and some drugs and cell-based therapy have been tested as alternatives. This work aims to evaluate the effects of the combined use of humanized recombinant monoclonal antibody capable of binding the IL-6 receptor (Tocilizumab), and umbilical cord tissue-derived mesenchymal stromal cells (UCT-MSC) in the treatment of a patient with severe COVID-19 admitted to the intensive care unit (IUC) and submitted to mechanical ventilation.

Methods

This study is part of a project approved by the National Research Ethics Commission (CONEP); CAAE: 30833820.8.0000.0020. The patient had a diagnostic criterion for the severe acute respiratory syndrome resulting from infection with SARS-CoV-2 and received two 400 mg doses of tocilizumab, three infusions of 500,000 CTM / kg plus full anticoagulation. TCU-MSC were obtained from healthy donors. The following parameters were evaluated in the pre-infusion of cells (D1), on the day following each infusion (D2, D4, and D6), on the 14th and 60th day after the first infusion (D14 and D60): viral load, immune response (Regulatory T lymphocytes), C-reactive protein level in plasma, oxygen saturation, respiratory rate, total lymphocyte count and subpopulations (platelets, inflammatory cells, and reticulocytes), TGO / TGP, increased prothrombin time, D-dimer, creatinine, troponin.

Results

The relative viral quantification decreased gradually from 1 (D1) to 0.06 (D6) RdRP / RNApol, undetectable in D14. An increase in the absolute number of total lymphocytes / µL has also been seen to have progressively increased from 281 (D1) to 954.9 (D6) and since then decreased to 641.6 in D60 in the same way as T lymphocytes 148.6 (D1) 642.6 (D6) 607.4 (D14) 485.7 (D60), CD4 T lymphocytes, 102 (D1) 481.2 (D6) 459.5 (D14) 358 (D60) and Treg lymphocytes 10.8 (D1) 34 (D6) 29.8 (D14), 25.9 (D60). Plasmablasts, in contrast, decreased from 52 (D1) to 4.5 (D6) to almost undetectable in D60 (0.2). Laboratory tests outside the reference values decreased during the follow-up from D1 to D14 were within the normal parameters at D60. The patient was extubated uneventfully on D6, discharged from the ICU on D10, and the hospital on D14.

Conclusion

the combined use of tocilizumab and MSC is safe, without adverse effects, and the results of this case report prove to be a promising alternative in the treatment of patients with severe acute respiratory syndrome due to SARS-CoV-2.

Recovery of motricity and micturition after transplantation of mesenchymal stem cells in rats subjected to spinal cord injury

The objective was to evaluate the effect of human adipose-derived stem cell (hADSC) infusion on impaired hindlimb function and urinary continence after spinal cord contusion in rats. hADSCs were transplanted into the injured spinal cords of rats 7 and 14 days after injury in two groups (B and C). Group C also received methylprednisolone sodium succinate (MPSS) after 3 h of injury. The control group (group A) did not receive corticoids or stem cells. Voiding and motor performance evaluations were performed daily for 90 days post-transplantation. Cells were labeled with PKH26 or PKH67 for in vitro monitoring. For in vivo screening, the cells were evaluated for bioluminescence. The levels of some cytokines were quantified in different times. Euthanasia was performed 90 days post-transplant. β-tubulin III expression was evaluated in the spinal cord of the animals from all groups. As a result, we observed a recovery of 66.6 % and 61.9 % in urinary continence of animals from groups B and C, respectively. Partial recovery of motor was observed in 23.8 % and 19 % of the animals from groups B and C, respectively. Cells remained viable at the site up to 90 days after transplantation. No significant difference was observed in levels of cytokines and thickness of urinary bladders between groups. A smaller percentage of tissue injury and higher concentrations of neuropils were observed in the spinal cords of the animals from groups B and C than control group. Thus, hADSCs transplantation with or without MPSS, contributed to the improvement in voiding and motor performance of Wistar rats submitted to compressive spinal cord injury.

Effects of mesenchymal stromal cells play a role the oxidant/antioxidant balance in a murine model of asthma

Asthma is a heterogeneous disease characterised by chronic airway inflammation. One of the most devastating consequences of this inflammatory process is the generation of reactive oxygen and nitrogen species responsible for oxidative stress. The aim of this study is to analyse the efficiency of treatment with human bone marrow-derived mesenchymal stromal cells (hMSC) in maintaining the oxidative balance in a murine model of allergic asthma by quantifying nitrotyrosine in lung tissues. After confirmation of asthma in the experimental model, samples of lung parenchyma were submitted to immunohistochemical assessment. Intravenous administration of hMSC reduced the levels of nitrotyrosine in the ASTHMA-hMSC group compared to those in the ASTHMA-SAL group. In conclusion, therapeutic administration of hMSC had a beneficial effect on oxidative stress, reducing the levels of nitrotyrosine in lung tissues in a model of allergic asthma.

The Effect of Mesenchymal Stem Cells on Fertility in Experimental Retrocervical Endometriosis

Purpose To evaluate the effect of mesenchymal stem cells (MSCs) on fertility in experimental retrocervical endometriosis. Methods A total of 27 New Zealand rabbits were divided into three groups: endometriosis, in which endometrial implants were created; mesenchymal, in which MSCs were applied in addition to the creation of endometrial implants; and control, the group without endometriosis. Fisher's exact test was performed to compare the dichotomous qualitative variables among the groups. The quantitative variables were compared by the nonparametric Mann-Whitney and Kruskal-Wallis tests. The Mann-Whitney test was used for post-hoc multiple comparison with Boniferroni correction. Results Regarding the beginning of the fertile period, the three groups had medians of 14 ± 12.7, 40 ± 5, and 33 ± 8.9 days respectively (p = 0.005). With regard to fertility (number of pregnancies), the endometriosis and control groups showed a rate of 77.78%, whereas the mesenchymal group showed a rate of 11.20% (p = 0.015). No differences in Keenan's histological classification were observed among the groups (p = 0.730). With regard to the macroscopic appearance of the lesions, the mesenchymal group showed the most pelvic adhesions. Conclusion The use of MSCs in endometriosis negatively contributed to fertility, suggesting the role of these cells in the development of this disease.

Emergence of clonal chromosomal alterations during the mesenchymal stromal cell cultivation

Background

Use of human mesenchymal stromal cells (MSCs) is a promising strategy for cell therapy in injured tissues recovery. However, MSCs acquire genetic changes when cultivated in vitro that make them more susceptible to undergo neoplastic transformation. Therefore, genomic integrity of stem cells should be monitored carefully for the use in basic research and clinical trials, including karyotype analysis to confirm the absence of genetic instability. Here, we report a case of a male 67-year-old patient selected to join the study: “Autologous transplantation of mesenchymal cells for treatment of severe and refractory ischemic cardiomyopathy”. He underwent nephrectomy for malignant tumor on the right kidney. Cytogenetic analysis on a bone marrow sample showed a normal karyotype: 46,XY[20]. However, the MSC at second passage showed a hyperdiploid clone, with clonal trisomies of chromosomes 4, 5, 10 and X. In order to investigate more, another sample from the same patient was used for a second cultivation and, at third passage, these cells showed a clonal translocation t(9;18)(p24;q11). The recurrent aberrations in MSC may indicate the beginning of a spontaneous transformation in culture, so, these cells were not used for cell therapy. Several analyses were performed at the Center for Cell Technology (152 samples), however this was the only case to show clonal cytogenetic abnormalities. Interestingly, two distinct clonal alterations were seen in two parallel cell cultivations from the same patient, suggesting a propensity for genetic instability. This highlights the need to evaluate these cells on a case-by-case basis, especially in patients with a history of cancer. Although there is controversy about the use of cells with cytogenetic abnormality for therapy, because their tumorigenic doubtful potential, we decided against the use of these cells for regenerative medicine.

Case presentation

Here, we report a case of a male 67-year-old patient selected to join the study: “Autologous transplantation of mesenchymal cells for treatment of severe and refractory ischemic cardiomyopathy”. He underwent nephrectomy for malignant tumor on the right kidney. Cytogenetic analysis on a bone marrow sample showed a normal karyotype: 46,XY[20]. However, the MSC at second passage showed a hyperdiploid clone, with clonal trisomies of chromosomes 4, 5, 10 and X. In order to investigate more, another sample from the same patient was used for a second cultivation and, at third passage, these cells showed a clonal translocation t(9;18)(p24;q11). The recurrent aberrations in MSC may indicate the beginning of a spontaneous transformation in culture, so, these cells were not used for cell therapy. Several analyses were performed at the Center for Cell Technology(152 samples), however this was the only case to show clonal cytogenetic abnormalities. Interestingly, two distinct clonal alterations were seen in two parallel cell cultivations from the same patient, suggesting a propensity for genetic instability. This highlights the need to evaluate these cells on a case-by-case basis, especially in patients with a history of cancer.

Conclusions

Although there is controversy about the use of cells with cytogenetic abnormality for therapy, because their tumorigenic doubtful potential, we decided against the use of these cells forregenerative medicine.

Comparison of two surgical techniques for creating an acute myocardial infarct in rats

Objective

To perform a comparative assessment of two surgical techniques that are used creating an acute myocardial infarc by occluding the left anterior descending coronary artery in order to generate rats with a left ventricular ejection fraction of less than 40%.

Methods

The study was completely randomized and comprised 89 halothane-anaesthetised rats, which were divided into three groups. The control group (SHAM) comprised fourteen rats, whose left anterior descending coronary artery was not occluded. Group 1 (G1): comprised by 35 endotracheally intubated and mechanically ventilated rats, whose left anterior descending coronary artery was occluded. Group 2 (G2): comprised 40 rats being manually ventilated using a nasal respirator whose left anterior descending coronary artery was occluded. Other differences between the two techniques include the method of performing the thoracotomy and removing the pericardium in order to expose the heart, and the use of different methods and suture types for closing the thorax. Seven days after surgery, the cardiac function of all surviving rats was determined by echocardiography.

Results

No rats SHAM group had progressed to death or had left ventricular ejection fraction less than 40%. Nine of the 16 surviving G1 rats (56.3%) and six of the 20 surviving G2 rats (30%) had a left ventricular ejection fraction of less than 40%.

Conclusion

The results indicate a tendency of the technique used in G1 to be better than in G2. This improvement is probably due to the greater duration of the open thorax, which reduces the pressure over time from the surgeon, allowing occlusion of left anterior descending coronary artery with higher accuracy.

Brazilian minipig as a large-animal model for basic research and stem cell-based tissue engineering. Characterization and in vitro differentiation of bone marrow-derived mesenchymal stem cells

Stem cell-based regenerative medicine is one of the most intensively researched medical issues. Pre-clinical studies in a large-animal model, especially in swine or miniature pigs, are highly relevant to human applications. Mesenchymal stem cells (MSCs) have been isolated and expanded from different sources.

Expression of pancreatic endocrine markers by mesenchymal stem cells from human adipose tissue

Mesenchymal stem cells (MSCs) from human adipose tissue have a great potential for use in cell therapy due to their ease of isolation, expansion, and differentiation, besides the relative acceptance from the ethical point of view. Our intention was to isolate and promote in vitro expansion and differentiation of MSCs from human adipose tissue into cells with a pancreatic endocrine phenotype. Human adipose tissue obtained from patients undergoing abdominal dermolipectomy was digested with type I collagenase. MSCs isolated by plastic adherence and characterized by cytochemistry and FACS were expanded in vitro. MSC differentiation into an endocrine phenotype was induced over 2 to 4 months with high glucose (25 mmol/L) media containing nicotinamide, exendin-4, and 2-mercaptoethanol. Insulin and glucagon expressions were analyzed by immunofluorescence. Cells isolated from human adipose tissue and expanded in vitro expressed MSC markers as confirmed by FACS and cytochemistry. Insulin but not glucagon production by differentiated cells was demonstrated by immunofluorescence. MSCs isolated from human adipose tissue were induced to differentiate in vitro into an endocrine phenotype that expressed insulin.

Cell transplantation after the coculture of skeletal myoblasts and mesenchymal stem cells in the regeneration of the myocardium scar: an experimental study in rats

In myocardial infarction and Chagas's disease, some physiopathological aspects are common: cardiomyocyte loss due to ischemia leads to a reduction of contractility and heart function. Different cells have been proposed for cellular cardiomioplasty.

OBJECTIVE

Our goal was to evaluate the method of co-culture of skeletal muscle (SM) and mesenchymal stem cells (MSC) for cell therapy of heart failure in Chagas's disease (CD) and myocardium postinfarction (MI).

METHODS

For MI, 39 rats completed the study at 1 month. Seventeen rats received cell therapy into the scar and 22 rats only medium. For CD, 15 rats completed the study at 1 month including 7 that received cell therapy and eight followed the natural evolution. All animals underwent ecocardiographic analysis at baseline and 1 month. Left ventricular, ejection fraction, end systolic, and end dyastolic volume were registered and analyzed by ANOVA. The co-culture method of SM and MSC was performed at 14 days (DMEM, with 15% FCS, 1% antibiotic, IGF-I, dexamethasone). Standard stain analysis was performed.

RESULTS

For MI ejection fraction in the animals that received the co-cultured cells increased from 23.52+/-8.67 to 31.45+/-8.87 (P=.006) versus the results in the control group: 26.68+/-6.92 to 22.32+/-6.94 (P=.004). For CD, ejection fraction in animals that received the co-cultured cells increased from 31.10+/-5.78 to 53.37+/-5.84 (P<.001) versus the control group values of 36.21+/-3.70 to 38.19+/-7.03 (P=0.426). Histopathological analysis of the animals receiving co-cultured cells demonstrated the presence of myogenesis and angiogenesis.

CONCLUSION

The results validated the product of SM and MSC co-cultures for treatment of diseases.

Major histocompatibility complex and central nervous system involvement by paracoccidioidomycosis

Paracoccidioidomycosis (PCM) is a chronic granulomatous infectious disease, whose etiologic agent is the fungus Paracoccidioides brasiliensis. The central nervous system (CNS) involvement with paracoccidioidomycosis (NPCM) occurs more frequently than has been admitted in the past. There are some major histocompatibility complex antigen association studies with systemic paracoccidioidomycosis. Some indicate a positive association with HLA antigens, but there is no study with the involvement of the CNS. To investigate why not all cases of systemic PCM show the involvement of the CNS and whether genetic factors are involved, we studied 6 patients with NPCM, from the neuroinfection outpatient clinic. The patients were typed for class I and class II antigens by a microlymphocytoxity standard test. The HLA antigen frequencies found in this study in patients with NPCM were not different from the alleles frequencies observed in the Paraná population.

Could the coculture of skeletal myoblasts and mesenchymal stem cells be a solution for postinfarction myocardial scar?

Currently two lines of research have been proposed for treatment of heart failure in an attempt to address its main cause: skeletal myoblast (SM) transplants, which increase the contractile muscular mass, and mesenchymal stem cell (MSC) transplants, which increase neoangiogenesis. The objective of this study was to establish methods whereby cocultures of SM and MSC proliferate and expand, making possible the interaction of these cell types prior to their transplantation to the myocardium. Seeking to support the survival of these cells after myocardial transplantation and achieve subsequent functional improvement, SM and MSC from 10 rats were isolated and cultivated in DMEM medium supplemented with 15% fetal calf serum, 1% ATB, and growth factors. Following plating in variable proportions of satellite cells/mononuclear cells namely 2:1, 1:1, 1:2, morphological observations were made regarding cell survival, adhesion to substrate, and confluence. After 48 hours nonadherent cells were aspirated from the flasks, leaving the adherent cells, SM, and MSC. The better level of cell proliferation was observed with the proportion 2:1 cocultivated at a concentration of 5 x 10(5)/mL for 14 days. The results were satisfactory; the cell production was up to 10(8), increasing the chances of transplant success after myocardial infarction. Transplants with this model are ongoing.

Aneural culture of rat myoblasts for myocardial transplant

Due to the peculiar characteristics of skeletal muscle, myoblast transplants have emerged as a therapy for cardiomyopathy, particularly after myocardial infarction. The objectives of this study were to define the mean time of cultivation necessary to obtain a cellular concentration of 10(6) to expand the mass for transplant, and to identify the proliferation phase of myoblasts. Ten myoblast cultures were performed using newborn Wistar rats. The isolation method used enzymatic dissociation in culture medium (HAM-F12 and 199) supplement with basic-fibroblast growth factor (b-FGF) and insulin growth factor (IGF-I). The mean cultivation time to obtain the desired concentration of 10(6) was 7 days, with expansion of up to 10(8)/g. When b-FGF was used, the cellular yield was approximately 10(7), with IGF-I the cellular yield was approximately 10(8), independent of the medium. We concluded that IGF-I is the better option for mass cellular expansion of myoblasts for application in myocardial transplants.