Use of Repeating Dispensers to Increase the Efficiency of the Intramuscular Myogenic Cell Injection Procedure

Human MuStem cells are competent to fuse with nonhuman primate myofibers in a clinically relevant transplantation context: A proof-of-concept study

We previously reported that human muscle-derived stem cells (hMuStem cells) contribute to tissue repair after local administration into injured skeletal muscle or infarcted heart in immunodeficient rodent models. However, extrapolation of these findings to a clinical context is problematic owing to the considerable differences often seen between in vivo findings in humans versus rodents. Therefore, we investigated whether the muscle regenerative behavior of hMuStem cells is maintained in a clinically relevant transplantation context. Human MuStem cells were intramuscularly administered by high-density microinjection matrices into nonhuman primates receiving tacrolimus-based immunosuppression thereby reproducing the protocol that has so far produced the best results in clinical trials of cell therapy in myopathies. Four and 9 weeks after administration, histological analysis of cell injection sites revealed large numbers of hMuStem cell-derived nuclei in all cases. Most graft-derived nuclei were distributed in small myofiber groups in which no signs of a specific immune response were observed. Importantly, hMuStem cells contributed to simian tissue repair by fusing mainly with host myofibers, demonstrating their capacity for myofiber regeneration in this model. Together, these findings obtained in a valid preclinical model provide new insights supporting the potential of hMuStem cells in future cell therapies for muscle diseases.

Duchenne and Becker muscular dystrophy: Cellular mechanisms, image analysis, and computational models: A review

The muscle is the principal tissue that is capable to transform potential energy into kinetic energy. This process is due to the transformation of chemical energy into mechanical energy to enhance the movements and all the daily activities. However, muscular tissues can be affected by some pathologies associated with genetic alterations that affect the expression of proteins. As the muscle is a highly organized structure in which most of the signaling pathways and proteins are related to one another, pathologies may overlap. Duchenne muscular dystrophy (DMD) is one of the most severe muscle pathologies triggering degeneration and muscle necrosis. Several mathematical models have been developed to predict muscle response to different scenarios and pathologies. The aim of this review is to describe DMD and Becker muscular dystrophy in terms of cellular behavior and molecular disorders and to present an overview of the computational models implemented to understand muscle behavior with the aim of improving regenerative therapy.

Human Muscle Precursor Cells Form Human-Derived Myofibers in Skeletal Muscles of Nonhuman Primates: A Potential New Preclinical Setting to Test Myogenic Cells of Human Origin for Cell Therapy of Myopathies

This study aimed to verify if human myogenic cells could participate in muscle regeneration in macaques. This experimental setting would grant researchers a model that could better evaluate the effects of cell therapies in myopathies with a better translation to human patients. Human muscle precursor cells (MPCs) were cultured in vitro and transduced with ß-galactosidase. The cells were subsequently injected into 1-cm3 muscle regions of 6 macaques immunosuppressed with tacrolimus and dexamethasone. Allogeneic ß-galactosidase+ MPCs were injected in other regions as positive controls. Some cell-grafted regions were electroporated to induce extensive muscle regeneration. MPC-grafted regions were sampled 1 month later and analyzed by histology. There were ß-galactosidase+ myofibers in both the regions grafted with human and macaque MPCs. Electroporation increased the engraftment of human MPCs in the same way as in macaque allografts. The histological analysis (hematoxylin and eosin, CD8, and CD4 immunodetection) demonstrated an absence of cellular rejection in most MPC-grafted regions, as well as minimal lymphocytic infiltration in the regions transplanted with human MPCs in the individual with the lowest tacrolimus levels. Circulating de novo anti-donor antibodies were not detected. In conclusion, we report the successful engraftment of human myogenic cells in macaques, which was possible using tacrolimus-based immunosuppression.

Biomedical applications of muscle-derived stem cells: from bench to bedside

INTRODUCTION

Skeletal muscle-derived stem cells (Sk-MDSCs) are considered promising sources of adult stem cell therapy. Skeletal muscle comprises approximately 40-50% of the total body mass with marked potential for postnatal adaptive response, such as muscle hypertrophy, hyperplasia, atrophy, and regenerative capacity. This strongly suggests that skeletal muscle contains various stem/progenitor cells related to muscle-nerve-vascular tissues, which would support the above postnatal events even in adulthood.

AREA COVERED

The focus of this review is the therapeutic potential of the Sk-MDSCs as an adult stem cell autograft. For this purpose, the validity of cell isolation and purification, tissue reconstitution capacity in vivo after transplantation, comparison of the results of basic mouse and preclinical human studies, potential problematic and beneficial aspects, and effective usage have been discussed following the history of clinical applications.

EXPERT OPINION

Although the clinical application of Sk-MDSCs began as a therapy for the systemic disease of Duchenne muscular dystrophy, here, through the unique local injection method, therapy for severely damaged peripheral nerves, particularly the long-gap nerve transection, has been introduced. The beneficial aspects of the use of Sk-MDSCs as the source of local tissue transplantation therapy have also been discussed.

Muscular Contribution to Adolescent Idiopathic Scoliosis from the Perspective of Stem Cell-Based Regenerative Medicine

Adolescent idiopathic scoliosis (AIS) is a relatively frequent disease within a range 0.5%-5.0% of population, with higher frequency in females. While a resultant spinal deformity is usually medically benign condition, it produces far going psychosocial consequences, which warrant attention. The etiology of AIS is unknown and current therapeutic approaches are symptomatic only, and frequently inconvenient or invasive. Muscular contribution to AIS is widely recognized, although it did not translate to clinical routine as yet. Muscle asymmetry has been documented by pathological examinations as well as systemic muscle disorders frequently leading to scoliosis. It has been also reported numerous genetic, metabolic and radiological alterations in patients with AIS, which are linked to muscular and neuromuscular aspects. Therefore, muscles might be considered an attractive and still insufficiently exploited therapeutic target for AIS. Stem cell-based regenerative medicine is rapidly gaining momentum based on the tremendous progress in understanding of developmental biology. It comes also with a toolbox of various stem cells such as satellite cells or mesenchymal stem cells, which could be transplanted; also, the knowledge acquired in research on regenerative medicine can be applied to manipulation of endogenous stem cells to obtain desired therapeutic goals. Importantly, paravertebral muscles are located relatively superficially; therefore, they can be an easy target for minimally invasive approaches to treatment of AIS. It comes in pair with a fast progress in image guidance, which allows for precise delivery of therapeutic agents, including stem cells to various organs such as brain, muscles, and others. Summing up, it seems that there is a link between AIS, muscles, and stem cells, which might be worth of further investigations with a long-term goal of setting foundations for eventual bench-to-bedside translation.

(Epi)genetic Modifications in Myogenic Stem Cells: From Novel Insights to Therapeutic Perspectives

The skeletal muscle is considered to be an ideal target for stem cell therapy as it has an inherent regenerative capacity. Upon injury, the satellite cells, muscle stem cells that reside under the basal lamina of the myofibres, start to differentiate in order to reconstitute the myofibres while maintaining the initial stem cell pool. In recent years, it has become more and more evident that epigenetic mechanisms such as histon modifications, DNA methylations and microRNA modulations play a pivatol role in this differentiation process. By understanding the mechanisms behind myogenesis, researchers are able to use this knowledge to enhance the differentiation and engraftment potential of different muscle stem cells. Besides manipulation on an epigenetic level, recent advances in the field of genome-engineering allow site-specific modifications in the genome of these stem cells. Combining epigenetic control of the stem cell fate with the ability to site-specifically correct mutations or add genes for further cell control, can increase the use of stem cells as treatment of muscular dystrophies drastically. In this review, we will discuss the advances that have been made in genome-engineering and the epigenetic regulation of muscle stem cells and how this knowledge can help to get stem cell therapy to its full potential.

De Novo Circulating Antidonor's Cell Antibodies During Induced Acute Rejection of Allogeneic Myofibers in Myogenic Cell Transplantation: A Study in Nonhuman Primates

Background

Transplantation of myogenic cells has potential applications in the treatment of muscle pathologies. Excluding purely autologous cell transplantation, graft viability depends on an adequate control of acute rejection (AR). To contribute in understanding AR in this context, we analyzed whether de novo circulating antibodies against donor’s cells are detected during induced AR of graft-derived myofibers in nonhuman primates.

Methods

We allotransplanted satellite cell-derived myoblasts in macaques immunosuppressed with tacrolimus. To induce AR of graft-derived myofibers, we administered tacrolimus for 4 weeks to allow complete myofiber formation, and then we stopped tacrolimus administration. Cell-grafted sites were biopsied at tacrolimus withdrawal and then every 2 weeks and analyzed by histology until AR completion. Blood samples were taken before immunosuppression, at tacrolimus withdrawal and then every 2 weeks to detect antibodies against the donor’s cells by flow cytometry.

Results

There was an increase of antibodies against the donor’s cells related to AR in all monkeys. This increase was variable in intensity, and preceded, coincided or followed the histological evidence of AR (focal accumulations of lymphocytes) and/or the loss of myofibers of donor origin, and remained until the end of the follow-up (up to 8 weeks after tacrolimus withdrawal).

Conclusions

Flow cytometry detection of de novo circulating antibodies against the donor’s cells was consistently associated with AR. A clear increase in this antibody detection indicated current or recent AR. Smaller increases in comparison to the preimmunosuppression values were not associated with AR.

The Process of Engraftment of Myogenic Cells in Skeletal Muscles of Primates: Understanding Clinical Observations and Setting Directions in Cell Transplantation Research

We studied in macaques the evolution of the intramuscular transplantation of muscle precursor cells between the time of administration and the time at which the graft is considered stable. Satellite cell–derived myoblasts labeled with ß-galactosidase were transplanted into 1 cm³ muscle regions following cell culture and transplantation protocols similar to our last clinical trials. These regions were biopsied 1 h, 1, 3, 7 d, and 3 wk later and analyzed by histology. We observed that the cell suspension leaks from the muscle bundles during injection toward the epimysium and perimysium, where most cells accumulate after transplantation. We observed evidence of necrosis, apoptosis, and mitosis in the accumulations of grafted cells, and of potential migration to participate in myofiber regeneration in the surrounding muscle bundles. After 3 wk, the compact accumulations of grafted cells left only some graft-derived myotubes and small myofibers in the perimysium. Hybrid myofibers were abundant in the muscle fascicles at 3 wk posttransplantation, and they most likely occur by grafted myoblasts that migrated from the peripheral accumulations than by the few remaining within the fascicles immediately after injection. These observations explain the findings in clinical trials of myoblast transplantation and provide information for the future research in cell therapy in myology.

Article Commentary: Stem Cell Research in Cell Transplantation: An Analysis of Geopolitical Influence by Publications

One of the fastest growing fields in researching treatments for neurodegenerative and other disorders is the use of stem cells. These cells are naturally occurring and can be obtained from three different stages of an organism's life: embryonic, fetal, and adult. In the US, political doctrine has restricted use of federal funds for stem cells, enhancing research towards an adult source. In order to determine how this legislation may be represented by the stem cell field, a retrospective analysis of stem cell articles published in the journal Cell Transplantation over a 2-year period was performed. Cell Transplantation is considered a translational journal from preclinical to clinical, so it was of interest to determine the publication outcome of stem cell articles 6 years after the US regulations. The distribution of the source of stem cells was found to be biased towards the adult stage, but relatively similar over the embryonic and fetal stages. The fetal stem cell reports were primarily neural in origin, whereas the adult stem cell ones were predominantly mesenchymal and used mainly in neural studies. The majority of stem cell studies published in Cell Transplantation were found to fall under the umbrella of neuroscience research. American scientists published the most articles using stem cells with a bias towards adult stem cells, supporting the effect of the legislation, whereas Europe was the leading continent with a bias towards embryonic and fetal stem cells, where research is “controlled” but not restricted. Japan was also a major player in the use of stem cells. Allogeneic transplants (where donor and recipient are the same species) were the most common transplants recorded, although the transplantation of human-derived stem cells into rodents was the most common specific transplantation performed. This demonstrates that the use of stem cells is an increasingly important field (with a doubling of papers between 2005 and 2006), which is likely to develop into a major therapeutic area over the next few decades and that funding restrictions can affect the type of research being performed.

Stem cells migration during skeletal muscle regeneration - the role of Sdf-1/Cxcr4 and Sdf-1/Cxcr7 axis

The skeletal muscle regeneration occurs due to the presence of tissue specific stem cells - satellite cells. These cells, localized between sarcolemma and basal lamina, are bound to muscle fibers and remain quiescent until their activation upon muscle injury. Due to pathological conditions, such as extensive injury or dystrophy, skeletal muscle regeneration is diminished. Among the therapies aiming to ameliorate skeletal muscle diseases are transplantations of the stem cells. In our previous studies we showed that Sdf-1 (stromal derived factor −1) increased migration of stem cells and their fusion with myoblasts in vitro. Importantly, we identified that Sdf-1 caused an increase in the expression of tetraspanin CD9 - adhesion protein involved in myoblasts fusion. In the current study we aimed to uncover the details of molecular mechanism of Sdf-1 action. We focused at the Sdf-1 receptors - Cxcr4 and Cxcr7, as well as signaling pathways induced by these molecules in primary myoblasts, as well as various stem cells - mesenchymal stem cells and embryonic stem cells, i.e. the cells of different migration and myogenic potential. We showed that Sdf-1 altered actin organization via FAK (focal adhesion kinase), Cdc42 (cell division control protein 42), and Rac-1 (Ras-Related C3 Botulinum Toxin Substrate 1). Moreover, we showed that Sdf-1 modified the transcription profile of genes encoding factors engaged in cells adhesion and migration. As the result, cells such as primary myoblasts or embryonic stem cells, became characterized by more effective migration when transplanted into regenerating muscle.

Duchenne muscular dystrophy: current cell therapies

Duchenne muscular dystrophy is a genetically determined X-linked disease and the most common, progressive pediatric muscle disorder. For decades, research has been conducted to find an effective therapy. This review presents current therapeutic methods for Duchenne muscular dystrophy, based on scientific articles in English published mainly in the period 2000 to 2014. We used the PubMed database to identify and review the most important studies. An analysis of contemporary studies of stem cell therapy and the use of granulocyte colony-stimulating factor (G-CSF) in muscular dystrophy was performed.

Cell therapy in muscular dystrophies: many promises in mice and dogs, few facts in patients

INTRODUCTION

Muscular dystrophies (MDs) are genetic diseases that produce progressive loss of skeletal muscle fibers. Cell therapy (CT) is an experimental approach to treat MD. The first clinical trials of CT in MD conducted in the 1990s were based on myoblast transplantation (MT). Since they did not yield the expected results, several researchers sought to discover other cells with more advantageous properties than myoblasts whereas others sought to improve MT.

AREAS COVERED

We explain the properties that are required for a cell to be used in CT of MD. We briefly review most of the cells that were proposed for this CT, and to what extent these properties were met not only in laboratory animals but also in clinical trials.

EXPERT OPINION

Although the repertoire of cells proposed for CT of MD has been expanded since the 1990s, only myoblasts have currently demonstrated unequivocally to significantly engraft in humans. Indeed, MT for MD involves significant technical challenges that need be solved. While it would be ideal to find cells involving less technical challenges for CT of MD, there is so far no clinical evidence that this is possible and therefore the work to improve MT should continue.

First study of intra-arterial delivery of myogenic mononuclear cells to skeletal muscles in primates

The main challenge of cell transplantation as a treatment of myopathies is the large amount of tissue to treat. Intravascular delivery of cells may be an ideal route if proven to be effective and safe. Given the importance of nonhuman primates for preclinical research in transplantation, we tested the intra-arterial injection of β-galactosidase (β-Gal)-labeled myoblasts in macaques. Cells were injected into one of the femoral arteries in seven monkeys. Some muscle sites were damaged concomitantly in three monkeys. Various organs and muscles were sampled 1 h, 1 day, 12 days, 3 weeks, and 5 weeks after transplantation. Samples were analyzed by histology. Most β-Gal(+) cells were observed in the capillaries and arterioles of muscles and other tissues of the leg homolateral to the cell injection. Groups of necrotic myofibers in the proximity of an arteriole plugged by a β-Gal(+) embolus were interpreted as microinfarcts. Scarce β-Gal(+) cells were observed in the lungs 1 h and 1 day posttransplantation. No β-Gal(+) cells were observed in other organs or muscles. β-Gal(+) myofibers were observed 12 days, 3 weeks, and 5 weeks after transplantation in muscles of the leg after the cell injection, in sites that were damaged at the time of cell injection. In conclusion, most intra-arterially injected myoblasts were retained in vessels of the leg homolateral to the cell injection site, and they fused with myofibers in regions in which there was a process of myofiber regeneration. This manuscript is published as part of the International Association of Neurorestoratology (IANR) special issue of Cell Transplantation.

Electroporation as a method to induce myofiber regeneration and increase the engraftment of myogenic cells in skeletal muscles of primates

Engraftment of intramuscularly transplanted myogenic cells in mice can be optimized after induction of massive myofiber damage that triggers myofiber regeneration and recruitment of grafted cells; this generally involves either myotoxin injection or cryodamage. There are no effective methods to produce a similar process in the muscles of large mammals such as primates. In this study, we tested the use of intramuscular electroporation for this purpose in 11 macaques. The test sites were 1 cm of skeletal muscle. Each site was treated with 3 penetrations of a 2-needle electrode with 1 cm spacing, applying 3 pulses of 400 V/cm, for a duration of 5 milliseconds and a delay of 200 milliseconds during each penetration. Transplantation of β-galactosidase-labeled myoblasts was done in electroporated and nonelectroporated sites. Electroporation induced massive myofiber necrosis that was followed by efficient muscle regeneration. Myoblast engraftment was substantially increased in electroporated compared with nonelectroporated sites. This suggests that electroporation may be a useful tool to study muscle regeneration in primates and other large mammals and as a method for increasing the engraftment of myoblasts and other myogenic cells in intramuscular transplantation.

Administration of a soluble activin type IIB receptor promotes the transplantation of human myoblasts in dystrophic mice

Duchenne muscular dystrophy (DMD) is a recessive disease caused by a dystrophin gene mutation. Myoblast transplantation permits the introduction of the dystrophin gene into dystrophic muscle fibers. However, this strategy has so far produced limited results. Modulation of transforming growth factor-β (TGF-β) superfamily signaling promotes skeletal muscle differentiation and growth and myogenic regeneration. We investigated the possibility that the combination of TGF-β superfamily signaling inhibition with myoblast transplantation might be an effective therapeutic approach in dystrophin-deficient patients. In vitro, blocking myostatin and other ligands with a soluble form of the extracellular domain of the activin IIB receptor (ActRIIB/Fc) upregulated the expression of myogenic differentiation factors and increased human myoblast fusion. In vivo, systemic inhibition of activin IIB receptor signaling by delivery of ActRIIB/Fc increased the success of the myoblast transplantation. This effect was further increased by forcing the mice to swim weekly to induce cycles of muscle degeneration and regeneration. Treatment of dystrophic mice with ActRIIB/Fc led to increased body weight, increased skeletal muscle mass, and improved myoblast transplantation. Thus, ActRIIB/Fc represents an effective therapeutic strategy for muscular dystrophies, and its effects are enhanced when combined with muscle exercise.

Necrosis, sarcolemmal damage and apoptotic events in myofibers rejected by CD8+ lymphocytes: Observations in nonhuman primates

To detect the mechanisms of death in allogeneic myofibers rejected by the immune system, myoblasts were allotransplanted in muscles of macaques immunosuppressed with tacrolimus. Immunosuppression was stopped 1month later to induce a massive rejection of allogeneic myofibers. Grafted sites were biopsied at 2-week intervals and analyzed by histology. The loss of allogeneic myofibers was rapid and concomitant with an intense infiltration of CD8+ lymphocytes. Several necrotic myofibers were observed in the lymphocyte accumulations by intracellular complement immunodetection. Dystrophin and spectrin immunodetection showed sarcolemmal damage in myofibers surrounded and invaded by CD8+ lymphocytes. Active caspase-3 was immunodetected in some myofibers surrounded by CD8+ lymphocytes. This is the first evidence that the collapse of myofibers attacked by T lymphocytes occurs by necrosis possibly due to damage of the sarcolemma. Caspase 3 is activated at least in some myofibers, but there was no evidence of a complete classical process of apoptosis.

Protective effect of sodium ascorbate on efficacy of intramuscular transplantation of autologous muscle-derived cells

INTRODUCTION

The possible reason for elimination of myogenic cells after transplantation is inflammation at the injection site associated with oxidative stress. The aim of this study was to determine whether preconditioning of muscle-derived cells with an antioxidant, sodium ascorbate, can influence the fate of transplanted cells.

METHODS

Autologous transplantation of muscle-derived cells was performed in rabbits. Isolated cells were identified, lipofected with β-galactosidase, preincubated or not with sodium ascorbate, and injected intramuscularly.

RESULTS

Two weeks after autologous transplantation in the edge of a previous muscle defect, donor cells formed multinucleated young myotubes. Pretreatment of cells with sodium ascorbate before injection resulted in a significant increase of donor cells at the injection site 2 weeks after transfer.

CONCLUSIONS

These results show that: (1) preincubation with antioxidant can increase the efficacy of myogenic cell transplantation; and (2) oxidative stress may play a role in elimination of cells after autologous transplantation.

The potential of stem cells in the treatment of skeletal muscle injury and disease

Tissue engineering is a pioneering field with huge advances in recent times. These advances are not only in the understanding of how cells can be manipulated but also in potential clinical applications. Thus, tissue engineering, when applied to skeletal muscle cells, is an area of huge prospective benefit to patients with muscle disease/damage. This could include damage to muscle from trauma and include genetic abnormalities, for example, muscular dystrophies. Much of this research thus far has been focused on satellite cells, however, mesenchymal stem cells have more recently come to the fore. In particular, results of trials and further research into their use in heart failure, stress incontinence, and muscular dystrophies are eagerly awaited. Although no doubt, stem cells will have much to offer in the future, the results of further research still limit their use.

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.

Intramuscular cell transplantation as a potential treatment of myopathies: clinical and preclinical relevant data

INTRODUCTION

Myopathies produce deficits in skeletal muscle function and, in some cases, literally progressive loss of skeletal muscles. The transplantation of cells able to differentiate into myofibers is an experimental strategy for the potential treatment of some of these diseases.

AREAS COVERED

Among the two routes used to deliver cells to skeletal muscles, that is intramuscular and intravascular, this paper focuses on the intramuscular route due to our expertise and because it is the most used in animal experiments and the only tested so far in humans. Given the absence of recent reviews about clinical observations and the profusion based on mouse results, this review prioritizes observations made in humans and non-human primates. The review provides a vision of cell transplantation in myology centered on what can be learned from clinical trials and from preclinical studies in non-human primates and leading mouse studies.

EXPERT OPINION

Experiments on myogenic cell transplantation in mice are essential to quickly identify potential treatments, but studies showing the possibility to scale up the methods in large mammals are indispensable to determine their applicability in humans and to design clinical protocols.

Repairing skeletal muscle: regenerative potential of skeletal muscle stem cells

Skeletal muscle damaged by injury or by degenerative diseases such as muscular dystrophy is able to regenerate new muscle fibers. Regeneration mainly depends upon satellite cells, myogenic progenitors localized between the basal lamina and the muscle fiber membrane. However, other cell types outside the basal lamina, such as pericytes, also have myogenic potency. Here, we discuss the main properties of satellite cells and other myogenic progenitors as well as recent efforts to obtain myogenic cells from pluripotent stem cells for patient-tailored cell therapy. Clinical trials utilizing these cells to treat muscular dystrophies, heart failure, and stress urinary incontinence are also briefly outlined.

A First Semimanual Device for Clinical Intramuscular Repetitive Cell Injections

Intramuscular cell transplantation in humans requires so far meticulous repetitive cell injections. Performed percutaneously with syringes operated manually, the procedure is very time consuming and requires a lot of concentration to deliver the cells exactly in the required region. This becomes impractical and inaccurate for large volumes of muscle. In order to accelerate this task, to render it more precise, and to perform injections more reproducible in large volumes of muscle, we developed a specific semimanual device for intramuscular repetitive cell injections. Our prototype delivers very small quantities of cell suspension, homogeneously throughout several needles, from a container in the device. It was designed in order to deliver the cells as best as possible only in a given subcutaneous region (in our case, skeletal muscles accessible from the surface), avoiding wasting in skin and hypodermis. The device was tested in monkeys by performing intramuscular allotransplantations of β-galactosidase-labeled myoblasts. During transplantations, it was more ergonomic and considerably faster than manually operated syringes, facilitating the cell graft in whole limb muscles. Biopsies of the myoblast-injected muscles 1 month later showed abundant β-galactosidase-positive myofibers with homogeneous distribution through the biopsy sections. This is the first device specifically designed for the needs of intramuscular cell transplantation in a clinical context.

Overexpression of Follistatin in Human Myoblasts Increases Their Proliferation and Differentiation, and Improves the Graft Success in SCID Mice

Duchenne muscular dystrophy is caused by the absence of functional dystrophin, leading to the myofiber membrane instability and progressive muscle atrophy. Myoblast transplantation in dystrophic muscles is a potential therapy, as it permits the long-term restoration of dystrophin expression in transplanted muscles. However, the success of this approach is limited by the short period of muscle repair following myoblast transplantation. Myostatin, a powerful inhibitor of muscle growth, is involved in terminating the period of muscle repair following injury by reducing myoblast proliferation and differentiation. Follistatin forms a complex with myostatin, preventing its interaction with its receptor and thus blocking the myostatin signal. Here, we used a lentivirus to overexpress the follistatin protein in normal myoblasts to block the myostatin signaling. We measured the potential of transduced myoblasts to proliferate and to form multinucleated myotubes in vitro. And finally, we considered the engraftment success of those transduced myoblasts in comparison with control cells in vivo within SCID mice TA muscle. Our results first confirmed the overexpression of follistatin into lentivirus transduced myoblasts, and second showed that the overexpression of the follistatin in normal human myoblasts improved in vitro their proliferation rate by about 1.5-fold after 96 h and also their differentiation rate by about 1.6- and 1.8-fold, respectively, in the absence and in the presence of recombinant myostatin. Finally, our data demonstrated that the engraftment of human normal myoblasts overexpressing the follistatin protein into SCID mouse muscles was enhanced by twofold.

Inhibiting myostatin with follistatin improves the success of myoblast transplantation in dystrophic mice

Duchenne muscular dystrophy is a recessive disease due to a mutation in the dystrophin gene. Myoblast transplantation permits to introduce the dystrophin gene in dystrophic muscle fibers. However, the success of this approach is reduced by the short duration of the regeneration following the transplantation, which reduces the number of hybrid fibers. Our aim was to verify whether the success of the myoblast transplantation is enhanced by blocking the myostatin signal with an antagonist, follistatin. Three different approaches were studied to overexpress follistatin in the muscles of mdx mice transplanted with myoblasts. First, transgenic follistatin/mdx mice were generated; second, a follistatin plasmid was electroporated in mdx muscles, and finally, follistatin was induced in mdx mice muscles by a treatment with a histone deacetylase inhibitor. The three approaches improved the success of the myoblast transplantation. Moreover, fiber hypertrophy was also observed in all muscles, demonstrating that myostatin inhibition by follistatin is a good method to improve myoblast transplantation and muscle function. Myostatin inhibition by follistatin in combination with myoblast transplantation is thus a promising novel therapeutic approach for the treatment of muscle wasting in diseases such as Duchenne muscular dystrophy.