Myoblast transplantation for inherited myopathies: a clinical approach

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.

Assessing and enhancing migration of human myogenic progenitors using directed iPS cell differentiation and advanced tissue modelling

Muscle satellite stem cells (MuSCs) are responsible for skeletal muscle growth and regeneration. Despite their differentiation potential, human MuSCs have limited in vitro expansion and in vivo migration capacity, limiting their use in cell therapies for diseases affecting multiple skeletal muscles. Several protocols have been developed to derive MuSC-like progenitors from human induced pluripotent stem (iPS) cells (hiPSCs) to establish a source of myogenic cells with controllable proliferation and differentiation. However, current hiPSC myogenic derivatives also suffer from limitations of cell migration, ultimately delaying their clinical translation. Here we use a multi-disciplinary approach including bioinformatics and tissue engineering to show that DLL4 and PDGF-BB improve migration of hiPSC-derived myogenic progenitors. Transcriptomic analyses demonstrate that this property is conserved across species and multiple hiPSC lines, consistent with results from single cell motility profiling. Treated cells showed enhanced trans-endothelial migration in transwell assays. Finally, increased motility was detected in a novel humanised assay to study cell migration using 3D artificial muscles, harnessing advanced tissue modelling to move hiPSCs closer to future muscle gene and cell therapies.

CRISPR/Cas9 editing of directly reprogrammed myogenic progenitors restores dystrophin expression in a mouse model of muscular dystrophy

Genetic mutations in dystrophin manifest in Duchenne muscular dystrophy (DMD), the most commonly inherited muscle disease. Here, we report on reprogramming of fibroblasts from two DMD mouse models into induced myogenic progenitor cells (iMPCs) by MyoD overexpression in concert with small molecule treatment. DMD iMPCs proliferate extensively, while expressing myogenic stem cell markers including Pax7 and Myf5. Additionally, DMD iMPCs readily give rise to multinucleated myofibers that express mature skeletal muscle markers; however, they lack DYSTROPHIN expression. Utilizing an exon skipping-based approach with CRISPR/Cas9, we report on genetic correction of the dystrophin mutation in DMD iMPCs and restoration of protein expression in vitro. Furthermore, engraftment of corrected DMD iMPCs into the muscles of dystrophic mice restored DYSTROPHIN expression and contributed to the muscle stem cell reservoir. Collectively, our findings report on a novel in vitro cellular model for DMD and utilize it in conjunction with gene editing to restore DYSTROPHIN expression in vivo.

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iMPCs generated from DMD mouse models

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DMD iMPCs are expandable and express satellite cell and differentiation markers

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Correction of the dystrophin mutation in DMD iMPCs utilizing CRISPR/Cas9

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Engraftment of corrected DMD iMPCs restores DYSTROPHIN expression in vivo

SMART approaches for genome-wide analyses of skeletal muscle stem and niche cells

Muscle stem cells (MuSCs) also called satellite cells are the building blocks of skeletal muscle, the largest tissue in the human body which is formed primarily of myofibers. While MuSCs are the principal cells that directly contribute to the formation of the muscle fibers, their ability to do so depends on critical interactions with a vast array of nonmyogenic cells within their niche environment. Therefore, understanding the nature of communication between MuSCs and their niche is of key importance to understand how the skeletal muscle is maintained and regenerated after injury. MuSCs are rare and therefore difficult to study in vivo within the context of their niche environment. The advent of single-cell technologies, such as switching mechanism at 5' end of the RNA template (SMART) and tagmentation based technologies using hyperactive transposase, afford the unprecedented opportunity to perform whole transcriptome and epigenome studies on rare cells within their niche environment. In this review, we will delve into how single-cell technologies can be applied to the study of MuSCs and muscle-resident niche cells and the impact this can have on our understanding of MuSC biology and skeletal muscle regeneration.

Cellular Therapy for Chronic Traumatic Brachial Plexus Injury

Cellular therapy is being actively pursued as a therapeutic modality in many of the neurological diseases. A variety of stem cells from diverse sources have been studied in detail and have been shown to exhibit angiogenetic and immunomodulatory properties in addition to other neuroprotective effects. Published clinical data have shown bone marrow mononuclear cell (BMMNC) injection in neurological disorders is safe and possesses regenerative potential. We illustrate a case of 27-year-old male with traumatic brachial plexus injury, administered with autologous BMMNCs intrathecally and intramuscularly, followed by multidisciplinary rehabilitation. At the follow-up assessment of 3 and 7 months after first cell transplantation, improvements were recorded in muscle strength and movements. Electromyography (EMG) performed after the intervention showed a response in biceps and deltoid muscles suggesting the process of reinnervation at the site of injury. In view of the improvements observed after the treatment, the patient underwent second cell transplantation 8 months after the first transplantation. Muscle wasting had completely stopped with an increase in the muscle girth. No adverse effects were noted. Improvements were maintained for 4 years. A comprehensive randomized study for this type of injury is needed to establish the therapeutic benefits of cellular therapy.

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.

HGF potentiates extracellular matrix-driven migration of human myoblasts: involvement of matrix metalloproteinases and MAPK/ERK pathway

Background

The hepatocyte growth factor (HGF) is required for the activation of muscle progenitor cells called satellite cells (SC), plays a role in the migration of proliferating SC (myoblasts), and is present as a soluble factor during muscle regeneration, along with extracellular matrix (ECM) molecules. In this study, we aimed at determining whether HGF is able to interact with ECM proteins, particularly laminin 111 and fibronectin, and to modulate human myoblast migration.

Methods

We evaluated the expression of the HGF-receptor c-Met, laminin, and fibronectin receptors by immunoblotting, flow cytometry, or immunofluorescence and used Transwell assays to analyze myoblast migration on laminin 111 and fibronectin in the absence or presence of HGF. Zymography was used to check whether HGF could modulate the production of matrix metalloproteinases by human myoblasts, and the activation of MAPK/ERK pathways was evaluated by immunoblotting.

Results

We demonstrated that human myoblasts express c-Met, together with laminin and fibronectin receptors. We observed that human laminin 111 and fibronectin have a chemotactic effect on myoblast migration, and this was synergistically increased when low doses of HGF were added. We detected an increase in MMP-2 activity in myoblasts treated with HGF. Conversely, MMP-2 inhibition decreased the HGF-associated stimulation of cell migration triggered by laminin or fibronectin. HGF treatment also induced in human myoblasts activation of MAPK/ERK pathways, whose specific inhibition decreased the HGF-associated stimulus of cell migration triggered by laminin 111 or fibronectin.

Conclusions

We demonstrate that HGF induces ERK phosphorylation and MMP production, thus stimulating human myoblast migration on ECM molecules. Conceptually, these data state that the mechanisms involved in the migration of human myoblasts comprise both soluble and insoluble moieties. This should be taken into account to optimize the design of therapeutic cell transplantation strategies by improving the migration of donor cells within the host tissue, a main issue regarding this approach.

Electronic supplementary material

The online version of this article (10.1186/s13395-017-0138-6) contains supplementary material, which is available to authorized users.

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

Intramuscular myoblast transplantation in humans and nonhuman primates requires precise repetitive cell injections very close to each other. Performed with syringes operated manually throughout large regions, this procedure takes a lot of time, becoming tiring and thus imprecise. We tested two repetitive dispensers with Hamilton syringes as cell injection devices to facilitate this procedure. Monkeys received intramuscular allotransplantations of β-galactosidase-labeled myoblasts, using either a monosyringe or a multisyringe repeating dispenser. The monosyringe repeating dispenser allowed performing cell injections faster and easier than with a manually operated syringe. The multisyringe dispenser accelerated the procedure still more, but it was not ergonomic. Biopsies of the myoblast-injected sites 1 month later showed abundant β-galactosidase-positive myofibers, with the same density and morphological pattern observed following myoblast transplantation with a syringe operated manually. We recommend the monosyringe repeating dispenser for myoblast transplantation in skeletal muscles and maybe in the heart.

1,25-Dihydroxyvitamin D3 Increases the Transplantation Success of Human Muscle Precursor Cells in SCID Mice

Human muscle precursor cell (hMPC) transplantation is a potential therapy for severe muscle trauma or myopathies. Some previous studies demonstrated that 1,25-dihydroxyvitamin-D3 (1,25-D3) acted directly on myoblasts, regulating their proliferation and fusion. 1,25-D3 is also involved in apoptosis modulation of other cell types and may thus contribute to protect the transplanted hMPCs. We have therefore investigated whether 1,25-D3 could improve the hMPC graft success. The 1,25-D3 effects on hMPC proliferation, fusion, and survival were initially monitored in vitro. hMPCs were also grafted in the tibialis anterior of SCID mice treated or not with 1,25-D3 to determine its in vivo effect. Graft success, proliferation, and viability of transplanted hMPCs were evaluated. 1,25-D3 enhanced proliferation and fusion of hMPCs in vitro and in vivo. However, 1,25-D3 did not protect hMPCs from various proapoptotic factors (in vitro) or during the early posttransplantation period. 1,25-D3 enhanced hMPC graft success because the number of muscle fibers expressing human dystrophin was significantly increased in the TA sections of 1,25-D3-treated mice (166.75 ± 20.64) compared to the control mice (97.5 ± 16.58). This result could be partly attributed to the improvement of the proliferation and differentiation of hMPCs in the presence of 1,25-D3. Thus, 1,25-D3 administration could improve the clinical potential of hMPC transplantation currently developed for muscle trauma or myopathies.

An acellular biologic scaffold treatment for volumetric muscle loss: results of a 13-patient cohort study

Volumetric muscle loss (VML) is a severe and debilitating clinical problem. Current standard of care includes physical therapy or orthotics, which do not correct underlying strength deficits, and surgical tendon transfers or muscle transfers, which involve donor site morbidity and fall short of restoring function. The results of a 13-patient cohort study are described herein and involve a regenerative medicine approach for VML treatment. Acellular bioscaffolds composed of mammalian extracellular matrix (ECM) were implanted and combined with aggressive and early physical therapy following treatment. Immunolabeling of ultrasound-guided biopsies, and magnetic resonance imaging and computed tomography imaging were performed to analyse the presence of stem/progenitor cells and formation of new skeletal muscle. Force production, range-of-motion and functional task performance were analysed by physical therapists. Electrodiagnostic evaluation was used to analyse presence of innervated skeletal muscle. This study is registered with ClinicalTrials.gov, numbers NCT01292876. In vivo remodelling of ECM bioscaffolds was associated with mobilisation of perivascular stem cells; formation of new, vascularised, innervated islands of skeletal muscle within the implantation site; increased force production; and improved functional task performance when compared with pre-operative performance. Compared with pre-operative performance, by 6 months after ECM implantation, patients showed an average improvement of 37.3% (P<0.05) in strength and 27.1% improvement in range-of-motion tasks (P<0.05). Implantation of acellular bioscaffolds derived from ECM can improve strength and function, and promotes site-appropriate remodelling of VML defects. These findings provide early evidence of bioscaffolding as a viable treatment of VML.

MMP1 gene expression enhances myoblast migration and engraftment following implanting into mdx/SCID mice

Myoblast transplantation (MT) is a method to introduce healthy genes into abnormal skeletal muscle. It has been considered as a therapeutic modality in the last few decades for diseases such as Duchenne Muscular Dystrophy (DMD). However, challenges including cell death and poor graft engraftment have limited its application. The current experiment utilizes MMP1 gene transfer to improve the efficacy of myoblast transplantation into the diseased dystrophic skeletal muscle of mdx mice. Our results indicated that MMP1 expression can promote myogenic differentiation and fusion capacities, increase migration of MMP1 expressing myoblasts in vitro, as well as improve engraftment of dystrophin positive myofibers in vivo. Taken together, our observation suggests that the addition of MMP1 can overcome limitations in MT and improve its clinical efficacy.

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.

Local injection of autologous bone marrow cells to regenerate muscle in patients with traumatic brachial plexus injury: a pilot study

Objectives

Traumatic brachial plexus injury causes severe functional impairment of the arm. Elbow flexion is often affected. Nerve surgery or tendon transfers provide the only means to obtain improved elbow flexion. Unfortunately, the functionality of the arm often remains insufficient. Stem cell therapy could potentially improve muscle strength and avoid muscle-tendon transfer. This pilot study assesses the safety and regenerative potential of autologous bone marrow-derived mononuclear cell injection in partially denervated biceps.

Methods

Nine brachial plexus patients with insufficient elbow flexion (i.e., partial denervation) received intramuscular escalating doses of autologous bone marrow-derived mononuclear cells, combined with tendon transfers. Effect parameters included biceps biopsies, motor unit analysis on needle electromyography and computerised muscle tomography, before and after cell therapy.

Results

No adverse effects in vital signs, bone marrow aspiration sites, injection sites, or surgical wound were seen. After cell therapy there was a 52% decrease in muscle fibrosis (p = 0.01), an 80% increase in myofibre diameter (p = 0.007), a 50% increase in satellite cells (p = 0.045) and an 83% increase in capillary-to-myofibre ratio (p < 0.001) was shown. CT analysis demonstrated a 48% decrease in mean muscle density (p = 0.009). Motor unit analysis showed a mean increase of 36% in motor unit amplitude (p = 0.045), 22% increase in duration (p = 0.005) and 29% increase in number of phases (p = 0.002).

Conclusions

Mononuclear cell injection in partly denervated muscle of brachial plexus patients is safe. The results suggest enhanced muscle reinnervation and regeneration.

Cite this article: Bone Joint Res 2014;3:38–47.

Satellite cell therapy - from mice to men

Satellite cells are rare mononuclear skeletal muscle-resident cells that are the chief contributors to regenerative myogenesis following muscle injury. Although first identified more than 50 years ago, it is only recently that the murine satellite cell has become molecularly defined with the ability to prospectively isolate these cells from their niche. Human satellite cells are considerably less well understood with relatively few studies having been performed on them. In this review, a critical evaluation of this literature is provided along with a discussion of the practical and methodological issues involved with research on human satellite cells. The therapeutic potential of these and other cells types is also discussed, and the various challenges that face satellite cell therapy are addressed.

Intramuscular transplantation of myogenic cells in primates: importance of needle size, cell number, and injection volume

The aim of this study was to quantitatively define the main measurable technical parameters for the intramuscular transplantation of myogenic cells in primates. Myoblasts transduced with the gene coding for β-galactosidase were injected into the skeletal muscles of 15 monkeys. The following parameters were studied: needle size, number of cells per injection, and volume of cell suspension per injection. Monkeys were immunosuppressed with tacrolimus. The cell-injected sites were biopsied 1 or 2 months later. Biopsies were examined histologically to assess the myoblast engraftment and the muscle structure. The conclusions were as follows: (1) Needles should be thin enough to avoid important tissue damage and allow muscle regeneration as satisfactory as possible. Among those tested, 27G should be the choice if the length is consistent with depth of injection. (2) At least 100,000 cells should be delivered per centimeter of needle trajectory. (3) The smallest volumes of cell suspension per injection should be used. In this study, 1 µl/cm of injection trajectory was sufficient. In principle, these parameters apply to muscles in which no damage occurred other than the injections.

Myoblasts derived from normal hESCs and dystrophic hiPSCs efficiently fuse with existing muscle fibers following transplantation

Human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs) have an endless self-renewal capacity and can theoretically differentiate into all types of lineages. They thus represent an unlimited source of cells for therapies of regenerative diseases, such as Duchenne muscular dystrophy (DMD), and for tissue repair in specific medical fields. However, at the moment, the low number of efficient specific lineage differentiation protocols compromises their use in regenerative medicine. We developed a two-step procedure to differentiate hESCs and dystrophic hiPSCs in myogenic cells. The first step was a culture in a myogenic medium and the second step an infection with an adenovirus expressing the myogenic master gene MyoD. Following infection, the cells expressed several myogenic markers and formed abundant multinucleated myotubes in vitro. When transplanted in the muscle of Rag/mdx mice, these cells participated in muscle regeneration by fusing very well with existing muscle fibers. Our findings provide an effective method that will permit to use hESCs or hiPSCs for preclinical studies in muscle repair.

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.

Intramuscular Transplantation of Muscle Precursor Cells over-expressing MMP-9 improves Transplantation Success

Duchenne muscular dystrophy (DMD) is characterized by the absence of dystrophin in muscles. A therapeutic approach to restore dystrophin expression in DMD patient's muscles is the transplantation of muscle precursor cells (MPCs). However, this transplantation is limited by the low MPC capacity to migrate beyond the injection trajectory. Matrix metalloproteases (MMPs) are key regulatory molecules in the remodeling of extracellular matrix (ECM) components. MPCs over-expressing MMP-9 were tested by zymography, migration and invasion assays in vitro and by transplantation in mouse muscle. In vitro, MPCs over-expressing MMP-9 have a better invasion capacity than control MPCs. When these cells are transplanted in mouse muscles, the transplantation success is increased by more than 50% and their dispersion is higher than normal cells. MMP-9 over-expression could thus be an approach to improve cell transplantation in DMD patients by increasing the dispersion capacity of transplanted cells.

Human muscle-derived cell populations isolated by differential adhesion rates: phenotype and contribution to skeletal muscle regeneration in Mdx/SCID mice

Muscle-derived stem cells (MDSCs) isolated from murine skeletal tissue by the preplate method have displayed the capability to commit to the myogenic lineage and regenerate more efficiently than myoblasts in skeletal and cardiac muscle in murine Duchenne Muscular Dystrophy mice (mdx). However, until now, these studies have not been translated to human muscle cells. Here, we describe the isolation, by a preplate technique, of candidate human MDSCs, which exhibit myogenic and regenerative characteristics similar to their murine counterparts. Using the preplate isolation method, we compared cells that adhere faster to the flasks, preplate 2 (PP2), and cells that adhere slower, preplate 6 (PP6). The human PP6 cells express several markers of mesenchymal stem cells and are distinct from human PP2 (a myoblast-like population) based on their expression of CD146 and myogenic markers desmin and CD56. After transplantation to the gastrocnemius muscle of mdx/SCID mice, we observe significantly higher levels of PP6 cells participating in muscle regeneration as compared with the transplantation of PP2 cells. This study supports some previous findings related to mouse preplate cells, and also identifies some differences between mouse and human muscle preplate cells.

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.

Dystrophin expression following the transplantation of normal muscle precursor cells protects mdx muscle from contraction-induced damage

Duchenne muscular dystrophy (DMD) is the most frequent muscular dystrophy. Currently, there is no cure for the disease. The transplantation of muscle precursor cells (MPCs) is one of the possible treatments, because it can restore the expression of dystrophin in DMD muscles. In this study, we investigated the effects of myoblasts injected with cardiotoxin on the contractile properties and resistance to eccentric contractions of transplanted and nontransplanted muscles. We used the extensor digitorum longus (EDL) as a model for our study. We conclude that the sole presence of dystrophin in a high percentage of muscle fibers is not sufficient by itself to increase the absolute or the specific force in the EDL of transplanted mdx muscle. This lack of strength increase may be due to the extensive damage that was produced by the cardiotoxin, which was coinjected with the myoblasts. However, the dystrophin presence is sufficient to protect muscle from eccentric damage as indicated by the force drop results.

Intramuscular transplantation of human postnatal myoblasts generates functional donor-derived satellite cells

Myogenic cell transplantation is an experimental approach for the treatment of myopathies. In this approach, transplanted cells need to fuse with pre-existing myofibers, form new myofibers, and generate new muscle precursor cells (MPCs). The last property was fully reported following myoblast transplantation in mice but remains poorly studied with human myoblasts. In this study, we provide evidence that the intramuscular transplantation of postnatal human myoblasts in immunodeficient mice generates donor-derived MPCs and specifically donor-derived satellite cells. In a first experiment, cells isolated from mouse muscles 1 month after the transplantation of human myoblasts proliferated in vitro as human myoblasts. These cells were retransplanted in mice and formed myofibers expressing human dystrophin. In a second experiment, we observed that inducing muscle regeneration 2 months following transplantation of human myoblasts led to myofiber regeneration by human-derived MPCs. In a third experiment, we detected by immunohistochemistry abundant human-derived satellite cells in mouse muscles 1 month after transplantation of postnatal human myoblasts. These human-derived satellite cells may correspond totally or partially to the human-derived MPCs evidenced in the first two experiments. Finally, we present evidence that donor-derived satellite cells may be produced in patients that received myoblast transplantation.

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.

Matrix metalloproteinase-1 promotes muscle cell migration and differentiation

Injured skeletal muscle has the capacity to regenerate through a highly coordinated sequence of events that involves both myoblast migration and differentiation into myofibers. Fibrosis may impede muscle regeneration by posing as a mechanical barrier to cell migration and fusion, providing inappropriate signals for cell differentiation, and limiting vascular perfusion of the injury site, subsequently leading to incomplete functional recovery. Our previous studies demonstrated that matrix metalloproteinase-1 (MMP-1) is able to digest fibrous scar tissue and improve muscle healing after injury. The goal of this study is to investigate whether MMP-1 could further enhance muscle regeneration by improving myoblast migration and differentiation. In vitro wound healing assays, flow cytometry, reverse transcriptase-polymerase chain reaction (RT-PCR), and Western blot analyses demonstrated that MMP-1 enhances myoblast migration but is not chemoattractive. We discovered that MMP-1 also enhances myoblast differentiation, which is a critical step in the sequence of muscle regeneration. In addition, RT-PCR and Western blot analyses demonstrated the up-regulation of myogenic factors after MMP-1 treatment. In vivo, we observed that myoblast transplantation was greatly improved after MMP-1 treatment within the dystrophic skeletal muscles of MDX mice. MMP-1 may therefore be able to improve muscle function recovery after injury or disease by increasing both the number of myofibers that are generated by activated myoblasts and the size of myoblast coverage area by promoting migration, thus fostering a greater degree of engraftment.

Ischemic central necrosis in pockets of transplanted myoblasts in nonhuman primates: implications for cell-transplantation strategies

BACKGROUND

Several cell-transplantation strategies implicate the injection of cells into tissues. Avascular accumulations of implanted cells are then formed. Because the diffusion of oxygen and nutrients from the surrounding tissue throughout the implanted cell accumulations may be limited, central ischemic necrosis could develop. We analyzed this possibility after myoblast transplantation in nonhuman primates.

METHODS

Macaca monkeys were injected intramuscularly with different amounts of myoblasts per single site. These sites were sampled 1 hr later and at posttransplantation days 1, 3, 5, and 7 and analyzed by histological techniques.

RESULTS

One day posttransplantation, the largest pockets of implanted cells showed cores of massive necrosis. The width of the peripheral layer of living cells was approximately 100-200 microm. We thus analyzed the relationship between the amount of myoblasts injected per site and the volume of ischemic necrosis. Delivering 0.1 x 10(6) and 0.3 x 10(6) myoblasts did not produce ischemic necrosis; pockets of 1 x 10(6), 3 x 10(6), 10 x 10(6), and 20 x 10(6) myoblasts exhibited, respectively, a mean of 2%, 9%, 41%, and 59% of central necrosis. Intense macrophage infiltration took place in the muscle, invading the accumulations of necrotic cells and eliminating them by posttransplantation days 5 to 7.

CONCLUSIONS

The desire to create more neoformed tissue by delivering more cells per injection site is confronted with the fact that the acute survival of the implanted cells is restricted to the peripheral layer that can profit of the diffusion of oxygen and nutriments from the surrounding recipient's tissue.

A synthetic mechano growth factor E Peptide enhances myogenic precursor cell transplantation success

Myogenic precursor cell (MPC) transplantation is a good strategy to introduce dystrophin expression in muscles of Duchenne muscular dystrophy (DMD) patients. Insulin-like growth factor (IGF-1) promotes MPC activities, such as survival, proliferation, migration and differentiation, which could enhance the success of their transplantation. Alternative splicing of the IGF-1 mRNA produces different muscle isoforms. The mechano growth factor (MGF) is an isoform, especially expressed after a mechanical stress. A 24 amino acids peptide corresponding to the C-terminal part of the MGF E domain (MGF-Ct24E peptide) was synthesized. This peptide had been shown to enhance the proliferation and delay the terminal differentiation of C(2)C(12) myoblasts. The present study showed that the MGF-Ct24E peptide improved human MPC transplantation by modulating their proliferation and differentiation. Indeed, intramuscular or systemic delivery of this synthetic peptide significantly promoted engraftment of human MPCs in mice. In vitro experiments demonstrated that the MGF-Ct24E peptide enhanced MPC proliferation by a different mechanism than the binding to the IGF-1 receptor. Moreover, MGF-Ct24E peptide delayed human MPC differentiation while having no outcome on survival. Those combined effects are probably responsible for the enhanced transplantation success. Thus, the MGF-Ct24E peptide is an interesting agent to increase MPC transplantation success in DMD patients.

Gelatin-based microcarriers as embryonic stem cell delivery system in bone tissue engineering: an in-vitro study

Mouse embryonic stem cells were cultured on commercially available biodegradable macroporous microcarriers. A culture period of 1-2 weeks was needed to colonize the microcarriers. Embryonic stem cells retained their pluripotency for up to 14 days when cultured in medium supplemented with leukemia inhibitory factor. Replacing this medium by differentiation medium for 2 weeks initiated osteogenic differentiation. Encapsulation of the cell-loaded microcarriers in photopolymerizable polymers (methacrylate-endcapped poly-D,L-lactide-co-caprolactone), triacetin/hydroxyethylmethacrylate (HEMA) as solvent and with/without gelatin as porogen, resulted in a homogeneous distribution of the microcarriers in the polymer. As observed by transmission electron microscopy, viability of the cells was optimal when gelatin was omitted and when using triacetin instead of HEMA.

First test of a "high-density injection" protocol for myogenic cell transplantation throughout large volumes of muscles in a Duchenne muscular dystrophy patient: eighteen months follow-up

A 26-years old Duchenne muscular dystrophy (DMD) patient received normal muscle-precursor cells, proliferated in vitro and implanted in a thenar eminence, biceps brachii, and in a portion of a gastrocnemius by injections placed 1mm from each other or less. Saline was injected in the contralateral gastrocnemius. The patient was immunosuppressed with tacrolimus. The protocol of cell transplantation was well tolerated and did not cause permanent sequels. Some injected sites were biopsied at 1, 14 and 18 months post-transplantation. Muscles were replaced by fat and fibrosis. In the cell-grafted site of the gastrocnemius, 27.5% of the myofiber profiles expressed donor-derived dystrophin 1 month post-transplantation and 34.5% 18 months post-transplantation. The contralateral gastrocnemius was dystrophin-negative. Myofibers were virtually absent in the biceps brachii, where only two dystrophin-positive myofibers were observed. In conclusion, a "high-density injection" protocol was feasible for intramuscular cell-transplantation in a DMD patient and long-term expression of donor-derived dystrophin was observed.

Dystrophin Expression in Muscles of Duchenne Muscular Dystrophy Patients After High-Density Injections of Normal Myogenic Cells

A clinical trial was conducted to test a new protocol of normal muscle precursor cell (MPC) allotransplantation in skeletal muscles of patients with Duchenne muscular dystrophy (DMD). Cultured MPCs obtained from one of the patient's parents were implanted in 0.25 or 1 cm of a Tibialis anterior in 9 patients with DMD. MPC injections were placed 1 to 2 mm from each other, and a similar pattern of saline injections was done in the contralateral muscle. The patients were immunosuppressed with tacrolimus. Muscle biopsies were performed at the injected sites 4 weeks later. In the biopsies of the cell-grafted sites, there were myofibers expressing donor's dystrophin in 8 patients. The percentage of myofibers expressing donor's dystrophin varied from 3.5% to 26%. Evidence of small myofiber neoformation was observed in some patients. Donor-derived dystrophin transcripts were detected by reverse transcriptase-polymerase chain reaction in the cell-grafted sites in all patients. The protocol of immunosuppression was sufficient to obtain these results, although it is not certain whether acute rejection was efficiently controlled in all the cases. In conclusion, intramuscular allotransplantation of normal MPCs can induce the expression of donor-derived dystrophin in skeletal muscles of patients with DMD, although this expression is restricted to the sites of MPC injection.