Preclinical studies with umbilical cord mesenchymal stromal cells in different animal models for muscular dystrophy

Urine-derived stem cells genetically modified with IGF1 improve muscle regeneration

OBJECTIVE

In this study we aimed to determine the impact of human urine derived stem cells (USC) and genetically modified USC that were designed to overexpress myogenic growth factor IGF1 (USCIGF), on the regenerative capacity of cardiotoxin (CTX)-injured murine skeletal muscle.

METHODS

We overexpressed IGF1 in USC and investigated the alterations in myogenic capacity and regenerative function in cardiotoxin-injured muscle tissues.

RESULTS

Compared with USC alone, USCIGF1 activated the IGF1-Akt-mTOR signaling pathway, significantly improved myogenic differentiation capacity in vitro, and enhanced the secretion of myogenic growth factors and cytokines. In addition, IGF1 overexpression increased the ability of USC to fuse with skeletal myocytes to form myotubes, regulated the pro-regenerative immune response and inflammatory cytokines, and increased myogenesis in an in vivo model of skeletal muscle injury.

CONCLUSION

Overall, USC genetically modified to overexpress IGF1 significantly enhanced skeletal muscle regeneration by regulating myogenic differentiation, paracrine effects, and cell fusion, as well as by modulating immune responses in injured skeletal muscles in vivo. This study provides a novel perspective for evaluating the myogenic function of USC as a nonmyogenic cell source in skeletal myogenesis. The combination of USC and IGF1 expression has the potential to provide a novel efficient therapy for skeletal muscle injury and associated muscular defects in patients with urinary incontinence.

Cell sources proposed for nucleus pulposus regeneration

Lower back pain (LBP) occurs in 80% of adults in their lifetime; resulting in LBP being one of the biggest causes of disability worldwide. Chronic LBP has been linked to the degeneration of the intervertebral disc (IVD). The current treatments for chronic back pain only provide alleviation of symptoms through pain relief, tissue removal, or spinal fusion; none of which target regenerating the degenerate IVD. As nucleus pulposus (NP) degeneration is thought to represent a key initiation site of IVD degeneration, cell therapy that specifically targets the restoration of the NP has been reviewed here. A literature search to quantitatively assess all cell types used in NP regeneration was undertaken. With key cell sources: NP cells; annulus fibrosus cells; notochordal cells; chondrocytes; bone marrow mesenchymal stromal cells; adipose-derived stromal cells; and induced pluripotent stem cells extensively analyzed for their regenerative potential of the NP. This review highlights: accessibility; expansion capability in vitro; cell survival in an IVD environment; regenerative potential; and safety for these key potential cell sources. In conclusion, while several potential cell sources have been proposed, iPSC may provide the most promising regenerative potential.

Soluble factors of mesenchimal stem cells (FS-MSC) as a potential tool to reduce inflammation in donor's lungs after hypovolemic shock

OBJECTIVE

The shortage of viable lungs is still a major obstacle for transplantation. Trauma victims who represent potential lung donors commonly present hypovolemic shock leading to pulmonary inflammation and deterioration and rejection after transplantation. Seeking to improve lung graft, new approaches to donor treatment have been tested. This study focuses on treatment with mesenchymal stem cells (MSCs) or soluble factors produced by MSCs (FS-MSC) using a rat model for lung donors after hemorrhagic shock.

METHODS

Forty-eight rats were divided into four groups: Sham (n=12), animals without induction of hypovolemic shock; Shock (n=12), animals submitted to hypovolemic shock (mean arterial pressure 40 mmHg); MSC (n=12), animals submitted to hypovolemic shock and treated with MSCs, and FS (n=12), animals submitted to hypovolemic shock and treated with FS-MSC. The animals were subjected to a 50-minute hypovolemic shock (40 mmHg) procedure. The treated animals were monitored for 115 minutes. We performed histopathology of lung tissue and quantification of inflammatory markers (TNF-α, IL-1β, IL-6, IL-10, iCAM and vCAM) in lung tissue and peripheral blood leukocytes (PBLs).

RESULTS

Hemorrhagic shock resulted in higher PBLs and neutrophil infiltrate in the lungs. FS animals had lower neutrophil density comparing with Shock and MSC animals (p<0.001). No differences in the cytokine levels in lung tissue were observed between the groups.

CONCLUSIONS

The lungs of rats submitted to hemorrhagic shock and treated with FS-MSC showed reduced inflammation indicated in a decrease in lung neutrophil infiltrate.

Murine endometrial-derived mesenchymal stem cells suppress experimental autoimmune encephalomyelitis depending on indoleamine-2,3-dioxygenase expression

Cellular therapy with mesenchymal stem cells (MSCs) is a huge challenge for scientists, as little translational relevance has been achieved. However, many studies using MSCs have proved their suppressive and regenerative capacity. Thus, there is still a need for a better understanding of MSCs biology and the establishment of newer protocols, or to test unexplored tissue sources. Here, we demonstrate that murine endometrial-derived MSCs (meMSCs) suppress Experimental Autoimmune Encephalomyelitis (EAE). MSC-treated animals had milder disease, with a significant reduction in Th1 and Th17 lymphocytes in the lymph nodes and in the central nervous system (CNS). This was associated with increased Il27 and Cyp1a1 expression, and presence of IL-10-secreting T CD4+ cells. At EAE peak, animals had reduced CNS infiltrating cells, histopathology and demyelination. qPCR analysis evidenced the down-regulation of several pro-inflammatory genes and up-regulation of indoleamine-2,3-dioxygenase (IDO). Consistently, co-culturing of WT and IDO-/- meMSCs with T CD4+ cells evidenced the necessity of IDO on the suppression of encephalitogenic lymphocytes, and IDO-/- meMSCs were not able to suppress EAE. In addition, WT meMSCs stimulated with IL-17A and IFN-γ increased IDO expression and secretion of kynurenines in vitro, indicating a negative feedback loop. Pathogenic cytokines were increased when CD4+ T cells from AhR-/- mice were co-cultured with WT meMSC. In summary, our research evidences the suppressive activity of the unexplored meMSCs population, and shows the mechanism depends on IDO-kynurenines-Aryl hydrocarbon receptor (AhR) axis. To our knowledge this is the first report evidencing that the therapeutic potential of meMSCs relying on IDO expression.

Human levator veli palatini muscle: a novel source of mesenchymal stromal cells for use in the rehabilitation of patients with congenital craniofacial malformations

Background

Bone reconstruction in congenital craniofacial differences, which affect about 2–3% of newborns, has long been the focus of intensive research in the field of bone tissue engineering. The possibility of using mesenchymal stromal cells in regenerative medicine protocols has opened a new field of investigation aimed at finding optimal sources of multipotent cells that can be isolated via non-invasive procedures. In this study, we analyzed whether levator veli palatini muscle fragments, which can be readily obtained in non-invasive manner during palatoplasty in cleft palate patients, represent a novel source of MSCs with osteogenic potential.

Methods

We obtained levator veli palatini muscle fragments (3–5 mm³), during surgical repair of cleft palate in 5 unrelated patients. Mesenchymal stromal cells were isolated from the muscle using a pre-plating technique and other standard practices. The multipotent nature of the isolated stromal cells was demonstrated via flow cytometry analysis and by induction along osteogenic, adipogenic, and chondrogenic differentiation pathways. To demonstrate the osteogenic potential of these cells in vivo, they were used to reconstruct a critical-sized full-thickness calvarial defect model in immunocompetent rats.

Results

Flow cytometry analysis showed that the isolated stromal cells were positive for mesenchymal stem cell antigens (CD29, CD44, CD73, CD90, and CD105) and negative for hematopoietic (CD34 and CD45) or endothelial cell markers (CD31). The cells successfully underwent osteogenic, chondrogenic, and adipogenic cell differentiation under appropriate cell culture conditions. Calvarial defects treated with CellCeram™ scaffolds seeded with the isolated levator veli palatini muscle cells showed greater bone healing compared to defects treated with acellular scaffolds.

Conclusion

Cells derived from levator veli palatini muscle have phenotypic characteristics similar to other mesenchymal stromal cells, both in vitro and in vivo. Our findings suggest that these cells may have clinical relevance in the surgical rehabilitation of patients with cleft palate and other craniofacial anomalies characterized by significant bone deficit.

Supplementary information

The online version contains supplementary material available at 10.1186/s13287-020-02017-7.

Canine Models of Inherited Musculoskeletal and Neurodegenerative Diseases

Mouse models of human disease remain the bread and butter of modern biology and therapeutic discovery. Nonetheless, more often than not mouse models do not reproduce the pathophysiology of the human conditions they are designed to mimic. Naturally occurring large animal models have predominantly been found in companion animals or livestock because of their emotional or economic value to modern society and, unlike mice, often recapitulate the human disease state. In particular, numerous models have been discovered in dogs and have a fundamental role in bridging proof of concept studies in mice to human clinical trials. The present article is a review that highlights current canine models of human diseases, including Alzheimer's disease, degenerative myelopathy, neuronal ceroid lipofuscinosis, globoid cell leukodystrophy, Duchenne muscular dystrophy, mucopolysaccharidosis, and fucosidosis. The goal of the review is to discuss canine and human neurodegenerative pathophysiologic similarities, introduce the animal models, and shed light on the ability of canine models to facilitate current and future treatment trials.

Is There a Noninvasive Source of MSCs Isolated with GMP Methods with Better Osteogenic Potential?

BACKGROUND

A new trend in the treatment for alveolar clefts in patients with cleft lip and palate involves the use of bone tissue engineering strategies to reduce or eliminate the morbidity associated with autologous bone grafting. The use of mesenchymal stem cells-autologous cells obtained from tissues such as bone marrow and fat-combined with various biomaterials has been proposed as a viable option for use in cleft patients. However, invasive procedures are necessary to obtain the mesenchymal stem cells from these two sources. To eliminate donor site morbidity, noninvasive stem cell sources such as the umbilical cord, orbicularis oris muscle, and deciduous dental pulp have been studied for use in alveolar cleft bone tissue engineering. In this study, we evaluate the osteogenic potential of these various stem cell types.

METHODS

Ten cellular strains obtained from each different source (umbilical cord, orbicularis oris muscle, or deciduous dental pulp) were induced to osteogenic differentiation in vitro, and the bone matrix deposition of each primary culture was quantified. To evaluate whether greater osteogenic potential of the established mesenchymal stem cell strains was associated with an increase in the expression profile of neural crest genes, real-time qPCR was performed on the following genes: SRY-box 9, SRY-box 10, nerve growth factor receptor, transcription factor AP-2 alpha, and paired box 3.

RESULTS

The mesenchymal stem cells obtained from deciduous dental pulp and orbicularis oris muscle demonstrated increased osteogenic potential with significantly more extracellular bone matrix deposition when compared to primary cultures obtained from the umbilical cord after twenty-one days in culture (p = 0.007 and p = 0.005, respectively). The paired box 3 gene was more highly expressed in the MSCs obtained from deciduous dental pulp and orbicularis oris muscle than in those obtained from the umbilical cord.

CONCLUSION

These results suggest that deciduous dental pulp and orbicularis oris muscle stem cells demonstrate superior osteogenic differentiation potential relative to umbilical cord-derived stem cells and that this increased potential is related to their neural crest origins. Based on these observations, and the distinct translational advantage of incorporating stem cells from noninvasive tissue sources into tissue engineering protocols, greater study of these specific cell lines in the setting of alveolar cleft repair is indicated.

Eminent Sources of Adult Mesenchymal Stem Cells and Their Therapeutic Imminence

In the recent times, stem cell biology has garnered the attention of the scientific fraternity and the general public alike due to the immense therapeutic potential that it holds in the field of regenerative medicine. A breakthrough in this direction came with the isolation of stem cells from human embryo and their differentiation into cell types of all three germ layers. However, the isolation of mesenchymal stem cells from adult tissues proved to be advantageous over embryonic stem cells due to the ethical and immunological naivety. Mesenchymal Stem Cells (MSCs) isolated from the bone marrow were found to differentiate into multiple cell lineages with the help of appropriate differentiation factors. Furthermore, other sources of stem cells including adipose tissue, dental pulp, and breast milk have been identified. Newer sources of stem cells have been emerging recently and their clinical applications are also being studied. In this review, we examine the eminent sources of Mesenchymal Stem Cells (MSCs), their immunophenotypes, and therapeutic imminence.

Stem Cells for Skeletal Muscle Tissue Engineering

Volumetric muscle loss (VML) is a debilitating condition wherein muscle loss overwhelms the body's normal physiological repair mechanism. VML is particularly common among military service members who have sustained war injuries. Because of the high social and medical cost associated with VML and suboptimal current surgical treatments, there is great interest in developing better VML therapies. Skeletal muscle tissue engineering (SMTE) is a promising alternative to traditional VML surgical treatments that use autogenic tissue grafts, and rather uses isolated stem cells with myogenic potential to generate de novo skeletal muscle tissues to treat VML. Satellite cells are the native precursors to skeletal muscle tissue, and are thus the most commonly studied starting source for SMTE. However, satellite cells are difficult to isolate and purify, and it is presently unknown whether they would be a practical source in clinical SMTE applications. Alternative myogenic stem cells, including adipose-derived stem cells, bone marrow-derived mesenchymal stem cells, perivascular stem cells, umbilical cord mesenchymal stem cells, induced pluripotent stem cells, and embryonic stem cells, each have myogenic potential and have been identified as possible starting sources for SMTE, although they have yet to be studied in detail for this purpose. These alternative stem cell varieties offer unique advantages and disadvantages that are worth exploring further to advance the SMTE field toward highly functional, safe, and practical VML treatments. The following review summarizes the current state of satellite cell-based SMTE, details the properties and practical advantages of alternative myogenic stem cells, and offers guidance to tissue engineers on how alternative myogenic stem cells can be incorporated into SMTE research.

Skeletal Muscle Regenerative Potential of Human MuStem Cells following Transplantation into Injured Mice Muscle

After intra-arterial delivery in the dystrophic dog, allogeneic muscle-derived stem cells, termed MuStem cells, contribute to long-term stabilization of the clinical status and preservation of the muscle regenerative process. However, it remains unknown whether the human counterpart could be identified, considering recent demonstrations of divergent features between species for several somatic stem cells. Here, we report that MuStem cells reside in human skeletal muscle and display a long-term ability to proliferate, allowing generation of a clinically relevant amount of cells. Cultured human MuStem (hMuStem) cells do not express hematopoietic, endothelial, or myo-endothelial cell markers and reproducibly correspond to a population of early myogenic-committed progenitors with a perivascular/mesenchymal phenotypic signature, revealing a blood vessel wall origin. Importantly, they exhibit both myogenesis in vitro and skeletal muscle regeneration after intramuscular delivery into immunodeficient host mice. Together, our findings provide new insights supporting the notion that hMuStem cells could represent an interesting therapeutic candidate for dystrophic patients.

The golden retriever model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is an X-linked disease caused by mutations in the DMD gene and loss of the protein dystrophin. The absence of dystrophin leads to myofiber membrane fragility and necrosis, with eventual muscle atrophy and contractures. Affected boys typically die in their second or third decade due to either respiratory failure or cardiomyopathy. Despite extensive attempts to develop definitive therapies for DMD, the standard of care remains prednisone, which has only palliative benefits. Animal models, mainly the mdx mouse and golden retriever muscular dystrophy (GRMD) dog, have played a key role in studies of DMD pathogenesis and treatment development. Because the GRMD clinical syndrome is more severe than in mice, better aligning with the progressive course of DMD, canine studies may translate better to humans. The original founder dog for all GRMD colonies worldwide was identified in the early 1980s before the discovery of the DMD gene and dystrophin. Accordingly, analogies to DMD were initially drawn based on similar clinical features, ranging from the X-linked pattern of inheritance to overlapping histopathologic lesions. Confirmation of genetic homology between DMD and GRMD came with identification of the underlying GRMD mutation, a single nucleotide change that leads to exon skipping and an out-of-frame DMD transcript. GRMD colonies have subsequently been established to conduct pathogenetic and preclinical treatment studies. Simultaneous with the onset of GRMD treatment trials, phenotypic biomarkers were developed, allowing definitive characterization of treatment effect. Importantly, GRMD studies have not always substantiated findings from mdx mice and have sometimes identified serious treatment side effects. While the GRMD model may be more clinically relevant than the mdx mouse, usage has been limited by practical considerations related to expense and the number of dogs available. This further complicates ongoing broader concerns about the poor rate of translation of animal model preclinical studies to humans with analogous diseases. Accordingly, in performing GRMD trials, special attention must be paid to experimental design to align with the approach used in DMD clinical trials. This review provides context for the GRMD model, beginning with its original description and extending to its use in preclinical trials.

Human Tubal-Derived Mesenchymal Stromal Cells Associated with Low Level Laser Therapy Significantly Reduces Cigarette Smoke-Induced COPD in C57BL/6 mice

Cigarette smoke-induced chronic obstructive pulmonary disease is a very debilitating disease, with a very high prevalence worldwide, which results in a expressive economic and social burden. Therefore, new therapeutic approaches to treat these patients are of unquestionable relevance. The use of mesenchymal stromal cells (MSCs) is an innovative and yet accessible approach for pulmonary acute and chronic diseases, mainly due to its important immunoregulatory, anti-fibrogenic, anti-apoptotic and pro-angiogenic. Besides, the use of adjuvant therapies, whose aim is to boost or synergize with their function should be tested. Low level laser (LLL) therapy is a relatively new and promising approach, with very low cost, no invasiveness and no side effects. Here, we aimed to study the effectiveness of human tube derived MSCs (htMSCs) cell therapy associated with a 30mW/3J-660 nm LLL irradiation in experimental cigarette smoke-induced chronic obstructive pulmonary disease. Thus, C57BL/6 mice were exposed to cigarette smoke for 75 days (twice a day) and all experiments were performed on day 76. Experimental groups receive htMSCS either intraperitoneally or intranasally and/or LLL irradiation either alone or in association. We show that co-therapy greatly reduces lung inflammation, lowering the cellular infiltrate and pro-inflammatory cytokine secretion (IL-1β, IL-6, TNF-α and KC), which were followed by decreased mucus production, collagen accumulation and tissue damage. These findings seemed to be secondary to the reduction of both NF-κB and NF-AT activation in lung tissues with a concomitant increase in IL-10. In summary, our data suggests that the concomitant use of MSCs + LLLT may be a promising therapeutic approach for lung inflammatory diseases as COPD.

The effects of human Wharton's jelly cell transplantation on the intervertebral disc in a canine disc degeneration model

Introduction

Cell-based therapy was a promising treatment method for disc degenerative diseases. Wharton’s jelly cell (WJC) has been explored to cure various human diseases, while it still remains unknown about this MSC for disc repair. In our prior work, WJCs could differentiate into nucleus pulposus (NP)-like cells by co-culturing with NP cells in vitro. Thence, the aim of this study was further to investigate the survival and function of WJCs in vivo after transplantation into degenerated canine discs.

Method

WJCs were isolated from human umbilical cords and labeled with EGFP. The degeneration of L4-5, L5-6, and L6-7 discs of beagles was induced by aspirating the NP tissues. Four weeks after the operation, the injured discs were left to be no treatment at L4-5 (DS group), injected with 0.9 % saline at L5-6 (FS group), and transplanted with EGFP-labeled WJCs at L6-7 (TS group). In all animals, the intact disc L3-4 served as a control (CS group). The animals were followed up for 24 weeks after initial operation. Spine imaging was evaluated at 4, 8, 12, and 24 weeks, respectively. Histologic, biomechanics and gene expression analyses were performed at 24 weeks. Immunohistochemistry for aggrecan, types II collagen, SOX-9 was employed to investigate the matrix formation in the NP.

Results

The TS group showed a significantly smaller reduction in the disc height and T2-weighted signal intensity, and a better spinal segmental stability than DS and FS groups. Histologic assay demonstrated that WJCs were specifically detected in TS group at 24 weeks and the discs of TS group maintained a relatively well preserved structure as compared to the discs of DS and FS groups. Furthermore, real-time PCR and immunohistochemistry demonstrated that expressions of disc matrix genes, aggrecan, type II collagen, and SOX-9, were up-regulated in TS group compared to DS and FS groups.

Conclusion

WJCs could not only survive in the degenerate IVDs, but also promote the disc matrix formation of aggrecan and type II collagen in the degenerate IVDs. It may have value in cell-based therapy for degenerative disc disease.

Concise review: mesoangioblast and mesenchymal stem cell therapy for muscular dystrophy: progress, challenges, and future directions

Mesenchymal stem cells (MSCs) and mesoangioblasts (MABs) are multipotent cells that differentiate into specialized cells of mesodermal origin, including skeletal muscle cells. Because of their potential to differentiate into the skeletal muscle lineage, these multipotent cells have been tested for their capacity to participate in regeneration of damaged skeletal muscle in animal models of muscular dystrophy. MSCs and MABs infiltrate dystrophic muscle from the circulation, engraft into host fibers, and bring with them proteins that replace the functions of those missing or truncated. The potential for systemic delivery of these cells increases the feasibility of stem cell therapy for the large numbers of affected skeletal muscles in patients with muscular dystrophy. The present review focused on the results of preclinical studies with MSCs and MABs in animal models of muscular dystrophy. The goals of the present report were to (a) summarize recent results, (b) compare the efficacy of MSCs and MABs derived from different tissues in restoration of protein expression and/or improvement in muscle function, and (c) discuss future directions for translating these discoveries to the clinic. In addition, although systemic delivery of MABs and MSCs is of great importance for reaching dystrophic muscles, the potential concerns related to this method of stem cell transplantation are discussed.

Human umbilical cord mesenchymal stromal cells exhibit immature nucleus pulposus cell phenotype in a laminin-rich pseudo-three-dimensional culture system

Introduction

Cell supplementation to the herniated or degenerated intervertebral disc (IVD) is a potential strategy to promote tissue regeneration and slow disc pathology. Human umbilical cord mesenchymal stromal cells (HUCMSCs) – originating from the Wharton’s jelly – remain an attractive candidate for such endeavors with their ability to differentiate into multiple lineages. Previously, mesenchymal stem cells (MSCs) have been studied as a potential source for disc tissue regeneration. However, no studies have demonstrated that MSCs can regenerate matrix with unique characteristics matching that of immature nucleus pulposus (NP) tissues of the IVD. In our prior work, immature NP cells were found to express specific laminin isoforms and laminin-binding receptors that may serve as phenotypic markers for evaluating MSC differentiation to NP-like cells. The goal of this study is to evaluate these markers and matrix synthesis for HUCMSCs cultured in a laminin-rich pseudo-three-dimensional culture system.

Methods

HUCMSCs were seeded on top of Transwell inserts pre-coated with Matrigel™, which contained mainly laminin-111. Cells were cultured under hypoxia environment with three differentiation conditions: NP differentiation media (containing 2.5% Matrigel™ solution to provide for a pseudo-three-dimensional laminin culture system) with no serum, or the same media supplemented with either insulin-like growth factor-1 (IGF-1) or transforming growth factor-β1 (TGF-β1). Cell clustering behavior, matrix production and the expression of NP-specific laminin and laminin-receptors were evaluated at days 1, 7, 13 and 21 of culture.

Results

Data show that a pseudo-three-dimensional culture condition (laminin-1 rich) promoted HUCMSC differentiation under no serum conditions. Starting at day 1, HUCMSCs demonstrated a cell clustering morphology similar to that of immature NP cells in situ and that observed for primary immature NP cells within the similar laminin-rich culture system (prior study). Differentiated HUCMSCs under all conditions were found to contain glycosaminoglycan, expressed extracellular matrix proteins of collagen II and laminin α5, and laminin receptors (integrin α3 and β4 subunits). However, neither growth factor treatment generated distinct differences in NP-like phenotype for HUCMSC as compared with no-serum conditions.

Conclusions

HUCMSCs have the potential to differentiate into cells sharing features with immature NP cells in a laminin-rich culture environment and may be useful for IVD cellular therapy.

Systemic delivery of human mesenchymal stromal cells combined with IGF-1 enhances muscle functional recovery in LAMA2 dy/2j dystrophic mice

The combination of cell therapy with growth factors could be a useful approach to treat progressive muscular dystrophies. Here, we demonstrate, for the first time, that IGF-1 considerably enhances the myogenesis of human umbilical cord (UC) mesenchymal stromal cells (MSCs) in vitro and that IGF-1 enhances interaction and restoration of dystrophin expression in co-cultures of MSCs and muscle cells from Duchenne patients. In vivo studies showed that human MSCs were able to reach the skeletal muscle of LAMA2(dy/2j) dystrophic mice, through systemic delivery, without immunosuppression. Moreover, we showed, for the first time, that IGF-1 injected systemically together with MSCs markedly reduced muscle inflammation and fibrosis, and significantly improved muscle strength in dystrophic mice. Our results suggest that a combined treatment with IGF-1 and MSCs enhances efficiency of muscle repair and, therefore, should be further considered as a potential therapeutic approach in muscular dystrophies.

Do mesenchymal stem cells function across species barriers? Relevance for xenotransplantation

BACKGROUND

Allogeneic mesenchymal stem (stromal) cells (MSC) are a promising therapy for various pathological conditions. Genetically modified pig MSC have been demonstrated to downregulate the human T-cell response to pig antigens in vitro. Before genetically modified pig MSC can be used clinically, however, evidence needs to be provided to indicate whether they will survive in a human (xenogeneic) host.

LITERATURE SEARCH AND RESULTS

A literature search through the end of 2011 identified 94 reports of the in vivo cross-species administration of MSC in a variety of experimental models. The majority (n = 89) involved the use of human MSC in various other species, with an occasional study using pig, rat, or guinea-pig MSC. When human MSC were used, they were largely derived from the bone marrow, adipose tissue, or umbilical cord blood. The routes of administration were varied, although almost half of the studies utilized the intravenous route. In 88 experiments (93.6%), there was evidence that the MSC engrafted and functioned across the species barrier, and in only six cases (6.4%) was there evidence of failure to function. Importantly, MSC function was confirmed in several different cross-species models. For example, human MSC functioned in no fewer than seven different recipient species.

CONCLUSIONS

The data provided by this literature search strengthen the hypothesis that pig MSC will function satisfactorily in a different species, for example, humans. The data also suggest that our own in vitro observations on the efficacy of pig MSC in downregulating the strength of the human T-cell response to pig antigens will likely be reproduced in vivo in pre-clinical large animal models and in clinical trials.

Canine models of Duchenne muscular dystrophy and their use in therapeutic strategies

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder in which the loss of dystrophin causes progressive degeneration of skeletal and cardiac muscle. Potential therapies that carry substantial risk, such as gene- and cell-based approaches, must first be tested in animal models, notably the mdx mouse and several dystrophin-deficient breeds of dogs, including golden retriever muscular dystrophy (GRMD). Affected dogs have a more severe phenotype, in keeping with that of DMD, so may better predict disease pathogenesis and treatment efficacy. Various phenotypic tests have been developed to characterize disease progression in the GRMD model. These biomarkers range from measures of strength and joint contractures to magnetic resonance imaging. Some of these tests are routinely used in clinical veterinary practice, while others require specialized equipment and expertise. By comparing serial measurements from treated and untreated groups, one can document improvement or delayed progression of disease. Potential treatments for DMD may be broadly categorized as molecular, cellular, or pharmacologic. The GRMD model has increasingly been used to assess efficacy of a range of these therapies. A number of these studies have provided largely general proof-of-concept for the treatment under study. Others have demonstrated efficacy using the biomarkers discussed. Importantly, just as symptoms in DMD vary among patients, GRMD dogs display remarkable phenotypic variation. Though confounding statistical analysis in preclinical trials, this variation offers insight regarding the role that modifier genes play in disease pathogenesis. By correlating functional and mRNA profiling results, gene targets for therapy development can be identified.