Dual transplantation of human neural stem cells into cervical and lumbar cord ameliorates motor neuron disease in SOD1 transgenic rats

Current status and new avenues of stem cell-based preclinical and therapeutic approaches in amyotrophic lateral sclerosis

INTRODUCTION

Cell therapy development represents a critical challenge in amyotrophic lateral sclerosis (ALS) research. Despite more than 20 years of basic and clinical research, no definitive safety and efficacy results of cell-based therapies for ALS have been published.

AREAS COVERED

This review summarizes advances using stem cells (SCs) in pre-clinical studies to promote clinical translation and in clinical trials to treat ALS. New technologies have been developed and new experimental in vitro and animal models are now available to facilitate pre-clinical research in this field and to determine the most promising approaches to pursue in patients. New clinical trial designs aimed at developing personalized SC-based treatment with biological endpoints are being defined.

EXPERT OPINION

Knowledge of the basic biology of ALS and on the use of SCs to study and potentially treat ALS continues to grow. However, a consensus has yet to emerge on how best to translate these results into therapeutic applications. The selection and follow-up of patients should be based on clinical, biological, and molecular criteria. Planning of SC-based clinical trials should be coordinated with patient profiling genetically and molecularly to achieve personalized treatment. Much work within basic and clinical research is still needed to successfully transition SC therapy in ALS.

Glial-restricted progenitor cells: a cure for diseased brain?

The central nervous system (CNS) is home to neuronal and glial cells. Traditionally, glia was disregarded as just the structural support across the brain and spinal cord, in striking contrast to neurons, always considered critical players in CNS functioning. In modern times this outdated dogma is continuously repelled by new evidence unravelling the importance of glia in neuronal maintenance and function. Therefore, glia replacement has been considered a potentially powerful therapeutic strategy. Glial progenitors are at the center of this hope, as they are the source of new glial cells. Indeed, sophisticated experimental therapies and exciting clinical trials shed light on the utility of exogenous glia in disease treatment. Therefore, this review article will elaborate on glial-restricted progenitor cells (GRPs), their origin and characteristics, available sources, and adaptation to current therapeutic approaches aimed at various CNS diseases, with particular attention paid to myelin-related disorders with a focus on recent progress and emerging concepts. The landscape of GRP clinical applications is also comprehensively presented, and future perspectives on promising, GRP-based therapeutic strategies for brain and spinal cord diseases are described in detail.

Iranian clinical practice guideline for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegeneration involving motor neurons. The 3-5 years that patients have to live is marked by day-to-day loss of motor and sometimes cognitive abilities. Enormous amounts of healthcare services and resources are necessary to support patients and their caregivers during this relatively short but burdensome journey. Organization and management of these resources need to best meet patients' expectations and health system efficiency mandates. This can only occur in the setting of multidisciplinary ALS clinics which are known as the gold standard of ALS care worldwide. To introduce this standard to the care of Iranian ALS patients, which is an inevitable quality milestone, a national ALS clinical practice guideline is the necessary first step. The National ALS guideline will serve as the knowledge base for the development of local clinical pathways to guide patient journeys in multidisciplinary ALS clinics. To this end, we gathered a team of national neuromuscular experts as well as experts in related specialties necessary for delivering multidisciplinary care to ALS patients to develop the Iranian ALS clinical practice guideline. Clinical questions were prepared in the Patient, Intervention, Comparison, and Outcome (PICO) format to serve as a guide for the literature search. Considering the lack of adequate national/local studies at this time, a consensus-based approach was taken to evaluate the quality of the retrieved evidence and summarize recommendations.

Spinal Cord Organoids to Study Motor Neuron Development and Disease

Motor neuron diseases (MNDs) are a heterogeneous group of disorders that affect the cranial and/or spinal motor neurons (spMNs), spinal sensory neurons and the muscular system. Although they have been investigated for decades, we still lack a comprehensive understanding of the underlying molecular mechanisms; and therefore, efficacious therapies are scarce. Model organisms and relatively simple two-dimensional cell culture systems have been instrumental in our current knowledge of neuromuscular disease pathology; however, in the recent years, human 3D in vitro models have transformed the disease-modeling landscape. While cerebral organoids have been pursued the most, interest in spinal cord organoids (SCOs) is now also increasing. Pluripotent stem cell (PSC)-based protocols to generate SpC-like structures, sometimes including the adjacent mesoderm and derived skeletal muscle, are constantly being refined and applied to study early human neuromuscular development and disease. In this review, we outline the evolution of human PSC-derived models for generating spMN and recapitulating SpC development. We also discuss how these models have been applied to exploring the basis of human neurodevelopmental and neurodegenerative diseases. Finally, we provide an overview of the main challenges to overcome in order to generate more physiologically relevant human SpC models and propose some exciting new perspectives.

Cell therapy in ALS: An update on preclinical and clinical studies

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by the loss of motor neurons and neuromuscular impairment leading to complete paralysis, respiratory failure and premature death. The pathogenesis of the disease is multifactorial and noncell-autonomous involving the central and peripheral compartments of the neuromuscular axis and the skeletal muscle. Advanced clinical trials on specific ALS-related pathways have failed to significantly slow the disease. Therapy with stem cells from different sources has provided a promising strategy to protect the motor units exerting their effect through multiple mechanisms including neurotrophic support and excitotoxicity and neuroinflammation modulation, as evidenced from preclinical studies. Several phase I and II clinical trial of ALS patients have been developed showing positive effects in terms of safety and tolerability. However, the modest results on functional improvement in ALS patients suggest that only a coordinated effort between basic and clinical researchers could solve many problems, such as selecting the ideal stem cell source, identifying their mechanism of action and expected clinical outcomes. A promising approach may be stem cells selected or engineered to deliver optimal growth factor support at multiple sites along the neuromuscular pathway. This review covers recent advances in stem cell therapies in animal models of ALS, as well as detailing the human clinical trials that have been done and are currently undergoing development.

Patching Up the Permeability: The Role of Stem Cells in Lessening Neurovascular Damage in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a debilitating disease with poor prognosis. The pathophysiology of ALS is commonly debated, with theories involving inflammation, glutamate excitotoxity, oxidative stress, mitochondria malfunction, neurofilament accumulation, inadequate nutrients or growth factors, and changes in glial support predominating. These underlying pathological mechanisms, however, act together to weaken the blood brain barrier and blood spinal cord barrier, collectively considered as the blood central nervous system barrier (BCNSB). Altering the impermeability of the BCNSB impairs the neurovascular unit, or interdependent relationship between the brain and advances the concept that ALS is has a significant neurovascular component contributing to its degenerative presentation. This unique categorization of ALS opens a variety of treatment options targeting the reestablishment of BCNSB integrity. This review will critically assess the evidence implicating the significant neurovascular components of ALS pathophysiology, while also offering an in-depth discussion regarding the use of stem cells to repair these pathological changes within the neurovascular unit.

Monoclonal antibody-mediated immunosuppression enables long-term survival of transplanted human neural stem cells in mouse brain

BACKGROUND

As the field of stem cell therapy advances, it is important to develop reliable methods to overcome host immune responses in animal models. This ensures survival of transplanted human stem cell grafts and enables predictive efficacy testing. Immunosuppressive drugs derived from clinical protocols are frequently used but are often inconsistent and associated with toxic side effects. Here, using a molecular imaging approach, we show that immunosuppression targeting costimulatory molecules CD4 and CD40L enables robust survival of human xenografts in mouse brain, as compared to conventional tacrolimus and mycophenolate mofetil.

METHODS

Human neural stem cells were modified to express green fluorescent protein and firefly luciferase. Cells were implanted in the fimbria fornix of the hippocampus and viability assessed by non-invasive bioluminescent imaging. Cell survival was assessed using traditional pharmacologic immunosuppression as compared to monoclonal antibodies directed against CD4 and CD40L. This paradigm was also implemented in a transgenic Alzheimer's disease mouse model.

RESULTS

Graft rejection occurs within 7 days in non-immunosuppressed mice and within 14 days in mice on a traditional regimen. The addition of dual monoclonal antibody immunosuppression extends graft survival past 7 weeks (p < .001) on initial studies. We confirm dual monoclonal antibody treatment is superior to either antibody alone (p < .001). Finally, we demonstrate robust xenograft survival at multiple cell doses up to 6 months in both C57BL/6J mice and a transgenic Alzheimer's disease model (p < .001). The dual monoclonal antibody protocol demonstrated no significant adverse effects, as determined by complete blood counts and toxicity screen.

CONCLUSIONS

This study demonstrates an effective immunosuppression protocol for preclinical testing of stem cell therapies. A transition towards antibody-based strategies may be advantageous by enabling stem cell survival in preclinical studies that could inform future clinical trials.

Potential of Cellular Therapy for ALS: Current Strategies and Future Prospects

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive upper and lower motor neuron (MN) degeneration with unclear pathology. The worldwide prevalence of ALS is approximately 4.42 per 100,000 populations, and death occurs within 3-5 years after diagnosis. However, no effective therapeutic modality for ALS is currently available. In recent years, cellular therapy has shown considerable therapeutic potential because it exerts immunomodulatory effects and protects the MN circuit. However, the safety and efficacy of cellular therapy in ALS are still under debate. In this review, we summarize the current progress in cellular therapy for ALS. The underlying mechanism, current clinical trials, and the pros and cons of cellular therapy using different types of cell are discussed. In addition, clinical studies of mesenchymal stem cells (MSCs) in ALS are highlighted. The summarized findings of this review can facilitate the future clinical application of precision medicine using cellular therapy in ALS.

Stem Cell Transplantation Therapy and Neurological Disorders: Current Status and Future Perspectives

Neurodegenerative diseases are a global health issue with inadequate therapeutic options and an inability to restore the damaged nervous system. With advances in technology, health scientists continue to identify new approaches to the treatment of neurodegenerative diseases. Lost or injured neurons and glial cells can lead to the development of several neurological diseases, including Parkinson's disease, stroke, and multiple sclerosis. In recent years, neurons and glial cells have successfully been generated from stem cells in the laboratory utilizing cell culture technologies, fueling efforts to develop stem cell-based transplantation therapies for human patients. When a stem cell divides, each new cell has the potential to either remain a stem cell or differentiate into a germ cell with specialized characteristics, such as muscle cells, red blood cells, or brain cells. Although several obstacles remain before stem cells can be used for clinical applications, including some potential disadvantages that must be overcome, this cellular development represents a potential pathway through which patients may eventually achieve the ability to live more normal lives. In this review, we summarize the stem cell-based therapies that have been explored for various neurological disorders, discuss the potential advantages and drawbacks of these therapies, and examine future directions for this field.

Stem cell in neurodegenerative disorders; an emerging strategy

Neurodegenerative disorders are a diversity of disorders, surrounding Alzheimer's (AD), Parkinson's (PD), Huntington's diseases (HD), and amyotrophic lateral sclerosis (ALS) accompanied by some other less common diseases generally characterized by either developed deterioration of central or peripheral nervous system structurally or functionally. Today, with the viewpoint of an increasingly aging society, the number of patients with neurodegenerative diseases and sociomedical burdens will spread intensely. During the last decade, stem cell technology has attracted great attention for treating neurodegenerative diseases worldwide because of its unique attributes. As acknowledged, there are several categories of stem cells being able to proliferate and differentiate into various cellular lineages, highlighting their significance in the context of regenerative medicine. In preclinical models, stem cell therapy using mesenchymal stem/stromal cells (MSCs), hematopoietic stem cells (HSCs), and neural progenitor or stem cells (NPCs or NSCs) along with pluripotent stem cells (PSCs)-derived neuronal cells could elicit desired therapeutic effects, enabling functional deficit rescue partially. Regardless of the noteworthy progress in our scientific awareness and understanding of stem cell biology, there still exist various challenges to defeat. In the present review, we provide a summary of the therapeutic potential of stem cells and discuss the current status and prospect of stem cell strategy in neurodegenerative diseases, in particular, AD, PD, ALS, and HD.

Studying ALS: Current Approaches, Effect on Potential Treatment Strategy

Amyotrophic lateral sclerosis (ALS) is one of the most common neurodegenerative diseases, characterized by inevitable progressive paralysis. To date, only two disease modifying therapeutic options are available for the patients with ALS, although they show very modest effect on disease course. The main reason of failure in the field of pharmacological correction of ALS is inability to untangle complex relationships taking place during ALS initiation and progression. Traditional methods of research, based on morphology or transgenic animal models studying provided lots of information about ALS throughout the years. However, translation of these results to humans was unsuccessful due to incomplete recapitulation of molecular pathology and overall inadequacy of the models used in the research.In this review we summarize current knowledge regarding ALS molecular pathology with depiction of novel methods applied recently for the studies. Furthermore we describe present and potential treatment strategies that are based on the recent findings in ALS disease mechanisms.

Neural Stem Cell Transplantation for Neurodegenerative Diseases

Neurodegenerative diseases are disabling and fatal neurological disorders that currently lack effective treatment. Neural stem cell (NSC) transplantation has been studied as a potential therapeutic approach and appears to exert a beneficial effect against neurodegeneration via different mechanisms, such as the production of neurotrophic factors, decreased neuroinflammation, enhanced neuronal plasticity and cell replacement. Thus, NSC transplantation may represent an effective therapeutic strategy. To exploit NSCs' potential, some of their essential biological characteristics must be thoroughly investigated, including the specific markers for NSC subpopulations, to allow profiling and selection. Another key feature is their secretome, which is responsible for the regulation of intercellular communication, neuroprotection, and immunomodulation. In addition, NSCs must properly migrate into the central nervous system (CNS) and integrate into host neuronal circuits, enhancing neuroplasticity. Understanding and modulating these aspects can allow us to further exploit the therapeutic potential of NSCs. Recent progress in gene editing and cellular engineering techniques has opened up the possibility of modifying NSCs to express select candidate molecules to further enhance their therapeutic effects. This review summarizes current knowledge regarding these aspects, promoting the development of stem cell therapies that could be applied safely and effectively in clinical settings.

Stem Cell Transplantation for Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a motor neuronal degeneration disease, in which the death of motor neurons causes lost control of voluntary muscles. The consequence is weakness of muscles with a wide range of disabilities and eventually death. Most patients died within 5 years after diagnosis, and there is no cure for this devastating neurodegenerative disease up to date. Stem cells, including non-neural stem cells and neural stem cells (NSCs) or neural progenitor cells (NPCs), are very attractive cell sources for potential neuroprotection and motor neuron replacement therapy which bases on the idea that transplant-derived and newly differentiated motor neurons can replace lost motor neurons to re-establish voluntary motor control of muscles in ALS. Our recent studies show that transplanted NSCs or NPCs not only survive well in injured spinal cord, but also function as neuronal relays to receive regenerated host axonal connection and extend their own axons to host for connectivity, including motor axons in ventral root. This reciprocal connection between host neurons and transplanted neurons provides a strong rationale for neuronal replacement therapy for ALS to re-establish voluntary motor control of muscles. In addition, a variety of new stem cell resources and the new methodologies to generate NSCs or motor neuron-specific progenitor cells have been discovered and developed. Together, it provides the basis for motor neuron replacement therapy with NSCs or NPCs in ALS.

Successes and Hurdles in Stem Cells Application and Production for Brain Transplantation

Brain regenerative strategies through the transplantation of stem cells hold the potential to promote functional rescue of brain lesions caused either by trauma or neurodegenerative diseases. Most of the positive modulations fostered by stem cells are fueled by bystander effects, namely increase of neurotrophic factors levels and reduction of neuroinflammation. Nevertheless, the ultimate goal of cell therapies is to promote cell replacement. Therefore, the ability of stem cells to migrate and differentiate into neurons that later become integrated into the host neuronal network replacing the lost neurons has also been largely explored. However, as most of the preclinical studies demonstrate, there is a small functional integration of graft-derived neurons into host neuronal circuits. Thus, it is mandatory to better study the whole brain cell therapy approach in order to understand what should be better comprehended concerning graft-derived neuronal and glial cells migration and integration before we can expect these therapies to be ready as a viable solution for brain disorder treatment. Therefore, this review discusses the positive mechanisms triggered by cell transplantation into the brain, the limitations of adult brain plasticity that might interfere with the neuroregeneration process, as well as some strategies tested to overcome some of these limitations. It also considers the efforts that have been made by the regulatory authorities to lead to better standardization of preclinical and clinical studies in this field in order to reduce the heterogeneity of the obtained results.

Optogenetically transduced human ES cell-derived neural progenitors and their neuronal progenies: Phenotypic characterization and responses to optical stimulation

Optogenetically engineered human neural progenitors (hNPs) are viewed as promising tools in regenerative neuroscience because they allow the testing of the ability of hNPs to integrate within nervous system of an appropriate host not only structurally, but also functionally based on the responses of their differentiated progenies to light. Here, we transduced H9 embryonic stem cell-derived hNPs with a lentivirus harboring human channelrhodopsin (hChR2) and differentiated them into a forebrain lineage. We extensively characterized the fate and optogenetic functionality of hChR2-hNPs in vitro with electrophysiology and immunocytochemistry. We also explored whether the in vivo phenotype of ChR2-hNPs conforms to in vitro observations by grafting them into the frontal neocortex of rodents and analyzing their survival and neuronal differentiation. Human ChR2-hNPs acquired neuronal phenotypes (TUJ1, MAP2, SMI-312, and synapsin 1 immunoreactivity) in vitro after an average of 70 days of coculturing with CD1 astrocytes and progressively displayed both inhibitory and excitatory neurotransmitter signatures by immunocytochemistry and whole-cell patch clamp recording. Three months after transplantation into motor cortex of naïve or injured mice, 60–70% of hChR2-hNPs at the transplantation site expressed TUJ1 and had neuronal cytologies, whereas 60% of cells also expressed ChR2. Transplant-derived neurons extended axons through major commissural and descending tracts and issued synaptophysin⁺ terminals in the claustrum, endopiriform area, and corresponding insular and piriform cortices. There was no apparent difference in engraftment, differentiation, or connectivity patterns between injured and sham subjects. Same trends were observed in a second rodent host, i.e. rat, where we employed longer survival times and found that the majority of grafted hChR2-hNPs differentiated into GABAergic neurons that established dense terminal fields and innervated mostly dendritic profiles in host cortical neurons. In physiological experiments, human ChR2⁺ neurons in culture generated spontaneous action potentials (APs) 100–170 days into differentiation and their firing activity was consistently driven by optical stimulation. Stimulation generated glutamatergic and GABAergic postsynaptic activity in neighboring ChR2^- cells, evidence that hChR2-hNP-derived neurons had established functional synaptic connections with other neurons in culture. Light stimulation of hChR2-hNP transplants in vivo generated complicated results, in part because of the variable response of the transplants themselves. Our findings show that we can successfully derive hNPs with optogenetic properties that are fully transferrable to their differentiated neuronal progenies. We also show that these progenies have substantial neurotransmitter plasticity in vitro, whereas in vivo they mostly differentiate into inhibitory GABAergic neurons. Furthermore, neurons derived from hNPs have the capacity of establishing functional synapses with postsynaptic neurons in vitro, but this outcome is technically challenging to explore in vivo. We propose that optogenetically endowed hNPs hold great promise as tools to explore de novo circuit formation in the brain and, in the future, perhaps launch a new generation of neuromodulatory therapies.

Stable Intracerebral Transplantation of Neural Stem Cells for the Treatment of Paralysis Due to Ischemic Stroke

NSI‐566 is a stable, primary adherent neural stem cell line derived from a single human fetal spinal cord and expanded epigenetically with no genetic modification. This cell line is being tested in clinical trials in the U.S. for treatment of amyotrophic lateral sclerosis and spinal cord injury. In a single‐site, phase I study, we evaluated the feasibility and safety of NSI‐566 transplantation for the treatment of hemiparesis due to chronic motor stroke and determined the maximum tolerated dose for future trials. Three cohorts (n = 3 per cohort) were transplanted with one‐time intracerebral injections of 1.2 × 10⁷, 2.4 × 10⁷, or 7.2 × 10⁷ cells. Immunosuppression therapy with tacrolimus was maintained for 28 days. All subjects had sustained chronic motor strokes, verified by magnetic resonance imaging (MRI), initiated between 5 and 24 months prior to surgery with modified Rankin Scores [MRSs] of 2, 3, or 4 and Fugl‐Meyer Motor Scores of 55 or less. At the 12‐month visit, the mean Fugl‐Meyer Motor Score (FMMS, total score of 100) for the nine participants showed 16 points of improvement (p = .0078), the mean MRS showed 0.8 points of improvement (p = .031), and the mean National Institutes of Health Stroke Scale showed 3.1 points of improvement (p = .020). For six participants who were followed up for 24 months, these mean changes remained stable. The treatment was well tolerated at all doses. Longitudinal MRI studies showed evidence indicating cavity‐filling by new neural tissue formation in all nine patients. Although this was a small, one‐arm study of feasibility, the results are encouraging to warrant further studies. stem cells translational medicine2019;8:999–1007

Transplantation of clinical-grade human neural stem cells reduces neuroinflammation, prolongs survival and delays disease progression in the SOD1 rats

Stem cells are emerging as a therapeutic option for incurable diseases, such as Amyotrophic Lateral Sclerosis (ALS). However, critical issues are related to their origin as well as to the need to deepen our knowledge of the therapeutic actions exerted by these cells. Here, we investigate the therapeutic potential of clinical-grade human neural stem cells (hNSCs) that have been successfully used in a recently concluded phase I clinical trial for ALS patients (NCT01640067). The hNSCs were transplanted bilaterally into the anterior horns of the lumbar spinal cord (four grafts each, segments L3–L4) of superoxide dismutase 1 G93A transgenic rats (SOD1 rats) at the symptomatic stage. Controls included untreated SOD1 rats (CTRL) and those treated with HBSS (HBSS). Motor symptoms and histological hallmarks of the disease were evaluated at three progressive time points: 15 and 40 days after transplant (DAT), and end stage. Animals were treated by transient immunosuppression (for 15 days, starting at time of transplantation). Under these conditions, hNSCs integrated extensively within the cord, differentiated into neural phenotypes and migrated rostro-caudally, up to 3.77 ± 0.63 cm from the injection site. The transplanted cells delayed decreases in body weight and deterioration of motor performance in the SOD1 rats. At 40DAT, the anterior horns at L3–L4 revealed a higher density of motoneurons and fewer activated astroglial and microglial cells. Accordingly, the overall survival of transplanted rats was significantly enhanced with no rejection of hNSCs observed. We demonstrated that the beneficial effects observed after stem cell transplantation arises from multiple events that counteract several aspects of the disease, a crucial feature for multifactorial diseases, such as ALS. The combination of therapeutic approaches that target different pathogenic mechanisms of the disorder, including pharmacology, molecular therapy and cell transplantation, will increase the chances of a clinically successful therapy for ALS.

Targeted intraspinal injections to assess therapies in rodent models of neurological disorders

Despite decades of research, pharmacological therapies for spinal cord motor pathologies are limited. Alternatives using macromolecular, viral, or cell-based therapies show early promise. However, introducing these substances into the spinal cord, past the blood-brain barrier, without causing injury is challenging. We describe a technique for intraspinal injection targeting the lumbar ventral horn in rodents. This technique preserves motor performance and has a proven track record of translation into phase 1 and 2 clinical trials in amyotrophic lateral sclerosis (ALS) patients. The procedure, in brief, involves exposure of the thoracolumbar spine and dissection of paraspinous muscles over the target vertebrae. Following laminectomy, the spine is affixed to a stereotactic frame, permitting precise and reproducible injection throughout the lumbar spine. We have used this protocol to inject various stem cell types, primarily human spinal stem cells (HSSCs); however, the injection is adaptable to any candidate therapeutic cell, virus, or macromolecule product. In addition to a detailed procedure, we provide stereotactic coordinates that assist in targeting of the lumbar spine and instructional videos. The protocol takes ~2 h per animal.

Concise Review: Human-Animal Neurological Chimeras: Humanized Animals or Human Cells in an Animal?

Blastocyst complementation is an emerging methodology in which human stem cells are transferred into genetically engineered preimplantation animal embryos eventually giving rise to fully developed human tissues and organs within the animal host for use in regenerative medicine. The ethical issues surrounding this method have caused the National Institutes of Health to issue a moratorium on funding for blastocyst complementation citing the potential for human cells to substantially contribute to the brain of the chimeric animal. To address this concern, we performed an in-depth review of the neural transplantation literature to determine how the integration of human cells into the nonhuman neural circuitry has altered the behavior of the host. Despite reports of widespread integration of human cell transplants, our review of 150 transplantation studies found no evidence suggestive of humanization of the animal host, and we thus conclude that, at present, concerns over humanization should not prevent research on blastocyst complementation to continue. We suggest proceeding in a controlled and transparent manner, however, and include recommendations for future research with careful consideration for how human cells may contribute to the animal host nervous system. Stem Cells 2019;37:444-452.

Quantification of motor neuron loss and muscular atrophy in ricin-induced focal nerve injury

BACKGROUND

Intrasciatic nerve injection of the Ricinus communis agglutinin (RCA or ricin) causes degeneration of motor neurons (MNs) with functional deficits, such as those that occur in amyotrophic lateral sclerosis (ALS). The objective of this study was to develop a new comprehensive platform for quantitative evaluation of MN loss, muscular atrophy and behavioral deficits using different ricin injection regimens.

NEW METHOD

Fluorogold (FG)-guided stereological quantification of MNs, in vivo magnetic resonance imaging (MRI) of muscular atrophy, and CatWalk behavioral testing were used to evaluate the outcome of rats treated with different ricin regimens (RCA60 0.5 μg, RCA60 3 μg, and RCA120 6 μg) as animal models of MN degeneration.

RESULTS

FG-guided stereological counting of MNs enabled identification, dissection and robust quantification of ricin-induced MN loss. The RCA60 0.5 μg and RCA120 6 μg regimens were found to be best suited as preclinical MN depletion models, with a low mortality and a reproducible MN loss, accompanied by muscle atrophy and functional deficits evaluated by MRI and the CatWalk method, respectively.

COMPARISON WITH EXISTING METHODS

1) Fluorogold neuronal tracing provides a robust and straightforward means for quantifying MN loss in the spinal cord; 2) MRI is well-suited to non-invasively assess muscle atrophy; and 3) The CatWalk method is more flexible than rotarod test for studying motor deficits.

CONCLUSION

Intrasciatic injection of RCA60 or RCA120 induces nerve injury and muscle atrophy, which can be properly evaluated by a comprehensive platform using FG-guided quantitative 3D topographic histological analysis, MRI and the CatWalk behavioral test.

Preconditioning and Cellular Engineering to Increase the Survival of Transplanted Neural Stem Cells for Motor Neuron Disease Therapy

Despite the extensive research effort that has been made in the field, motor neuron diseases, namely, amyotrophic lateral sclerosis and spinal muscular atrophies, still represent an overwhelming cause of morbidity and mortality worldwide. Exogenous neural stem cell-based transplantation approaches have been investigated as multifaceted strategies to both protect and repair upper and lower motor neurons from degeneration and inflammation. Transplanted neural stem cells (NSCs) exert their beneficial effects not only through the replacement of damaged cells but also via bystander immunomodulatory and neurotrophic actions. Notwithstanding these promising findings, the clinical translatability of such techniques is jeopardized by the limited engraftment success and survival of transplanted cells within the hostile disease microenvironment. To overcome this obstacle, different methods to enhance graft survival, stability, and therapeutic potential have been developed, including environmental stress preconditioning, biopolymers scaffolds, and genetic engineering. In this review, we discuss current engineering techniques aimed at the exploitation of the migratory, proliferative, and secretive capacity of NSCs and their relevance for the therapeutic arsenal against motor neuron disorders and other neurological disorders.

Long-term Phase 1/2 intraspinal stem cell transplantation outcomes in ALS

Objective

Intraspinal human spinal cord‐derived neural stem cell (HSSC) transplantation is a potential therapy for amyotrophic lateral sclerosis (ALS); however, previous trials lack controls. This post hoc analysis compared ambulatory limb‐onset ALS participants in Phase 1 and 2 (Ph1/2) open‐label intraspinal HSSC transplantation studies up to 3 years after transplant to matched participants in Pooled Resource Open‐Access ALS Clinical Trials (PRO‐ACT) and ceftriaxone datasets to provide required analyses to inform future clinical trial designs.

Methods

Survival, ALSFRS‐R, and a composite statistic (ALS/SURV) combining survival and ALS Functional Rating Scale revised (ALSFRS‐R) functional status were assessed for matched participant subsets: PRO‐ACT n = 1108, Ph1/2 n = 21 and ceftriaxone n = 177, Ph1/2 n = 20.

Results

Survival did not differ significantly between cohorts: Ph1/2 median survival 4.7 years, 95% CI (1.2, ∞) versus PRO‐ACT 2.3 years (1.9, 2.5), P = 1.0; Ph1/2 3.0 years (1.2, 5.6) versus ceftriaxone 2.3 years (1.8, 2.8), P = 0.88. Mean ALSFRS‐R at 24 months significantly differed between Ph1/2 and both comparison cohorts (Ph1/2 30.1 ± 8.6 vs. PRO‐ACT 24.0 ± 10.2, P = 0.048; Ph1/2 30.7 ± 8.8 vs. ceftriaxone 19.2 ± 9.5, P = 0.0023). Using ALS/SURV, median PRO‐ACT and ceftriaxone participants died by 24 months, whereas median Ph1/2 participant ALSFRS‐Rs were 23 (P = 0.0038) and 19 (P = 0.14) in PRO‐ACT and ceftriaxone comparisons at 24 months, respectively, supporting improved functional outcomes in the Ph1/2 study.

Interpretation

Comparison of Ph1/2 studies to historical datasets revealed significantly improved survival and function using ALS/SURV versus PRO‐ACT controls. While results are encouraging, comparison against historical populations demonstrate limitations in noncontrolled studies. These findings support continued evaluation of HSSC transplantation in ALS, support the benefit of control populations, and enable necessary power calculations to design a randomized, sham surgery‐controlled efficacy study.

Transplantation of Neural Progenitor Cells Expressing Glial Cell Line-Derived Neurotrophic Factor into the Motor Cortex as a Strategy to Treat Amyotrophic Lateral Sclerosis

Early dysfunction of cortical motor neurons may underlie the initiation of amyotrophic lateral sclerosis (ALS). As such, the cortex represents a critical area of ALS research and a promising therapeutic target. In the current study, human cortical-derived neural progenitor cells engineered to secrete glial cell line-derived neurotrophic factor (GDNF) were transplanted into the SOD1^G93A ALS rat cortex, where they migrated, matured into astrocytes, and released GDNF. This protected motor neurons, delayed disease pathology and extended survival of the animals. These same cells injected into the cortex of cynomolgus macaques survived and showed robust GDNF expression without adverse effects. Together this data suggests that introducing cortical astrocytes releasing GDNF represents a novel promising approach to treating ALS. Stem Cells 2018;36:1122-1131.

Early electrical field stimulation prevents the loss of spinal cord anterior horn motoneurons and muscle atrophy following spinal cord injury

Our previous study revealed that early application of electrical field stimulation (EFS) with the anode at the lesion and the cathode distal to the lesion reduced injury potential, inhibited secondary injury and was neuroprotective in the dorsal corticospinal tract after spinal cord injury (SCI). The objective of this study was to further evaluate the effect of EFS on protection of anterior horn motoneurons and their target musculature after SCI and its mechanism. Rats were randomized into three equal groups. The EFS group received EFS for 30 minutes immediately after injury at T₁₀. SCI group rats were only subjected to SCI and sham group rats were only subjected to laminectomy. Luxol fast blue staining demonstrated that spinal cord tissue in the injury center was better protected; cross-sectional area and perimeter of injured tissue were significantly smaller in the EFS group than in the SCI group. Immunofluorescence and transmission electron microscopy showed that the number of spinal cord anterior horn motoneurons was greater and the number of abnormal neurons reduced in the EFS group compared with the SCI group. Wet weight and cross-sectional area of vastus lateralis muscles were smaller in the SCI group to in the sham group. However, EFS improved muscle atrophy and behavioral examination showed that EFS significantly increased the angle in the inclined plane test and Tarlov's motor grading score. The above results confirm that early EFS can effectively impede spinal cord anterior horn motoneuron loss, promote motor function recovery and reduce muscle atrophy in rats after SCI.

Advances, challenges and future directions for stem cell therapy in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative condition where loss of motor neurons within the brain and spinal cord leads to muscle atrophy, weakness, paralysis and ultimately death within 3–5 years from onset of symptoms. The specific molecular mechanisms underlying the disease pathology are not fully understood and neuroprotective treatment options are minimally effective.

In recent years, stem cell transplantation as a new therapy for ALS patients has been extensively investigated, becoming an intense and debated field of study. In several preclinical studies using the SOD1^G93A mouse model of ALS, stem cells were demonstrated to be neuroprotective, effectively delayed disease onset and extended survival. Despite substantial improvements in stem cell technology and promising results in preclinical studies, several questions still remain unanswered, such as the identification of the most suitable and beneficial cell source, cell dose, route of delivery and therapeutic mechanisms. This review will cover publications in this field and comprehensively discuss advances, challenges and future direction regarding the therapeutic potential of stem cells in ALS, with a focus on mesenchymal stem cells. In summary, given their high proliferation activity, immunomodulation, multi-differentiation potential, and the capacity to secrete neuroprotective factors, adult mesenchymal stem cells represent a promising candidate for clinical translation. However, technical hurdles such as optimal dose, differentiation state, route of administration, and the underlying potential therapeutic mechanisms still need to be assessed.

Ex vivo gene therapy for the treatment of neurological disorders

Ex vivo gene therapy involves the genetic modification of cells outside of the body to produce therapeutic factors and their subsequent transplantation back into patients. Various cell types can be genetically engineered. However, with the explosion in stem cell technologies, neural stem/progenitor cells and mesenchymal stem cells are most often used. The synergy between the effect of the new cell and the additional engineered properties can often provide significant benefits to neurodegenerative changes in the brain. In this review, we cover both preclinical animal studies and clinical human trials that have used ex vivo gene therapy to treat neurological disorders with a focus on Parkinson's disease, Huntington's disease, Alzheimer's disease, ALS, and stroke. We highlight some of the major advances in this field including new autologous sources of pluripotent stem cells, safer ways to introduce therapeutic transgenes, and various methods of gene regulation. We also address some of the remaining hurdles including tunable gene regulation, in vivo cell tracking, and rigorous experimental design. Overall, given the current outcomes from researchers and clinical trials, along with exciting new developments in ex vivo gene and cell therapy, we anticipate that successful treatments for neurological diseases will arise in the near future.

Stem cells for ALS: An overview of possible therapeutic approaches

Amyotrophic lateral sclerosis (ALS) is an unusual, fatal, neurodegenerative disorder leading to the loss of motor neurons. After diagnosis, the average lifespan ranges from 3 to 5 years, and death usually results from respiratory failure. Although the pathogenesis of ALS remains unclear, multiple factors are thought to contribute to the progression of ALS, such as network interactions between genes, environmental exposure, impaired molecular pathways and many others. The neuroprotective properties of neural stem cells (NSCs) and the paracrine signaling of mesenchymal stem cells (MSCs) have been examined in multiple pre-clinical trials of ALS with promising results. The data from these initial trials indicate a reduction in the rate of disease progression. The mechanism through which stem cells achieve this reduction is of major interest. Here, we review the to-date pre-clinical and clinical therapeutic approaches employing stem cells, and discuss the most promising ones.

Serial in vivo imaging of transplanted allogeneic neural stem cell survival in a mouse model of amyotrophic lateral sclerosis

Neural stem cells (NSCs) are being investigated as a possible treatment for amyotrophic lateral sclerosis (ALS) through intraspinal transplantation, but no longitudinal imaging studies exist that describe the survival of engrafted cells over time. Allogeneic firefly luciferase-expressing murine NSCs (Luc⁺-NSCs) were transplanted bilaterally (100,000 cells/2μl) into the cervical spinal cord (C5) parenchyma of pre-symptomatic (63day-old) SOD1^G93A ALS mice (n=14) and wild-type age-matched littermates (n=14). Six control SOD1^G93A ALS mice were injected with saline. Mice were immunosuppressed using a combination of tacrolimus+sirolimus (1mg/kg each, i.p.) daily. Compared to saline-injected SOD1^G93A ALS control mice, a transient improvement (p<0.05) in motor performance (rotarod test) was observed after NSC transplantation only at the early disease stage (weeks 2 and 3 post-transplantation). Compared to day one post-transplantation, there was a significant decline in bioluminescent imaging (BLI) signal in SOD1^G93A ALS mice at the time of disease onset (71.7±17.9% at 4weeks post-transplantation, p<0.05), with a complete loss of BLI signal at endpoint (120day-old mice). In contrast, BLI signal intensity was observed in wild-type littermates throughout the entire study period, with only a 41.4±8.7% decline at the endpoint. In SOD1^G93A ALS mice, poor cell survival was accompanied by accumulation of mature macrophages and the presence of astrogliosis and microgliosis. We conclude that the disease progression adversely affects the survival of engrafted murine Luc⁺-NSCs in SOD1^G93A ALS mice as a result of the hostile ALS spinal cord microenvironment, further emphasizing the challenges that face successful cell therapy of ALS.

Transplantation of spinal cord-derived neural stem cells for ALS: Analysis of phase 1 and 2 trials

OBJECTIVE

To test the safety of spinal cord transplantation of human stem cells in patients with amyotrophic lateral sclerosis (ALS) with escalating doses and expansion of the trial to multiple clinical centers.

METHODS

This open-label trial included 15 participants at 3 academic centers divided into 5 treatment groups receiving increasing doses of stem cells by increasing numbers of cells/injection and increasing numbers of injections. All participants received bilateral injections into the cervical spinal cord (C3-C5). The final group received injections into both the lumbar (L2-L4) and cervical cord through 2 separate surgical procedures. Participants were assessed for adverse events and progression of disease, as measured by the ALS Functional Rating Scale-Revised, forced vital capacity, and quantitative measures of strength. Statistical analysis focused on the slopes of decline of these phase 2 trial participants alone or in combination with the phase 1 participants (previously reported), comparing these groups to 3 separate historical control groups.

RESULTS

Adverse events were mostly related to transient pain associated with surgery and to side effects of immunosuppressant medications. There was one incident of acute postoperative deterioration in neurologic function and another incident of a central pain syndrome. We could not discern differences in surgical outcomes between surgeons. Comparisons of the slopes of decline with the 3 separate historical control groups showed no differences in mean rates of progression.

CONCLUSIONS

Intraspinal transplantation of human spinal cord-derived neural stem cells can be safely accomplished at high doses, including successive lumbar and cervical procedures. The procedure can be expanded safely to multiple surgical centers.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that for patients with ALS, spinal cord transplantation of human stem cells can be safely accomplished and does not accelerate the progression of the disease. This study lacks the precision to exclude important benefit or safety issues.

Autocrine production of IGF-I increases stem cell-mediated neuroprotection

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder resulting in motor neuron (MN) loss. There are currently no effective therapies; however, cellular therapies using neural progenitor cells protect MNs and attenuate disease progression in G93A-SOD1 ALS rats. Recently, we completed a phase I clinical trial examining intraspinal human spinal stem cell (HSSC) transplantation in ALS patients which demonstrated our approach was safe and feasible, supporting the phase II trial currently in progress. In parallel, efforts focused on understanding the mechanisms underlying the preclinical benefit of HSSCs in vitro and in animal models of ALS led us to investigate how insulin-like growth factor-I (IGF-I) production contributes to cellular therapy neuroprotection. IGF-I is a potent growth factor with proven efficacy in preclinical ALS studies, and we contend that autocrine IGF-I production may enhance the salutary effects of HSSCs. By comparing the biological properties of HSSCs to HSSCs expressing sixfold higher levels of IGF-I, we demonstrate that IGF-I production augments the production of glial-derived neurotrophic factor and accelerates neurite outgrowth without adversely affecting HSSC proliferation or terminal differentiation. Furthermore, we demonstrate that increased IGF-I induces more potent MN protection from excitotoxicity via both indirect and direct mechanisms, as demonstrated using hanging inserts with primary MNs or by culturing with organotypic spinal cord slices, respectively. These findings support our theory that combining autocrine growth factor production with HSSC transplantation may offer a novel means to achieve additive neuroprotection in ALS.

Advances in the Development of Disease-Modifying Treatments for Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive adult-onset, neurodegenerative disease characterized by the degeneration of upper and lower motor neurons. Over recent years, numerous genes ha ve been identified that promote disease pathology, including SOD1, TARDBP, and the expanded hexanucleotide repeat (GGGGCC) within C9ORF72. However, despite these major advances in identifying genes contributing to ALS pathogenesis, there remains only one currently approved therapeutic: the glutamate antagonist, riluzole. Seminal breakthroughs in the pathomechanisms and genetic factors associated with ALS have heavily relied on the use of rodent models that recapitulate the ALS phenotype; however, while many therapeutics have proved to be significant in animal models by prolonging life and rescuing motor deficits, they have failed in human clinical trials. This may be due to fundamental differences between rodent models and human disease, the fact that animal models are based on overexpression of mutated genes, and confounding issues such as difficulties mimicking the dosing schedules and regimens implemented in mouse models to humans. Here, we review the major pathways associated with the pathology of ALS, the rodent models engineered to test efficacy of candidate drugs, the advancements being made in stem cell therapy for ALS, and what strategies may be important to circumvent the lack of successful translational studies in the clinic.

Efficacy of Stem Cell Therapy in Amyotrophic Lateral Sclerosis: A Systematic Review and Meta-Analysis

BACKGROUND

Published studies seeking to improve survival in amyotrophic lateral sclerosis (ALS) have poor results in humans, although there are several studies in animal models with positive results.

METHODS

We conducted a systematic review and meta-analysis of studies that were published between March 2009 and March 2015 on stem cell therapy and survival in animal models and patients with ALS. A total of 714 articles were identified, and from these, we selected preclinical in vivo studies and retrospective clinical studies.

RESULTS AND CONCLUSIONS

A meta-analysis confirmed the efficacy of stem cell therapy in improving survival in preclinical trials, where a mean difference of 9.79 days (95% confidence interval: 4.45 - 15.14) in lifespan favored stem cell therapy. In contrast, the number of clinical studies is still insufficient to assess their effectiveness, and these studies only demonstrate the absence of serious adverse events. However, even this conclusion should be interpreted with caution because clinical studies are retrospective and heterogeneous and have an unsatisfactory quality.

Intraspinal stem cell transplantation for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder in which the loss of upper and lower motor neurons produces progressive weakness and eventually death. In the decades since the approval of riluzole, the only US Food and Drug Administration-approved medication to moderately slow progression of ALS, no new therapeutics have arisen to alter the course of the disease. This is partly due to our incomplete understanding of the complex pathogenesis of motor neuron degeneration. Stem cells have emerged as an attractive option in treating ALS, because they come armed with equally complex cellular machinery and may modulate the local microenvironment in many ways to rescue diseased motor neurons. Various stem cell types are being evaluated in preclinical and early clinical applications; here, we review the preclinical strategies and advances supporting the recent clinical translation of neural progenitor cell therapy for ALS. Specifically, we focus on the use of spinal cord neural progenitor cells and the pipeline starting from preclinical studies to the designs of phase I and IIa clinical trials involving direct intraspinal transplantation in humans.

Inhibitory dysfunction in amyotrophic lateral sclerosis: future therapeutic opportunities

In amyotrophic lateral sclerosis, motor neuron hyperexcitability and inhibitory dysfunction is emerging as a potential causative link in the dysfunction and degeneration of the motoneuronal circuitry that characterizes the disease. Interneurons, as key regulators of excitability, may mediate much of this imbalance, yet we know little about the way in which inhibitory deficits perturb excitability. In this review, we explore inhibitory control of excitability and the potential contribution of altered inhibition to amyotrophic lateral sclerosis disease processes and vulnerabilities, identifying important windows of therapeutic opportunity and potential interventions, specifically targeting inhibitory control at key disease stages.

Amyotrophic lateral sclerosis: Current perspectives from basic research to the clinic

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive degeneration of upper and lower motoneurons, leading to muscle weakness and paralysis, and finally death. Considerable recent advances have been made in basic research and preclinical therapeutic attempts using experimental models, leading to increasing clinical and translational research in the context of this disease. In this review we aim to summarize the most relevant findings from a variety of aspects about ALS, including evaluation methods, animal models, pathophysiology, and clinical findings, with particular emphasis in understanding the role of every contributing mechanism to the disease for elucidating the causes underlying degeneration of motoneurons and the development of new therapeutic strategies.

Neural and glial progenitor transplantation as a neuroprotective strategy for Amyotrophic Lateral Sclerosis (ALS)

ALS is a neurodegenerative disease with a prevalence rate of up to 7.4/100,000 and the overall risk of developing ALS over a lifetime is 1:400. Most patients die from respiratory failure following a course of progressive weakness. To date, only one traditional pharmaceutical agent-riluzole, has been shown to afford a benefit on survival but numerous pharmaceutical interventions have been studied in preclinical models of ALS without subsequent translation to patient efficacy. Despite the relative selectivity of motor neuron cell death, animal and tissue culture models of familial ALS suggest that non-neuronal cells significantly contribute to neuronal dysfunction and death. Early efforts to transplant stem cells had focused on motor neuron replacement. More practically for this aggressive neurodegenerative disease, recent studies, preclinical efforts, and early clinical trials have focused on the transplantation of neural stem cells, mesenchymal stem cells, or glial progenitors. Using transgenic mouse or rat models of ALS, a number of studies have shown neuroprotection through a variety of different mechanisms that have included neurotrophic factor secretion, glutamate transporter regulation, and modulation of neuroinflammation, among others. However, given that cell replacement could involve a number of biologically relevant factors, identifying the key pathway(s) that may contribute to neuroprotection remains a challenge. Nevertheless, given the abundant data supporting the interplay between non-neuronal cell types and motor neuron disease propagation, the replacement of disease-carrying host cells by normal cells may be sufficient to confer neuroprotection. Key preclinical issues that currently are being addressed include the most appropriate methods and routes for delivery of cells to disease-relevant regions of the neuraxis, cell survival and migration, and tracking the cells following transplantation. Central to the initial development of stem cell transplantation into patients with ALS is the demonstration that transplanted cells lack tumorigenicity and have the appropriate biodistribution to ensure the safety of ALS patients receiving these therapies. Here, we review preclinical and clinical studies focusing on the transplantation of neural and glial progenitor cells as a promising neuroprotective therapy for ALS. The rationale for stem cell transplantation for neuroprotection, proof-of-concept animal studies, and current challenges facing translation of these therapies to the clinic is presented. Lastly, we discuss advancements on the horizon including induced pluripotent stem cell technology and developments for cellular tracking and detection post-transplantation. With the safe completion of the first-in-human Phase I clinical trial for intraspinal stem cell transplantation for ALS in the United States, the time is ripe for stem cell therapies to be translated to the clinic and excitingly, evaluated for neuroprotection for ALS. This article is part of a Special Issue entitled SI: Neuroprotection.

Moving stem cells to the clinic: potential and limitations for brain repair

Stem cell-based therapies hold considerable promise for many currently devastating neurological disorders. Substantial progress has been made in the derivation of disease-relevant human donor cell populations. Behavioral data in relevant animal models of disease have demonstrated therapeutic efficacy for several cell-based approaches. Consequently, cGMP grade cell products are currently being developed for first in human clinical trials in select disorders. Despite the therapeutic promise, the presumed mechanism of action of donor cell populations often remains insufficiently validated. It depends greatly on the properties of the transplanted cell type and the underlying host pathology. Several new technologies have become available to probe mechanisms of action in real time and to manipulate in vivo cell function and integration to enhance therapeutic efficacy. Results from such studies generate crucial insight into the nature of brain repair that can be achieved today and push the boundaries of what may be possible in the future.

Therapeutic applications of mesenchymal stem cells for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting the neuromuscular system and does not have a known singular cause. Genetic mutations, extracellular factors, non-neuronal support cells, and the immune system have all been shown to play varied roles in clinical and pathological disease progression. The therapeutic plasticity of mesenchymal stem cells (MSCs) may be well matched to this complex disease pathology, making MSCs strong candidates for cellular therapy in ALS. In this review, we summarize a variety of explored mechanisms by which MSCs play a role in ALS progression, including neuronal and non-neuronal cell replacement, trophic factor delivery, and modulation of the immune system. Currently relevant techniques for applying MSC therapy in ALS are discussed, focusing in particular on delivery route and cell source. We include examples from in vitro, preclinical, and clinical investigations to elucidate the remaining progress that must be made to understand and apply MSCs as a treatment for ALS.

Transplantation of human oligodendrocyte progenitor cells in an animal model of diffuse traumatic axonal injury: survival and differentiation

Introduction

Diffuse axonal injury is an extremely common type of traumatic brain injury encountered in motor vehicle crashes, sports injuries, and in combat. Although many cases of diffuse axonal injury result in chronic disability, there are no current treatments for this condition. Its basic lesion, traumatic axonal injury, has been aggressively modeled in primate and rodent animal models. The inexorable axonal and perikaryal degeneration and dysmyelination often encountered in traumatic axonal injury calls for regenerative therapies, including therapies based on stem cells and precursors. Here we explore the proof of concept that treatments based on transplants of human oligodendrocyte progenitor cells can replace or remodel myelin and, eventually, contribute to axonal regeneration in traumatic axonal injury.

Methods

We derived human oligodendrocyte progenitor cells from the human embryonic stem cell line H9, purified and characterized them. We then transplanted these human oligodendrocyte progenitor cells into the deep sensorimotor cortex next to the corpus callosum of nude rats subjected to traumatic axonal injury based on the impact acceleration model of Marmarou. We explored the time course and spatial distribution of differentiation and structural integration of these cells in rat forebrain.

Results

At the time of transplantation, over 90 % of human oligodendrocyte progenitor cells expressed A2B5, PDGFR, NG2, O4, Olig2 and Sox10, a profile consistent with their progenitor or early oligodendrocyte status. After transplantation, these cells survived well and migrated massively via the corpus callosum in both injured and uninjured brains. Human oligodendrocyte progenitor cells displayed a striking preference for white matter tracts and were contained almost exclusively in the corpus callosum and external capsule, the striatopallidal striae, and cortical layer 6. Over 3 months, human oligodendrocyte progenitor cells progressively matured into myelin basic protein(+) and adenomatous polyposis coli protein(+) oligodendrocytes. The injured environment in the corpus callosum of impact acceleration subjects tended to favor maturation of human oligodendrocyte progenitor cells. Electron microscopy revealed that mature transplant-derived oligodendrocytes ensheathed host axons with spiral wraps intimately associated with myelin sheaths.

Conclusions

Our findings suggest that, instead of differentiating locally, human oligodendrocyte progenitor cells migrate massively along white matter tracts and differentiate extensively into ensheathing oligodendrocytes. These features make them appealing candidates for cellular therapies of diffuse axonal injury aiming at myelin remodeling and axonal protection or regeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0087-0) contains supplementary material, which is available to authorized users.

Recent Advances and the Future of Stem Cell Therapies in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis is a progressive neurodegenerative disease of the motor neurons without a known cure. Based on the possibility of cellular neuroprotection and early preclinical results, stem cells have gained widespread enthusiasm as a potential treatment strategy. Preclinical models demonstrate a protective role of engrafted stem cells and provided the basis for human trials carried out using various types of stem cells, as well as a range of cell delivery methods. To date, no trial has demonstrated a clear therapeutic benefit; however, results remain encouraging and are the basis for ongoing studies. In addition, stem cell technology continues to improve, and induced pluripotent stem cells may offer additional therapeutic options in the future. Improved disease models and clinical trials will be essential in order to validate stem cells as a beneficial therapy.

Concise review: Stem cell therapies for amyotrophic lateral sclerosis: recent advances and prospects for the future

Amyotrophic lateral sclerosis (ALS) is a lethal disease involving the loss of motor neurons. Although the mechanisms responsible for motor neuron degeneration in ALS remain elusive, the development of stem cell-based therapies for the treatment of ALS has gained widespread support. Here, we review the types of stem cells being considered for therapeutic applications in ALS, and emphasize recent preclinical advances that provide supportive rationale for clinical translation. We also discuss early trials from around the world translating cellular therapies to ALS patients, and offer important considerations for future clinical trial design. Although clinical translation is still in its infancy, and additional insight into the mechanisms underlying therapeutic efficacy and the establishment of long-term safety are required, these studies represent an important first step toward the development of effective cellular therapies for the treatment of ALS.

Focal transplantation of human iPSC-derived glial-rich neural progenitors improves lifespan of ALS mice

Transplantation of glial-rich neural progenitors has been demonstrated to attenuate motor neuron degeneration and disease progression in rodent models of mutant superoxide dismutase 1 (SOD1)-mediated amyotrophic lateral sclerosis (ALS). However, translation of these results into a clinical setting requires a renewable human cell source. Here, we derived glial-rich neural progenitors from human iPSCs and transplanted them into the lumbar spinal cord of ALS mouse models. The transplanted cells differentiated into astrocytes, and the treated mouse group showed prolonged lifespan. Our data suggest a potential therapeutic mechanism via activation of AKT signal. The results demonstrated the efficacy of cell therapy for ALS by the use of human iPSCs as cell source.

Stem cell transplantation in neurological diseases: improving effectiveness in animal models

Neurological diseases afflict a growing proportion of the human population. There are two reasons for this: first, the average age of the population (especially in the industrialized world) is increasing, and second, the diagnostic tools to detect these pathologies are now more sophisticated and can be used on a higher percentage of the population. In many cases, neurological disease has a pharmacological treatment which, as in the case of Alzheimer's disease, Parkinson's disease, Epilepsy, and Multiple Sclerosis can reduce the symptoms and slow down the course of the disease but cannot reverse its effects or heal the patient. In the last two decades the transplantation approach, by means of stem cells of different origin, has been suggested for the treatment of neurological diseases. The choice of slightly different animal models and the differences in methods of stem cell preparation make it difficult to compare the results of transplantation experiments. Moreover, the translation of these results into clinical trials with human subjects is difficult and has so far met with little success. This review seeks to discuss the reasons for these difficulties by considering the differences between human and animal cells (including isolation, handling and transplantation) and between the human disease model and the animal disease model.