Autologous olfactory ensheathing cell transplantation in human spinal cord injury

Regenerative medicine for the treatment of spinal cord injury: more than just promises?

Spinal cord injury triggers a complex set of events that lead to tissue healing without the restoration of normal function due to the poor regenerative capacity of the spinal cord. Nevertheless, current knowledge about the intrinsic regenerative ability of central nervous system axons, when in a supportive environment, has made the prospect of treating spinal cord injury a reality. Among the range of strategies under investigation, cell-based therapies offer the most promising results, due to the multifactorial roles that these cells can fulfil. However, the best cell source is still a matter of debate, as are clinical issues that include the optimal cell dose as well as the timing and route of administration. In this context, the role of biomaterials is gaining importance. These can not only act as vehicles for the administered cells but also, in the case of chronic lesions, can be used to fill the permanent cyst, thus creating a more favourable and conducive environment for axonal regeneration in addition to serving as local delivery systems of therapeutic agents to improve the regenerative milieu. Some of the candidate molecules for the future are discussed in view of the knowledge derived from studying the mechanisms that facilitate the intrinsic regenerative capacity of central nervous system neurons. The future challenge for the multidisciplinary teams working in the field is to translate the knowledge acquired in basic research into effective combinatorial therapies to be applied in the clinic.

Neurotrophic factors in spinal cord injury

A major challenge in repairing the injured spinal cord is to assure survival of damaged cells and to encourage regrowth of severed axons. Because neurotrophins are known to affect these processes during development, many experimental approaches to improving function of the injured spinal cord have made use of these agents, particularly Brain derived neurotrophic factor (BDNF) and Neurotrophin-3 (NT-3). More recently, neurotrophins have also been shown to affect the physiology of cells and synapses in the spinal cord. The effect of neurotrophins on circuit performance adds an important dimension to their consideration as agents for repairing the injured spinal cord. In this chapter we discuss the role of neurotrophins in promoting recovery after spinal cord injury from both a structural and functional perspective.

Crucial roles for olfactory ensheathing cells and olfactory mucosal cells in the repair of damaged neural tracts

Olfactory ensheathing cells, the glial cells of the olfactory nervous system, exhibit unique growth-promoting and migratory properties that make them interesting candidates for cell therapies targeting neuronal injuries such as spinal cord injury. Transplantation of olfactory cells is feasible and safe in humans; however, functional outcomes are highly variable with some studies showing dramatic improvements and some no improvements at all. We propose that the reason for this is that the identity and purity of the cells is different in each individual study. We have shown that olfactory ensheathing cells are not a uniform cell population and that individual subpopulations of OECs are present in different regions of the olfactory nervous system, with strikingly different behaviors. Furthermore, the presence of fibroblasts and other cell types in the transplant can dramatically alter the behavior of the transplanted glial cells. Thus, a thorough characterization of the differences between olfactory ensheathing cell subpopulations and how the behavior of these cells is affected by the presence of other cell types is highly warranted.

Cotransplantation of Glial Restricted Precursor Cells and Schwann Cells Promotes Functional Recovery after Spinal Cord Injury

Oligodendrocyte (OL) replacement can be a promising strategy for spinal cord injury (SCI) repair. However, the poor posttransplantation survival and inhibitory properties to axonal regeneration are two major challenges that limit their use as donor cells for repair of CNS injuries. Therefore, strategies aimed at enhancing the survival of grafted oligodendrocytes as well as reducing their inhibitory properties, such as the use of more permissive oligodendrocyte progenitor cells (OPCs), also called glial restricted precursor cells (GRPs), should be highly prioritized. Schwann cell (SC) transplantation is a promising translational strategy to promote axonal regeneration after CNS injuries, partly due to their expression and secretion of multiple growth-promoting factors. Whether grafted SCs have any effect on the biological properties of grafted GRPs remains unclear. Here we report that either SCs or SC-conditioned medium (SCM) promoted the survival, proliferation, and migration of GRPs in vitro. When GRPs and SCs were cografted into the normal or injured spinal cord, robust survival, proliferation, and migration of grafted GRPs were observed. Importantly, grafted GRPs differentiated into mature oligodendrocytes and formed new myelin on axons caudal to the injury. Finally, cografts of GRPs and SCs promoted recovery of function following SCI. We conclude that cotransplantation of GRPs and SCs, the only two kinds of myelin-forming cells in the nervous system, act complementarily and synergistically to promote greater anatomical and functional recovery after SCI than when either cell type is used alone.

From basics to clinical: a comprehensive review on spinal cord injury

Spinal cord injury (SCI) is a devastating neurological disorder that affects thousands of individuals each year. Over the past decades an enormous progress has been made in our understanding of the molecular and cellular events generated by SCI, providing insights into crucial mechanisms that contribute to tissue damage and regenerative failure of injured neurons. Current treatment options for SCI include the use of high dose methylprednisolone, surgical interventions to stabilize and decompress the spinal cord, and rehabilitative care. Nonetheless, SCI is still a harmful condition for which there is yet no cure. Cellular, molecular, rehabilitative training and combinatorial therapies have shown promising results in animal models. Nevertheless, work remains to be done to ascertain whether any of these therapies can safely improve patient's condition after human SCI. This review provides an extensive overview of SCI research, as well as its clinical component. It starts covering areas from physiology and anatomy of the spinal cord, neuropathology of the SCI, current clinical options, neuronal plasticity after SCI, animal models and techniques to assess recovery, focusing the subsequent discussion on a variety of promising neuroprotective, cell-based and combinatorial therapeutic approaches that have recently moved, or are close, to clinical testing.

Cellular therapeutics delivery to the spinal cord: technical considerations for clinical application

Current literature demonstrates the efficacy of cell-based therapeutics in small animal models of varied spinal cord diseases. However, logistic challenges remain towards development of an optimized delivery approach to the human spinal cord. Clinical trials utilize a variety of methods to achieve this aim. In this article, the authors review currently employed delivery methods, compare the merits of alternate delivery paradigms, introduce their implementation in completed and ongoing clinical trials, and discuss promising near-term advances in image-guided delivery and in vivo graft tracking.

Control of olfactory ensheathing cell behaviors by electrospun silk fibroin fibers

Olfactory ensheathing cells (OECs), the only glial cell type that normally penetrates the transition zone between the peripheral and central nervous systems, are one of the most promising candidates for cell transplantation in repairing spinal cord injury (SCI). However, we must manipulate and regulate OECs' behavior to make these cells effective in cell transplantation. In the present study, we assessed the response of rat OECs to different variants of nanofibrous silk fibroin mats with regard to cell morphology, adhesion, proliferation, and migration and the related gene and protein expression. Results showed that OECs adhere and spread more easily on Tussah silk fibroin (TSF) fibers than Bombyx mori silk fibroin fibers, resulting in a higher rate of cell proliferation and gene and protein expression, examined by RT-PCR and ELISA. In addition, the morphology of OECs on microfibers is mainly polygonal with short protrusions, whereas the OECs on nanofibers exhibit a bipolar shape with long protrusions that align along the fibers, especially when aligned fibers are employed. Moreover, OECs on silk fibroin nanofibers migrate more efficiently than those on poly-L-lysine (PLL). Based on the experimental results, the morphology, adhesion, spread, gene and protein expression, and migration of OECs could be modulated and regulated by adjusting the contents and structure of silk fibroin nanofibers, shedding light on the control of OECs' behavior in nerve tissue engineering and thus the future therapeutic intervention for nerve repair after injury. This manuscript is published as part of the International Association of Neurorestoratology (IANR) supplement issue of Cell Transplantation.

Fibroblasts isolated from human middle turbinate mucosa cause neural progenitor cells to differentiate into glial lineage cells

Transplantation of olfactory ensheathing cells (OECs) is a potential therapy for repair of spinal cord injury (SCI). Autologous transplantation of OECs has been reported in clinical trials. However, it is still controversial whether purified OECs or olfactory mucosa containing OECs, fibroblasts and other cells should be used for transplantation. OECs and fibroblasts were isolated from olfactory mucosa of the middle turbinate from seven patients. The percentage of OECs with p75^NTR+ and GFAP⁺ ranged from 9.2% to 73.2%. Fibroblasts were purified and co-cultured with normal human neural progenitors (NHNPs). Based on immunocytochemical labeling, NHNPs were induced into glial lineage cells when they were co-cultured with the mucosal fibroblasts. These results demonstrate that OECs can be isolated from the mucosa of the middle turbinate bone as well as from the dorsal nasal septum and superior turbinates, which are the typical sites for harvesting OECs. Transplantation of olfactory mucosa containing fibroblasts into the central nervous system (CNS) needs to be further investigated before translation to clinical application.

Intracranial transplant of olfactory ensheathing cells can protect both upper and lower motor neurons in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal disease that involves the degeneration of cortical and spinal motor neurons. Mutant SOD1(G93A) rats constitute a good animal model for this pathological condition. We have previously demonstrated that transplantation of neonatal olfactory ensheathing cells (OECs) into the dorsal funiculus of the spinal cord of mutant SOD1(G93A) transgenic rats increases the survival of spinal motor neurons and remyelinates the impaired axons through the pyramidal tract. In the present study, we examine whether intracranial cell implantation could also exert a similar effect on cortical motor neurons and on the lower motor neurons in the spinal cord. We injected OECs from the bulb of 7-day-old GFP green rats into the corona radiata of adult SOD1 mutant rats stereotaxically to observe any changes of the upper motor neurons as well as the lower motor neurons. We found that more motor neurons at both the motor cortices and ventral horns of the spinal cord survived in grafted ALS rats than in control rats. Prolonged survival and behavioral tests including a screen test, hind limb extension, rotarod, and gait control showed that the treated animals were better than the control group. This manuscript is published as part of the International Association of Neurorestoratology (IANR) supplement issue of Cell Transplantation.

Culture of olfactory ensheathing cells for central nerve repair: the limitations and potential of endoscopic olfactory mucosal biopsy

BACKGROUND

Autotransplantation of olfactory ensheathing cells (OECs) into the damaged central nervous system is a potential therapeutic strategy for spinal cord and root cord injuries. One limiting factor has been the poor OEC yields from human mucosal biopsies. Previous studies have only commented on their success in obtaining mucosal specimens containing olfactory mucosa, but have not commented on the yield of OECs from those specimens.

OBJECTIVE

To describe a reproducible and safe surgical technique for obtaining human olfactory mucosa and identify patient factors that possibly affect the yield of OEC cultures from the human olfactory mucosa.

METHODS

We obtained mucosal biopsies from 43 consecutive patients by using a novel reproducible surgical technique and our laboratory culture protocol. The Spearman rank correlation coefficient was used to assess the relationship between OECs and fibroblast yield with patient characteristics and specimen factors.

RESULTS

A greater yield of OECs was obtained from patients of younger age. In addition, patients with worse mucosal disease yielded poorer cell cultures. Greatest yields were found in patients with absence of mucosal disease. Furthermore, a higher yield of OECs was obtained from specimens harvested from the more caudal portions of the superior turbinate, and OEC yield did not correlate with the ventroposterior location of the biopsy.

CONCLUSION

We have provided evidence that biopsies closer to the cribriform plate can produce larger yields of OECs, and that patient factors like age and mucosal disease adversely affect the culture yield.

Olfactory ensheathing cells: Part II--source of cells and application to patients

OBJECTIVE

To assess clinical methods of sourcing human olfactory ensheathing cells (OECs), and the results of present day clinical studies in OEC transplantation.

METHODS

Review of literature.

RESULTS

Present clinical studies of OEC transplantation have demonstrated the feasibility and safety of the technique, and no significant complications have occurred from harvest of the olfactory mucosa to culture OECs. These reported studies have not been designed to determine whether clinical outcome is improved by transplantation.

CONCLUSIONS

OEC transplantation strategies need to be studied further. At present clinical models for testing OECs vary in methodology and quality, and until high-quality, well-designed, and sufficiently powered studies have been performed, the true effect of OEC treatment for patients will remain unclear.

The therapeutic role of interleukin-10 after spinal cord injury

Spinal cord injury (SCI) is a devastating condition affecting 270,000 people in the United States. A potential treatment for decreasing the secondary inflammation, excitotoxic damage, and neuronal apoptosis associated with SCI, is the anti-inflammatory cytokine interleukin-10. The best characterized effects of IL-10 are anti-inflammatory-it downregulates pro-inflammatory species interleukin-1β (IL-1β), interleukin-2 (IL-2), interleukin-6 (IL-6), tumor necrosis factor-α, interferon-γ, matrix metalloproteinase-9, nitric oxide synthase, myeloperoxidase, and reactive oxygen species. Pro-apoptotic factors cytochrome c, caspase 3, and Bax are downregulated by IL-10, whereas anti-apoptotic factors B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X, B-cell lymphoma-extra large (Bcl-xl) are upregulated by IL-10. IL-10 also provides trophic support to neurons through the IL-10 receptor. Increased tissue sparing, functional recovery, and neuroprotection are seen with an immediate post-SCI systemic administration of IL-10. Treatment of SCI with IL-10 has been used successfully in combination with Schwann cell and olfactory glial cell grafts, as well as methylprednisolone. Minocycline, tetramethylpyrazine, and hyperbaric oxygen treatment all increase IL-10 levels in a SCI models and result in increased tissue sparing and functional recovery. A chronic systemic administration of IL-10 does not appear to be beneficial to SCI recovery and causes increased susceptibility to septicemia, pneumonia, and peripheral neuropathy. However, a localized upregulation of IL-10 has been shown to be beneficial and can be achieved by herpes simplex virus gene therapy, injection of poliovirus replicons, or surgical placement of a slow-release compound. IL-10 shows promise as a treatment for SCI, although research on local IL-10 delivery timeline and dosage needs to be expanded.

Acute and chronic MRI changes in the spine and spinal cord after surgical stem cell grafting in patients with definite amyotrophic lateral sclerosis: post-infusion injuries are unrelated with clinical impairment

OBJECTIVE

To report MRI spinal changes after surgical infusion of bone marrow stem cells (BMSc) in ALS patients and assess their correlation with clinical events and functional performance.

METHODS

BMSc were surgically injected in the thoracic spinal cord of 11 ALS patients (6/5 male/female; median age 46years). We performed first-week and third, sixth, ninth and twelfth post-surgical months spinal MRIs. The spinal changes in the postsurgical week and follow-up MRIs, as well as clinical events, functional scales and respiratory and electromyography data, were longitudinally monitored. Correlations between the imaging and clinical data were evaluated with the Spearman's test.

RESULTS

Transient extradural fluid collections (100%), transient spinal cord T2 hyperintensity (81.8%), and chronic spinal cord deformities (63.6%) were the dominating MRI changes. Spinal cord hemorrhages (27.3%) and cystic myelomalacia (1/11 patients) were important although unusual findings. During the follow-up, minor adverse events of mild to moderate intensity eventually improved. Initial and follow-up imaging scores showed a strongly positive correlation (r 0.879, P<0.001). The initial and delayed clinical scores did not correlate. There was no significant correlation between any of the imaging scores and clinical data.

CONCLUSIONS

Infusion of BMSc produces a variety of spinal changes apparently unrelated with clinical events and disease worsening.

Role of Matrix Metalloproteinases in Migration and Neurotrophic Properties of Nasal Olfactory Stem and Ensheathing Cells

Adult olfactory ectomesenchymal stem cells (OE-MSCs) and olfactory ensheathing cells (OECs), both from the nasal olfactory lamina propria, display robust regenerative properties when transplanted into the nervous system, but the mechanisms supporting such therapeutic effects remain unknown. Matrix metalloproteinases (MMPs) are an important family of proteinases contributing to cell motility and axonal outgrowth across the extracellular matrix (ECM) in physiological and pathological conditions. In this study, we have characterized for the first time in nasal human OE-MSCs the expression profile of some MMPs currently associated with cell migration and invasiveness. We demonstrate different patterns of expression for MMP-1, MMP-2, MMP-9, and MT1-MMP upon cell migration when compared with nonmigrating cells. Our results establish a correspondence between the localization of these proteinases in the migration front with the ability of cells to migrate. Using various modulators of MMP activity, we also show that at least MMP-2, MMP-9, and MT1-MMP contribute to OE-MSC migration in an in vitro 3D test. Furthermore, we demonstrate under the same conditions of culture used for in vivo transplantation that OE-MSCs and OECs secrete neurotrophic factors that promote neurite outgrowth of cortical and dorsal root ganglia (DRG) neurons, as well as axo-dendritic differentiation of cortical neurons. These effects were abolished by the depletion of MMP-2 and MMP-9 from the culture conditioned media. Altogether, our results provide the first evidence that MMPs may contribute to the therapeutic features of OE-MSCs and OECs through the control of their motility and/or their neurotrophic properties. Our data provide new insight into the mechanisms of neuroregeneration and will contribute to optimization of cell therapy strategies.

Devices for cell transplantation into the central nervous system: Design considerations and emerging technologies

Successful use of cell-based therapies for the treatment of neurological diseases is dependent upon effective delivery to the central nervous system (CNS). The CNS poses several challenges to the delivery of cell-based therapeutics, including the blood-brain barrier, anatomic complexity, and regional specificity. Targeted delivery methods are therefore required for the selective treatment of specific CNS regions. In addition, CNS tissues are mechanically and physiologically delicate and even minor injury to normal brain or spinal cord can cause devastating neurological deficits. Targeted delivery methods must therefore minimize tissue trauma. At present, direct injection into brain or spinal cord parenchyma promises to be the most versatile and accurate method of targeted CNS therapeutic delivery. While direct injection methods have already been employed in clinical trials of cell transplantation for a wide variety of neurological diseases, there are many shortcomings with the devices and surgical approaches currently used. Some of these technical limitations may hinder the clinical development of cell transplantation therapies despite validity of the underlying biological mechanisms. In this review, we discuss some of the important technical considerations of CNS injection devices such as targeting accuracy, distribution of infused therapeutic, and overall safety to the patient. We also introduce and discuss an emerging technology - radially branched deployment - that may improve our ability to safely distribute cell-based therapies and other therapeutic agents to the CNS. Finally, we speculate on future technological developments that may further enhance the efficacy of CNS therapeutic delivery.

Retinoic acid and human olfactory ensheathing cells cooperate to promote neural induction from human bone marrow stromal stem cells

The generation of induced neuronal cells from human bone marrow stromal stem cells (hBMSCs) provides new avenues for basic research and potential transplantation therapies for nerve injury and neurological disorders. However, clinical application must seriously consider the risk of tumor formation by hBMSCs, neural differentiation efficiency and biofunctions resembling neurons. Here, we co-cultured hBMSCs exposed to retinoic acid (RA) with human olfactory ensheathing cells (hOECs) to stimulate its differentiation into neural cells, and found that hBMSCs following 1 and 2 weeks of stimulation promptly lost their immunophenotypical profiles, and gradually acquired neural cell characteristics, as shown by a remarkable up-regulation of expression of neural-specific markers (Tuj-1, GFAP and Galc) and down-regulation of typical hBMSCs markers (CD44 and CD90), as well as a rapid morphological change. Concomitantly, in addition to a drastic decrease in the number of BrdU incorporated cells, there was a more elevated synapse formation (a hallmark for functional neurons) in the differentiated hBMSCs. Compared with OECs alone, this specific combination of RA and hOECs was significantly potentiated neuronal differentiation of hBMSCs. The results suggest that RA can enhance and orchestrate hOECs to neural differentiation of hBMSCs. Therefore, these findings may provide an alternative strategy for the repair of traumatic nerve injury and neurological diseases with application of the optimal combination of RA and OECs for neuronal differentiation of hBMSCs.

Clinical trials for the treatment of spinal cord injury: not so simple

The fast pace of research in stem cell biology and regenerative medicine is feeding hopes of the scientific community and the public that a new revolution in treatments is upon us. There are increasing numbers of examples of stem cell therapies that are effective in treating animal injuries and diseases. There is an expectation that stem cell transplantation will soon be commonplace in the human clinic, especially with the beginnings of clinical trials of embryonic stem cell transplantation for bone repair, spinal cord injury, macular degeneration, Stargardt's disease, and Batten's disease. This may be an appropriate point at which to review our experiences in moving from the lab to the clinic to initiate a Phase I clinical trial of autologous olfactory ensheathing cells in spinal cord injured humans.

Isolation of adult stem cells from the human olfactory mucosa

The olfactory mucosa, located in the nasal cavity, is the only nervous tissue that is exposed to the external environment and easily accessible in every living individual. In addition, this organ is home of a continuing neurogenesis that is sustained by a large population of stem cells. Here, we describe a method for biopsying olfactory mucosa from human nasal cavities and isolating multipotent adult stem cells that can be used to either identify biomarkers in brain disorders or repair the pathological/traumatized nervous system.

Effectiveness of intense, activity-based physical therapy for individuals with spinal cord injury in promoting motor and sensory recovery: is olfactory mucosa autograft a factor?

BACKGROUND/OBJECTIVES

Rehabilitation for individuals with spinal cord injury (SCI) is expanding to include intense, activity-based, out-patient physical therapy (PT). The study's primary purposes were to (i) examine the effectiveness of intense PT in promoting motor and sensory recovery in individuals with SCI and (ii) compare recovery for individuals who had an olfactory mucosa autograft (OMA) with individuals who did not have the OMA while both groups participated in the intense PT program.

METHODS

Prospective, non-randomized, non-blinded, intervention study. Using the American Spinal Injury Association examination, motor and sensory scores for 23 (7 OMA, 6 matched control and 10 other) participants were recorded.

RESULTS

Mean therapy dosage was 137.3 total hours. The participants' total, upper and lower extremity motor scores improved significantly while sensory scores did not improve during the first 60 days and from initial to discharge examination. Incomplete SCI or paraplegia was associated with greater motor recovery. Five of 14 participants converted from motor-complete to motor-incomplete SCI. Individuals who had the OMA and participated in intense PT did not have greater sensory or greater magnitude or rate of motor recovery as compared with participants who had intense PT alone.

CONCLUSION

This study provides encouraging evidence as to the effectiveness of intense PT for individuals with SCI. Future research is needed to identify the optimal therapy dosage and specific therapeutic activities required to generate clinically meaningful recovery for individuals with SCI including those who elect to undergo a neural recovery/regenerative surgical procedure and those that elect intense therapy alone.

Human mesenchymal stem cells isolated from olfactory biopsies but not bone enhance CNS myelination in vitro

Spinal cord injury (SCI) is a devastating condition with limited capacity for repair. Cell transplantation is a potential strategy to promote SCI repair with cells from the olfactory system being promising candidates. Although transplants of human olfactory mucosa (OM) are already ongoing in clinical trials, the repair potential of this tissue remains unclear. Previously, we identified mesenchymal-like stem cells that reside in the lamina propria (LP-MSCs) of rat and human OM. Little is known about these cells or their interactions with glia such as olfactory ensheathing cells (OECs), which would be co-transplanted with MSCs from the OM, or endogenous CNS glia such as oligodendrocytes. We have characterized, purified, and assessed the repair potential of human LP-MSCs by investigating their effect on glial cell biology with specific emphasis on CNS myelination in vitro. Purified LP-MSCs expressed typical bone marrow MSC (BM-MSC) markers, formed spheres, were clonogenic and differentiated into bone and fat. LP-MSC conditioned medium (CM) promoted oligodendrocyte precursor cell (OPC) and OEC proliferation and induced a highly branched morphology. LP-MSC-CM treatment caused OEC process extension. Both LP and BM-MSCs promoted OPC proliferation and differentiation, but only myelinating cultures treated with CM from LP and not BM-MSCs had a significant increase in myelination. Comparison with fibroblasts and contaminating OM fibroblast like-cells showed the promyelination effect was LP-MSC specific. Thus LP-MSCs harvested from human OM biopsies may be an important candidate for cell transplantation by contributing to the repair of SCI.

Implications of olfactory lamina propria transplantation on hyperreflexia and myelinated fiber regeneration in rats with complete spinal cord transection

Transplantation with olfactory ensheathing cells (OECs) has been adopted after several models of spinal cord injury (SCI) with the purpose of creating a favorable environment for the re-growth of injured axons. However, a consensus on the efficacy of this cellular transplantation has yet to be reached. In order to explore alternative parameters that could demonstrate the possible restorative properties of such grafts, the present study investigated the effects of olfactory lamina propria (OLP) transplantation on hyperreflexia and myelinated fiber regeneration in adult rats with complete spinal cord transection. The efficacy of OLP (graft containing OECs) and respiratory lamina propria (RLP, graft without OECs) was tested at different post-injury times (acutely, 2- and 4-week delayed), to establish the optimum period for transplantation. In the therapeutic windows used, OLP and RLP grafts produced no considerable improvements in withdrawal reflex responses or on the low-frequency dependent depression of H-reflex. Both lamina propria grafts produced comparable results for the myelinated fiber density and for the estimated total number of myelinated fibers at the lesion site, indicating that the delayed transplantation approach does not seem to limit the regenerative effects. However, animals transplanted with OLP 2 or 4 weeks after injury exhibit smaller myelin sheath thickness and myelinated fiber area and diameter at the lesion site compared to their respective RLP groups. Despite the ongoing clinical use of OECs, it is important to emphasize the need for more experimental studies to clarify the exact nature of the repair capacity of these grafts in the treatment of SCI.

Experimental and therapeutic opportunities for stem cells in multiple sclerosis

Multiple Sclerosis (MS) is an inflammatory demyelinating neurodegenerative disorder of the brain and spinal cord that causes significant disability in young adults. Although the precise aetiopathogenesis of MS remains unresolved, its pathological hallmarks include inflammation, demyelination, axonal injury (acute and chronic), astrogliosis and variable remyelination. Despite major recent advances in therapeutics for the early stage of the disease there are currently no disease modifying treatments for the progressive stage of disease, whose pathological substrate is axonal degeneration. This represents the great and unmet clinical need in MS. Against this background, human stem cells offer promise both to improve understanding of disease mechanism(s) through in-vitro modeling as well as potentially direct use to supplement and promote remyelination, an endogenous reparative process where entire myelin sheaths are restored to demyelinated axons. Conceptually, stem cells can act directly to myelinate axons or indirectly through different mechanisms to promote endogenous repair; importantly these two mechanisms of action are not mutually exclusive. We propose that discovery of novel methods to invoke or enhance remyelination in MS may be the most effective therapeutic strategy to limit axonal damage and instigate restoration of structure and function in this debilitating condition. Human stem cell derived neurons and glia, including patient specific cells derived through reprogramming, provide an unprecedented experimental system to model MS “in a dish” as well as enable high-throughput drug discovery. Finally, we speculate upon the potential role for stem cell based therapies in MS.

Improvement in sensory function via granulocyte-macrophage colony-stimulating factor in rat spinal cord injury models

OBJECT

The aim in this study was to determine whether granulocyte-macrophage colony-stimulating factor (GM-CSF) leads to sensory improvement in rat spinal cord injury (SCI) models.

METHODS

Thirty male Sprague-Dawley rats were included in this study: 10 in the sham group (laminectomy alone without SCI), 10 in the SCI group (SCI treated with phosphate-buffered saline), and 10 in the GM-CSF treatment group (SCI treated with GM-CSF). A locomotor function test and pain sensitivity test were conducted weekly for 9 weeks after SCI or sham injury. Spinal tissue samples from all rats were immunohistochemically examined for the expression of calcitonin gene-related peptide (CGRP) and abnormal sprouting at Week 9 post-SCI.

RESULTS

Granulocyte-macrophage colony-stimulating factor treatment improves functional recovery after SCI. In the tactile withdrawal threshold and frequency of the hindlimb paw, the GM-CSF group always responded with a statistically significant lower threshold than the SCI group 9 weeks after SCI (p < 0.05). The response of the forelimb and hindlimb paws to cold in the GM-CSF group always reflected a statistically significant lower threshold than in the SCI group 9 weeks after injury (p < 0.05). Decreased CGRP expression, observed by density and distribution area, was noted in the GM-CSF group (optical density 113.5 ± 20.4) compared with the SCI group (optical density 143.1 ± 18.7; p < 0.05).

CONCLUSIONS

Treatment with GM-CSF results in functional recovery, improving tactile and cold sense recovery in a rat SCI model. Granulocyte-macrophage colony-stimulating factor also minimizes abnormal sprouting of sensory nerves after SCI.

Peripheral nerve injuries and transplantation of olfactory ensheathing cells for axonal regeneration and remyelination: fact or fiction?

Successful nerve regeneration after nerve trauma is not only important for the restoration of motor and sensory functions, but also to reduce the potential for abnormal sensory impulse generation that can occur following neuroma formation. Satisfying functional results after severe lesions are difficult to achieve and the development of interventional methods to achieve optimal functional recovery after peripheral nerve injury is of increasing clinical interest. Olfactory ensheathing cells (OECs) have been used to improve axonal regeneration and functional outcome in a number of studies in spinal cord injury models. The rationale is that the OECs may provide trophic support and a permissive environment for axonal regeneration. The experimental transplantation of OECs to support and enhance peripheral nerve regeneration is much more limited. This chapter reviews studies using OECs as an experimental cell therapy to improve peripheral nerve regeneration.

Clinical observation of fetal olfactory ensheathing glia transplantation (OEGT) in patients with complete chronic spinal cord injury

This study was designed to observe the functional changes after fetal olfactory ensheathing glia transplantation (OEGT) into the spinal cord of patients with chronic spinal cord injury (SCI). Patients whose recovery had plateaued for longer than 6 months were enrolled. Six thoracic patients were tested for safety and five cervical patients for efficacy. OEGT was performed according to the method developed by Huang. Average follow-up was 14 months (range 1.0-1.5 years). Sensation improved moderately (light touch 14.2, pin prick 13.6); as did spasticity (1-2 modified Ashworth scale down). Locomotion recovery was minimal (1.6). Useful reticular formation functions were observed, but due to a lack of appropriate outcome measure, they were not recorded and reported.

Stem cell-based therapy for spinal cord injury

Stem cells (SCs) represent a new therapeutic approach for spinal cord injury (SCI) by enabling improved sensory and motor functions in animal models. The main goal of SC-based therapy for SCI is the replacement of neurons and glial cells that undergo cell death soon after injury. Stem cells are able to promote remyelination via oligodendroglia cell replacement to produce trophic factors enhancing neurite outgrowth, axonal elongation, and fiber density and to activate resident or transplanted progenitor cells across the lesion cavity. While several SC transplantation strategies have shown promising yet partial efficacy, mechanistic proof is generally lacking and is arguably the largest impediment toward faster progress and clinical application. The main challenge ahead is to spur on cooperation between clinicians, researchers, and patients in order to define and optimize the mechanisms of SC function and to establish the ideal source/s of SCs that produce efficient and also safe therapeutic approaches.

Potential role of stem cells in severe spinal cord injury: current perspectives and clinical data

Stem cell transplantation for spinal cord injury (SCI) along with new pharmacotherapy research offers the potential to restore function and ease the associated social and economic burden in the years ahead. Various sources of stem cells have been used in the treatment of SCI, but the most convincing results have been obtained with neural progenitor cells in preclinical models. Although the use of cell-based transplantation strategies for the repair of chronic SCI remains the long sought after holy grail, these approaches have been to date the most successful when applied in the subacute phase of injury. Application of cell-based strategies for the repair and regeneration of the chronically injured spinal cord will require a combinational strategy that may need to include approaches to overcome the effects of the glial scar, inhibitory molecules, and use of tissue engineering strategies to bridge the lesion. Nonetheless, cell transplantation strategies are promising, and it is anticipated that the Phase I clinical trials of some form of neural stem cell-based approach in SCI will commence very soon.

[Acute traumatic spinal cord injuries: Epidemiology and prospects]

OBJECTIVE

Specify the epidemiological data on the acute spinal cord injuries and define a group of patients that could benefit from cellular transplantation therapy designed with the aim of repair and regeneration of damaged spinal cord tissues.

MATERIAL AND METHODS

Five years monocentric (Gui-de-Chauliac Hospital, Montpellier, France) retrospective analysis of patients suffering from spinal cord injury (SCI). Spinal cord injured-patients, defined as sensory-motor complete, underwent a clinical evaluation following American Spinal Injury Association (ASIA) and functional type 2 Spinal Cord Independence Measure (SCIM2) scorings as well as radiological evaluation through spinal cord magnetic resonance imaging (MRI).

RESULTS

One hundred and fifty-seven medical records were reviewed and we selected and re-examined 20 patients with complete thoracic spinal cord lesion. Clinical and radiological evaluations of these patients demonstrated, in 75 % of the cases, an absence of clinical progression after a mean of 49months. Radiological abnormalities were constantly present in the initial (at the admission to hospital) and control (re-evaluation) MRI and no reliable predictive criteria of prognosis had been found.

DISCUSSION/CONCLUSION

We compare our results to the literature and discuss advantages and limits of cellular transplantation strategies for these patients.

Noninvasive Bioluminescence Imaging of Olfactory Ensheathing Glia and Schwann Cells following Transplantation into the Lesioned Rat Spinal Cord

In this study, we assess the feasibility of bioluminescence imaging to monitor the survival of Schwann cells (SCs) and olfactory ensheathing glia cells (OECs) after implantation in the lesioned spinal cord of adult rats. To this end, purified SCs and OECs were genetically modified with lentiviral vectors encoding luciferase-2 and GFP and implanted in the lesioned dorsal column. The bioluminescent signal was monitored for over 3 months, and at 7 and 98 days postsurgery, the signal was compared to standard histological analysis of GFP expression in the spinal cords. The temporal profile of the bioluminescent signal showed three distinct phases for both cell types. (I) A relatively stable signal in the first week. (II) A progressive decline in signal strength in the second and third week. (III) After the third week, the average bioluminescent signal stabilized for both cell types. Interestingly, in the first week, the peak of the bioluminescent signal after luciferin injection was delayed when compared to later time points. Similar to in vitro, our data indicated a linear relationship between the in vivo bioluminescent signal and the GFP signal of the SCs and OECs in the spinal cords when the results of both the 7 and 98 day time points are combined. This is the first report of the use of in vivo bioluminescence to monitor cell survival in the lesioned rat spinal cord. Bioluminescence could be a potentially powerful, non-invasive strategy to examine the efficacy of treatments that aim to improve the survival of proregenerative cells transplanted in the injured rat spinal cord.

Evaluation of clinical experience using cell-based therapies in patients with spinal cord injury: a systematic review

Object

Using a systematic approach, the authors evaluated the current utilization, safety, and effectiveness of cellular therapies for traumatic spinal cord injuries (SCIs) in humans.

Methods

A systematic search and critical review of the literature published through mid-January 2012 was performed. Articles included in the search were restricted to the English language, studies with at least 10 patients, and those analyzing cellular therapies for traumatic SCI. Citations were evaluated for relevance using a priori criteria, and those that met the inclusion criteria were critically reviewed. Each article was then designated a level of evidence that was developed by the Oxford Centre for Evidence-Based Medicine.

Results

The initial literature search identified 651 relevant articles, which decreased to 350 after excluding case reports and reviews. Evaluation of articles at the title/abstract level, and later at the full-text level, limited the final article set to 12 papers. The following cellular therapies employed in humans with SCI are reviewed: bone marrow mesenchymal and hematopoietic stem cells (8 studies), olfactory ensheathing cells (2 studies), Schwann cells (1 study), and fetal neurogenic tissue (1 study). Overall the quality of the literature was very low, with 3 Grade III levels of evidence and 9 Grade IV studies.

Conclusions

Several different cellular-mediated strategies for adult SCI have been reported to be relatively safe with varying degrees of neurological recovery. However, the literature is of low quality and there is a need for improved preclinical studies and prospective, controlled clinical trials.

Translating cellular therapies from bench to bedside for amyotrophic lateral sclerosis

The last decade has witnessed an increasing number of biologic (e.g., cell- or viral vector-based) therapeutics supported by preclinical efficacy data for the treatment of afflictions to the CNS. While some international investigators have undertaken preliminary clinical safety studies, published literature indicate varying degrees of rigor with respect to study design and technical approach. To our knowledge, ours is the first group to have systematically generated preclinical validation data for a delivery approach and translated this into a Phase I trial attempting to covalidate the safety of a direct, targeted delivery approach, as well as a cell-based therapeutic. This article discusses the rationale for cell-based therapy in amyotrophic lateral sclerosis and several of the unique considerations encountered during this process.

Stem cell therapy for the spinal cord

Injury and disease of the spinal cord are generally met with a poor prognosis. This poor prognosis is due not only to the characteristics of the diseases but also to our poor ability to deliver therapeutics to the spinal cord. The spinal cord is extremely sensitive to direct manipulation, and delivery of therapeutics has proven a challenge for both scientists and physicians. Recent advances in stem cell technologies have opened up a new avenue for the treatment of spinal cord disease and injury. Stem cells have proven beneficial in rodent models of spinal cord disease and injury. In these animal models, stem cells have been shown to produce their effect by the dual action of cell replacement and the trophic support of the factors secreted by these cells. In this review we look at the main clinical trials involving stem cell transplant into the spinal cord, focusing on motor neuron diseases and spinal cord injury. We will also discuss the major hurdles in optimizing stem cell delivery methods into the spinal cord. We shall examine current techniques such as functional magnetic resonance imaging guidance and cell labeling and will look at the current research striving to improve these techniques. With all caveats and future research taken into account, this is a very exciting time for stem cell transplant into the spinal cord. We are only beginning to realize the huge potential of stem cells in a central nervous system setting to provide cell replacement and trophic support. Many more trials will need to be undertaken before we can fully exploit the attributes of stem cells.

Autologous stem cells for personalised medicine

Increasing understanding of stem cell biology, the ability to reprogramme differentiated cells to a pluripotent state and evidence of multipotency in certain adult somatic stem cells has opened the door to exciting therapeutic advances as well as a great deal of regulatory and ethical issues. Benefits will come from the possibility of modelling human diseases and develop individualised therapies, and from their use in transplantation and bioengineering. The use of autologous stem cells is highly desirable, as it avoids the problem of tissue rejection, and also reduces ethical and regulatory issues. Identification of the most appropriate cell sources for different potential applications, development of appropriate clinical grade methodologies and large scale well controlled clinical trials will be essential to assess safety and value of cell based therapies, which have been generating much hope, but are by and large not yet close to becoming standard clinical practice. We briefly discuss stem cells in the context of tissue repair and regenerative medicine, with a focus on individualised clinical approaches, and give examples of sources of autologous cells with potential for clinical intervention.

Smell and taste disorders

Smell and taste disorders can markedly affect the quality of life. In recent years we have become much better in the assessment of the ability to smell and taste. In addition, information is now available to say something about the prognosis of individual patients. With regard to therapy there also seems to be low but steady progress. Of special importance for the treatment is the ability of the olfactory epithelium to regenerate.

The migration of olfactory ensheathing cells during development and regeneration

The primary olfactory nervous system is unique in that it continuously renews itself and regenerates after injury. These properties are attributed to the presence of olfactory glia, termed olfactory ensheathing cells (OECs). Evidence is now emerging that individual OEC populations exist with distinct anatomical localisations and physiological properties, but their differential roles have not been determined. Unlike other glia, OECs can migrate from the periphery into the central nervous system, and organised OEC migration can enhance axonal extension after injury. Despite this, the mechanisms regulating OEC migration are largely unknown. Here, we provide an overview of the roles of OECs in development and adulthood. We review the latest research describing the differences between individual OEC subpopulations and discuss potential regulatory mechanisms for OEC guidance and migration. Using advanced time lapse techniques, we have obtained novel insights into how OECs behave in a complex multicellular environment which we discuss here with particular focus on cell-cell interactions. Significantly, transplantation of OECs constitutes a promising novel therapy for nerve injuries, but results are highly variable and the method needs improvement. We here review the roles of transplanted OECs in neural repair of damaged neuronal tracts distinct from the primary olfactory nervous system.

Cellular therapies for treating pain associated with spinal cord injury

Spinal cord injury leads to immense disability and loss of quality of life in human with no satisfactory clinical cure. Cell-based or cell-related therapies have emerged as promising therapeutic potentials both in regeneration of spinal cord and mitigation of neuropathic pain due to spinal cord injury. This article reviews the various options and their latest developments with an update on their therapeutic potentials and clinical trialing.

Platform and cannula design improvements for spinal cord therapeutics delivery

BACKGROUND

Only recently have data been published attempting to validate a technology and technique suitable for targeted delivery of biological payloads to the human spinal cord.

OBJECTIVE

To characterize the development and evolution of a spine-stabilized microinjection platform as a vehicle for biologics delivery to the cervical and thoracolumbar spine on the basis of preclinical experience in both non-Good Laboratory Practice (GLP) experimental series and GLP studies.

METHODS

Our laboratory completed > 100 cervical and lumbar porcine microinjection procedures between July 2004 and June 2010. This included both non-GLP- and GLP-adherent survival series to validate the safety and accuracy achievable with intraspinal microinjection. During this time, 3 different microinjection platforms, injection stages, and cannula designs were tested.

RESULTS

Repetitive technological improvements reduced incision length, decreased procedural complexity, and simplified ventral horn targeting and accuracy. These changes reduced procedural invasiveness and the likelihood of neurological morbidity while improving targeting accuracy. In part as a result of these technological improvements and procedural modifications, we have safely progressed from single unilateral microinjections to multiple bilateral injections without long-term neurological sequelae.

CONCLUSION

Technological and procedural refinements have significantly enhanced the capabilities of intraspinal microinjection-based biologics delivery. Reductions in procedural invasiveness and the capability to deliver sequential biological payloads effectively have broadened the flexibility of intraspinal microinjection to a widened array of intrinsic spinal cord pathologies. These advances have laid the groundwork for clinical translation of spinal cord microinjections.

Spinal cord clinical trials and the role for bioengineering

There is considerable need for bringing effective therapies for spinal cord injury (SCI) to the clinic. Excellent medical and surgical management has mitigated poor prognoses after SCI; however, few advances have been made to return lost function. Bioengineering approaches have shown great promise in preclinical rodent models, yet there remains a large translational gap to carry these forward in human trials. Herein, we provide a framework of human clinical trials, an overview of past trials for SCI, as well as bioengineered approaches that include: directly applied pharmacologics, cellular transplantation, biomaterials and functional neurorehabilitation. Success of novel therapies will require the correct application of comprehensive preclinical studies with well-designed and expertly conducted human clinical trials. While biologics and bioengineered strategies are widely considered to represent the high potential benefits for those who have sustained a spinal injury, few such therapies have been thoroughly tested with appreciable efficacy for use in human SCI. With these considerations, we propose that bioengineered strategies are poised to enter clinical trials.

Clinical Achievements, Obstacles, Falsehoods, and Future Directions of Cell-Based Neurorestoratology

Neurorestoratology is a newborn and emerging distinct discipline in the neuroscience family. Its establishment will definitely speed up the advance of this promising frontier realm. A worldwide association for Neurorestoratology and several official journals covering this discipline have recently been set up. Clinical practice has demonstrated that the sequelae of damages and diseases of the CNS can be functionally restored to some degree. Obstacles that hinder the promising methods of Neurorestoratology to be translated from the bench to the bedside include political, governmental, religious, ethical, economic, and scientific factors or in most instances they work in combination. Falsehoods against the recognition of neurorestoratology include: 1) no therapeutic method is currently available that suggests that it is possible to repair, even partially, neurological functions; 2) according to the media, a cure will be very soon found for patients with severe spinal cord injury, brain trauma, and progressively deteriorated CNS degenerative diseases; 3) randomizing double blind control designed studies are the only gold standard for clinical study; self-comparison designed studies should be ignored and neglected. Future directions for neurorestoratology include the comparison and integration of current and upcoming available neurorestoration methods to look for the optimization regimes, and edit and publish clinical neurorestoratology treatment guidelines.

Translating preclinical approaches into human application

In recent decades, several novel approaches of spinal cord repair have revealed promising findings in animal models. However, for a successful translation of these into a clinical trial in humans the specific conditions pertaining to human spinal cord injuries (SCI) have to be appreciated. Firstly, transection of the spinal cord is commonly applied in animal models, whereas spinal cord contusion is the predominant type of injury in humans, and generally leads to more extensive injury in two to three spinal cord segments. Secondly, the quadrupedal organization of locomotion in animals and the more complex autonomic functions in humans challenge the translation of animal behavior into recovery from human SCI. Thirdly, so far, no adequate animal model has been developed to resemble spastic movement disorder in human SCI. Fourthly, the extensive damage to spinal motor neurons and nerve roots in human cervical and thoracolumbar in spine trauma is but little addressed in current translational studies. This damage has direct implications for rehabilitation and repair strategies. Fifthly, there is increasing evidence for a neuronal dysfunction below the level of the lesion in chronic complete SCI. The relevance of this dysfunction for a regeneration-inducing treatment needs to be investigated. Lastly, an approach to facilitate an appropriate reconnection of regenerating tract fibers by functional training in the postacute stage has yet to be confirmed.

CNPase expression in olfactory ensheathing cells

A large body of work supports the proposal that transplantation of olfactory ensheathing cells (OECs) into nerve or spinal cord injuries can promote axonal regeneration and remyelination. Yet, some investigators have questioned whether the transplanted OECs associate with axons and form peripheral myelin, or if they recruit endogenous Schwann cells that form myelin. Olfactory bulbs from transgenic mice expressing the enhanced green fluorescent protein (eGFP) under the control of the 2-3-cyclic nucleotide 3-phosphodiesterase (CNPase) promoter were studied. CNPase is expressed in myelin-forming cells throughout their lineage. We examined CNPase expression in both in situ in the olfactory bulb and in vitro to determine if OECs express CNPase commensurate with their myelination potential. eGFP was observed in the outer nerve layer of the olfactory bulb. Dissociated OECs maintained in culture had both intense eGFP expression and CNPase immunostaining. Transplantation of OECs into transected peripheral nerve longitudinally associated with the regenerated axons. These data indicate that OECs in the outer nerve layer of the olfactory bulb of CNPase transgenic mice express CNPase. Thus, while OECs do not normally form myelin on olfactory nerve axons, their expression of CNPase is commensurate with their potential to form myelin when transplanted into injured peripheral nerve.

Two phases of replacement replenish the olfactory ensheathing cell population after injury in postnatal mice

Olfactory ensheathing cells (OECs) support the regeneration of olfactory sensory neurons throughout life, however, it remains unclear how OECs respond to a major injury. We have examined the proliferation and migration of OECs following unilateral bulbectomy in postnatal mice. S100ß-DsRed and OMP-ZsGreen transgenic mice were used to visualize OECs and olfactory neurons, respectively, and we used the thymidine analogue ethynyl deoxyuridine (EdU) to identify cells that were proliferating at the time of administration. Following unilateral bulbectomy, there was an initial phase of OEC proliferation throughout the olfactory pathway with a peak of proliferation occurring 2 to 7 days after the injury. A second phase of proliferation also occurred in which precursors localized within the olfactory mucosa divided to replenish the OEC population. We then tracked the positions of OECs that had proliferated and found that there was a progressive increase in OECs in the cavity for at least 12 to 16 days after injury which could not be accounted for solely by local proliferation of OECs within the cavity. These results suggest that OECs migrated from the peripheral olfactory nerve to populate the mass of cells that filled cavity left by bulbectomy. Our results demonstrate that following injury to the olfactory nervous system, the OEC population is replenished by migration of cells that arise from both local proliferation of OECs throughout the olfactory nerve pathway as well as from precursor cells in the olfactory mucosa.

Olfactory and respiratory lamina propria transplantation after spinal cord transection in rats: effects on functional recovery and axonal regeneration

Spinal cord injury (SCI) has very poor clinical prospects, resulting in irreversible loss of function below the injury site. Although applied in clinical trials, olfactory ensheathing cells transplantation (OEC) derived from lamina propria (OLP) is still a controversial repair strategy. The present study explored the efficacy of OLP or respiratory lamina propria (RLP) transplantation and the optimum period after SCI for application of this potential therapy. Adult male rats were submitted to spinal cord transection and underwent acute, 2-week or 4-week post-injury transplantation with pieces of OLP (containing OECs) or RLP (without OECs). After grafting, animals with OLP and RLP showed discrete and similar hindlimb motor improvement, with comparable spinal cord tissue sparing and sprouting in the lesion area. Acute transplantation of OLP and RLP seems to foster limited supraspinal axonal regeneration as shown by the presence of neurons stained by retrograde tracing in the brainstem nuclei. A larger number of 5-HT positive fibers were found in the cranial stump of the OLP and RLP groups compared to the lesion and caudal regions. Calcitonin gene-related peptide fibers were present in considerable numbers at the SCI site in both types of transplantation. Our results failed to verify differences between acute, 2-week and 4-week delayed transplantation of OLP and RLP, suggesting that the limited functional and axon reparative effects observed could not be exclusively related to OECs. A greater understanding of the effects of these tissue grafts is necessary to strengthen the rationale for application of this treatment in humans.

Cellular treatments for spinal cord injury: the time is right for clinical trials

More than 1 million people in the United States live with a spinal cord injury (SCI). Despite medical advances, many patients with SCIs still experience substantial neurological disability, with loss of motor, sensory, and autonomic function. Cell therapy is ideally suited to address the multifactorial nature of the secondary events following SCI. Remarkable advances in our understanding of the pathophysiology of SCI, structural and functional magnetic resonance imaging, image-guided micro-neurosurgical techniques, and transplantable cell biology have enabled the use of cell-based regenerative techniques in the clinic. It is important to note that there are more than a dozen recently completed, ongoing, or recruiting cell therapy clinical trials for SCI that reflect the views of many key stakeholders. The field of regenerative neuroscience has reached a stage in which the clinical trials are scientifically and ethically justified. Although experimental models and analysis methods and techniques continue to evolve, no model will completely replicate the human condition. It is recognized that more work with cervical models of contusive/compressive SCI are required in parallel with clinical trials. It is also important that the clinical translation of advances made through well-established and validated experimental approaches in animal models move forward to meet the compelling needs of individuals with SCI and to advance the field of regenerative neuroscience. However, it is imperative that such efforts at translation be done in the most rigorous and informed fashion to determine safety and possible efficacy, and to provide key information to clinicians and basic scientists, which will allow improvements in regenerative techniques and the validation and refinement of existing preclinical animal models and research approaches. The field of regenerative neuroscience should not be stalled at the animal model stage, but instead the clinical trials need to be focused, safe, and ethical, backed up by a robust, translationally relevant preclinical research strategy.