Functional Repair of Rat Corticospinal Tract Lesions Does Not Require Permanent Survival of an Immunoincompatible Transplant

Transplantation of Cryopreserved Olfactory Ensheathing Cells Restores Loss of Functions in an Experimental Model

In the past decades, the properties of olfactory ensheathing cells (OECs) have been widely investigated. Studies have shown that transplantation of OECs cultured from the olfactory bulb mediates axonal regeneration, remyelination and restores lost functions in experimental central nervous system (CNS) injury models. Autologously sourcing the cells from the nasal mucosa or the olfactory bulb to treat patients with spinal cord injuries would be ideal, but the cell yield achieved may be inadequate to cover the surface area of the lesions typically encountered in human spinal cord contusion injuries. Therefore, banking allogenic cryopreserved olfactory bulb cells from donors or generating cell lines could provide a marked increase in cell stock available for transplantation. This study is undertaken in two control and two intervention groups. The control groups have lesions alone and lesions with collagen gel but without cells. The intervention groups have either transplantation of primary cultured olfactory bulb OECs (bOECs) encapsulated in collagen gel or cryopreserved bulb OECs (CbOECs) encapsulated in collagen gel. Here, we report that transplantation of cryopreserved rat bOECs encapsulated in collagen restored the loss of function in a vertical climbing test in a unilateral C6-T1 dorsal root injury model. The loss of function returns in 80% of rats with injuries in about 3 weeks comparable to that we observed after transplantation of primary cultured bOECs. The regeneration axons induced by the transplant are identified by neurofilament antibodies and ensheathed by OECs. Our results indicate that cryopreserved OECs retain their properties of inducing axon regeneration and restoring loss of function in the experimental model. This is a step forward to translate the research into future clinical applications.

Designing a Clinical Trial with Olfactory Ensheathing Cell Transplantation-Based Therapy for Spinal Cord Injury: A Position Paper

Spinal cord injury (SCI) represents an urgent unmet need for clinical reparative therapy due to its largely irreversible and devastating effects on patients, and the tremendous socioeconomic burden to the community. While different approaches are being explored, therapy to restore the lost function remains unavailable. Olfactory ensheathing cell (OEC) transplantation is a promising approach in terms of feasibility, safety, and limited efficacy; however, high variability in reported clinical outcomes prevent its translation despite several clinical trials. The aims of this position paper are to present an in-depth analysis of previous OEC transplantation-based clinical trials, identify existing challenges and gaps, and finally propose strategies to improve standardization of OEC therapies. We have reviewed the study design and protocols of clinical trials using OEC transplantation for SCI repair to investigate how and why the outcomes show variability. With this knowledge and our experience as a team of biologists and clinicians with active experience in the field of OEC research, we provide recommendations regarding cell source, cell purity and characterisation, transplantation dosage and format, and rehabilitation. Ultimately, this position paper is intended to serve as a roadmap to design an effective clinical trial with OEC transplantation-based therapy for SCI repair.

Considering the Cellular Composition of Olfactory Ensheathing Cell Transplants for Spinal Cord Injury Repair: A Review of the Literature

Olfactory ensheathing cells (OECs) are specialized glia cells of the olfactory system that support the continual regeneration of olfactory neurons throughout adulthood. Owing to their pro-regenerative properties, OECs have been transplanted in animal models of spinal cord injuries (SCI) and trialed in clinical studies on SCI patients. Although these studies have provided convincing evidence to support the continued development of OEC transplantation as a treatment option for the repair of SCI, discrepancies in the reported outcome has shown that OEC transplantation requires further improvement. Much of the variability in the reparative potential of OEC transplants is due to the variations in the cell composition of transplants between studies. As a result, the optimal cell preparation is currently a subject of debate. Here we review, the characterization as well as the effect of the cell composition of olfactory cell transplantation on therapeutic outcome in SCI. Firstly, we summarize and review the cell composition of olfactory cell preparations across the different species studied prior to transplantation. Since the purity of cells in olfactory transplants might affect the study outcome we also examine the effect of the proportions of OECs and the different cell types identified in the transplant on neuroregeneration. Finally, we consider the effect of the yield of cells on neuroregeneration by assessing the cell dose of transplants on therapeutic outcome.

Optimizing Olfactory Ensheathing Cell Transplantation for Spinal Cord Injury Repair

Cell transplantation constitutes an important avenue for development of new treatments for spinal cord injury (SCI). These therapies are aimed at supporting neural repair and/or replacing lost cells at the injury site. To date, various cell types have been trialed, with most studies focusing on different types of stem cells or glial cells. Here, we review commonly used cell transplantation approaches for spinal cord injury (SCI) repair, with focus on transplantation of olfactory ensheathing cells (OECs), the glial cells of the primary olfactory nervous system. OECs are promising candidates for promotion of neural repair given that they support continuous regeneration of the olfactory nerve that occurs throughout life. Further, OECs can be accessed from the nasal mucosa (olfactory neuroepithelium) at the roof of the nasal cavity and can be autologously transplanted. OEC transplantation has been trialed in many animal models of SCI, as well as in human clinical trials. While several studies have been promising, outcomes are variable and the method needs improvement to enhance aspects such as cell survival, integration, and migration. As a case study, we include the approaches used by our team (the Clem Jones Centre for Neurobiology and Stem Cell Research, Griffith University, Nathan, QLD, Australia) to address the current problems with OEC transplantation and discuss how the therapeutic potential of OEC transplantation can be improved. Our approach includes discovery research to improve our knowledge of OEC biology, identifying natural and synthetic compounds to stimulate the neural repair properties of OECs, and designing three-dimensional cell constructs to create stable and transplantable cell structures.

Current evidence on mesenchymal stem cell therapy for traumatic spinal cord injury: systematic review and meta-analysis

BACKGROUND AIMS

The authors aim to analyze the evidence in the literature regarding the efficacy and safety of mesenchymal stem cell (MSC) therapy in human subjects with traumatic spinal cord injury (SCI) and identify its potential role in the management of SCI.

METHODS

The authors conducted independent and duplicate searches of electronic databases, including PubMed, Embase and the Cochrane Library, until May 2020 for studies analyzing the efficacy and safety of stem cell therapy for SCI. American Spine Injury Association (ASIA) impairment scale (AIS) grade improvement, ASIA sensorimotor score, activities of daily living score, residual urine volume, bladder function improvement, somatosensory evoked potential (SSEP) improvement and adverse reactions were the outcomes analyzed. Analysis was performed in R platform using OpenMeta[Analyst] software.

RESULTS

Nineteen studies involving 670 patients were included for analysis. On analysis, the intervention group showed statistically significant improvement in AIS grade (P < 0.001), ASIA sensory score (P < 0.017), light touch (P < 0.001), pinprick (P = 0.046), bladder function (P = 0.012), residual urine volume (P = 0.023) and SSEP (P = 0.002). However, no significant difference was noted in motor score (P = 0.193) or activities of daily living score (P = 0.161). Although the intervention group had a significant increase in complications (P < 0.001), no serious or permanent adverse events were reported. On subgroup analysis, low concentration of MSCs (<5 × 10⁷ cells) and initial AIS grade A presentation showed significantly better outcomes than their counterparts.

CONCLUSIONS

The authors' analysis establishes the efficacy and safety of MSC transplantation in terms of improvement in AIS grade, ASIA sensory score, bladder function and electrophysiological parameters like SSEP compared with controls, without major adverse events. However, further research is needed to standardize dose, timing, route and source of MSCs used for transplantation.

Reliable cell purification and determination of cell purity: crucial aspects of olfactory ensheathing cell transplantation for spinal cord repair

Transplantation of olfactory ensheathing cells, the glia of the primary olfactory nervous system, has been trialed for spinal cord injury repair with promising but variable outcomes in animals and humans. Olfactory ensheathing cells can be harvested either from the lamina propria beneath the neuroepithelium in the nasal cavity, or from the olfactory bulb in the brain. As these areas contain several other cell types, isolating and purifying olfactory ensheathing cells is a critical part of the process. It is largely unknown how contaminating cells such as fibroblasts, other glial cell types and supporting cells affect olfactory ensheathing cell function post-transplantation; these cells may also cause unwanted side-effects. It is also, however, possible that the presence of some of the contaminant cells can improve outcomes. Here, we reviewed the last decade of olfactory ensheathing cell transplantation studies in rodents, with a focus on olfactory ensheathing cell purity. We analyzed how purification methods and resultant cell purity differed between olfactory mucosa- and olfactory bulb-derived cell preparations. We analyzed how the studies reported on olfactory ensheathing cell purity and which criteria were used to define cells as olfactory ensheathing cells. Finally, we analyzed the correlation between cell purity and transplantation outcomes. We found that olfactory bulb-derived olfactory ensheathing cell preparations are typically purer than mucosa-derived preparations. We concluded that there is an association between high olfactory ensheathing cell purity and favourable outcomes, but the lack of olfactory ensheathing cell-specific markers severely hampers the field.

Transplantation of sh-miR-199a-5p-Modified Olfactory Ensheathing Cells Promotes the Functional Recovery in Rats with Contusive Spinal Cord Injury

MicroRNAs (miRNAs) function as gene expression switches, and participate in diverse pathophysiological processes of spinal cord injury (SCI). Olfactory ensheathing cells (OECs) can alleviate pathological injury and facilitate functional recovery after SCI. However, the mechanisms by which OECs restore function are not well understood. This study aims to determine whether silencing miR-199a-5p would enhance the beneficial effects of the OECs. In this study, we measured miR-199a-5p levels in rat spinal cords with and without injury, with and without OEC transplants. Then, we transfected OECs with the sh-miR-199a-5p lentiviral vector to reduce miR-199a-5p expression and determined the effects of these OECs in SCI rats by Basso-Beattie-Bresnahan (BBB) locomotor scores, diffusion tensor imaging (DTI), and histological methods. We used western blotting to measure protein levels of Slit1, Robo2, and srGAP2. Finally, we used the dual-luciferase reporter assay to assess the relationship between miR-199-5p and Slit1, Robo2, and srGAP2 expression. We found that SCI significantly increased miR-199a-5p levels (P < 0.05), and OEC transplants significantly reduced miR-199a-5p expression (P < 0.05). Knockdown of miR-199a-5p in OECs had a better therapeutic effect on SCI rats, indicated by higher BBB scores and fractional anisotropy values on DTI, as well as histological findings. Reducing miR-199a-5p levels in transplanted OECs markedly increased spinal cord protein levels of Slit1, Robo2, and srGAP2. Our results demonstrated that transplantation of sh-miR-199a-5p-modified OECs promoted functional recovery in SCI rats, suggesting that miR-199a-5p knockdown was more beneficial to the therapeutic effects of OEC transplants. These findings provided new insights into miRNAs-mediated therapeutic mechanisms of OECs, which helps us to develop therapeutic strategies based on miRNAs and optimize cell therapy for SCI.

Survival and Integration of Transplanted Olfactory Ensheathing Cells are Crucial for Spinal Cord Injury Repair: Insights from the Last 10 Years of Animal Model Studies

Olfactory ensheathing cells (OECs), the glial cells of the primary olfactory nervous system, support the natural regeneration of the olfactory nerve that occurs throughout life. OECs thus exhibit unique properties supporting neuronal survival and growth. Transplantation of OECs is emerging as a promising treatment for spinal cord injury; however, outcomes in both animals and humans are variable and the method needs improvement and standardization. A major reason for the discrepancy in functional outcomes is the variability in survival and integration of the transplanted cells, key factors for successful spinal cord regeneration. Here, we review the outcomes of OEC transplantation in rodent models over the last 10 years, with a focus on survival and integration of the transplanted cells. We identify the key factors influencing OEC survival: injury type, source of transplanted cells, co-transplantation with other cell types, number and concentration of cells, method of delivery, and time of transplantation after the injury. We found that two key issues are hampering optimization and standardization of OEC transplantation: lack of (1) reliable methods for identifying transplanted cells, and (2) three-dimensional systems for OEC delivery. To develop OEC transplantation as a successful and standardized therapy for spinal cord injury, we must address these issues and increase our understanding of the complex parameters influencing OEC survival.

The Efficacy and Safety of Mesenchymal Stem Cell Transplantation for Spinal Cord Injury Patients: A Meta-Analysis and Systematic Review

Spinal cord injury (SCI) is a devastating disease, with a high rate of disability. In this meta-analysis, we aimed to comprehensively assess the efficacy and safety of mesenchymal stem cells (MSCs) in treating clinical SCI patients. We systematically searched the PUBMED, EMBASE, Chinese Biomedical (CBM), Web of Science and Cochrane databases using the strategy of combination of free-text words and MeSH terms. The indicators of the American Spinal Injury Association (ASIA) impairment scale (AIS)-grading improvement rate and adverse effects were displayed with an overall relative risk (RR). For the continuous variables of the ASIA motor score, light-touch score, pinprick score, activities of daily living (ADL) score, and residual urine volume, we used odds ratio (OR) to analyze the data. Eleven studies comprising 499 patients meeting all inclusion and exclusion criteria were included. No serious heterogeneity or publication bias was observed across each study. The results showed that significant improvements of total AIS grade (RR: 3.70; P < 0.001), AIS grade A (RR: 3.57; P < 0.001), ASIA sensory score (OR: 8.63; P < 0.001) and reduction of residual urine volume (OR: -36.37; P = 0.03) were observed in experimental group compared with control group. However, no significant differences of motor score (OR: 1.37, P = 0.19) and ADL score (OR: 2.61, P = 0.27) were observed between experimental and control groups. In addition, there were no serious and permanent adverse effects after cell transplantation. Cell transplantation with MSCs is effective and safe in improving the sensory and bladder functions of SCI patients.

Evidence of axon connectivity across a spinal cord transection in rats treated with epidural stimulation and motor training combined with olfactory ensheathing cell transplantation

Olfactory ensheathing cells (OECs) are unique glia that support axon outgrowth in the olfactory system, and when used as cellular therapy after spinal cord injury, improve recovery and axon regeneration. Here we assessed the effects of combining OEC transplantation with another promising therapy, epidural electrical stimulation during a rehabilitative motor task. Sprague-Dawley rats received a mid-thoracic transection and transplantation of OECs or fibroblasts (FBs) followed by lumbar stimulation while climbing an inclined grid. We injected pseudorabies virus (PRV) into hindlimb muscles 7 months post-injury to assess connectivity across the transection. Analyses showed that the number of serotonergic (5-HT) axons that crossed the rostral scar border and the area of neurofilament-positive axons in the injury site were both greater in OEC- than FB-treated rats. We detected PRV-labeled cells rostral to the transection and remarkable evidence of 5-HT and PRV axons crossing the injury site in 1 OEC- and 1 FB-treated rat. The axons that crossed suggested either axon regeneration (OEC) or small areas of probable tissue sparing (FB). Most PRV-labeled thoracic neurons were detected in laminae VII or X, and ~25% expressed Chx10, a marker for V2a interneurons. These findings suggest potential regeneration or sparing of circuits that connect thoracic interneurons to lumbar somatic motor neurons. Despite evidence of axonal connectivity, no behavioral changes were detected in this small-scale study. Together these data suggest that when supplemented with epidural stimulation and climbing, OEC transplantation can increase axonal growth across the injury site and may promote recovery of propriospinal circuitry.

Mechanisms and use of neural transplants for brain repair

Under appropriate conditions, neural tissues transplanted into the adult mammalian brain can survive, integrate, and function so as to influence the behavior of the host, opening the prospect of repairing neuronal damage, and alleviating symptoms associated with neuronal injury or neurodegenerative disease. Alternative mechanisms of action have been postulated: nonspecific effects of surgery; neurotrophic and neuroprotective influences on disease progression and host plasticity; diffuse or locally regulated pharmacological delivery of deficient neurochemicals, neurotransmitters, or neurohormones; restitution of the neuronal and glial environment necessary for proper host neuronal support and processing; promoting local and long-distance host and graft axon growth; formation of reciprocal connections and reconstruction of local circuits within the host brain; and up to full integration and reconstruction of fully functional host neuronal networks. Analysis of neural transplants in a broad range of anatomical systems and disease models, on simple and complex classes of behavioral function and information processing, have indicated that all of these alternative mechanisms are likely to contribute in different circumstances. Thus, there is not a single or typical mode of graft function; rather grafts can and do function in multiple ways, specific to each particular context. Consequently, to develop an effective cell-based therapy, multiple dimensions must be considered: the target disease pathogenesis; the neurodegenerative basis of each type of physiological dysfunction or behavioral symptom; the nature of the repair required to alleviate or remediate the functional impairments of particular clinical relevance; and identification of a suitable cell source or delivery system, along with the site and method of implantation, that can achieve the sought for repair and recovery.

Effects of Neural Stem Cell and Olfactory Ensheathing Cell Co-transplants on Tissue Remodelling After Transient Focal Cerebral Ischemia in the Adult Rat

Effective transplant-mediated repair of ischemic brain lesions entails extensive tissue remodeling, especially in the ischemic core. Neural stem cells (NSCs) are promising reparative candidates for stroke induced lesions, however, their survival and integration with the host-tissue post-transplantation is poor. In this study, we address this challenge by testing whether co-grafting of NSCs with olfactory ensheathing cells (OECs), a special type of glia with proven neuroprotective, immunomodulatory, and angiogenic effects, can promote graft survival and host tissue remodelling. Transient focal cerebral ischemia was induced in adult rats by a 60-min middle cerebral artery occlusion (MCAo) followed by reperfusion. Ischemic lesions were verified by neurological testing and magnetic resonance imaging. Transplantation into the globus pallidus of NSCs alone or in combination with OECs was performed at two weeks post-MCAo, followed by histological analyses at three weeks post-transplantation. We found evidence of extensive vascular remodelling in the ischemic core as well as evidence of NSC motility away from the graft and into the infarct border in severely lesioned animals co-grafted with OECs. These findings support a possible role of OECs as part of an in situ tissue engineering paradigm for transplant mediated repair of ischemic brain lesions.

Common olfactory ensheathing glial markers in the developing human olfactory system

The in situ immunocytochemical properties of olfactory ensheathing cells (OECs) have been well studied in several small to medium sized animal models including rats, mice, guinea pigs, cats and canines. However, we know very little about the antigenic characteristics of OECs in situ within the adult and developing human olfactory bulb and nerve roots. To address this gap in knowledge we undertook an immunocytochemical analysis of the 11–19 pcw human foetal olfactory system. Human foetal OECs in situ possessed important differences compared to rodents in the expression of key surface markers. P75^NTR was not observed in OECs but was strongly expressed by human foetal Schwann cells and perineurial olfactory nerve fibroblasts surrounding OECs. We define OECs throughout the 11–19 pcw human olfactory system as S100/vimentin/SOX10+ with low expression of GFAP. Our results suggest that P75^NTR is a robust marker that could be utilised with cell sorting techniques to generate enriched OEC cultures by first removing P75^NTR expressing Schwann cells and fibroblasts, and subsequently to isolate OECs after P75^NTR upregulation in vitro. O4 and PSA-NCAM were not found to be suitable surface antigens for OEC purification owing to their ambiguous and heterogeneous expression. Our results highlight the importance of corroborating cell markers when translating cell therapies from animal models to the clinic.

Taking a bite out of spinal cord injury: do dental stem cells have the teeth for it?

Dental stem cells are an emerging star on a stage that is already quite populated. Recently, there has been a lot of hype concerning these cells in dental therapies, especially in regenerative endodontics. It is fitting that most research is concentrated on dental regeneration, although other uses for these cells need to be explored in more detail. Being a true mesenchymal stem cell, their capacities could also prove beneficial in areas outside their natural environment. One such field is the central nervous system, and in particular, repairing the injured spinal cord. One of the most formidable challenges in regenerative medicine is to restore function to the injured spinal cord, and as yet, a cure for paralysis remains to be discovered. A variety of approaches have already been tested, with graft-based strategies utilising cells harbouring appropriate properties for neural regeneration showing encouraging results. Here we present a review focusing on properties of dental stem cells that endorse their use in regenerative medicine, with particular emphasis on repairing the damaged spinal cord.