Transplantation dose alters the dynamics of human neural stem cell engraftment, proliferation and migration after spinal cord injury

Transplantation of dorsal root ganglia overexpressing the NaChBac sodium channel improves locomotion after complete SCI

Spinal cord injury (SCI) is a debilitating condition currently lacking treatment. Severe SCI causes the loss of most supraspinal inputs and neuronal activity caudal to the injury, which, coupled with the limited endogenous capacity for spontaneous regeneration, can lead to complete functional loss even in anatomically incomplete lesions. We hypothesized that transplantation of mature dorsal root ganglia (DRGs) genetically modified to express the NaChBac sodium channel could serve as a therapeutic option for functionally complete SCI. We found that NaChBac expression increased the intrinsic excitability of DRG neurons and promoted cell survival and neurotrophic factor secretion in vitro. Transplantation of NaChBac-expressing dissociated DRGs improved voluntary locomotion 7 weeks after injury compared to control groups. Animals transplanted with NaChBac-expressing DRGs also possessed higher tubulin-positive neuronal fiber and myelin preservation, although serotonergic descending fibers remained unaffected. We observed early preservation of the corticospinal tract 14 days after injury and transplantation, which was lost 7 weeks after injury. Nevertheless, transplantation of NaChBac-expressing DRGs increased the neuronal excitatory input by an increased number of VGLUT2 contacts immediately caudal to the injury. Our work suggests that the transplantation of NaChBac-expressing dissociated DRGs can rescue significant motor function, retaining an excitatory neuronal relay activity immediately caudal to injury.

Clinical Trials Targeting Secondary Damage after Traumatic Spinal Cord Injury

Spinal cord injury (SCI) often causes loss of sensory and motor function resulting in a significant reduction in quality of life for patients. Currently, no therapies are available that can repair spinal cord tissue. After the primary SCI, an acute inflammatory response induces further tissue damage in a process known as secondary injury. Targeting secondary injury to prevent additional tissue damage during the acute and subacute phases of SCI represents a promising strategy to improve patient outcomes. Here, we review clinical trials of neuroprotective therapeutics expected to mitigate secondary injury, focusing primarily on those in the last decade. The strategies discussed are broadly categorized as acute-phase procedural/surgical interventions, systemically delivered pharmacological agents, and cell-based therapies. In addition, we summarize the potential for combinatorial therapies and considerations.

Subacute traumatic spinal cord injury: a systematic review and network meta-analysis of therapeutic strategies based on bone marrow mesenchymal stromal cells in animal models

BACKGROUND AIMS

To explore the optimal transplantation strategy of bone marrow mesenchymal stem cells in subacute traumatic spinal cord injury in animal experiments in order to provide reference for future animal studies and clinical research.

METHODS

The PubMed, Embase and Web of Science databases were systematically searched (inception to January 4, 2022). Literature search, data extraction and bias assessment were performed by two independent reviewers.

RESULTS

A total of 50 articles were included for analysis. Results of both traditional meta-analysis and network meta-analysis showed that high-dose (≥1 × 10⁶) transplantation was significantly better than low-dose (<1 × 10⁶) transplantation and intralesional transplantation was significantly better than intravenous transplantation.

CONCLUSIONS

Given the limited quality of evidence from current animal studies, more high-quality head-to-head comparisons are needed in the future to delve into the optimal transplantation strategy for stem cells.

Cell–Cell Contact Mediates Gene Expression and Fate Choice of Human Neural Stem/Progenitor Cells

Transplantation of Neural Stem/Progenitor Cells (NPCs) is a promising regenerative strategy to promote neural repair following injury and degeneration because of the ability of these cells to proliferate, migrate, and integrate with the host tissue. Precise in vitro control of NPC proliferation without compromising multipotency and differentiation ability is critical in stem cell maintenance. This idea was highlighted in recent clinical trials, where discrepancies in NPC culturing protocols produced inconsistent therapeutic benefits. Of note, cell density plays an important role in regulating the survival, proliferation, differentiation, and fate choice of stem cells. To determine the extent of variability produced by inconsistent culturing densities, the present study cultured human-induced pluripotent NPCs (hiPSC-NPCs) at either a low or high plating density. hiPSC-NPCs were then isolated for transcriptomic analysis or differentiation in vitro. Following sequencing analysis, genes involved in cell–cell contact-mediated pathways, including Hippo-signaling, NOTCH, and WNT were differentially expressed. Modulation of these pathways was highly associated with the regulation of pro-neuronal transcription factors, which were also upregulated in response to higher-density hiPSC-NPC culture. Moreover, higher plating density translated into a greater neuronal and less astrocytic differentiation in vitro. This study highlights the importance of precisely controlling culture conditions during the development of NPC transplantation therapies.

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.

Biomaterial Strategies to Bolster Neural Stem Cell-Mediated Repair of the Central Nervous System

Stem cell therapies have the potential to not only repair, but to regenerate tissue of the central nervous system (CNS). Recent studies demonstrate that transplanted stem cells can differentiate into neurons and integrate with the intact circuitry after traumatic injury. Unfortunately, the positive findings described in rodent models have not been replicated in clinical trials, where the burden to maintain the cell viability necessary for tissue repair becomes more challenging. Low transplant survival remains the greatest barrier to stem cell-mediated repair of the CNS, often with fewer than 1-2% of the transplanted cells remaining after 1 week. Strategic transplantation parameters, such as injection location, cell concentration, and transplant timing achieve only modest improvements in stem cell transplant survival and appear inconsistent across studies. Biomaterials provide researchers with a means to significantly improve stem cell transplant survival through two mechanisms: (1) a vehicle to deliver and protect the stem cells and (2) a substrate to control the cytotoxic injury environment. These biomaterial strategies can alleviate cell death associated with delivery to the injury and can be used to limit cell death after transplantation by limiting cell exposure to cytotoxic signals. Moreover, it is likely that control of the injury environment with biomaterials will lead to a more reliable support for transplanted cell populations. This review will highlight the challenges associated with cell delivery in the CNS and the advances in biomaterial development and deployment for stem cell therapies necessary to bolster stem cell-mediated repair.

Optimal Preclinical Conditions for Using Adult Human Multipotent Neural Cells in the Treatment of Spinal Cord Injury

Stem cell-based therapeutics are amongst the most promising next-generation therapeutic approaches for the treatment of spinal cord injury (SCI), as they may promote the repair or regeneration of damaged spinal cord tissues. However, preclinical optimization should be performed before clinical application to guarantee safety and therapeutic effect. Here, we investigated the optimal injection route and dose for adult human multipotent neural cells (ahMNCs) from patients with hemorrhagic stroke using an SCI animal model. ahMNCs demonstrate several characteristics associated with neural stem cells (NSCs), including the expression of NSC-specific markers, self-renewal, and multi neural cell lineage differentiation potential. When ahMNCs were transplanted into the lateral ventricle of the SCI animal model, they specifically migrated within 24 h of injection to the damaged spinal cord, where they survived for at least 5 weeks after injection. Although ahMNC transplantation promoted significant locomotor recovery, the injection dose was shown to influence treatment outcomes, with a 1 × 10⁶ (medium) dose of ahMNCs producing significantly better functional recovery than a 3 × 10⁵ (low) dose. There was no significant gain in effect with the 3 × 10⁶ ahMNCs dose. Histological analysis suggested that ahMNCs exert their effects by modulating glial scar formation, neuroprotection, and/or angiogenesis. These data indicate that ahMNCs from patients with hemorrhagic stroke could be used to develop stem cell therapies for SCI and that the indirect injection route could be clinically relevant. Moreover, the optimal transplantation dose of ahMNCs defined in this preclinical study might be helpful in calculating its optimal injection dose for patients with SCI in the future.

Grafted human induced pluripotent stem cells improve the outcome of spinal cord injury: modulation of the lesion microenvironment

Spinal cord injury results in irreversible tissue damage followed by a very limited recovery of function. In this study we investigated whether transplantation of undifferentiated human induced pluripotent stem cells (hiPSCs) into the injured rat spinal cord is able to induce morphological and functional improvement. hiPSCs were grafted intraspinally or intravenously one week after a thoracic (T11) spinal cord contusion injury performed in Fischer 344 rats. Grafted animals showed significantly better functional recovery than the control rats which received only contusion injury. Morphologically, the contusion cavity was significantly smaller, and the amount of spared tissue was significantly greater in grafted animals than in controls. Retrograde tracing studies showed a statistically significant increase in the number of FB-labeled neurons in different segments of the spinal cord, the brainstem and the sensorimotor cortex. The extent of functional improvement was inversely related to the amount of chondroitin-sulphate around the cavity and the astrocytic and microglial reactions in the injured segment. The grafts produced GDNF, IL-10 and MIP1-alpha for at least one week. These data suggest that grafted undifferentiated hiPSCs are able to induce morphological and functional recovery after spinal cord contusion injury.

Alternatively Polarized Macrophages Regulate the Growth and Differentiation of Ependymal Stem Cells through the SIRT2 Pathway

Ependymal stem cells (EpSCs) are dormant stem cells in the adult spinal cord that proliferate rapidly and migrate to the site of injury after spinal cord injury (SCI). Although they can differentiate into neurons under appropriate conditions in vitro, EpSCs mainly differentiate into astrocytes in vivo. Our previous study confirmed that alternatively polarized macrophages (M2) facilitate the differentiation of EpSCs towards neurons, but the detailed mechanism remains elusive. In the present study, we found that M2 conditioned medium could upregulate the expression of Sirtuin 2 (SIRT2) in EpSCs in vitro through the BDNF/TrkB-MEK/ERK signaling pathway. As an important deacetylase, SIRT2 deacetylated stable Ac-α-tubulin (Acetyl alpha Tubulin) in microtubules and thus promoted EpSC differentiation into neurons. The present study provides a theoretical basis and a new way to improve neural recovery, such as regulating the growth and differentiation of EpSCs by increasing the proportion of M2 cells in the local microenvironment or upregulating the expression of SIRT2 in EpSCs.

Designer, injectable gels to prevent transplanted Schwann cell loss during spinal cord injury therapy

Transplantation of patient-derived Schwann cells is a promising regenerative medicine therapy for spinal cord injuries; however, therapeutic efficacy is compromised by inefficient cell delivery. We present a materials-based strategy that addresses three common causes of transplanted cell death: (i) membrane damage during injection, (ii) cell leakage from the injection site, and (iii) apoptosis due to loss of endogenous matrix. Using protein engineering and peptide-based assembly, we designed injectable hydrogels with modular cell-adhesive and mechanical properties. In a cervical contusion model, our hydrogel matrix resulted in a greater than 700% improvement in successful Schwann cell transplantation. The combination therapy of cells and gel significantly improved the spatial distribution of transplanted cells within the endogenous tissue. A reduction in cystic cavitation and neuronal loss were also observed with substantial increases in forelimb strength and coordination. Using an injectable hydrogel matrix, therefore, can markedly improve the outcomes of cellular transplantation therapies.

Effects of neural stem cell transplantation on the motor function of rats with contusion spinal cord injuries: a meta-analysis

Objective

To judge the efficacies of neural stem cell (NSC) transplantation on functional recovery following contusion spinal cord injuries (SCIs).

Data sources

Studies in which NSCs were transplanted into a clinically relevant, standardized rat model of contusion SCI were identified by searching the PubMed, Embase and Cochrane databases, and the extracted data were analyzed by Stata 14.0.

Data selection

Inclusion criteria were that NSCs were used in in vivo animal studies to treat contusion SCIs and that behavioral assessment of locomotor functional recovery was performed using the Basso, Beattie, and Bresnahan lo-comotor rating scale. Exclusion criteria included a follow-up of less than 4 weeks and the lack of control groups.

Outcome measures

The restoration of motor function was assessed by the Basso, Beattie, and Bresnahan locomotor rating scale.

Results

We identified 1756 non-duplicated papers by searching the aforementioned electronic databases, and 30 full-text articles met the inclusion criteria. A total of 37 studies reported in the 30 articles were included in the meta-analysis. The meta-analysis results showed that transplanted NSCs could improve the motor function recovery of rats following contusion SCIs, to a moderate extent (pooled standardized mean difference (SMD) = 0.73; 95% confidence interval (CI): 0.47-1.00; P < 0.001). NSCs obtained from different donor species (rat: SMD = 0.74; 95% CI: 0.36-1.13; human: SMD = 0.78; 95% CI: 0.31-1.25), at different donor ages (fetal: SMD = 0.67; 95% CI: 0.43-0.92; adult: SMD = 0.86; 95% CI: 0.50-1.22) and from different origins (brain-derived: SMD = 0.59; 95% CI: 0.27-0.91; spinal cord-derived: SMD = 0.51; 95% CI: 0.22-0.79) had similar efficacies on improved functional recovery; however, adult induced pluripotent stem cell-derived NSCs showed no significant efficacies. Furthermore, the use of higher doses of transplanted NSCs or the administration of immunosuppressive agents did not promote better locomotor function recovery (SMD = 0.45; 95% CI: 0.21-0.70). However, shorter periods between the contusion induction and the NSC transplantation showed slightly higher efficacies (acute: SMD = 1.22; 95% CI: 0.81-1.63; subacute: SMD = 0.75; 95% CI: 0.42-1.09). For chronic injuries, NSC implantation did not significantly improve functional recovery (SMD = 0.25; 95% CI: -0.16 to 0.65).

Conclusion

NSC transplantation alone appears to be a positive yet limited method for the treatment of contusion SCIs.

High-Dose Neural Stem/Progenitor Cell Transplantation Increases Engraftment and Neuronal Distribution and Promotes Functional Recovery in Rats after Acutely Severe Spinal Cord Injury

Severe spinal cord injury (SCI) leads to permanent, complete paraplegia and places considerable mental and economic burdens on patients, compared with mild to moderate SCI. However, the dose-related effects of the neural stem/precursor cell (NSPC) transplantation on the injury microenvironment, NSPC survival, axonal growth, neuronal distribution, the composition of neurons, oligodendrocytes, and astrocytes in the lesion area and functional recovery have not yet been quantitatively evaluated in the context of severe SCI. In our study, we acutely transplanted 2.5 × 10⁴ or 1.5 × 10⁵ NSPCs/μl into the site of transection SCI. We found that high-dose NSPC transplantation exerted immunomodulatory and neuroprotective effects in the acute phase of severe SCI. In addition, one week later, a remarkable positive relationship was observed between the transplantation dose and the number of surviving NSPCs in severe SCI. At 8 weeks postgrafting, subjects that received the higher cell dose exhibited abundant nerve regeneration, extensive neuronal distribution, increased proportions of neurons and oligodendrocytes, and nascent functional neural network formation in the lesion area. Notably, a significant functional recovery was also observed. Our data suggest that it is important to consider potential dose-related effects on donor cell survival, neuronal distribution, and locomotor recovery in the development of preclinical NSPC transplantation therapy for severe SCI.

Assessment of stem cell viability in the initial healing period in rabbits with a cranial bone defect according to the type and form of scaffold

Purpose

Increased bone regeneration has been achieved through the use of stem cells in combination with graft material. However, the survival of transplanted stem cells remains a major concern. The purpose of this study was to evaluate the viability of transplanted mesenchymal stem cells (MSCs) at an early time point (24 hours) based on the type and form of the scaffold used, including type I collagen membrane and synthetic bone.

Methods

The stem cells were obtained from the periosteum of the otherwise healthy dental patients. Four symmetrical circular defects measuring 6 mm in diameter were made in New Zealand white rabbits using a trephine drill. The defects were grafted with 1) synthetic bone (β-tricalcium phosphate/hydroxyapatite [β-TCP/HA]) and 1×10⁵ MSCs, 2) collagen membrane and 1×10⁵ MSCs, 3) β-TCP/HA+collagen membrane and 1×10⁵ MSCs, or 4) β-TCP/HA, a chipped collagen membrane and 1×10⁵ MSCs. Cellular viability and the cell migration rate were analyzed.

Results

Cells were easily separated from the collagen membrane, but not from synthetic bone. The number of stem cells attached to synthetic bone in groups 1, 3, and 4 seemed to be similar. Cellular viability in group 2 was significantly higher than in the other groups (P<0.05). The cell migration rate was highest in group 2, but this difference was not statistically significant (P>0.05).

Conclusions

This study showed that stem cells can be applied when a membrane is used as a scaffold under no or minimal pressure. When space maintenance is needed, stem cells can be loaded onto synthetic bone with a chipped membrane to enhance the survival rate.

Filling the Gap: Neural Stem Cells as A Promising Therapy for Spinal Cord Injury

Spinal cord injury (SCI) can lead to severe motor, sensory and social impairments having a huge impact on patients’ lives. The complex and time-dependent SCI pathophysiology has been hampering the development of novel and effective therapies. Current treatment options include surgical interventions, to stabilize and decompress the spinal cord, and rehabilitative care, without providing a cure for these patients. Novel therapies have been developed targeting different stages during trauma. Among them, cell-based therapies hold great potential for tissue regeneration after injury. Neural stem cells (NSCs), which are multipotent cells with inherent differentiation capabilities committed to the neuronal lineage, are especially relevant to promote and reestablish the damaged neuronal spinal tracts. Several studies demonstrate the regenerative effects of NSCs in SCI after transplantation by providing neurotrophic support and restoring synaptic connectivity. Therefore, human clinical trials have already been launched to assess safety in SCI patients. Here, we review NSC-based experimental studies in a SCI context and how are they currently being translated into human clinical trials.

Do Neural Stem Cells Have a Choice? Heterogenic Outcome of Cell Fate Acquisition in Different Injury Models

The adult mammalian central nervous system (CNS) is generally considered as repair restricted organ with limited capacities to regenerate lost cells and to successfully integrate them into damaged nerve tracts. Despite the presence of endogenous immature cell types that can be activated upon injury or in disease cell replacement generally remains insufficient, undirected, or lost cell types are not properly generated. This limitation also accounts for the myelin repair capacity that still constitutes the default regenerative activity at least in inflammatory demyelinating conditions. Ever since the discovery of endogenous neural stem cells (NSCs) residing within specific niches of the adult brain, as well as the description of procedures to either isolate and propagate or artificially induce NSCs from various origins ex vivo, the field has been rejuvenated. Various sources of NSCs have been investigated and applied in current neuropathological paradigms aiming at the replacement of lost cells and the restoration of functionality based on successful integration. Whereas directing and supporting stem cells residing in brain niches constitutes one possible approach many investigations addressed their potential upon transplantation. Given the heterogeneity of these studies related to the nature of grafted cells, the local CNS environment, and applied implantation procedures we here set out to review and compare their applied protocols in order to evaluate rate-limiting parameters. Based on our compilation, we conclude that in healthy CNS tissue region specific cues dominate cell fate decisions. However, although increasing evidence points to the capacity of transplanted NSCs to reflect the regenerative need of an injury environment, a still heterogenic picture emerges when analyzing transplantation outcomes in injury or disease models. These are likely due to methodological differences despite preserved injury environments. Based on this meta-analysis, we suggest future NSC transplantation experiments to be conducted in a more comparable way to previous studies and that subsequent analyses must emphasize regional heterogeneity such as accounting for differences in gray versus white matter.

New perspectives on the mechanisms establishing the dorsal-ventral axis of the spinal cord

Distinct classes of neurons arise at different positions along the dorsal-ventral axis of the spinal cord leading to spinal neurons being segregated along this axis according to their physiological properties and functions. Thus, the neurons associated with motor control are generally located in, or adjacent to, the ventral horn whereas the interneurons (INs) that mediate sensory activities are present within the dorsal horn. Here, we review classic and recent studies examining the developmental mechanisms that establish the dorsal-ventral axis in the embryonic spinal cord. Intriguingly, while the cellular organization of the dorsal and ventral halves of the spinal cord looks superficially similar during early development, the underlying molecular mechanisms that establish dorsal vs ventral patterning are markedly distinct. For example, the ventral spinal cord is patterned by the actions of a single growth factor, sonic hedgehog (Shh) acting as a morphogen, i.e., concentration-dependent signal. Recent studies have shed light on the mechanisms by which the spatial and temporal gradient of Shh is transduced by cells to elicit the generation of different classes of ventral INs, and motor neurons (MNs). In contrast, the dorsal spinal cord is patterned by the action of multiple factors, most notably by members of the bone morphogenetic protein (BMP) and Wnt families. While less is known about dorsal patterning, recent studies have suggested that the BMPs do not act as morphogens to specify dorsal IN identities as previously proposed, rather each BMP has signal-specific activities. Finally, we consider the promise that elucidation of these mechanisms holds for neural repair.

Spinal Progenitor-Laden Bridges Support Earlier Axon Regeneration Following Spinal Cord Injury

IMPACT STATEMENT

Spinal cord injury (SCI) results in loss of tissue innervation below the injury. Spinal progenitors have a greater ability to repair the damage and can be injected into the injury, but their regenerative potential is hampered by their poor survival after transplantation. Biomaterials can create a cell delivery platform and generate a more hospitable microenvironment for the progenitors within the injury. In this work, polymeric bridges are used to deliver embryonic spinal progenitors to the injury, resulting in increased progenitor survival and subsequent regeneration and functional recovery, thus demonstrating the importance of combined therapeutic approaches for SCI.

Controlled release of dextrin-conjugated growth factors to support growth and differentiation of neural stem cells

An essential aspect of stem cell in vitro culture and in vivo therapy is achieving sustained levels of growth factors to support stem cell survival and expansion, while maintaining their multipotency and differentiation potential. This study investigated the ability of dextrin (~74,000 g/mol; 27.8 mol% succinoylation) conjugated to epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF; or FGF-2) (3.9 and 6.7% w/w protein loading, respectively) to support the expansion and differentiation of stem cells in vitro via sustained, controllable growth factor release. Supplementation of mouse neural stem cells (mNSCs) with dextrin-growth factor conjugates led to greater and prolonged proliferation compared to unbound EGF/bFGF controls, with no detectable apoptosis after 7 days of treatment. Immunocytochemical detection of neural precursor (nestin) and differentiation (Olig2, MAP2, GFAP) markers verified that controlled release of dextrin-conjugated growth factors preserves stem cell properties of mNSCs for up to 7 days. These results show the potential of dextrin-growth factor conjugates for localized delivery of bioactive therapeutic agents to support stem cell expansion and differentiation, and as an adjunct to direct neuronal repair.

Repeated injections of human umbilical cord blood-derived mesenchymal stem cells significantly promotes functional recovery in rabbits with spinal cord injury of two noncontinuous segments

Background

Spinal cord injuries (SCIs) are sustained by an increasing number of patients each year worldwide. The treatment of SCIs has long been a hard nut to crack for doctors around the world. Mesenchymal stem cells (MSCs) have shown benefits for the repair of SCI and recovery of function. Our present study aims to investigate the effects of intravenously infused human umbilical cord blood-derived MSCs (hUCB-MSCs) on functional recovery after subacute spinal cord compression injury of two noncontinuous segments. In addition, we compared the effects of single infusion and repeated intravenous (i.v.) injections on the recovery of spinal cord function.

Methods

A total of 43 adult rabbits were randomly divided into four groups: control, single injection (SI), repeated injection at a 3-day (3RI) or repeated injection at a 7-day interval (7RI) groups. Non-immunosuppressed rabbits in the transplantation groups were infused with either a single complete dose or three divided doses of 2 × 10⁶ hUCB-MSCs (3-day or 7-day intervals) on the first day post decompression. Behavioural scores and somatosensory evoked potentials (SEPs) were used to evaluate hindlimb functional recovery. The survival and differentiation of the transplanted human cells and the activation of the host glial and inflammatory reaction in the injured spinal cord were studied by immunohistochemical staining.

Results

Our results showed that hUCB-MSCs survived, proliferated, and primarily differentiated into oligodendrocytes in the injured area. Treatment with hUCB-MSCs reduced the extent of astrocytic activation, increased axonal preservation, potentially promoted axonal regeneration, decreased the number of Iba-1+ and TUNEL+ cells, increased the amplitude and decreased the onset latency of SEPs and significantly promoted functional improvement. However, these effects were more pronounced in the 3RI group compared with the SI and 7RI groups.

Conclusions

Our results suggest that treatment with i.v. injected hUCB-MSCs after subacute spinal cord compression injury of two noncontinuous segments can promote functional recovery through the differentiation of hUCB-MSCs into specific cell types and the enhancement of anti-inflammatory, anti-astrogliosis, anti-apoptotic and axonal preservation effects. Furthermore, the recovery was more pronounced in the rabbits repeatedly injected with cells at 3-day intervals. The results of this study may provide a novel and useful treatment strategy for the transplantation treatment of SCI.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0879-0) contains supplementary material, which is available to authorized users.

Combined delivery of chondroitinase ABC and human induced pluripotent stem cell-derived neuroepithelial cells promote tissue repair in an animal model of spinal cord injury

The lack of tissue regeneration after traumatic spinal cord injury in animal models is largely attributed to the local inhibitory microenvironment. To overcome this inhibitory environment while promoting tissue regeneration, we investigated the combined delivery of chondroitinase ABC (chABC) with human induced pluripotent stem cell-derived neuroepithelial stem cells (NESCs). ChABC was delivered to the injured spinal cord at the site of injury by affinity release from a crosslinked methylcellulose (MC) hydrogel by injection into the intrathecal space. NESCs were distributed in a hydrogel comprised of hyaluronan and MC and injected into the spinal cord tissue both rostral and caudal to the site of injury. Cell transplantation led to reduced cavity formation, but did not improve motor function. While few surviving cells were found 2 weeks post injury, the majority of live cells were neurons, with only few astrocytes, oligodendrocytes, and progenitor cells. At 9 weeks post injury, there were more progenitor cells and a more even distribution of cell types compared to those at 2 weeks post injury, suggesting preferential survival and differentiation. Interestingly, animals that received cells and chABC had more neurons than animals that received cells alone, suggesting that chABC influenced the injury environment such that neuronal differentiation or survival was favoured.

Fingolimod Enhances Oligodendrocyte Differentiation of Transplanted Human Induced Pluripotent Stem Cell-Derived Neural Progenitors

Multiple sclerosis (MS) is an autoimmune disease which affects myelin in the central nervous system (CNS) and leads to serious disability. Currently available treatments for MS mainly suppress the immune system. Regenerative medicine-based approaches attempt to increase myelin repair by targeting endogenous progenitors or transplanting stem cells or their derivatives. Fingolimod exerts anti-inflammatory effects and directly affects neural cells. In this study we assessed the effect of fingolimod on transplanted human induced pluripotent stem cell derived neural progenitors (hiPSC-NPs). hiPSC-NPs were labeled by green fluorescence protein (GFP) and transplanted into the corpus callosum of mice which were chronically demyelinated after cuprizone (CPZ) feedings for 10 weeks. The animals received fingolimod from 1 day prior to NPs transplantation via gavage as well as daily intraperitoneal cyclosporine A from 2 days before cell transplantation until the time of sampling. At either 7 or 21 days after NPs transplantation, the animals were sacrificed and their brains were histologically evaluated for the number of transplanted cells and their fate. In the animals treated with fingolimod, we observed higher numbers of NPs within the injection site compared to the animals who did not receive fingolimod showing that hiPSC- NPs were more efficiently differentiated to the oligodendrocyte lineage. These data have suggested that repetitive treatment with fingolimod, beside its anti-inflammatory effect, may enhance the survival and differentiation of transplanted NPs to oligodendrocyte lineage cells to participate in myelin repair.

Preclinical Efficacy Failure of Human CNS-Derived Stem Cells for Use in the Pathway Study of Cervical Spinal Cord Injury

We previously showed the efficacy of multiple research cell lines (RCLs) of human CNS neural stem cells (HuCNS-SCs) in mouse and rat models of thoracic spinal cord injury (SCI), supporting a thoracic SCI clinical trial. Experts recommend in vivo preclinical testing of the intended clinical cell lot/line (CCL) in models with validity for the planned clinical target. We therefore tested the efficacy of two HuCNS-SC lines in cervical SCI: one RCL, and one CCL intended for use in the Pathway Study of cervical SCI in man. We assessed locomotor recovery and sensory function, as well as engraftment, migration, and fate. No evidence of efficacy of the CCL was observed; some data suggested a negative impact of the CCL on outcomes. These data raise questions about the development and validation of potency/comparability assays for clinical testing of cell products, and lack of US Food and Drug Administration requirements for in vivo testing of intended clinical cell lines.

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Human CNS stem cells (HuCNS-SCs) have been used in multiple clinical trials

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Research cell lines of HuCNS-SCs are efficacious in spinal cord injury (SCI) models

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The clinical cell line (CCL) of HuCNS-SC was not efficacious in a cervical SCI model

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Despite lack of in vivo efficacy, the CCL was used in the Pathways clinical study

Overexpression of miR‑21 promotes neural stem cell proliferation and neural differentiation via the Wnt/β‑catenin signaling pathway in vitro

The primary aim of the present study was to examine the effects of microRNA‑21 (miR‑21) on the proliferation and differentiation of rat primary neural stem cells (NSCs) in vitro. miR‑21 was overexpressed in NSCs by transfection with a miR‑21 mimic. The effects of miR‑21 overexpression on NSC proliferation were revealed by Cell Counting kit 8 and 5‑ethynyl‑2'‑deoxyuridine incorporation assay, and miR‑21 overexpression was revealed to increase NSC proliferation. miR‑21 overexpression was confirmed using reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). mRNA and protein expression levels of key molecules (β‑catenin, cyclin D1, p21 and miR‑21) in the Wnt/β‑catenin signaling pathway were studied by RT‑qPCR and western blot analysis. RT‑qPCR and western blot analyses revealed that miR‑21 overexpression increased β‑catenin and cyclin D1 expression, and decreased p21 expression. These results suggested that miR‑21‑induced increase in proliferation was mediated by activation of the Wnt/β‑catenin signaling pathway, since overexpression of miR‑21 increased β‑catenin and cyclin D1 expression and reduced p21 expression. Furthermore, inhibition of the Wnt/β‑catenin pathway with FH535 attenuated the influence of miR‑21 overexpression on NSC proliferation, indicating that the factors activated by miR‑21 overexpression were inhibited by FH535 treatment. Furthermore, overexpression of miR‑21 enhanced the differentiation of NSCs into neurons and inhibited their differentiation into astrocytes. The present study indicated that in primary rat NSCs, overexpression of miR‑21 may promote proliferation and differentiation into neurons via the Wnt/β‑catenin signaling pathway in vitro.

Increasing Human Neural Stem Cell Transplantation Dose Alters Oligodendroglial and Neuronal Differentiation after Spinal Cord Injury

Multipotent human central nervous system-derived neural stem cells transplanted at doses ranging from 10,000 (low) to 500,000 (very high) cells differentiated predominantly into the oligodendroglial lineage. However, while the number of engrafted cells increased linearly in relationship to increasing dose, the proportion of oligodendrocytic cells declined. Increasing dose resulted in a plateau of engraftment, enhanced neuronal differentiation, and increased distal migration caudal to the transplantation sites. Dose had no effect on terminal sensory recovery or open-field locomotor scores. However, total human cell number and decreased oligodendroglial proportion were correlated with hindlimb girdle coupling errors. Conversely, greater oligodendroglial proportion was correlated with increased Ab step pattern, decreased swing speed, and increased paw intensity, consistent with improved recovery. These data suggest that transplant dose, and/or target niche parameters can regulate donor cell engraftment, differentiation/maturation, and lineage-specific migration profiles.

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SCI niche may have a limited capacity for donor cell engraftment

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Dose alters the donor cell lineage-specific fate and migration profile

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Increasing hindlimb girdle couplings errors may be due to increased total cell numbers

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Greater proportion of oligodendroglial cells improves locomotor recovery

Formyl peptide receptors promotes neural differentiation in mouse neural stem cells by ROS generation and regulation of PI3K-AKT signaling

This study aimed to determine whether formyl peptide receptors (FPRs) regulated the differentiation of neural stem cells (NSCs). FPRs promote the migration of NSCs both in vitro and in vivo. However, the role of FPRs during differentiation of NSCs is unknown. Analysis by Western blot showed significantly increased expression of FPR1 and FPR2 during differentiation of NSCs. The activation of FPRs promotes NSCs to differentiate into neurons with more primary neurites and branch points and longer neurites per cell. Meanwhile, this activation also inhibits the differentiation of NSC into astrocytes. This bidirectional effect can be inhibited by the FPRs-specific inhibitor. Moreover, it was found that the activation of FPRs increased the generation of reactive oxygen species (ROS) and phosphorylation of AKT in the NSCs, while N-acetylcysteine and LY294002 inhibited the FPRs-stimulated increase in ROS generation and AKT phosphorylation, and blocked the FPRs-stimulated neural differentiation into neurons. Therefore, FPRs-stimulated neural differentiation was mediated via ROS and PI3K-AKT signaling pathways. Collectively, the present findings provided a novel insight into the functional role of FPRs in neurogenesis, with important implications for its potential use as a candidate for treating brain or spinal cord injury.

Pathological classification of human iPSC-derived neural stem/progenitor cells towards safety assessment of transplantation therapy for CNS diseases

The risk of tumorigenicity is a hurdle for regenerative medicine using induced pluripotent stem cells (iPSCs). Although teratoma formation is readily distinguishable, the malignant transformation of iPSC derivatives has not been clearly defined due to insufficient analysis of histology and phenotype. In the present study, we evaluated the histology of neural stem/progenitor cells (NSPCs) generated from integration-free human peripheral blood mononuclear cell (PBMC)-derived iPSCs (iPSC-NSPCs) following transplantation into central nervous system (CNS) of immunodeficient mice. We found that transplanted iPSC-NSPCs produced differentiation patterns resembling those in embryonic CNS development, and that the microenvironment of the final site of migration affected their maturational stage. Genomic instability of iPSCs correlated with increased proliferation of transplants, although no carcinogenesis was evident. The histological classifications presented here may provide cues for addressing potential safety issues confronting regenerative medicine involving iPSCs.

Achieving Informed Consent for Cellular Therapies: A Preclinical Translational Research Perspective on Regulations versus a Dose of Reality

A central principle of bioethics is "subject autonomy," the acknowledgement of the primacy of the informed consent of the subject of research. Autonomy requires informed consent - the assurance that the research participant is informed about the possible risks and benefits of the research. In fact, informed consent is difficult when a single drug is being tested, although subjects have a baseline understanding of the testing of a pharmacological agent and the understanding that they can stop taking the drug if there were an adverse event. However, informed consent is even less easily achieved in the modern arena of complex new molecular and cellular therapies. In this article, we argue that as science confronts new issues such as transplantation of stem cell products, which may live within the participant for the rest of their lives, researchers must carefully consider and constantly re-examine how they properly inform subjects considering participation trials of these novel therapeutic strategies.For example, the manufacture of a vial of a cell product that consists of a collection of growing cells is very different than the production of a vial of identical pills, which can be presumed to be identical. The scientific concepts on which these cellular approaches are based may seem alien and incomprehensible to a research subject, who thinks of a clinical trial as simply the selection and testing of the most efficacious pharmaceutical agent already proven to work in preclinical animal studies. The research subject would be wrong.

Targeting human oligodendrocyte progenitors for myelin repair

Oligodendrocyte development has been studied for several decades, and has served as a model system for both neurodevelopmental and stem/progenitor cell biology. Until recently, the vast majority of studies have been conducted in lower species, especially those focused on rodent development and remyelination. In humans, the process of myelination requires the generation of vastly more myelinating glia, occurring over a period of years rather than weeks. Furthermore, as evidenced by the presence of chronic demyelination in a variety of human neurologic diseases, it appears likely that the mechanisms that regulate development and become dysfunctional in disease may be, in key ways, divergent across species. Improvements in isolation techniques, applied to primary human neural and oligodendrocyte progenitors from both fetal and adult brain, as well as advancements in the derivation of defined progenitors from human pluripotent stem cells, have begun to reveal the extent of both species-conserved signaling pathways and potential key differences at cellular and molecular levels. In this article, we will review the commonalities and differences in myelin development between rodents and man, describing the approaches used to study human oligodendrocyte differentiation and myelination, as well as heterogeneity within targetable progenitor pools, and discuss the advances made in determining which conserved pathways may be both modeled in rodents and translate into viable therapeutic strategies to promote myelin repair.

Olfactory Ensheathing Cell Transplantation in Experimental Spinal Cord Injury: Effect size and Reporting Bias of 62 Experimental Treatments: A Systematic Review and Meta-Analysis

Olfactory ensheathing cell (OEC) transplantation is a candidate cellular treatment approach for human spinal cord injury (SCI) due to their unique regenerative potential and autologous origin. The objective of this study was, through a meta-epidemiologic approach, (i) to assess the efficacy of OEC transplantation on locomotor recovery after traumatic experimental SCI and (ii) to estimate the likelihood of reporting bias and/or missing data. A study protocol was finalized before data collection. Embedded into a systematic review and meta-analysis, we conducted a literature research of databases including PubMed, EMBASE, and ISI Web of Science from 1949/01 to 2014/10 with no language restrictions, screened by two independent investigators. Studies were included if they assessed neurobehavioral improvement after traumatic experimental SCI, administrated no combined interventions, and reported the number of animals in the treatment and control group. Individual effect sizes were pooled using a random effects model. Details regarding the study design were extracted and impact of these on locomotor outcome was assessed by meta-regression. Missing data (reporting bias) was determined by Egger regression and Funnel-plotting. The primary study outcome assessed was improvement in locomotor function at the final time point of measurement. We included 49 studies (62 experiments, 1,164 animals) in the final analysis. The overall improvement in locomotor function after OEC transplantation, measured using the Basso, Beattie, and Bresnahan (BBB) score, was 20.3% (95% CI 17.8–29.5). One missing study was imputed by trim and fill analysis, suggesting only slight publication bias and reducing the overall effect to a 19.2% improvement of locomotor activity. Dose-response ratio supports neurobiological plausibility. Studies were assessed using a 9-point item quality score, resulting in a median score of 5 (interquartile range [IQR] 3–5). In conclusion, OEC transplantation exerts considerable beneficial effects on neurobehavioral recovery after traumatic experimental SCI. Publication bias was minimal and affirms the translational potential of efficacy, but safety cannot be adequately assessed. The data justify OECs as a cellular substrate to develop and optimize minimally invasive and safe cellular transplantation paradigms for the lesioned spinal cord embedded into state-of-the-art Phase I/II clinical trial design studies for human SCI.

This meta-analysis study examines the effects of transplanting olfactory ensheathing cells in rodents with experimental spinal cord injury, finding evidence for significant recovery and identifying aspects of the procedure that influence the effect size.

Spinal cord injury converts into a debilitating disease affecting millions of chronic patients worldwide. Despite increased molecular knowledge over the last decades, no causal pharmacological or cellular therapy has proven effective so far. Due to their unique regenerative capabilities and their autologous origin, olfactory ensheathing cells (OECs) constitute an appealing candidate for topical cell transplantation. In contrast to few and heterogeneous experimental reports of OEC transplantation after spinal cord injury in humans, a considerable number of preclinical studies have been conducted applying OEC transplantation in rodent models. We set out to conduct a systematic review and meta-analysis to assess preclinical efficacy of OEC transplantation. We detected a significant overall increase of functional neurological recovery in animals after OEC transplantation compared to the control group. This effect was not distorted by publication bias. We identified several specific hallmarks of the cell transplantation procedure that determine the effect size of the transplantation. Our findings delineate conditions for optimized OEC transplantation into lesioned spinal cords and its relevance for effective translation to human trials.