Technical aspects of spinal cord injections for cell transplantation. Clinical and translational considerations

Challenges in Translating Regenerative Therapies for Spinal Cord Injury

Regenerating the injured spinal cord is a substantial challenge with many obstacles that need to be overcome to achieve robust functional benefits. This abundance of hurdles can partly explain the limited success when applying regenerative intervention treatments in animal models and/or people. In this article, we elaborate on a few of these obstacles, starting with the applicability of animal models and how they compare to the clinical setting. We then discuss the requirement for combinatorial interventions and the associated problems in experimental design, including the addition of rehabilitative training. The article expands on differences in lesion sizes and locations between humans and common animal models, and how this difference can determine the success or failure of an intervention. An additional and frequently overlooked problem in the translation of interventions that applies beyond the field of neuroregeneration is the reporting bias and the lack of transparency in reporting findings. New data mandates are tackling this problem and will eventually result in a more balanced view of the field. Finally, we will discuss strategies to negotiate the challenging course of successful translation to facilitate successful translation of regeneration promoting interventions.

Interstitial-fluid shear stresses induced by vertically oscillating head motion lower blood pressure in hypertensive rats and humans

The mechanisms by which physical exercise benefits brain functions are not fully understood. Here, we show that vertically oscillating head motions mimicking mechanical accelerations experienced during fast walking, light jogging or treadmill running at a moderate velocity reduce the blood pressure of rats and human adults with hypertension. In hypertensive rats, shear stresses of less than 1 Pa resulting from interstitial-fluid flow induced by such passive head motions reduced the expression of the angiotensin II type-1 receptor in astrocytes in the rostral ventrolateral medulla, and the resulting antihypertensive effects were abrogated by hydrogel introduction that inhibited interstitial-fluid movement in the medulla. Our findings suggest that oscillatory mechanical interventions could be used to elicit antihypertensive effects.

A Multi-Stage Bioprocess for the Expansion of Rodent Skin-Derived Schwann Cells in Computer-Controlled Bioreactors

Regenerative therapies for the treatment of peripheral nerve and spinal cord injuries can require hundreds of millions of autologous cells. Current treatments involve the harvest of Schwann cells (SCs) from nerves; however, this is an invasive procedure. Therefore, a promising alternative is using skin-derived Schwann cells (Sk-SCs), in which between 3–5 million cells can be harvested from a standard skin biopsy. However, traditional static planar culture is still inefficient at expanding cells to clinically relevant numbers. As a result, bioreactors can be used to develop reproducible bioprocesses for the large-scale expansion of therapeutic cells. Here, we present a proof-of-concept SC manufacturing bioprocess using rat Sk-SCs. With this integrated process, we were able to simulate a feasible bioprocess, taking into consideration the harvest and shipment of cells to a production facility, the generation of the final cell product, and the cryopreservation and shipment of cells back to the clinic and patient. This process started with 3 million cells and inoculated and expanded them to over 200 million cells in 6 days. Following the harvest and post-harvest cryopreservation and thaw, we were able to maintain 150 million viable cells that exhibited a characteristic Schwann cell phenotype throughout each step of the process. This process led to a 50-fold expansion, producing a clinically relevant number of cells in a 500 mL bioreactor in just 1 week, which is a dramatic improvement over current methods of expansion.

Silk-Elastin-like Polymers for Acute Intraparenchymal Treatment of the Traumatically Injured Spinal Cord: A First Systematic Experimental Approach

Despite the promising potential of hydrogel-based therapeutic approaches for spinal cord injury (SCI), the need for new biomaterials to design effective strategies for SCI treatment and the outstanding properties of silk-elastin-like polymers (SELP), the potential use of SELPs in SCI is currently unknown. In this context, we assessed the effects elicited by the in vivo acute intraparenchymal injection of an SELP named (EIS)₂-RGD6 in a clinically relevant model of SCI. After optimization of the injection system, the distribution, structure, biodegradability, and cell infiltration capacity of (EIS)₂-RGD6 were assessed. Finally, the effects exerted by the (EIS)₂-RGD6 injection-in terms of motor function, myelin preservation, astroglial and microglia/macrophage reactivity, and fibrosis-were evaluated. We found that (EIS)₂-RGD6 can be acutely injected in the lesioned spinal cord without inducing further damage, showing a widespread distribution covering all lesioned areas with a single injection and facilitating the formation of a slow-degrading porous scaffold at the lesion site that allows for the infiltration and/or proliferation of endogenous cells with no signs of collapse and without inducing further microglial and astroglial reactivity, as well as even reducing SCI-associated fibrosis. Altogether, these observations suggest that (EIS)₂-RGD6-and, by extension, SELPs-could be promising polymers for the design of therapeutic strategies for SCI treatment.

Phase 1 Safety Trial of Autologous Human Schwann Cell Transplantation in Chronic Spinal Cord Injury

A phase 1 open-label, non-randomized clinical trial was conducted to determine feasibility and safety of autologous human Schwann cell (ahSC) transplantation accompanied by rehabilitation in participants with chronic spinal cord injury (SCI). Magnetic resonance imaging (MRI) was used to screen eligible participants to estimate an individualized volume of cell suspension to be implanted. The trial incorporated standardized multi-modal rehabilitation before and after cell delivery. Participants underwent sural nerve harvest, and ahSCs were isolated and propagated in culture. The dose of culture-expanded ahSCs injected into the chronic spinal cord lesion of each individual followed a cavity-filling volume approach. Primary outcome measures for safety and trend-toward efficacy were assessed. Two participants with American Spinal Injury Association Impairment Scale (AIS) A and two participants with incomplete chronic SCI (AIS B, C) were each enrolled in cervical and thoracic SCI cohorts (n = 8 total). All participants completed the study per protocol, and no serious adverse events related to sural nerve harvest or ahSC transplantation were reported. Urinary tract infections and skin abrasions were the most common adverse events reported. One participant experienced a 4-point improvement in motor function, a 6-point improvement in sensory function, and a 1-level improvement in neurological level of injury. Follow-up MRI in the cervical (6 months) and thoracic (24 months) cohorts revealed a reduction in cyst volume after transplantation with reduced effect over time. This phase 1 trial demonstrated the feasibility and safety of ahSC transplantation combined with a multi-modal rehabilitation protocol for participants with chronic SCI.

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.

Elucidating the Pivotal Neuroimmunomodulation of Stem Cells in Spinal Cord Injury Repair

Spinal cord injury (SCI) is a distressing incident with abrupt onset of the motor as well as sensory dysfunction, and most often, the injury occurs as result of high-energy or velocity accidents as well as contact sports and falls in the elderly. The key challenges associated with nerve repair are the lack of self-repair as well as neurotrophic factors and primary and secondary neuronal apoptosis, as well as factors that prevent the regeneration of axons locally. Neurons that survive the initial traumatic damage may be lost due to pathogenic activities like neuroinflammation and apoptosis. Implanted stem cells are capable of differentiating into neural cells that replace injured cells as well as offer local neurotrophic factors that aid neuroprotection, immunomodulation, axonal sprouting, axonal regeneration, and remyelination. At the microenvironment of SCI, stem cells are capable of producing growth factors like brain-derived neurotrophic factor and nerve growth factor which triggers neuronal survival as well as axonal regrowth. Although stem cells have proven to be of therapeutic value in SCI, the major disadvantage of some of the cell types is the risk for tumorigenicity due to the contamination of undifferentiated cells prior to transplantation. Local administration of stem cells via either direct cellular injection into the spinal cord parenchyma or intrathecal administration into the subarachnoid space is currently the best transplantation modality for stem cells during SCI.

Interneuron transplantation: a prospective surgical therapy for medically refractory epilepsy

Excitatory-inhibitory imbalance is central to epilepsy pathophysiology. Current surgical therapies for epilepsy, such as brain resection, laser ablation, and neurostimulation, target epileptic networks on macroscopic scales, without directly correcting the circuit-level aberrations responsible for seizures. The transplantation of inhibitory cortical interneurons represents a novel neurobiological method for modifying recipient neural circuits in a physiologically corrective manner. Transplanted immature interneurons have been found to disperse in the recipient brain parenchyma, where they develop elaborate structural morphologies, express histochemical markers of mature interneurons, and form functional inhibitory synapses onto recipient neurons. Transplanted interneurons also augment synaptic inhibition and alter recipient neural network synchrony, two physiological processes disrupted in various epilepsies. In rodent models of epilepsy, interneuron transplantation corrects recipient seizure phenotypes and associated behavioral abnormalities. As such, interneuron transplantation may represent a novel neurobiological approach to the surgical treatment of human epilepsy. Here, the authors describe the preclinical basis for applying interneuron transplantation to human epilepsy, discuss its potential clinical applications, and consider the translational hurdles to its development as a surgical therapy.

Neurophysiological Changes in the First Year After Cell Transplantation in Sub-acute Complete Paraplegia

Neurophysiological testing can provide quantitative information about motor, sensory, and autonomic system connectivity following spinal cord injury (SCI). The clinical examination may be insufficiently sensitive and specific to reveal evolving changes in neural circuits after severe injury. Neurophysiologic data may provide otherwise imperceptible circuit information that has rarely been acquired in biologics clinical trials in SCI. We reported a Phase 1 study of autologous purified Schwann cell suspension transplantation into the injury epicenter of participants with complete subacute thoracic SCI, observing no clinical improvements. Here, we report longitudinal electrophysiological assessments conducted during the trial. Six participants underwent neurophysiology screening pre-transplantation with three post-transplantation neurophysiological assessments, focused on the thoracoabdominal region and lower limbs, including MEPs, SSEPs, voluntarily triggered EMG, and changes in GSR. We found several notable signals not detectable by clinical exam. In all six participants, thoracoabdominal motor connectivity was detected below the clinically assigned neurological level defined by sensory preservation. Additionally, small voluntary activations of leg and foot muscles or positive lower extremity MEPs were detected in all participants. Voluntary EMG was most sensitive to detect leg motor function. The recorded MEP amplitudes and latencies indicated a more caudal thoracic level above which amplitude recovery over time was observed. In contrast, further below, amplitudes showed less improvement, and latencies were increased. Intercostal spasms observed with EMG may also indicate this thoracic “motor level.” Galvanic skin testing revealed autonomic dysfunction in the hands above the injury levels. As an open-label study, we can establish no clear link between these observations and cell transplantation. This neurophysiological characterization may be of value to detect therapeutic effects in future controlled studies.

Method and Apparatus for the Automated Delivery of Continuous Neural Stem Cell Trails Into the Spinal Cord of Small and Large Animals

BACKGROUND

Immature neurons can extend processes after transplantation in adult animals. Neuronal relays can form between injected neural stem cells (NSCs) and surviving neurons, possibly improving recovery after spinal cord injury (SCI). Cell delivery methods of single or multiple bolus injections of concentrated cell suspensions thus far tested in preclinical and clinical experiments are suboptimal for new tract formation. Nonuniform injectate dispersal is often seen due to gravitational cell settling and clumping. Multiple injections have additive risks of hemorrhage, parenchymal damage, and cellular reflux and require additional surgical exposure. The deposition of multiply delivered cells boluses may be uneven and discontinuous.

OBJECTIVE

To develop an injection apparatus and methodology to deliver continuous cellular trails bridging spinal cord lesions.

METHODS

We improved the uniformity of cellular trails by formulating NSCs in hyaluronic acid. The TrailmakerTM stereotaxic injection device was automatized to extend a shape memory needle from a single-entry point in the spinal cord longitudinal axis to "pioneer" a new trail space and then retract while depositing an hyaluronic acid-NSC suspension. We conducted testing in a collagen spinal models, and animal testing using human NSCs (hNSCs) in rats and minipigs.

RESULTS

Continuous surviving trails of hNSCs within rat and minipig naive spinal cords were 12 and 40 mm in length. hNSC trails were delivered across semi-acute contusion injuries in rats. Transplanted hNSCs survived and were able to differentiate into neural lineage cells and astrocytes.

CONCLUSION

The TrailmakerTM creates longitudinal cellular trails spanning multiple levels from a single-entry point. This may enhance the ability of therapeutics to promote functional relays after SCI.

Efficacy of human HC016 cell transplants on neuroprotection and functional recovery in a rat model of acute spinal cord injury

Spinal cord injury (SCI) is a devastating event with huge personal and social costs, for which there is no effective treatment. Cell therapy constitutes a promising therapeutic approach for SCI; however, its clinical potential is seriously limited by their low survival in the hostile conditions encompassing the acute phase of SCI. Human HC016 (hHC016) cells, generated from expanded human adipose mesenchymal stem cells (hAMSCs) and pulsed with a patented protocol with hydrogen peroxide (H₂ O₂ ), are expected to acquire improved resistance to oxidative environments which appears as a major limiting factor hampering the engrafting success. Our specific aim was to assess whether H₂ O₂ -pulsed hHC016 cells had an improved survival and thus therapeutic efficacy in a rat contusion model of acute SCI when grafted 48 hr after injury. Functional recovery was evaluated up to 56 days post-injury (dpi) by locomotor (open field test and CatWalk) and sensory (Von Frey and Hargreaves) tests. Besides, histological evaluation of transplanted cell survival and tissue protection/regeneration was also performed. Functional results showed a statistically significant improvement on locomotor recovery outcomes with hHC016 cells. Accordingly, superior cell survival in correlation with long-term neuroprotection, higher axonal regeneration, and reduced astroglial and microglial reactivity was also observed with hHC016 cells. These results demonstrate an enhanced survival capacity of hHC016 cells resulting in improved functional and histological outcomes as compared with hAMSCs, indicating that hHC016 cell transplants may constitute a promising cell therapy for acute SCI.

Emerging Safety of Intramedullary Transplantation of Human Neural Stem Cells in Chronic Cervical and Thoracic Spinal Cord Injury

BACKGROUND

Human central nervous system stem cells (HuCNS-SC) are multipotent adult stem cells with successful engraftment, migration, and region-appropriate differentiation after spinal cord injury (SCI).

OBJECTIVE

To present data on the surgical safety profile and feasibility of multiple intramedullary perilesional injections of HuCNS-SC after SCI.

METHODS

Intramedullary free-hand (manual) transplantation of HuCNS-SC cells was performed in subjects with thoracic (n = 12) and cervical (n = 17) complete and sensory incomplete chronic traumatic SCI.

RESULTS

Intramedullary stem cell transplantation needle times in the thoracic cohort (20 M HuCNS-SC) were 19:30 min and total injection time was 42:15 min. The cervical cohort I (n = 6), demonstrated that escalating doses of HuCNS-SC up to 40 M range were well tolerated. In cohort II (40 M, n = 11), the intramedullary stem cell transplantation needle times and total injection time was 26:05 ± 1:08 and 58:14 ± 4:06 min, respectively. In the first year after injection, there were 4 serious adverse events in 4 of the 12 thoracic subjects and 15 serious adverse events in 9 of the 17 cervical patients. No safety concerns were considered related to the cells or the manual intramedullary injection. Cervical magnetic resonance images demonstrated mild increased T2 signal change in 8 of 17 transplanted subjects without motor decrements or emerging neuropathic pain. All T2 signal change resolved by 6 to 12 mo post-transplant.

CONCLUSION

A total cell dose of 20 M cells via 4 and up to 40 M cells via 8 perilesional intramedullary injections after thoracic and cervical SCI respectively proved safe and feasible using a manual injection technique.

Biodistribution of Glial Progenitors in a Three Dimensional-Printed Model of the Piglet Cerebral Ventricular System

White matter damage persists in hypoxic-ischemic newborns even when treated with hypothermia. We have previously shown that intraventricular delivery of human glial progenitors (GPs) at the neonatal stage is capable of replacing abnormal host glia and rescuing the lifespan of dysmyelinated mice. However, such transplantation in the human brain poses significant challenges as related to high-volume ventricles and long cell migration distances. These challenges can only be studied in large animal model systems. In this study, we developed a three dimensional (3D)-printed model of the ventricular system sized to a newborn pig to investigate the parameters that can maximize a global biodistribution of injected GPs within the ventricular system, while minimizing outflow to the subarachnoid space. Bioluminescent imaging and magnetic resonance imaging were used to image the biodistribution of luciferase-transduced GPs in simple fluid containers and a custom-designed, 3D-printed model of the piglet ventricular system. Seven independent variables were investigated. The results demonstrated that a low volume (0.1 mL) of cell suspension is essential to keep cells within the ventricular system. If higher volumes (1 mL) are needed, a very slow infusion speed (0.01 mL/min) is necessary. Real-time magnetic resonance imaging demonstrated that superparamagnetic iron oxide (SPIO) labeling significantly alters the rheological properties of the GP suspension, such that, even at high speeds and high volumes, the outflow to the subarachnoid space is reduced. Several other factors, including GP species (human vs. mouse), type of catheter tip (end hole vs. side hole), catheter length (0.3 vs. 7.62 m), and cell concentration, had less effect on the overall distribution of GPs. We conclude that the use of a 3D-printed phantom model represents a robust, reproducible, and cost-saving alternative to in vivo large animal studies for determining optimal injection parameters.

Clinical Outcomes from a Multi-Center Study of Human Neural Stem Cell Transplantation in Chronic Cervical Spinal Cord Injury

Human neural stem cell transplantation (HuCNS-SC^®) is a promising central nervous system (CNS) tissue repair strategy in patients with stable neurological deficits from chronic spinal cord injury (SCI). These immature human neural cells have been demonstrated to survive when transplanted in vivo, extend neural processes, form synaptic contacts, and improve functional outcomes after experimental SCI. A phase II single blind, randomized proof-of-concept study of the safety and efficacy of HuCNS-SC transplantation into the cervical spinal cord was undertaken in patients with chronic C5-7 tetraplegia, 4-24 months post-injury. In Cohort I (n = 6) dose escalation from 15,000,000 to 40,000,000 cells was performed to determine the optimum dose. In Cohort II an additional six participants were transplanted at target dose (40,000,000) and compared with four untreated controls. Within the transplant group, there were nine American Spinal Injury Association Impairment Scale (AIS) B and three AIS A participants with a median age at transplant of 28 years with an average time to transplant post-injury of 1 year. Immunosuppression was continued for 6 months post-transplant, and immunosuppressive blood levels of tacrolimus were achieved and well tolerated. At 1 year post-transplantation, there was no evidence of additional spinal cord damage, new lesions, or syrinx formation on magnetic resonance (MR) imaging. In summary, the incremental dose escalation design established surgical safety, tolerability, and feasibility in Cohort I. Interim analysis of Cohorts I and II demonstrated a trend toward Upper Extremity Motor Score (UEMS) and Graded Redefined Assessment of Strength, Sensibility, and Prehension (GRASSP) motor gains in the treated participants, but at a magnitude below the required clinical efficacy threshold set by the sponsor to support further development resulting in early study termination.

Noninvasive imaging of nanoparticle-labeled transplant populations within polymer matrices for neural cell therapy

AIM

To develop a 3D neural cell construct for encapsulated delivery of transplant cells; develop hydrogels seeded with magnetic nanoparticle (MNP)-labeled cells suitable for cell tracking by MRI.

MATERIALS & METHODS

Astrocytes were exogenously labeled with MRI-compatible iron-oxide MNPs prior to intra-construct incorporation within a 3D collagen hydrogel.

RESULTS

A connective, complex cellular network was clearly observable within the 3D constructs, with high cellular viability. MNP accumulation in astrocytes provided a hypointense MRI signal at 24 h & 14 days.

CONCLUSION

Our findings support the concept of developing a 3D construct possessing the dual advantages of (i) support of long-term cell survival of neural populations with (ii) the potential for noninvasive MRI-tracking of intra-construct cells for neuroregenerative applications.

Culture and Expansion of Rodent and Porcine Schwann Cells for Preclinical Animal Studies

Cell-based therapies have become a major focus in preclinical research that leads to clinical application of a therapeutic product. Since 1990, scientists at the Miami Project to Cure Paralysis have generated extensive data demonstrating that Schwann cell (SC) transplantation supports spinal cord repair in animals with spinal cord injury. After preclinical efforts in SC transplantation strategies, efficient methods for procuring large, essentially pure populations of SCs from the adult peripheral nerve were developed for rodent and pig studies. This chapter describes a series of simple procedures to obtain and cryopreserve large cultures of highly purified adult nerve-derived SCs without the need for additional purification steps. This protocol permits the derivation of ≥90% pure rodent and porcine SCs within 2-4 weeks of culture.

Intraspinal Delivery of Schwann Cells for Spinal Cord Injury

Cell transplant-mediated tissue repair of the damaged spinal cord is being tested in several clinical trials. The current candidates are neural stem cells, stromal cells, and autologous Schwann cells (aSC). Due to their peripheral origin and limited penetration of astrocytic regions, aSC are transplanted intralesionally as compared to neural stem cells that are transplanted into intact spinal cord. Injections into either location can cause iatrogenic injury, and thus technical precision is important in the therapeutic risk-benefit equation. In this chapter, we discuss how we bridged from transplant studies in large animals to human application for two Phase 1 aSC transplant studies, one subacute and one chronic. Preclinical SC transplant studies conducted at the University of Miami in 2009-2012 in rodents, minipigs, and primates supported a successful Investigational New Drug (IND) submission for a Phase 1 trial in subacute complete spinal cord injury (SCI). Our studies optimized the safety and efficiency of intralesional cell delivery for subacute human SCI and led to the development of new simpler techniques for cell delivery into subjects with chronic SCI. Key parameters of delivery methodology include precision localization of the injury site, stereotaxic devices to control needle trajectory, method of entry into the spinal cord, spinal cord motion reduction, the volume and density of the cell suspension, rate of delivery, and control of shear stresses on cells.

Comparison of intramedullary transplantation of olfactory ensheathing cell for patients with chronic complete spinal cord injury worldwide

Objectives:

Traumatic spinal cord injury (tSCI) remains a major clinical challenge. Cell transplantation brings a glimmer of light, among them olfactory ensheathing cells (OECs) have shown some neurorestorative effect. Due to the results of each group lack basic consistency, many technical details are believed to affect the overall outcome. We compare the clinical outcome of intramedullary transplant of olfactory ensheathing cells for patients with spinal cord injury at multi-centers worldwide, and to explore the potential standardized transplantation that suits for the clinical requirements.

Methods:

Here, we used the Pubmed and CNKI databases to search online the literatures published in the last 20 years for the clinical studies/trials of OECs for chronic spinal cord injury in the representative clinical center. The results of these representative clinical treatment centers were searched and analyzed. The parameters which may affect the effect including the concentration of cells, the total number of cells, the choice of incision, the site of transplantation, the number of transplantation sites, the advantages and disadvantages of transplantation equipment, and postoperative management, were compared carefully to clarify its impact on the clinical results.

Results:

In these literatures, 2 Chinese centers, 1 Australian center and 1 European center were selected for intraspinal transplantation. The reason of different results may be due to the excessive injection times and/or the excessive total injection volume.

Conclusions:

Cell implant to the spinal cord parenchyma is effective for restoring neurological functions, but improper procedures may lead to ineffective results. Concise surgery appears to be more suitable for clinical application than ostensibly precise and complex injection procedures. Sufficient rehabilitation training is surely necessary for the integration of motor recovery after cell transplantation.

Peripheral blood detection of systemic graft-specific xeno-antibodies following transplantation of human neural progenitor cells into the porcine spinal cord

Extensive pre-clinical and clinical studies have searched for therapeutic efficacy of cell-based therapeutics in diseases of the Central Nervous System (CNS) with no other viable options. Allogeneic cells represent the primary source of these therapies and immunosuppressive regimens have been empirically employed based on experience with solid organ transplantation, attempting to avoid immune mediated graft rejection. In this study, we aimed to 1) characterize the host immune response to stem cells transplanted into the CNS and 2) develop a non-invasive method for detecting immune response to transplanted cell grafts. Human neural progenitor cells were transplanted into the spinal cord of 10 Göttingen minipigs, of which 5 received no immunosuppression and 5 received Tacrolimus. Peripheral blood samples were collected longitudinally for flow cytometry cross match studies. Necropsy was performed at day 21 and spinal cord tissue analysis. We observed a transient increase in xeno-reactive antibodies was detected on post-operative day 7 and 14 in pigs that did not receive immunosuppression. This response was not detected in pigs that received Tacrolimus immunosuppression. No difference in graft survival was observed between the groups. Infiltration of numerous immune mediators including granulocytes, T lymphocytes, and activated microglia, and complement deposition were detected. In summary, a systemic immunologic response to stem cell grafts was detected for two weeks after transplantation using peripheral blood. This could be used as a non-invasive biomarker by investigators for detection of immunologic rejection. However, the absence of a detectable response in peripheral blood does not rule out a parenchymal immune response.

Translational considerations in injectable cell-based therapeutics for neurological applications: concepts, progress and challenges

Significant progress has been made during the past decade towards the clinical adoption of cell-based therapeutics. However, existing cell-delivery approaches have shown limited success, with numerous studies showing fewer than 5% of injected cells persisting at the site of injection within days of transplantation. Although consideration is being increasingly given to clinical trial design, little emphasis has been given to tools and protocols used to administer cells. The different behaviours of various cell types, dosing accuracy, precise delivery, and cell retention and viability post-injection are some of the obstacles facing clinical translation. For efficient injectable cell transplantation, accurate characterisation of cellular health post-injection and the development of standardised administration protocols are required. This review provides an overview of the challenges facing effective delivery of cell therapies, examines key studies that have been carried out to investigate injectable cell delivery, and outlines opportunities for translating these findings into more effective cell-therapy interventions.

Creation of an intramedullary cavity by hemorrhagic necrosis removal 24 h after spinal cord contusion in rats for eventual intralesional implantation of restorative materials

Intramedullary hemorrhagic necrosis occurs early after spinal cord injury at the site of injury and adjacent segments. It is considered harmful because of its potential to aggravate secondary injury, and to interfere with axonal regeneration; it might also lead to an unfavorable environment for intralesional implants. Removal of hemorrhagic necrosis has been attempted before with variable results. The invasive nature of these procedures carries the risk of exacerbating damage to the injured cord. The overall objective for this study was to test several strategies for non-damaging removal of hemorrhagic necrosis and characterize the resulting cavity looking for a space for future intralesional therapeutic implants in rats with acute cord injury. Rats were subjected to graded cord contusion, and hemorrhagic necrosis was removed after 24h. Three grades of myelotomy (extensive, medium sized, and small) were tested. Using the small surgical approach to debridement, early and late effects of the intervention were determined by histology and by analytical and behavioral analysis. Appearance and capacity of the resulting cavity were characterized. Satisfactory removal of hemorrhagic necrosis was achieved with all three surgical approaches to debridement. However, bleeding in spared cord tissue was excessive after medium sized and extensive myelotomies but similar to control injured rats after small cord surgery. Small surgical approach to debridement produced no swelling nor acute inflammation changes, nor did it affect long-term spontaneous locomotor recovery, but resulted in modest improvement of myelination in rats subjected to both moderate and severe injuries. Cavity created after intervention was filled with 10 to 15 μL of hydrogel. In conclusion, by small surgical approach to debridement, removal of hemorrhagic necrosis was achieved after acute cord contusion thereby creating intramedullary spaces without further damaging the injured spinal cord. Resulting cavities appear suitable for future intralesional placement of pro-reparative cells or other regenerative biomaterials in a clinically relevant model of spinal cord injury.

From transplanting Schwann cells in experimental rat spinal cord injury to their transplantation into human injured spinal cord in clinical trials

Among the potential therapies designed to repair the injured spinal cord is cell transplantation, notably the use of autologous adult human Schwann cells (SCs). Here, we detail some of the critical research accomplished over the last four decades to establish a foundation that enables these cells to be tested in clinical trials. New culture systems allowed novel information to be gained about SCs, including discovering ways to stimulate their proliferation to acquire adequately large numbers for transplantation into the injured human spinal cord. Transplantation of rat SCs into rat models of spinal cord injury has demonstrated that SCs promote repair of injured spinal cord. Additional work required to gain approval from the Food and Drug Administration for the first SC trial in the Miami Project is disclosed. This trial and a second one now underway are described.

Magnetic Resonance Imaging-Guided Transplantation of Neural Stem Cells into the Porcine Spinal Cord

BACKGROUND

Cell-based therapies are a promising treatment option for traumatic, tumorigenic and degenerative diseases of the spinal cord. Transplantation into the spinal cord is achieved with intravascular, intrathecal, or direct intraparenchymal injection. The current standard for direct injection is limited by surgical invasiveness, difficulty in reinjection, and the inability to directly target anatomical or pathological landmarks. The objective of this study was to present the proof of principle for minimally invasive, percutaneous transplantation of stem cells into the spinal cord parenchyma of live minipigs under MR guidance.

METHODS

An MR-compatible spine injection platform was developed to work with the ClearPoint SmartFrame system (MRI Interventions Inc.). The system was attached to the spine of 2 live minipigs, a percutaneous injection cannula was advanced into the spinal cord under MR guidance, and cells were delivered to the cord.

RESULTS

A graft of 2.5 × 106 human (n = 1) or porcine (n = 1) neural stem cells labeled with ferumoxytol nanoparticles was transplanted into the ventral horn of the spinal cord with MR guidance in 2 animals. Graft delivery was visualized with postprocedure MRI, and characteristic iron precipitates were identified in the spinal cord by Prussian blue histochemistry. Grafted stem cells were observed in the spinal cord of the pig injected with porcine neural stem cells. No postoperative morbidity was observed in either animal.

CONCLUSION

This report supports the proof of principle for transplantation and visualization of pharmacological or biological agents into the spinal cord of a large animal under the guidance of MRI.

Characterization of Motor and Somatosensory Evoked Potentials in the Yucatan Micropig Using Transcranial and Epidural Stimulation

Yucatan micropigs have brain and spinal cord dimensions similar to humans and are useful for certain spinal cord injury (SCI) translational studies. Micropigs are readily trained in behavioral tasks, allowing consistent testing of locomotor loss and recovery. However, there has been little description of their motor and sensory pathway neurophysiology. We established methods to assess motor and sensory cortical evoked potentials in the anesthetized, uninjured state. We also evaluated epidurally evoked motor and sensory stimuli from the T6 and T9 levels, spanning the intended contusion injury epicenter. Response detection frequency, mean latency and amplitude values, and variability of evoked potentials were determined. Somatosensory evoked potentials were reliable and best detected during stimulation of peripheral nerve and epidural stimulation by referencing the lateral cortex to midline Fz. The most reliable hindlimb motor evoked potential (MEP) occurred in tibialis anterior. We found MEPs in forelimb muscles in response to thoracic epidural stimulation likely generated from propriospinal pathways. Cranially stimulated MEPs were easier to evoke in the upper limbs than in the hindlimbs. Autopsy studies revealed substantial variations in cortical morphology between animals. This electrophysiological study establishes that neurophysiological measures can be reliably obtained in micropigs in a time frame compatible with other experimental procedures, such as SCI and transplantation. It underscores the need to better understand the motor control pathways, including the corticospinal tract, to determine which therapeutics are suitable for testing in the pig model.

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.

Neural Stem Cell Therapy and Rehabilitation in the Central Nervous System: Emerging Partnerships

The goal of regenerative medicine is to restore function through therapy at levels such as the gene, cell, tissue, or organ. For many disorders, however, regenerative medicine approaches in isolation may not be optimally effective. Rehabilitation is a promising adjunct therapy given the beneficial impact that physical activity and other training modalities can offer. Accordingly, "regenerative rehabilitation" is an emerging concentration of study, with the specific goal of improving positive functional outcomes by enhancing tissue restoration following injury. This article focuses on one emerging example of regenerative rehabilitation-namely, the integration of clinically based protocols with stem cell technologies following central nervous system injury. For the purposes of this review, the state of stem cell technologies for the central nervous system is summarized, and a rationale for a synergistic benefit of carefully orchestrated rehabilitation protocols in conjunction with cellular therapies is provided. An overview of practical steps to increase the involvement of physical therapy in regenerative rehabilitation research also is provided.

Injectable biomaterials: a perspective on the next wave of injectable therapeutics

We are experiencing a new wave of injectable therapeutics (namely/injectable biomaterials) to complement injectable drugs and injectable biologics, and to serve as the basis for injectable combinatorial therapeutics. Injectable biomaterials contribute to the treatment of the fluid-filled defects which often result from disease and injury, by providing the missing physical framework (i.e. the stroma). However, while injectable matrices may be necessary for the successful treatment of certain lesions, they will not likely be sufficient. Chemoattractants for select endogenous cells, or cells themselves, may need to be incorporated into the matrix prior to its injection to ensure the necessary cellular repopulation of the cavitary defect. These agents and others (drugs and biologics) delivered by the matrix represent the new category of injectable combinatorial therapeutics.

Stem cells in canine spinal cord injury--promise for regenerative therapy in a large animal model of human disease

The use of cell transplantation for spinal cord injury is a rapidly evolving field in regenerative medicine. Numerous animal models are currently being used. However, translation to human patients is still a challenging step. Dogs are of increasing importance as a translational model for human disease since there is a greater awareness of the need to increase the quality of preclinical data. The use of dogs ultimately brings benefit to both human and veterinary medicine. In this review we analyze experimental and clinical studies using cell transplantation for canine spinal cord injury. Overall, in experimental studies, transplantation groups showed improvement over control groups. Improvements were measured at the functional, electrophysiological, histological, RNA and protein levels. Most clinical studies support beneficial effects of cell transplantation despite the fact that methodological limitations preclude definitive conclusions. However, the mechanisms of action and underlying the behavior of transplanted cells in the injured spinal cord remain unclear. Overall, we conclude here that stem cell interventions are a promising avenue for the treatment of spinal cord injury. Canines are a promising model that may help bridge the gap between translational research and human clinical trials.

Preclinical Validation of Multilevel Intraparenchymal Stem Cell Therapy in the Porcine Spinal Cord

BACKGROUND:

Although multiple clinical trials are currently testing different stem cell therapies as treatment alternatives for many neurodegenerative diseases and spinal cord injury, the optimal injection parameters have not yet been defined.

OBJECTIVE:

To test the spinal cord's tolerance to increasing volumes and numbers of stem cell injections in the pig.

METHODS:

Twenty-seven female Göttingen minipigs received human neural progenitor cell injections using a stereotactic platform device. Cell transplantation in groups 1 to 5 (5–7 pigs in each) was undertaken with the intent of assessing the safety of an injection volume escalation (10, 25, and 50 µL) and an injection number escalation (20, 30, and 40 injections). Motor function and general morbidity were assessed for 21 days. Full necropsy was performed; spinal cords were analyzed for graft survival and microscopic tissue damage.

RESULTS:

No mortality or permanent surgical complications were observed during the 21-day study period. All animals returned to preoperative baseline within 14 days, showing complete motor function recovery. The histological analysis showed that there was no significant decrease in neuronal density between groups, and cell engraftment ranged from 12% to 31% depending on the injection paradigm. However, tissue damage was identified when injecting large volumes into the spinal cord (50 μL).

CONCLUSION:

This series supports the functional safety of various injection volumes and numbers in the spinal cord and gives critical insight into important safety thresholds. These results are relevant to all translational programs delivering cell therapeutics to the spinal cord.

Is the subarachnoid administration of mesenchymal stromal cells a useful strategy to treat chronic brain damage?

BACKGROUND AIMS

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity worldwide. Developing effective protocols for the administration of mesenchymal stromal cells (MSCs) is a promising therapeutic strategy to treat TBI. It is important to develop alternatives to direct parenchymal injection at the injury site because direct injection is an expensive and invasive technique. Subarachnoid transplantation, a minimally invasive and low-risk procedure, may be an important and clinically applicable strategy. The aim of this study was to test the therapeutic effect of subarachnoid administration of MSCs on functional outcome 2 months after an experimental TBI in rats.

METHODS

Two months after TBI, 30 female Wistar rats were divided into 3 groups (n = 10 in each group): sham, MSC (received 2 × 10(6) MSCs) and saline (received only saline) groups. Neurological function, brain and spinal cords samples and cerebrospinal fluid were studied.

RESULTS

No significant differences were found in neurological evaluation and after histological analysis; differences in the expression of neurotrophins were present but were not statistically significant. MSCs survived in the host tissue, and some expressed neural markers.

CONCLUSIONS

Similar to direct parenchymal injections, transplanted MSCs survive, migrate to the injury cavity and differentiate into mature neural cell types for at least 6 months after engraftment. These results open the possibility that MSC administration through subarachnoid administration may be a treatment for the consequences of TBI. The transplantation technique and cell number should be adjusted to obtain functional outcome and neurotrophin production differences.

Advances in regenerative therapies for spinal cord injury: a biomaterials approach

Spinal cord injury results in the permanent loss of function, causing enormous personal, social and economic problems. Even though neural regeneration has been proven to be a natural mechanism, central nervous system repair mechanisms are ineffective due to the imbalance of the inhibitory and excitatory factors implicated in neuroregeneration. Therefore, there is growing research interest on discovering a novel therapeutic strategy for effective spinal cord injury repair. To this direction, cell-based delivery strategies, biomolecule delivery strategies as well as scaffold-based therapeutic strategies have been developed with a tendency to seek for the answer to a combinatorial approach of all the above. Here we review the recent advances on regenerative/neural engineering therapies for spinal cord injury, aiming at providing an insight to the most promising repair strategies, in order to facilitate future research conduction.

Gene therapy strategies for the treatment of spinal cord injury

Spinal cord injury is a complex pathology often resulting in functional impairment and paralysis. Gene therapy has emerged as a possible solution to the problems of limited neural tissue regeneration through the administration of factors promoting axonal growth, while also offering long-term local delivery of therapeutic molecules at the injury site. Of note, gene therapy is our response to the requirements of neural and glial cells following spinal cord injury, providing, in a time-dependent manner, growth substances for axonal regeneration and eliminating axonal growth inhibitors. Herein, we explore different gene therapy strategies, including targeting gene expression to modulate the presence of neurotrophic growth or survival factors and increase neural tissue plasticity. Special attention is given to describing advances in viral and non-viral gene delivery systems, as well as the available routes of gene delivery. Finally, we discuss the future of combinatorial gene therapies and give consideration to the implementation of gene therapy in humans.

Very high resolution ultrasound imaging for real-time quantitative visualization of vascular disruption after spinal cord injury

Spinal cord injury (SCI) is characterized by vascular disruption with intramedullary hemorrhage, alterations in blood-spinal cord barrier integrity, and perilesional ischemia. A safe and easily applied imaging technique to quantify evolving intraspinal vascular changes after SCI is lacking. We evaluated the utility of very high resolution ultrasound (VHRUS) imaging to assess SCI-induced vascular disruption in a clinically relevant rodent model. The spinal cords of Wistar rats were lesioned at the 11th thoracic vertebra (Th11) by a 35 g 1-minute clip compression. Three-dimensional quantification of intraspinal hemorrhage using VHRUS (at an acute 90-min and subacute 24-h time point post-SCI) was compared with lesional hemoglobin and extravasated Evans blue dye measured spectrophotometrically. The anatomy of hemorrhage was comparatively assessed using VHRUS and histology. Time-lapse videos demonstrated the evolution of parenchymal hemorrhage. VHRUS accurately depicted the structural (gray and white matter) and vascular anatomy of the spinal cord (after laminectomy) and was safely repeated in the same animal. After SCI, a hyperechoic signal extended from the lesion epicenter. Significant correlations were found between VHRUS signal and hemorrhage in the acute (r=0.88, p<0.0001) and subacute (r=0.85, p<0.0001) phases and extravasated Evans blue (a measure of vascular disruption) in the subacute phase (r=0.94, p<0.0001). Time-lapse videos demonstrated that the expanding parenchymal hemorrhage is preceded by new perilesional hemorrhagic foci. VHRUS enables real-time quantitative live anatomical imaging of acute and subacute vascular disruption after SCI in rats. This technique has important scientific and clinical translational applications.

Clinical translation of autologous Schwann cell transplantation for the treatment of spinal cord injury

PURPOSE OF REVIEW

To describe the current status of testing Schwann cell transplantation as a therapy for human spinal cord injury (SCI).

RECENT FINDINGS

Transplanted Schwann cells have reparative effects in the damaged spinal cord. A few clinical studies have reported that Schwann cell transplantation appears safe. Compared with allogeneic cell transplants, autologous cells do not require immune suppression, but the workload of cell manufacturing is greater. Preclinical Schwann cell transplant studies conducted at the University of Miami in 2009-2012 supported an investigational new drug approved by the Food and Drug Administration. A Phase 1 safety study has been initiated.

SUMMARY

Spinal cord repair after severe SCI requires that axonal regeneration and myelination occur in a context of reduced inhibition, enhanced plasticity, and new circuit formation. Evolving clinical experience with Schwann cell transplantation may provide a basis upon which additionally combined therapeutics can be tested to increase the extent of repair after SCI. Safety is the primary consideration when ex-vivo manipulated cells are introduced into the damaged nervous system. Preclinical studies across several species have not indicated safety concerns regarding Schwann cells. Initial clinical reports from studies in Iran and China are suggestive of clinical safety, although more rigorous characterization of the implanted cells is needed.

Mesenchymal stromal cells integrate and form longitudinally-aligned layers when delivered to injured spinal cord via a novel fibrin scaffold

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MSCs can be delivered to injured spinal cord through use of a fibrin scaffold.

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Scaffold-delivered MSCs form longitudinally-aligned layers over the lesion site.

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Regenerating axons enter scaffold-delivered grafts and grow longitudinally.

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MSCs delivered via injection orient perpendicular to the plane of the spinal cord.

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Regenerating axons in injected grafts grow perpendicular to the plane of the cord.

Mesenchymal stromal cells (MSCs) have been shown to promote healing and regeneration in a number of CNS injury models and therefore there is much interest in the clinical use of these cells. For spinal cord injuries, a standard delivery method for MSCs is intraspinal injection, but this can result in additional injury and provides little control over how the cells integrate into the tissue. The present study examines the use of a novel fibrin scaffold as a new method of delivering MSCs to injured spinal cord. Use of the fibrin scaffold resulted in the formation of longitudinally-aligned layers of MSCs growing over the spinal cord lesion site. Host neurites were able to migrate into this MSC architecture and grow longitudinally. The length of the MSC bridge corresponded to the length of the fibrin scaffold. MSCs that were delivered via intraspinal injection were mainly oriented perpendicular to the plane of the spinal cord and remained largely restricted to the lesion site. Host neurites within the injected MSC graft were also oriented perpendicular to the plane of the spinal cord.

Transplantation of mesenchymal stem cells in ALS

Amyotrophic lateral sclerosis (ALS) is a devastating incurable, neurodegenerative disease that targets motor neurons (MNs) in the primary motor cortex, brainstem, and spinal cord, leading to muscle atrophy, paralysis, and death due to respiratory failure within 2-5 years. Currently, there is no cure for ALS. The development of a therapy that can support or restore MN function and attenuate toxicity in the spinal cord provides the most comprehensive approach for treating ALS. Mesenchymal stem cells might be suitable for cell therapy in ALS because of their immunomodulatory and protective properties. In this review, the authors discuss the major challenges to the translation of in vitro and animal studies of MSCs therapy in the clinical setting.

Mesenchymal stem cells improve locomotor recovery in traumatic spinal cord injury: systematic review with meta-analyses of rat models

Traumatic spinal cord injury (SCI) is a devastating event with huge personal and societal costs. A limited number of treatments exist to ameliorate the progressive secondary damage that rapidly follows the primary mechanical impact. Mesenchymal stem or stromal cells (MSCs) have anti-inflammatory and neuroprotective effects and may thus reduce secondary damage after administration. We performed a systematic review with quantitative syntheses to assess the evidence of MSCs versus controls for locomotor recovery in rat models of traumatic SCI, and identified 83 eligible controlled studies comprising a total of 1,568 rats. Between-study heterogeneity was large. Fifty-three studies (64%) were reported as randomised, but only four reported adequate methodologies for randomisation. Forty-eight studies (58%) reported the use of a blinded outcome assessment. A random-effects meta-analysis yielded a difference in behavioural Basso-Beattie-Bresnahan (BBB) locomotor score means of 3.9 (95% confidence interval [CI] 3.2 to 4.7; P<0.001) in favour of MSCs. Trial sequential analysis confirmed the findings of the meta-analyses with the upper monitoring boundary for benefit being crossed by the cumulative Z-curve before reaching the diversity-adjusted required information size. Only time from intervention to last follow-up remained statistically significant after adjustment using multivariate random-effects meta-regression modelling. Lack of other demonstrable explanatory variables could be due to insufficient meta-analytic study power. MSCs would seem to demonstrate a substantial beneficial effect on locomotor recovery in a widely-used animal model of traumatic SCI. However, the animal results should be interpreted with caution concerning the internal and external validity of the studies in relation to the design of future clinical trials.

Biomaterial-based interventions for neuronal regeneration and functional recovery in rodent model of spinal cord injury: a systematic review

CONTEXT

There is considerable interest in translating laboratory advances in neuronal regeneration following spinal cord injury (SCI). A multimodality approach has been advocated for successful functional neuronal regeneration. With this goal in mind several biomaterials have been employed as neuronal bridges either to support cellular transplants, to release neurotrophic factors, or to do both. A systematic review of this literature is lacking. Such a review may provide insight to strategies with a high potential for further investigation and potential clinical application.

OBJECTIVE

To systematically review the design strategies and outcomes after biomaterial-based multimodal interventions for neuronal regeneration in rodent SCI model. To analyse functional outcomes after implantation of biomaterial-based multimodal interventions and to identify predictors of functional outcomes.

METHODS

A broad PubMed, CINHAL, and a manual search of relevant literature databases yielded data from 24 publications; 14 of these articles included functional outcome information. Studies reporting behavioral data in rat model of SCI and employing biodegradable polymer-based multimodal intervention were included. For behavioral recovery, studies using severe injury models (transection or severe clip compression (>16.9 g) or contusion (50 g/cm)) were categorized separately from those investigating partial injury models (hemisection or moderate-to-severe clip compression or contusion).

RESULTS

The cumulative mean improvements in Basso, Beattie, and Bresnahan scores after biomaterial-based interventions are 5.93 (95% CI = 2.41 - 9.45) and 4.44 (95% CI = 2.65 - 6.24) for transection and hemisection models, respectively. Factors associated with improved outcomes include the type of polymer used and a follow-up period greater than 6 weeks.

CONCLUSION

The functional improvement after implantation of biopolymer-based multimodal implants is modest. The relationship with neuronal regeneration and functional outcome, the effects of inflammation at the site of injury, the prolonged survival of supporting cells, the differentiation of stem cells, the effective delivery of neurotrophic factors, and longer follow-up periods are all topics for future elucidation. Future investigations should strive to further define specific factors associated with improved functional outcomes in clinically relevant models.

A novel porcine model of traumatic thoracic spinal cord injury

Spinal cord injury (SCI) researchers have predominately utilized rodents and mice for in vivo SCI modeling and experimentation. From these small animal models have come many insights into the biology of SCI, and a growing number of novel treatments that promote behavioral recovery. It has, however, been difficult to demonstrate the efficacy of such treatments in human clinical trials. A large animal SCI model that is an intermediary between rodent and human SCI may be a valuable translational research resource for pre-clinically evaluating novel therapies, prior to embarking upon lengthy and expensive clinical trials. Here, we describe the development of such a large animal model. A thoracic spinal cord injury at T10/11 was induced in Yucatan miniature pigs (20-25 kg) using a weight drop device. Varying degrees of injury severity were induced by altering the height of the weight drop (5, 10, 20, 30, 40, and 50 cm). Behavioral recovery over 12 weeks was measured using a newly developed Porcine Thoracic Injury Behavior Scale (PTIBS). This scale distinguished locomotor recovery among animals of different injury severities, with strong intra-observer and inter-observer reliability. Histological analysis of the spinal cords 12 weeks post-injury revealed that animals with the more biomechanically severe injuries had less spared white matter and gray matter and less neurofilament immunoreactivity. Additionally, the PTIBS scores correlated strongly with the extent of tissue sparing through the epicenter of injury. This large animal model of SCI may represent a useful intermediary in the testing of novel pharmacological treatments and cell transplantation strategies.

Animal models of neurologic disorders: a nonhuman primate model of spinal cord injury

Primates are an important and unique animal resource. We have developed a nonhuman primate model of spinal cord injury (SCI) to expand our knowledge of normal primate motor function, to assess the impact of disease and injury on sensory and motor function, and to test candidate therapies before they are applied to human patients. The lesion model consists of a lateral spinal cord hemisection at the C7 spinal level with subsequent examination of behavioral, electrophysiological, and anatomical outcomes. Results to date have revealed significant neuroanatomical and functional differences between rodents and primates that impact the development of candidate therapies. Moreover, these findings suggest the importance of testing some therapeutic approaches in nonhuman primates prior to the use of invasive approaches in human clinical trials. Our primate model is intended to: 1) lend greater positive predictive value to human translatable therapies, 2) develop appropriate methods for human translation, 3) lead to basic discoveries that might not be identified in rodent models and are relevant to human translation, and 4) identify new avenues of basic research to "reverse-translate" important questions back to rodent models.

Translational spinal cord injury research: preclinical guidelines and challenges

Advances in the neurobiology of spinal cord injury (SCI) have prompted increasing attention to opportunities for moving experimental strategies towards clinical applications. Preclinical studies are the centerpiece of the translational process. A major challenge is to establish strategies for achieving optimal translational progression while minimizing potential repetition of previous disappointments associated with clinical trials. This chapter reviews and expands upon views pertaining to preclinical design reported in recently published opinion surveys. Subsequent discussion addresses other preclinical considerations more specifically related to current and potentially imminent cellular and pharmacological approaches to acute/subacute and chronic SCI. Lastly, a retrospective and prospective analysis examines how guidelines currently under discussion relate to select examples of past, current, and future clinical translations. Although achieving definition of the "perfect" preclinical scenario is difficult to envision, this review identifies therapeutic robustness and independent replication of promising experimental findings as absolutely critical prerequisites for clinical translation. Unfortunately, neither has been fully embraced thus far. Accordingly, this review challenges the notion "everything works in animals and nothing in humans", since more rigor must first be incorporated into the bench-to-bedside translational process by all concerned, whether in academia, clinical medicine, or corporate circles.

Translational stem cell therapy for amyotrophic lateral sclerosis

Effective treatments are urgently needed for amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease characterized by the loss of motor neurons. In 2009, the FDA approved the first phase I safety trial of direct intraspinal transplantation of neural stem cells into patients with ALS, which is currently in progress. Stem cell technologies represent a promising approach for treating ALS, but several issues must be addressed when translating promising experimental ALS therapies to patients. This article highlights the key research that supports the use of stem cells as a therapy for ALS, and discusses the rationale behind and approach to the phase I trial. Completion of the trial could pave the way for continued advances in stem cell therapy for ALS and other neurodegenerative diseases.