Characterization of the technique involved in isolating Schwann cells from adult human peripheral nerve

Assessing Survival, Distribution, and Optimal Loading Technique of Schwann Cell-Derived Exosomes Into Second-generation Axon Guidance Channels

INTRODUCTION

Peripheral nerve injury (PNI) occurs in approximately 3% of all trauma patients and can be challenging to treat, particularly when injury is severe such as with a long-segmental gap. Although peripheral nerves can regenerate after injury, functional recovery is often insufficient, leading to deficits in the quality of life of patients with PNI. Although nerve autografts are the gold standard of care, there are several disadvantages to their use, namely a lack of autologous nerve material for repair. This has led to the pursuit of alternative treatment methods such as axon guidance channels (AGCs). Second-generation AGCs have been shown to be able to deliver growth-enhancing substrates for nerve repair directly to the injury site. Although our laboratory has had success with second-generation AGCs filled with Schwann cells (SCs), SCs have their own set of issues clinically. Because of this, we have begun to utilize SC-derived exosomes as an alternative, as they have the appropriate protein markers, associate to axons in high concentrations, and are able to improve nerve regeneration. However, it is unknown how SC-derived exosomes may react within second-generation AGCs; thus, the aim of the present study was to assess the ability of SC-derived exosomes to be loaded into a second-generation AGC and how they would distribute within it.

MATERIALS AND METHODS

A total of 4 dry second-generation AGCs were loaded with SC-derived exosomes that were derived from green fluorescent protein (GFP)-labeled SCs. They were subsequently frozen and sliced before imaging.

RESULTS

Here, we present findings that SC-derived exosomes can be loaded into second-generation AGCs through our established loading method utilizing negative pressure and are able to survive and equally distribute along the length of the AGC.

CONCLUSIONS

Although only 4 second-generation AGCs were utilized, these findings indicate a potential use for SC-derived exosomes within second-generation AGCs to treat severe PNI. Future research should focus on exploring this in greater detail and in different contexts to assess the ability of SC-derived exosomes to survive at the site of injury and treat PNI.

Human Schwann Cells in vitro II. Passaging, Purification, Banking, and Labeling of Established Cultures

This manuscript describes step-by-step procedures to establish and manage fresh and cryopreserved cultures of nerve-derived human Schwann cells (hSCs) at the desired scale. Adaptable protocols are provided to propagate hSC cultures through serial passaging and perform routine manipulations such as enzymatic dissociation, purification, cryogenic preservation, live-cell labeling, and gene delivery. Expanded hSCs cultures are metabolically active, proliferative, and phenotypically stable for at least three consecutive passages. Cell yields are expected to be variable as determined by the rate of growth of individual batches and the rounds of subculture. The purity, however, can be maintained high at >95% hSC regardless of passage. The cells obtained in this manner are suitable for various applications, including small drug screens, in vitro modeling of neurodevelopmental processes, and cell transplantation. One caveat of this protocol is that continued expansion of same-batch hSC populations is eventually restricted due to senescence-linked growth arrest.

Systematic review of the therapeutic use of Schwann cells in the repair of peripheral nerve injuries: Advancements from animal studies to clinical trials

Objective

To systematically evaluate the literature on the therapeutic use of Schwann cells (SC) in the repair of peripheral nerve injuries.

Methods

The Cochrane Library and PubMed databases were searched using terms [(“peripheral nerve injury” AND “Schwann cell” AND “regeneration”) OR (“peripheral nerve injuries”)]. Studies published from 2008 to 2022 were eligible for inclusion in the present study. Only studies presenting data from in-vivo investigations utilizing SCs in the repair of peripheral nerve injuries qualified for review. Studies attempting repair of a gap of ≥10 mm were included. Lastly, studies needed to have some measure of quantifiable regenerative outcome data such as histomorphometry, immunohistochemical, electrophysiology, or other functional outcomes.

Results

A search of the PubMed and Cochrane databases revealed 328 studies. After screening using the abstracts and methods, 17 studies were found to meet our inclusion criteria. Good SC adherence and survival in conduit tubes across various studies was observed. Improvement in morphological and functional outcomes with the use of SCs in long gap peripheral nerve injuries was observed in nearly all studies.

Conclusion

Based on contemporary literature, SCs have demonstrated clear potential in the repair of peripheral nerve injury in animal studies. It has yet to be determined which nerve conduit or graft will prove superior for delivery and retention of SCs for nerve regeneration. Recent developments in isolation and culturing techniques will enable further translational utilization of SCs in future clinical trials.

Optimal Technique for Introducing Schwann Cells Into Peripheral Nerve Repair Sites

Peripheral nerve injury (PNI) is found in a relatively large portion of trauma patients. If the injury is severe, such as with the presence of a long segmental gap, PNI can present a challenge for treatment. The current clinical standard of nerve harvest for the repair of long segmental gap PNI can lead to many potential complications. While other methods have been utilized, recent evidence indicates the relevance of cell therapies, particularly through the use of Schwann cells, for the treatment of PNI. Schwann cells (SCs) are integral in the regeneration and restoration of function following PNI. SCs are able to dedifferentiate and proliferate, remove myelin and axonal debris, and are supportive in axonal regeneration. Our laboratory has demonstrated that SCs are effective in the treatment of severe PNI when axon guidance channels are utilized. However, in order for this treatment to be effective, optimal techniques for cellular placement must be used. Thus, here we provide relevant background information, preclinical, and clinical evidence for our method in the treatment of severe PNI through the use of SCs and axon guidance channels.

Nerve guidance conduit development for primary treatment of peripheral nerve transection injuries: A commercial perspective

Commercial nerve guidance conduits (NGCs) for repair of peripheral nerve discontinuities are of little use in gaps larger than 30 mm, and for smaller gaps they often fail to compete with the autografts that they are designed to replace. While recent research to develop new technologies for use in NGCs has produced many advanced designs with seemingly positive functional outcomes in animal models, these advances have not been translated into viable clinical products. While there have been many detailed reviews of the technologies available for creating NGCs, none of these have focussed on the requirements of the commercialisation process which are vital to ensure the translation of a technology from bench to clinic. Consideration of the factors essential for commercial viability, including regulatory clearance, reimbursement processes, manufacturability and scale up, and quality management early in the design process is vital in giving new technologies the best chance at achieving real-world impact. Here we have attempted to summarise the major components to consider during the development of emerging NGC technologies as a guide for those looking to develop new technology in this domain. We also examine a selection of the latest academic developments from the viewpoint of clinical translation, and discuss areas where we believe further work would be most likely to bring new NGC technologies to the clinic. STATEMENT OF SIGNIFICANCE: NGCs for peripheral nerve repairs represent an adaptable foundation with potential to incorporate modifications to improve nerve regeneration outcomes. In this review we outline the regulatory processes that functionally distinct NGCs may need to address and explore new modifications and the complications that may need to be addressed during the translation process from bench to clinic.

Schwann cell delivery via a novel 3D collagen matrix conduit improves outcomes in critical length nerve gap repairs

OBJECTIVE

The current clinical standard of harvesting a nerve autograft for repair of long-segment peripheral nerve injuries (PNIs) is associated with many potential complications. Guidance channels offer an alternative therapy. The authors investigate whether autologous Schwann cells (SCs) implanted within a novel collagen-glycosaminoglycan conduit will improve axonal regeneration in a long-segment PNI model.

METHODS

Novel NeuraGen 3D collagen matrix conduits were implanted with autologous SCs to investigate axonal regeneration across a critical size defect (13 mm) in male Fischer rat sciatic nerve. Reversed sciatic nerve autografts served as positive controls, and conduits filled with serum only as negative controls. Electrophysiological assessments were made in vivo. Animals were killed at 4 or 16 weeks postinjury, muscle weights were measured, and grafts underwent immunohistochemical and morphometric analysis.

RESULTS

SC survival was confirmed by the presence of green fluorescent protein-labeled SCs within regenerated fibers. Regeneration and elongation of myelinated axons in all segments of the graft were significantly enhanced at 16 weeks in the SC-filled conduits compared to the conduit alone and were statistically similar to those of the autograft. Nerves repaired with SC-filled conduits exhibited onset latencies and nerve conduction amplitudes similar to those of the contralateral controls and autograft (p < 0.05). Adding SCs to the conduit also significantly reduced muscle atrophy compared to conduit alone (p < 0.0001).

CONCLUSIONS

Repair of long-segment PNI of rat sciatic nerve is significantly enhanced by SC-filled NeuraGen 3D conduits. Improvements in the total number of myelinated axons, axon diameter, and myelin thickness throughout SC-filled conduits allow for significant recovery in nerve conduction and a decrease in muscle atrophy.

Scalable culture techniques to generate large numbers of purified human Schwann cells for clinical trials in human spinal cord and peripheral nerve injuries

OBJECTIVE

Schwann cells (SCs) have been shown to play an essential role in axon regeneration in both peripheral nerve injuries (PNIs) and spinal cord injuries (SCIs). The transplantation of SCs as an adjunctive therapy is currently under investigation in human clinical trials due to their regenerative capacity. Therefore, a reliable method for procuring large quantities of SCs from peripheral nerves is necessary. This paper presents a well-developed, validated, and optimized manufacturing protocol for clinical-grade SCs that are compliant with Current Good Manufacturing Practices (CGMPs).

METHODS

The authors evaluated the SC culture manufacturing data from 18 clinical trial participants who were recruited for autologous SC transplantation due to subacute SCI (n = 7), chronic SCI (n = 8), or PNIs (n = 3). To initiate autologous SC cultures, a mean nerve length of 11.8 ± 3.7 cm was harvested either from the sural nerve alone (n = 17) or with the sciatic nerve (n = 1). The nerves were digested with enzymes and SCs were isolated and further expanded in multiple passages to meet the dose requirements for transplantation.

RESULTS

An average yield of 87.2 ± 89.2 million cells at P2 and 150.9 ± 129.9 million cells at P3 with high viability and purity was produced. Cell counts and rates of expansion increased with each subsequent passage from P0 to P3, with the largest rate of expansion between P2 and P3. Larger harvest nerve lengths correlated significantly with greater yields at P0 and P1 (p < 0.05). In addition, a viability and purity above 90% was sustained throughout all passages in nearly all cell products.

CONCLUSIONS

This study presents reliable CGMP-compliant manufacturing methods for autologous SC products that are suitable for regenerative treatment of patients with SCI, PNI, or other conditions.

Automated image analysis of stained cytospins to quantify Schwann cell purity and proliferation

In response to injury, adult Schwann cells (SCs) re-enter the cell cycle, change their expression profile, and exert repair functions important for wound healing and the re-growth of axons. While this phenotypical instability of SCs is essential for nerve regeneration, it has also been implicated in cancer progression and de-myelinating neuropathies. Thus, SCs became an important research tool to study the molecular mechanisms involved in repair and disease and to identify targets for therapeutic intervention. A high purity of isolated SC cultures used for experimentation must be demonstrated to exclude that novel findings are derived from a contaminating fibroblasts population. In addition, information about the SC proliferation status is an important parameter to be determined in response to different treatments. The evaluation of SC purity and proliferation, however, usually depends on the time consuming, manual assessment of immunofluorescence stainings or comes with the sacrifice of a large amount of SCs for flow cytometry analysis. We here show that rat SC culture derived cytospins stained for SC marker SOX10, proliferation marker EdU, intermediate filament vimentin and DAPI allowed the determination of SC identity and proliferation by requiring only a small number of cells. Furthermore, the CellProfiler software was used to develop an automated image analysis pipeline that quantified SCs and proliferating SCs from the obtained immunofluorescence images. By comparing the results of total cell count, SC purity and SC proliferation rate between manual counting and the CellProfiler output, we demonstrated applicability and reliability of the established pipeline. In conclusion, we here combined the cytospin technique, a multi-colour immunofluorescence staining panel, and an automated image analysis pipeline to enable the quantification of SC purity and SC proliferation from small cell aliquots. This procedure represents a solid read-out to simplify and standardize the quantification of primary SC culture purity and proliferation.

The properties of human Schwann cells: Lessons from in vitro culture and transplantation studies

Human Schwann cells (hSCs) can be isolated directly from peripheral nerve and cultured using methods similar to those used for SCs from other species. Yet, important interspecies differences are revealed when the primary or expanded hSCs are compared to their nonhuman counterparts. This review addresses the special properties of nerve-derived hSCs that have resulted to date from both in vitro studies and in vivo research on cell transplantation in animal models and human subjects. A consensus has yet to emerge about the essential attributes of cultured normal hSCs. Thus, an emphasis is placed on the importance of validating hSC cultures by means of purity, identity, and biological activity to reliably use them as in vitro models of the SC phenotype and cell therapy products for injury repair. Combining traditional immunological methods, high-resolution omics approaches, and assorted cell-based assays is so far the best approach to unequivocally identify hSC populations obtained by direct isolation or derivation from stem cells. Special considerations are required to understand and manage the variability and heterogeneity proper of donor batches, as well as to evaluate risk factors. This is particularly important if the intended use of the hSCs is implantation in the human body, diagnosis of disease, or drug testing aimed at targeting any aspect of SC function in human patients. To conclude, in view of their unique properties, new concepts and methods are needed to better understand the biology of hSCs and exploit their full potential in basic science and regenerative medicine.

Phenotypic and Functional Characteristics of Human Schwann Cells as Revealed by Cell-Based Assays and RNA-SEQ

This study comprehensively addresses the phenotype, function, and whole transcriptome of primary human and rodent Schwann cells (SCs) and highlights key species-specific features beyond the expected donor variability that account for the differential ability of human SCs to proliferate, differentiate, and interact with axons in vitro. Contrary to rat SCs, human SCs were insensitive to mitogenic factors other than neuregulin and presented phenotypic variants at various stages of differentiation, along with a mixture of proliferating and senescent cells, under optimal growth-promoting conditions. The responses of human SCs to cAMP-induced differentiation featured morphological changes and cell cycle exit without a concomitant increase in myelin-related proteins and lipids. Human SCs efficiently extended processes along those of other SCs (human or rat) but failed to do so when placed in co-culture with sensory neurons under conditions supportive of myelination. Indeed, axon contact-dependent human SC alignment, proliferation, and differentiation were not observed and could not be overcome by growth factor supplementation. Strikingly, RNA-seq data revealed that ~ 44 of the transcriptome contained differentially expressed genes in human and rat SCs. A bioinformatics approach further highlighted that representative SC-specific transcripts encoding myelin-related and axon growth-promoting proteins were significantly affected and that a deficient expression of key transducers of cAMP and adhesion signaling explained the fairly limited potential of human SCs to differentiate and respond to axonal cues. These results confirmed the significance of combining traditional bioassays and high-resolution genomics methods to characterize human SCs and identify genes predictive of cell function and therapeutic value.

Nerve stepping stone has minimal impact in aiding regeneration across long acellular nerve allografts

INTRODUCTION

Acellular nerve allografts (ANAs) yield less consistent favorable outcomes compared with autografts for long gap reconstructions. We evaluated whether a hybrid ANA can improve 6-cm gap reconstruction.

METHODS

Rat sciatic nerve was transected and repaired with either 6-cm hybrid or control ANAs. Hybrid ANAs were generated using a 1-cm cellular isograft between 2.5-cm ANAs, whereas control ANAs had no isograft. Outcomes were assessed by graft gene and marker expression (n = 4; at 4 weeks) and motor recovery and nerve histology (n = 10; at 20 weeks).

RESULTS

Hybrid ANAs modified graft gene and marker expression and promoted modest axon regeneration across the 6-cm defect compared with control ANA (P < 0.05), but yielded no muscle recovery. Control ANAs had no appreciable axon regeneration across the 6-cm defect.

DISCUSSION

A hybrid ANA confers minimal motor recovery benefits for regeneration across long gaps. Clinically, the authors will continue to reconstruct long nerve gaps with autografts. Muscle Nerve 57: 260-267, 2018.

First human experience with autologous Schwann cells to supplement sciatic nerve repair: report of 2 cases with long-term follow-up

OBJECTIVE Long-segment injuries to large peripheral nerves present a challenge to surgeons because insufficient donor tissue limits repair. Multiple supplemental approaches have been investigated, including the use of Schwann cells (SCs). The authors present the first 2 cases using autologous SCs to supplement a peripheral nerve graft repair in humans with long-term follow-up data. METHODS Two patients were enrolled in an FDA-approved trial to assess the safety of using expanded populations of autologous SCs to supplement the repair of long-segment injuries to the sciatic nerve. The mechanism of injury included a boat propeller and a gunshot wound. The SCs were obtained from both the sural nerve and damaged sciatic nerve stump. The SCs were expanded and purified in culture by using heregulin β1 and forskolin. Repair was performed with sural nerve grafts, SCs in suspension, and a Duragen graft to house the construct. Follow-up was 36 and 12 months for the patients in Cases 1 and 2, respectively. RESULTS The patient in Case 1 had a boat propeller injury with complete transection of both sciatic divisions at midthigh. The graft length was approximately 7.5 cm. In the postoperative period the patient regained motor function (Medical Research Council [MRC] Grade 5/5) in the tibial distribution, with partial function in peroneal distribution (MRC Grade 2/5 on dorsiflexion). Partial return of sensory function was also achieved, and neuropathic pain was completely resolved. The patient in Case 2 sustained a gunshot wound to the leg, with partial disruption of the tibial division of the sciatic nerve at the midthigh. The graft length was 5 cm. Postoperatively the patient regained complete motor function of the tibial nerve, with partial return of sensation. Long-term follow-up with both MRI and ultrasound demonstrated nerve graft continuity and the absence of tumor formation at the repair site. CONCLUSIONS Presented here are the first 2 cases in which autologous SCs were used to supplement human peripheral nerve repair in long-segment injury. Both patients had significant improvement in both motor and sensory function with correlative imaging. This study demonstrates preliminary safety and efficacy of SC transplantation for peripheral nerve repair.

The Use of Autologous Schwann Cells to Supplement Sciatic Nerve Repair With a Large Gap: First in Human Experience

Insufficient donor nerve graft material in peripheral nerve surgery remains an obstacle for successful long-distance regeneration. Schwann cells (SCs) can be isolated from adult mammalian peripheral nerve biopsies and can be grown in culture and retain their capacity to enhance peripheral nerve regeneration within tubular repair strategies in multiple animal models. Human Schwann cells (hSCs) can be isolated, expanded in number, and retain their ability to promote regeneration and myelinate axons, but have never been tested in a clinical case of peripheral nerve injury. A sural nerve biopsy and peripheral nerve tissue from the traumatized sciatic nerve stumps was obtained after Food and Drug Administration (FDA) and Institutional Review Board (IRB) approval as well as patient consent. The SCs were isolated after enzymatic digestion of the nerve and expanded with the use of heregulin β1 (0.1 µg/ml) and forskolin (15 mM). After two passages the Schwann cell isolates were combined with sural nerve grafts to repair a large sciatic nerve defect (7.5 cm) after a traumatic nerve injury. The sural nerve and the traumatized sciatic nerve ends both served as an excellent source of purified (90% and 97%, respectively) hSCs. Using ultrasound and magnetic resonance imaging (MRI) we were able to determine continuity of the nerve graft repair and the absence of tumor formation. The patient had evidence of proximal sensory recovery and definitive motor recovery distal to the repair in the distribution of the tibial and common peroneal nerve. The patient did experience an improvement in her pain scores over time. The goals of this approach were to determine the safety and clinical feasibility of implementing a new cellular repair strategy. In summary, this approach represents a novel strategy in the treatment of peripheral nerve injury and represents the first reported use of autologous cultured SCs after human peripheral nerve injury.

Biotherapies in multiple sclerosis: a step toward remyelination and neuroprotection?

Multiple sclerosis (MS) is a complex disease of the central nervous system (CNS), characterized by CNS-restricted inflammation with subsequent demyelination and neurodegeneration. Current disease-modifying therapies efficiently reduce relapse rate and new lesions appearance, but still fail to impact the progressive course of the disease. There is a great need for the avenue of new therapies aimed at promoting myelin repair or reducing neurodegeneration that should result in the prevention of neurological disability in this chronic disease. This review will focus on the potentials and limitations of biotherapies that are currently developed for the promotion of CNS repair in MS, either monoclonal antibodies targeting axonal growth and remyelination, or cell therapies aimed at replacing the depleted myelinating cells within the CNS. As other researches aimed at promoting neuroprotection or remyelination are following a classical pharmacological approach, they will not be described in this review, which will focus on antibody-based therapies and cell therapies.

Transplantation of Schwann cells in a collagen tube for the repair of large, segmental peripheral nerve defects in rats

Object

Segmental nerve defects pose a daunting clinical challenge, as peripheral nerve injury studies have established that there is a critical nerve gap length for which the distance cannot be successfully bridged with current techniques. Construction of a neural prosthesis filled with Schwann cells (SCs) could provide an alternative treatment to successfully repair these long segmental gaps in the peripheral nervous system. The object of this study was to evaluate the ability of autologous SCs to increase the length at which segmental nerve defects can be bridged using a collagen tube.

Methods

The authors studied the use of absorbable collagen conduits in combination with autologous SCs (200,000 cells/μl) to promote axonal growth across a critical size defect (13 mm) in the sciatic nerve of male Fischer rats. Control groups were treated with serum only–filled conduits of reversed sciatic nerve autografts. Animals were assessed for survival of the transplanted SCs as well as the quantity of myelinated axons in the proximal, middle, and distal portions of the channel.

Results

Schwann cell survival was confirmed at 4 and 16 weeks postsurgery by the presence of prelabeled green fluorescent protein–positive SCs within the regenerated cable. The addition of SCs to the nerve guide significantly enhanced the regeneration of myelinated axons from the nerve stump into the proximal (p < 0.001) and middle points (p < 0.01) of the tube at 4 weeks. The regeneration of myelinated axons at 16 weeks was significantly enhanced throughout the entire length of the nerve guide (p < 0.001) as compared with their number in a serum–only filled tube and was similar in number compared with the reversed autograft. Autotomy scores were significantly lower in the animals whose sciatic nerve was repaired with a collagen conduit either without (p < 0.01) or with SCs (p < 0.001) when compared with a reversed autograft.

Conclusions

The technique of adding SCs to a guidance channel significantly enhanced the gap distance that can be repaired after peripheral nerve injury with long segmental defects and holds promise in humans. Most importantly, this study represents some of the first essential steps in bringing autologous SC-based therapies to the domain of peripheral nerve injuries with long segmental defects.

Tissue engineered constructs for peripheral nerve surgery

BACKGROUND

Tissue engineering has been defined as "an interdisciplinary field that applies the principles of engineering and life sciences toward the development of biological substitutes that restore, maintain, or improve tissue function or a whole organ". Traumatic peripheral nerve injury resulting in significant tissue loss at the zone of injury necessitates the need for a bridge or scaffold for regenerating axons from the proximal stump to reach the distal stump.

METHODS

A review of the literature was used to provide information on the components necessary for the development of a tissue engineered peripheral nerve substitute. Then, a comprehensive review of the literature is presented composed of the studies devoted to this goal.

RESULTS

Extensive research has been directed toward the development of a tissue engineered peripheral nerve substitute to act as a bridge for regenerating axons from the proximal nerve stump seeking the distal nerve. Ideally this nerve substitute would consist of a scaffold component that mimics the extracellular matrix of the peripheral nerve and a cellular component that serves to stimulate and support regenerating peripheral nerve axons.

CONCLUSIONS

The field of tissue engineering should consider its challenge to not only meet the autograft "gold standard" but also to understand what drives and inhibits nerve regeneration in order to surpass the results of an autograft.

Realizing the maximum potential of Schwann cells to promote recovery from spinal cord injury

Transplantation of Schwann cells (SCs) has been extensively investigated as a therapeutic intervention in rodent models of spinal cord injury (SCI). Here we review both strengths and weaknesses of this approach and discuss additional strategies for maximizing the potential of SCs to repair the injured spinal cord. With no additional treatments, SCs were consistently shown to provide a bridge across the lesion site, supporting the ingrowth of sensory and propriospinal axons, to myelinate axons and to decrease the size of cavities formed after injury. Supraspinal axons did not, however, grow onto the bridge, axons failed to traverse the caudal SC-host cord interface and transplanted SC survival was poor. More recent studies have shown that the potential of SC transplantation as a therapeutic approach can be strongly enhanced by combining additional strategies . For example, combining SC transplantation with elevation of cAMP levels resulted in growth of brainstem axons into the SC graft and caudal to the lesion and in significant improvements in locomotion. Axon growth (and functional improvement) have been increased by strategies to raise neurotrophin levels, either by injection or by genetic modification of the SCs before transplantation. A major problem in maximizing SC potential in injured cord has been in achieving good integration of the transplanted cells with the adjacent cord parenchyma. Several previous studies suggested an ability of SCs to migrate extensively in CNS tissue when astroctyes were absent and to myelinate CNS axons. Furthermore, in some cases involving very limited injury, SCs migrated and integrated well even in the presence of host astrocytes. Consistent with these observations, treatments with an enzyme, chondroitinase, to modify the SC-astrocyte interface surrounding the graft, have shown much promise. Very new studies have shown that SCs derived from SC precursors show a higher ability to survive, integrate well with host tissue and support brainstem axon growth into and beyond the graft, confirming the innate promise of SCs in spinal cord repair. We review one clinical trial already underway in Iran testing SC transplantation in patients with SCI. Finally, we briefly describe a protocol, adaptable to the principles of good manufacturing practice, for generating large numbers of human SCs. Overall, the available evidence suggests that SCs, especially when used in combination with other treatments, offer one of the best hopes we have today of devising an effective treatment for spinal cord repair.

Culture and proliferation of highly purified adult Schwann cells from rat, dog, and man

This chapter presents fast and easy protocols to obtain highly purified cultures of proliferating adult rat, canine, and human Schwann cells. Cell preparation from predegenerated adult sciatic nerves combined with the use of melanocyte growth medium supplemented with forskolin, fibroblast growth factor-2, pituitary extract, and heregulin as selective, serum-free culture medium and two methods for a consecutive cell-enrichment step are described. Our protocols result in approximately 90% pure Schwann cell cultures (or higher). The average time to obtain highly purified in vitro cultures of adult Schwann cells is 21 days.

Promoting survival, migration, and integration of transplanted Schwann cells by over-expressing polysialic acid

The poor survival and migration of transplanted Schwann cells (SCs) are major drawbacks for their clinical application in cell therapy for neurotrauma. To overcome such drawbacks we genetically modified SCs to over-express polysialic acid (PSA) by lentiviral delivery of polysialyltransferase (PST) to study whether over-expression of PSA could enhance their survival, migration, and integration when transplanted into the spinal cord. It was found that more PSA-expressing SCs (PST/SCs) survived than GFP-expressing SCs (GFP/SCs) after transplantation, although cell loss was still quite significant. PSA expression did not enhance the motility of transplanted SCs in uninjured spinal cord. However, in a spinal cord crush injury model PST/SCs transplanted caudal to the lesion showed that increased number of PST/SCs migrated to the injury site compared with that of GFP/SCs. Induced expression of PSA in spinal cord can further facilitate the infiltration of PST/SCs into the lesion site. PST/SCs were also shown to intermingle well with host spinal cells while GFP/SCs formed boundaries with host tissue. This was confirmed by an in vitro confrontation assay showing that more PST/SCs crossed over to astrocyte territory than GFP/SCs. Furthermore, PST/SCs induced much less expression of glial fibrillary acidic protein and chondroitin sulfate proteoglycan in the surrounding tissues than GFP/SCs, indicating that expression of PSA on SCs do not cause significant stress response of astrocytes. These results demonstrate that expression of PSA on SCs significantly changes their biological properties and makes them more feasible for neural repair after neurotrauma.

Aligned and random nanofibrous substrate for the in vitro culture of Schwann cells for neural tissue engineering

The current challenge in peripheral nerve tissue engineering is to produce an implantable scaffold capable of bridging long nerve gaps that will produce results similar to autograft without requiring the harvest of autologous donor tissue. Aligned and random polycaprolactone/gelatin (PCL/gelatin) nanofibrous scaffolds were fabricated for the in vitro culture of Schwann cells that assist in directing the growth of regenerating axons in nerve tissue engineering. The average fiber diameter attained by electrospinning of polymer blend (PCL/gelatin) ranged from 232+/-194 to 160+/-86nm with high porosity (90%). Blending PCL with gelatin resulted in increased hydrophilicity of nanofibrous scaffolds and yielded better mechanical properties, approaching those of PCL nanofibers. The biocompatibility of fabricated nanofibers was assessed for culturing and proliferation of Schwann cells by MTS assay. The results of the MTS assay and scanning electron microscopy confirmed that aligned and random PCL/gelatin nanofibrous scaffolds are suitable substrates for Schwann cell growth as compared to PCL nanofibrous scaffolds for neural tissue engineering.

Transplantation of autologous Schwann cells for the repair of segmental peripheral nerve defects

Peripheral nerve injuries are a source of chronic disability. Incomplete recovery from such injuries results in motor and sensory dysfunction and the potential for the development of chronic pain. The repair of human peripheral nerve injuries with traditional surgical techniques has limited success, particularly when a damaged nerve segment needs to be replaced. An injury to a long segment of peripheral nerve is often repaired using autologous grafting of "noncritical" sensory nerve. Although extensive axonal regeneration can be observed extending into these grafts, recovery of function may be absent or incomplete if the axons fail to reach their intended target. The goal of this review was to summarize the progress that has occurred in developing an artificial neural prosthesis consisting of autologous Schwann cells (SCs), and to detail future directions required in translating this promising therapy to the clinic. In the authors' laboratory, methods are being explored to combine autologous SCs isolated using cell culture techniques with axon guidance channel (AGC) technology to develop the potential to repair critical gap length lesions within the peripheral nervous system. To test the clinical efficacy of such constructs, it is critically important to characterize the fate of the transplanted SCs with regard to cell survival, migration, differentiation, and myelin production. The authors sought to determine whether the use of SC-filled channels is superior or equivalent to strategies that are currently used clinically (for example, autologous nerve grafts). Finally, although many nerve repair paradigms demonstrate evidence of regeneration within the AGC, the authors further sought to determine if the regeneration observed was physiologically relevant by including electrophysiological, behavioral, and pain assessments. If successful, the development of this reparative approach will bring together techniques that are readily available for clinical use and should rapidly accelerate the process of bringing an effective nerve repair strategy to patients with peripheral nerve injury prior to the development of pain and chronic disability.

Remyelination of the central nervous system: a valuable contribution from the periphery

The loss of myelin, a major element involved in the saltatory conduction of the electrical impulse of the nervous system, is a major target of current research. Serious long-term disabilities are observed in patients with demyelinating disease of the central nervous system, such as multiple sclerosis. New therapeutic strategies aimed at overcoming myelin damage and axonal loss focus on the repair potential of myelin-forming cells. This review examines the use of peripheral myelin-forming cells, the Schwann cells, to promote myelin repair.

Peripheral nerve regeneration using a three dimensionally cultured schwann cell conduit

The use of artificial nerve conduit containing viable Schwann cells is one of the most promising strategies to repair peripheral nerve injury. To fabricate an effective nerve conduit whose microstructure and internal environment are more favorable in nerve regeneration than those currently existing, a new three-dimensional (3D) Schwann cell culture technique using Matrigel and dorsal root ganglion (DRG) was developed. Nerve conduit of 3D arranged Schwann cells was fabricated using direct seeding of freshly harvested DRG into Matrigel-filled silicone tubes (inner diameter 1.98 mm, 14 mm length) and in vitro rafting culture for 2 weeks. The nerve regeneration efficacy of 3D cultured Schwann cell conduit (3D conduit group, n = 6) was assessed using an Sprague-Dawley rat sciatic nerve defect of 10 mm and compared with that of a silicone conduit filled with Matrigel and Schwann cells prepared with the conventional plain culture method (two-dimensional [2D] conduit group, n = 6). After 12 weeks, sciatic function was evaluated with sciatic function index (SFI) and gait analysis, and histomorphology of nerve conduit and the innervated tissues of sciatic nerve were examined using image analyzer and electromicroscopic methods. The SFI and ankle stance angle in the functional evaluation were -60.1 +/- 13.9, 37.9 degrees +/- 5.4 degrees in the 3D conduit group (n = 5) and -87.0 +/- 12.9, 32.2 degrees +/- 4.8 degrees in the 2D conduit group (n = 4). The myelinated axon was 44.91% +/- 0.13% in the 3D conduit group and 13.05% +/- 1.95% in the 2D conduit group. In the transmission electron microscope study, the 3D conduit group showed more abundant myelinated nerve fibers with well-organized and thickened extracellular collagen than the 2D conduit group, and the gastrocnemius muscle and biceps femoris tendon in the 3D conduit group were less atrophied and showed decreased fibrosis with less fatty infiltration than the 2D conduit group. A new 3D Schwann cell culture technique was established, and nerve conduit fabricated using this technique showed much improved nerve regeneration capacity than the silicone tube filled with Matrigel and Schwann cells prepared from the conventional plain culture method.

Human and rat adult Schwann cell cultures: fast and efficient enrichment and highly effective non-viral transfection protocol

We present a fast protocol that can be used to obtain highly purified cultures of proliferating adult human and rat Schwann cells accessible for non-viral transfection methods. The use of enriched genetically modified adult Schwann cells is of interest in the context of autologous cell transplantation within nerve transplants for peripheral nerve repair. Cell preparation from pre-degenerated adult peripheral nerves is described, together with the use of melanocyte growth medium plus forskolin, fibroblast growth factor-2 (FGF-2), pituitary extract and heregulin as a selective, serum-free culture medium and a subsequent cell enrichment step (cold jet). Proliferating adult Schwann cells can be efficiently genetically modified using optimized, non-viral electroporation protocols. The protocol results in Schwann cell cultures that are more than 90-95% pure, and transfection efficiencies vary depending on the initial cell constitution from 20 to 40%. The procedure takes up to 21 d, depending on the length of the pre-degeneration period.

Autologous adult human Schwann cells genetically modified to provide alternative cellular transplants in peripheral nerve regeneration

Object

The purpose of this study was to provide genetically modified adult human Schwann cells as tools for cell transplantation in peripheral nerve repair. The application of transfected autologous Schwann cells overexpressing regeneration-promoting proteins, for example, neurotrophic or growth factors, is a promising approach in the aforementioned context. To achieve an optimal clinical outcome, it is highly important to perform enrichment, genetic modification, and retransplantation of cells in a short time.

Methods

To enable the development of these autologous cellular prostheses, the authors tested the properties of adult human Schwann cells obtained from differently treated human peripheral nerve biopsy samples. The use of “cold jet,” a fast and effective enrichment procedure, as well as selective, serum-free culture conditions, resulted in very pure adult human Schwann cell cultures. Using an optimized electroporation protocol, as many as 48.4% of adult human Schwann cells were successfully transfected.

Conclusions

The authors present a very fast protocol to establish adult human Schwann cell cultures that demonstrably express plasmid proteins after plasmid DNA insertion by electroporation. These autologous human Schwann cells transfected to enhance the endogenous production of regeneration-supporting proteins will likely constitute a major component of tissue-engineered peripheral nerve grafts.

Changes in the axonal membrane potential and Ca2+ concentration associated with peripheral nerve grafting after spinal cord injury

We performed peripheral nerve allografting in rats with spinal cord injury, and measured motor function and axonal membrane potential as well as Ca(2+) concentration of the nerve grafting spinal cord area by using a behavior observation system and a confocal laser-scanning microscope, respectively. In our experiments, we produced a model of peripheral nerve grafting after spinal cord injury by peripheral nerve allografting (sciatic nerve) in rats with spinal cord injury (thoracic cord hemisection). The group with spinal cord injury that underwent peripheral nerve grafting showed improvement in motor function, a significant increase in the axonal action potential, and a slight increase in the Ca(2+) concentration compared with the group that did not undergo nerve grafting.

Adhesion and proliferation of human Schwann cells on adhesive coatings

Attachment to and proliferation on the substrate are deemed important considerations when Schwann cells (SCs) are to be seeded in synthetic nerve grafts. Attachment is a prerequisite for the SCs to survive and fast proliferation will yield large numbers of SCs in a short time, which appears promising for stimulation of peripheral nerve regeneration. The aim of the present study was to compare the adhesion and proliferation of human Schwann cells (HSCs) on different substrates. The following were selected for their suitability as an internal coating of synthetic nerve grafts; the extracellular matrix proteins fibronectin, laminin and collagen type I and the poly-electrolytes poly(d-lysine) (PDL) and poly(ethylene-imine) (PEI). On all coatings, attachment of HSCs was satisfactory and comparable, indicating that this factor is not a major consideration in choosing a suitable coating. Proliferation was best on fibronectin, laminin and PDL, and worst on collagen type I and PEI. Since nerve regeneration is enhanced by laminin and/or fibronectin, these are preferred as coatings for synthetic nerve grafts seeded with SCs.

Labeling Schwann cells with CFSE-an in vitro and in vivo study

Schwann cell (SC) transplantation is a promising strategy for axonal regeneration in the nervous system. Identifying the grafted SCs is an important aspect of this approach. The current study sought to establish a simple, reliable, fluorescent labeling method for SCs with a lipophilic molecule, 5-(and-6)-carboxyfluorescein diacetate succinimidyl ester (CFSE). Human SCs were incubated with varying concentrations of CFSE for different time periods. Based on the viability of labeled SCs and its plating efficiency, 1 min incubation with 5 microM CFSE at 37 degrees C was selected as the optimal labeling condition. Flow cytometric analysis and fluorescence microscopy demonstrated that the fluorescence of labeled SCs would fade over 4 weeks. Immunostaining for the phenotypic expression of SC markers, including S100, GFAP, P75, and MHC-I/II at 1 and 4 weeks after incubation with CFSE showed no difference between labeled and non-labeled SCs. Mixed cultures of labeled human SCs and rat SCs for 48 h were performed in triplicate and demonstrated that no leakage of dye from labeled SCs in cell culture occurred across species. A total of 14 injections of 2x10(5) labeled SCs were performed within the spinal cord at T8 and/or L1 level in 9 nude rats. The animals were euthanized at 1 (6 injections) and 4 weeks (8 injections). Grafted labeled SCs survived for at least 4 weeks, and could be easily recognized in the nude rat spinal cord without leakage of dye to surrounding cells. The SCs migrated in white and gray matter 3-6 mm away from the injection and in the central canal for up to 12 mm. These results suggest that CFSE can be used as a fluorescent tracer of human SCs for both in vitro and in vivo studies, for a period of at least 4 weeks.

Purification of Schwann cells by selection of p75 low affinity nerve growth factor receptor expressing cells from adult peripheral nerve

The intrinsic capacity of Schwann cells to promote regeneration after limited peripheral nerve lesions has been successfully transferred to extensive peripheral nerve injuries and central nervous system lesions by autologous transplantation strategies. However, both the intrinsic ability of axotomized neurons to regenerate and the permissiveness of the parenchyma surrounding the acute injury site diminish over time. Therefore, the autologous transplantation mode requires a fast and effective method to isolate Schwann cells from peripheral nerve biopsies. Here, we report a method to purify p75 low affinity nerve growth factor receptor (p75LNGFr) expressing Schwann cells from peripheral nerve biopsies in adult rats using magnetic-activated cell separation (MACS). After 1 week of nerve degeneration in culture, nerve fragments were dissociated resulting in mixed cultures containing Schwann cells and fibroblasts. After incubation with specific anti-p75LNGFr antibodies and secondary magnetic bead conjugated antibodies followed by one cycle of MACS, 95% pure Schwann cell cultures were generated as confirmed by flow-cytometry and immunocytochemistry. In contrast to established methods, MACS separation of p75LNGFr expressing cells allows the reliable purification of Schwann cells within 9 days after biopsy employing direct selection of Schwann cells rather than fibroblast depletion assays. Therefore, this method represents an effective and fast means to generate autologous Schwann cells for clinical transplantation strategies aiming for axon repair and remyelination.

Magnetic cell sorting for enriching Schwann cells from adult mouse peripheral nerves

We have devised a simple method to purify mitotically active Schwann cells (SC) from peripheral nerves of adult mice. Nerves were predegenerated in vitro for 7 days and after dissociation cells were plated on poly-L-lysine/laminin coated dishes in N2 serum-free culture medium supplemented with forskolin and heregulin-beta1. Primary cultures were purified from contaminating fibroblasts by magnetic cell sorting (MACS) based on SC membrane specific expression of p75(NGFR) and enriched to about 99% of SC after MACS from 34 to 91% before sorting. After sorting, purified adult mouse SC were propagated for three passages until confluent to a total surface of 160 cm(2) per mouse (two sciatic and two trigeminal nerves). In addition, we show that this method can be used to purify tumoral SC from mouse NF2-related schwannomas.

A novel technique to isolate adult Schwann cells for an artificial nerve conduit

The use of an artificial nerve conduit containing viable Schwann cells (SCs) is one of the most promising approaches to repair nerve injuries. Obtaining a large number of viable SCs in a short period is demanded for the clinical use of this technique. However, the previous methods using mitogens are not clinically acceptable, and other methods that do not require mitogens, failed to isolate adult SCs effectively or required a long period of time. In this study, we have developed a novel technique to isolate SCs from adult rat peripheral nerves for an artificial nerve conduit without mitogens, which has produced a total number of 1.21 x 10(5) cells per mg, with an average purity of 93.0+/-0.58% at 21 days in vitro. The Bottenstein-Sato (BS) medium used in this study, had originally been developed for oligodendrocyte culture, but here it is shown to have an effect on SC proliferation and survival. By changing fetal bovine serum (FBS) concentrations from 0 to 10% serially, SCs could be isolated maximally from the predegenerated nerves while suppressing fibroblast overgrowth. The combination of this technique and the altered medium promoted the migration and proliferation of SCs selectively by utilizing the supporting cells of SCs instead of discarding them by changing the culture dishes and media.

Adhesion and growth of human Schwann cells on trimethylene carbonate (co)polymers

Seeding of artificial nerve grafts with Schwann cells is a promising strategy for bridging large nerve defects. The aim of the present study was to evaluate the adhesion and growth of human Schwann cells (HSCs) on 1,3-trimethylene carbonate (TMC) and epsilon-caprolactone copolymers, with the final goal of using these materials in the development of an artificial nerve graft. The adhesion, proliferation, and morphology of HSCs on copolymers containing 10 and 82 mol % of TMC and on the parent homopolymers were investigated. HSCs adhered faster and in greater numbers on the copolymer with 82 mol % of TMC and on the TMC homopolymer compared with the other (co)polymers. On all polymer films, cell adhesion was lower than on gelatin (positive control). Despite differences in cell adhesion, cells displayed exponential growth on all tested surfaces, with similar growth rates. Cell numbers doubled approximately every 3 days on all substrates. When the polymer films were coated with fibronectin, no significant differences in cell adhesion and proliferation were observed between coated polymer surfaces and gelatin. The results indicate that all tested materials support the adhesion and proliferation of HSCs and can in principle be used for the preparation of flexible and slowly degrading nerve guides.

Schwann cell-enriched cultures from adult human peripheral nerve: a technique combining short enzymatic dissociation and treatment with cytosine arabinoside (Ara-C)

Attempts to design the nerve cellular prostheses have focused on the production of autologous Schwann cells expanded in vitro as the essential component in the regeneration process of injured peripheral nerves. To obtain human Schwann cells of high quality we tested a short enzymatic dissociation protocol that optimized cellular viability levels. We also assessed patterns of bromodeoxyuridine (BrdU) incorporation in both Schwann cells and fibroblasts in the presence or absence of the antimitotic Ara-C, an enrichment option for adult human Schwann cell cultures. The Ara-C treated cultures showed a significantly higher Schwann cell percentage (95%), compared with that obtained in the absence of Ara-C (70%), indicating that this antimitotic acts to eliminate fibroblasts in each one of the applied pulses (four pulses). However, we have observed that the use of this antimitotic during prolonged periods of time produced a cumulative effect causing Schwann cell cytotoxicity. Therefore, we consider that our enzymatic dissociation technique and the application of only two pulses of Ara-C to the cultures are enough to achieve enrichment of adult human Schwann cells in culture.

Bioactive poly(L-lactic acid) conduits seeded with Schwann cells for peripheral nerve regeneration

This study attempted to enhance the efficacy of peripheral nerve regeneration using our previously tested poly(L-lactic acid) (PLLA) conduits by incorporating them with allogeneic Schwann cells (SCs). The SCs were harvested, cultured to obtain confluent monolayers and two concentrations (1 x 10(4) and 1 x 10(6) SC/ml) were combined with a collagen matrix (Vitrogen) and injected into the PLLA conduits. The conduits were then implanted into a 12 mm right sciatic nerve defect in rats. Three control groups were used: isografts, PLLA conduits filled with collagen alone and empty silicone tubes. The sciatic functional index (SFI) was calculated monthly through four months. At the end of second and fourth months, the gastrocnemius muscle was harvested and weighed for comparison and the graft conduit and distal nerve were harvested for histomorphologic analysis. The mean SFI demonstrated no group differences from isograft control. By four months, there was no significant difference in gastrocnemius muscle weight between the experimental groups compared to isograft controls. At four months, the distal nerve demonstrated a statistically lower number of axons mm2 for the high and low SC density groups and collagen control. The nerve fiber density was significantly lower in all of the groups compared to isograft controls by four months. The development of a "bioactive" nerve conduit using tissue engineering to replace autogenous nerve grafts offers a potential approach to improved patient care. Although equivalent nerve regeneration to autografts was not achieved, this study provides promising results for further investigation.

Neurotrophic factors and gene therapy in spinal cord injury

Although it was once thought that the central nervous system (CNS) of mammals was incapable of substantial recovery from injury, it is now clear that the adult CNS remains responsive to various substances that can promote cell survival and stimulate axonal growth. Among these substances are growth factors, including the neurotrophins and cytokines, and growth-supportive cells such as Schwann cells, olfactory ensheathing glia, and stem cells. We review the effects of these substances on promoting axonal growth after spinal cord injury, placing particular emphasis on the genetic delivery of nervous system growth factors to specific sites of injury as a means of promoting axonal growth and, in limited instances, functional recovery.

Variable galactocerebroside expression by human Schwann cells in dissociated and peripheral nerve explant cultures

It has been well established that rat Schwann cells down regulate their cell-surface expression of galactocerebroside (GalC) in vitro under normal cell culture conditions. To determine whether human Schwann cells exhibit a similar down-regulation of GalC in vitro we examined GalC expression in dissociated human Schwann cell cultures derived from normal adult peripheral nerve. Twenty-four hours post-dissociation up to 63% of human Schwann cells were found to express detectable levels of GalC on their surface whereas less than 8% of the Schwann cells expressed detectable levels of GalC at 14 days post-dissociation. In contrast, after nearly 3 months of peripheral nerve explant culture, greater than 30% of human Schwann cells still retained their GalC expression. A similar pattern was also observed when analyzing Schwann cell purity with dissociated cultures exhibiting a rapid decrease in Schwann cell purity under normal culturing conditions although Schwann cell purity was found to be largely unaffected during the period of peripheral nerve explant culture. In summary, we found there was less variation in both GalC expression and Schwann cell purity with time in peripheral nerve explant cultures than dissociated cultures.

Neuroma: a donor-age independent source of human Schwann cells for tissue engineered nerve grafts

Schwann cells are used in combination with biological matrices as tissue engineered nerve grafts in animal models offering a new therapeutic approach for treatment of lesions of the peripheral nervous system. A high yield of human Schwann cells from adult donors is only achieved by pharmacological stimulation, which should, however, be avoided in clinical therapy. Here, we establish cultures of activated human Schwann cells which were isolated from peripheral nerve neuroma which developed after a median nerve lesion. To allow nerve reconstruction neuroma have to be resected. Such neuroma tissue is virtually predegenerated and shows activation of Schwann cells, implying good adherence and high mitotic activity. This allows, irrespective of donor age, growing within a short time period and without any pharmacological treatment.

Expansion of adult Schwann cells from mouse predegenerated peripheral nerves

We present an effective technique for culture and expansion of Schwann cells (SC) from adult peripheral nerves. Cultures from adult mouse sciatic nerves (one to six nerves per culture) in defined medium showed markedly higher purity and density of SC when the nerve was predegenerated in vivo for 7 days than when it was harvested fresh. SC from degenerated nerves were then cultured in defined media conditioned by primary cultures of adult SC. The best results were obtained with a conditioned medium supplemented with 1% fetal calf serum. In these conditions the purity of SC was about 90% and the density about 190 cell/mm(2) by 7-10 days in vitro. These findings indicate that adult SC can be expanded from small preinjured nerve fragments in a short time period to provide a source of SC for autologous cellular transplants.

Transplantation options for therapeutic central nervous system remyelination

Persistent demyelination, in addition to being the major pathology of multiple sclerosis and the leucodystrophies, is also a feature of spinal cord trauma where there is evidence that it contributes to the functional deficit. In experimental animals it is possible to remyelinate demyelinated CNS axons by transplanting cultures containing central or peripheral myelinogenic cells. Using functional testing we have been able to show that transplant-mediated remyelination results in restoration of function lost as a consequence of demyelination. Glial cell transplantation may therefore provide a therapeutic strategy for remyelinating areas of chronic demyelination. This article reviews issues that have to be addressed before glial transplantation can be undertaken in humans. These include: what cells to use, where would the cells come from, and can we predict how much remyelination will be achieved? It concludes that the most promising approach will be to use neural multipotential stem cells isolated from embryonic CNS, expanded in vitro as neurospheres and then committed to oligodendrocyte lineage differentiation prior to implantation. However, even with such preparations, which have considerable myelinating potential, the extent of remyelination that will be achieved cannot currently be predicted with any degree of certainty.

Nerve guides seeded with autologous schwann cells improve nerve regeneration

This study evaluates the ability of Schwann cells (SCs) transplanted into a nerve guide to improve regeneration and reinnervation after sciatic nerve resection and repair, leaving a 6-mm gap, in the mouse. SCs were isolated from predegenerated adult sciatic nerves and expanded in culture using a chemically defined medium. Syngeneic, isogeneic, and autologous SCs were suspended in Matrigel and seeded in resorbable, permeable poly(l-lactide-co-epsilon-caprolactone) guides at 150,000 cells/tube. Guides containing SCs were compared to guides filled with Matrigel alone and with peroneal nerve autografts. Functional reinnervation was assessed by noninvasive methods to determine recovery of sweating, nociceptive, sensory, and motor functions in the hindpaw during 4 months postoperation. Morphological analysis of the regenerated nerves was performed at the end of follow-up. The group with an autograft achieved faster and higher levels of reinnervation and higher number of regenerated myelinated fibers than groups repaired by tubulization. The immunogenicity of transplanted SCs influenced the outcome of nerve regeneration. Transplants of autologous SCs resulted in slightly lower levels of reinnervation than autografts, but higher recovery and number of regenerated fibers reaching the distal nerve than transplants of isologous and syngeneic SCs, although most of the differences were not statistically significant. Syngeneic SCs did not improve regeneration with respect to acellular guides. Prelabeled transplanted SCs were found to survive into the guide 1-3 months after implantation, to a larger number when they were autologous than syngeneic. Cellular prostheses composed of a resorbable guide seeded with autologous SCs appear as an alternative for repairing long gaps in injured nerves, approaching the success of autografts.

Isolation and serum-free culture of primary Schwann cells from human fetal peripheral nerve

We have developed a method for isolating Schwann cells (SC) from human fetal peripheral nerve and maintaining these SC in vitro under serum-free conditions. This method yields essentially pure SC which have a bipolar, spindle-shaped morphology; align in fascicles; and express typical glial cell markers. Human fetal SC can be maintained for months under serum-free conditions with the neuregulin NDF beta. These human fetal SC can mimic axonal contact in vivo by retaining the functional capacity to strongly associate with neurites of cultured human fetal dorsal root ganglia. These isolation, culture, and coculture techniques provide a method for investigating SC-neuron interactions as well as development and function of human fetal SC.

The levels of leukemia inhibitory factor mRNA in a Schwann cell line are regulated by multiple second messenger pathways

Axotomy of sympathetic and sensory neurons leads to changes in their neuropeptide phenotypes. These changes are mediated in part by the induction of leukemia inhibitory factor (LIF) by nonneuronal cells. In the present study, we identified satellite/Schwann cells as a possible source of the injury-induced LIF. Using a Schwann cell line, SC-1 cells, we examined mechanisms of LIF induction. LIF mRNA levels increased rapidly when the cells were treated with 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate, phorbol 12-myristate 13-acetate (PMA), or A23187. Among these reagents, PMA was the most efficacious. Inhibition of protein kinase C (PKC) by GF-1 09203X significantly reduced the PMA-induced LIF mRNA levels. As PKC is known to activate the extracellular signal-regulated kinase (ERK) signaling pathway, the involvement of this pathway in the PMA-stimulated induction of LIF mRNA was examined. Phosphorylation of ERKs was increased following PMA treatment in SC-1 cells. Moreover, inhibition of ERK kinase activity by PD98059 dramatically reduced PMA-stimulated phosphorylation of ERKs and induction of LIF mRNA. These results indicate that LIF mRNA levels can be regulated by ERK activation via stimulation of PKC in Schwann cells.