Sensory recovery after cell therapy in peripheral nerve repair: effects of naïve and skin precursor-derived Schwann cells

Hybrid construction of tissue-engineered nerve graft using skin derived precursors induced neurons and Schwann cells to enhance peripheral neuroregeneration

Peripheral nerve injury is a major challenge in clinical treatment due to the limited intrinsic capacity for nerve regeneration. Tissue engineering approaches offer promising solutions by providing biomimetic scaffolds and cell sources to promote nerve regeneration. In the present work, we investigated the potential role of skin-derived progenitors (SKPs), which are induced into neurons and Schwann cells (SCs), and their extracellular matrix in tissue-engineered nerve grafts (TENGs) to enhance peripheral neuroregeneration. SKPs were induced to differentiate into neurons and SCs in vitro and incorporated into nerve grafts composed of a biocompatible scaffold including chitosan neural conduit and silk fibroin filaments. In vivo experiments using a rat model of peripheral nerve injury showed that TENGs significantly enhanced nerve regeneration compared to the scaffold control group, catching up with the autograft group. Histological analysis showed improved axonal regrowth, myelination and functional recovery in animals treated with these TENGs. In addition, immunohistochemical staining confirmed the presence of induced neurons and SCs within the regenerated nerve tissue. Our results suggest that SKP-induced neurons and SCs in tissue-engineered nerve grafts have great potential for promoting peripheral nerve regeneration and represent a promising approach for clinical translation in the treatment of peripheral nerve injury. Further optimization and characterization of these engineered constructs is warranted to improve their clinical applicability and efficacy.

Advances of Schwann cells in peripheral nerve regeneration: From mechanism to cell therapy

Peripheral nerve injuries (PNIs) frequently occur due to various factors, including mechanical trauma such as accidents or tool-related incidents, as well as complications arising from diseases like tumor resection. These injuries frequently result in persistent numbness, impaired motor and sensory functions, neuropathic pain, or even paralysis, which can impose a significant financial burden on patients due to outcomes that often fall short of expectations. The most frequently employed clinical treatment for PNIs involves either direct sutures of the severed ends or bridging the proximal and distal stumps using autologous nerve grafts. However, autologous nerve transplantation may result in sensory and motor functional loss at the donor site, as well as neuroma formation and scarring. Transplantation of Schwann cells/Schwann cell-like cells has emerged as a promising cellular therapy to reconstruct the microenvironment and facilitate peripheral nerve regeneration. In this review, we summarize the role of Schwann cells and recent advances in Schwann cell therapy in peripheral nerve regeneration. We summarize current techniques used in cell therapy, including cell injection, 3D-printed scaffolds for cell delivery, cell encapsulation techniques, as well as the cell types employed in experiments, experimental models, and research findings. At the end of the paper, we summarize the challenges and advantages of various cells (including ESCs, iPSCs, and BMSCs) in clinical cell therapy. Our goal is to provide the theoretical and experimental basis for future treatments targeting peripheral nerves, highlighting the potential of cell therapy and tissue engineering as invaluable resources for promoting nerve regeneration.

Hallmarks of peripheral nerve injury and regeneration

Peripheral nerves are functional networks in the body. Disruption of these networks induces varied functional consequences depending on the types of nerves and organs affected. Despite the advances in microsurgical repair and understanding of nerve regeneration biology, restoring full functions after severe traumatic nerve injuries is still far from achieved. While a blunted growth response from axons and errors in axon guidance due to physical barriers may surface as the major hurdles in repairing nerves, critical additional cellular and molecular aspects challenge the orderly healing of injured nerves. Understanding the systematic reprogramming of injured nerves at the cellular and molecular levels, referred to here as "hallmarks of nerve injury regeneration," will offer better ideas. This chapter discusses the hallmarks of nerve injury and regeneration and critical points of failures in the natural healing process. Potential pharmacological and nonpharmacological intervention points for repairing nerves are also discussed.

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.

The Effect of Schwann Cells/Schwann Cell-Like Cells on Cell Therapy for Peripheral Neuropathy

Peripheral neuropathy is a common neurological issue that leads to sensory and motor disorders. Over time, the treatment for peripheral neuropathy has primarily focused on medications for specific symptoms and surgical techniques. Despite the different advantages of these treatments, functional recovery remains less than ideal. Schwann cells, as the primary glial cells in the peripheral nervous system, play crucial roles in physiological and pathological conditions by maintaining nerve structure and functions and secreting various signaling molecules and neurotrophic factors to support both axonal growth and myelination. In addition, stem cells, including mesenchymal stromal cells, skin precursor cells and neural stem cells, have the potential to differentiate into Schwann-like cells to perform similar functions as Schwann cells. Therefore, accumulating evidence indicates that Schwann cell transplantation plays a crucial role in the resolution of peripheral neuropathy. In this review, we summarize the literature regarding the use of Schwann cell/Schwann cell-like cell transplantation for different peripheral neuropathies and the potential role of promoting nerve repair and functional recovery. Finally, we discuss the limitations and challenges of Schwann cell/Schwann cell-like cell transplantation in future clinical applications. Together, these studies provide insights into the effect of Schwann cells/Schwann cell-like cells on cell therapy and uncover prospective therapeutic strategies for peripheral neuropathy.

Brachial plexus bridging with specific extracellular matrix modified chitosan/silk scaffold: a new expand of tissue engineered nerve graft

OBJECTIVE

Brachial plexus injuries result in serious dysfunction and are currently treated using autologous nerve graft (autograft) transplantation. With the development of tissue engineering, tissue engineered nerve grafts (TENGs) have emerged as promising alternatives to autografts but have not yet been widely applied to the treatment of brachial plexus injuries. Herein, we developed a TENG modified with extracellular matrix (ECM) generated by skin-derived precursor Schwann cells (SKP-SCs) and expand its application in upper brachial plexus defects in rats.

APPROACH

SKP-SCs were co-cultured with chitosan neural conduits or silk fibres and subjected to decellularization treatment. Ten bundles of silk fibres (five fibres per bundle) were placed into a conduit to obtain the TENG, which was used to bridge an 8 mm gap in the upper brachial plexus. The efficacy of this treatment was examined for TENG-, autograft- and scaffold-treated groups at several times after surgery using immunochemical staining, behavioural tests, electrophysiological measurements, and electron microscopy.

MAIN RESULTS

Histological analysis conducted two weeks after surgery showed that compared to scaffold bridging, TENG treatment enhanced the growth of regenerating axons. Behavioural tests conducted four weeks after surgery showed that TENG-treated rats performed similarly to autograft-treated ones, with a significant improvement observed in both cases compared with the scaffold treatment group. Electrophysiological and retrograde tracing characterisations revealed that the target muscles were reinnervated in both TENG and autograft groups, while transmission electron microscopy and immunohistochemical staining showed the occurrence of the superior myelination of regenerated axons in these groups.

SIGNIFICANCE

Treatment with the developed TENG allows the effective bridging of proximal nerve defects in the upper extremities, and the obtained results provide a theoretical basis for clinical transformation to expand the application scope of TENGs.

Peripheral Nerve Regeneration Using Different Germ Layer-Derived Adult Stem Cells in the Past Decade

Peripheral nerve injuries (PNIs) are some of the most common types of traumatic lesions affecting the nervous system. Although the peripheral nervous system has a higher regenerative ability than the central nervous system, delayed treatment is associated with disturbances in both distal sensory and functional abilities. Over the past decades, adult stem cell-based therapies for peripheral nerve injuries have drawn attention from researchers. This is because various stem cells can promote regeneration after peripheral nerve injuries by differentiating into neural-line cells, secreting various neurotrophic factors, and regulating the activity of in situ Schwann cells (SCs). This article reviewed research from the past 10 years on the role of stem cells in the repair of PNIs. We concluded that adult stem cell-based therapies promote the regeneration of PNI in various ways.

Improvement of sensory neuron growth and survival via negatively regulating PTEN by miR-21-5p-contained small extracellular vesicles from skin precursor-derived Schwann cells

Background

Patients with peripheral nerve injury (PNI) often suffer from hypoxic ischemic impairments, in particular when combined with vascular damage, causing neuronal dysfunction and death. Increasing attention has been paid on skin precursor-derived Schwann cells (SKP-SCs), and previous study has shown that SKP-SCs could promote sensory recovery after cell therapy for PNI, resembling the effect of naive SCs, and SKP-SC-derived extracellular vesicles (SKP-SC-EVs) are putatively supposed to be promising therapeutic agents for neural regeneration.

Methods

SKPs were induced to differentiate towards SCs with cocktail factors (N2, neuregulin-1β, and forskolin) in vitro. SKP-SC-EVs were isolated by exoEasy Maxi Kit and characterized by morphology and phenotypic markers of EVs. Rat sensory neurons from dorsal root ganglions (DRGs) were primarily cultured in regular condition or exposed to oxygen-glucose-deprivation (OGD) condition. SKP-SC-EVs were applied to DRGs or sensory neurons, with LY294002 (a PI3K inhibitor) added; the effect on neurite outgrowth and cell survival was observed. Moreover, microRNA (miR) candidate contained in SKP-SC-EVs was screened out, and miR-mimics were transfected into DRG neurons; meanwhile, the negative regulation of PTEN/PI3K/Akt axis and downstream signaling molecules were determined.

Results

It was shown that SKP-SC-EVs could improve the neurite outgrowth of DRGs and sensory neurons. Furthermore, SKP-SC-EVs enhanced the survival of sensory neurons after OGD exposure by alleviating neuronal apoptosis and strengthening cell viability, and the expression of GAP43 (a neuron functional protein) in neurons was upregulated. Moreover, the neuro-reparative role of SKP-SC-EVs was implicated in the activation of PI3K/Akt, mTOR, and p70S6k, as well as the reduction of Bax/Bcl-2 ratio, that was compromised by LY294002 to some extent. In addition, transferring miR-21-5p mimics into sensory neurons could partly protect them from OGD-induced impairment.

Conclusions

Sum up, SKP-SC-EVs could improve neurite outgrowth of DRG sensory neurons in physiological and pathological condition. Moreover, the in vitro therapeutic potential of SKP-SC-EVs on the survival and restoration of OGD-injured sensory neurons was evidenced to be associated with miR-21-5p contained in the small EVs and miR-21-5p/PTEN/PI3K/Akt axis.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-020-02125-4.

Insights Into the Role and Potential of Schwann Cells for Peripheral Nerve Repair From Studies of Development and Injury

Peripheral nerve injuries arising from trauma or disease can lead to sensory and motor deficits and neuropathic pain. Despite the purported ability of the peripheral nerve to self-repair, lifelong disability is common. New molecular and cellular insights have begun to reveal why the peripheral nerve has limited repair capacity. The peripheral nerve is primarily comprised of axons and Schwann cells, the supporting glial cells that produce myelin to facilitate the rapid conduction of electrical impulses. Schwann cells are required for successful nerve regeneration; they partially “de-differentiate” in response to injury, re-initiating the expression of developmental genes that support nerve repair. However, Schwann cell dysfunction, which occurs in chronic nerve injury, disease, and aging, limits their capacity to support endogenous repair, worsening patient outcomes. Cell replacement-based therapeutic approaches using exogenous Schwann cells could be curative, but not all Schwann cells have a “repair” phenotype, defined as the ability to promote axonal growth, maintain a proliferative phenotype, and remyelinate axons. Two cell replacement strategies are being championed for peripheral nerve repair: prospective isolation of “repair” Schwann cells for autologous cell transplants, which is hampered by supply challenges, and directed differentiation of pluripotent stem cells or lineage conversion of accessible somatic cells to induced Schwann cells, with the potential of “unlimited” supply. All approaches require a solid understanding of the molecular mechanisms guiding Schwann cell development and the repair phenotype, which we review herein. Together these studies provide essential context for current efforts to design glial cell-based therapies for peripheral nerve regeneration.

Advances and clinical challenges for translating nerve conduit technology from bench to bed side for peripheral nerve repair

Injuries to the peripheral nervous system remain a large-scale clinical problem. These injuries often lead to loss of motor and/or sensory function that significantly affects patients' quality of life. The current neurosurgical approach for peripheral nerve repair involves autologous nerve transplantation, which often leads to clinical complications. The most pressing need is to increase the regenerative capacity of existing tubular constructs in the repair of large nerve gaps through development of tissue-engineered approaches that can surpass the performance of autografts. To fully realize the clinical potential of nerve conduit technology, there is a need to reconsider design strategies, biomaterial selection, fabrication techniques and the various potential modifications to optimize a conduit microenvironment that can best mimic the natural process of regeneration. In recent years, a significant progress has been made in the designing and functionality of bioengineered nerve conduits to bridge long peripheral nerve gaps in various animal models. However, translation of this work from lab to commercial scale has not been achieve. The current review summarizes recent advances in the development of tissue engineered nerve guidance conduits (NGCs) with regard to choice of material, novel fabrication methods, surface modifications and regenerative cues such as stem cells and growth factors to improve regeneration performance. Also, the current clinical potential and future perspectives to achieve therapeutic benefits of NGCs will be discussed in context of peripheral nerve regeneration.

Repair strategies for injured peripheral nerve: Review

Compromised functional regains in about half of the patients following surgical nerve repair pose a serious socioeconomic burden to the society. Although surgical strategies such as end-to-end neurorrhaphy, nerve grafting and nerve transfer are widely applied in distal injuries leading to optimal recovery; however in proximal nerve defects functional outcomes remain unsatisfactory. Biomedical engineering approaches unite the efforts of the surgeons, engineers and biologists to develop regeneration facilitating structures such as extracellular matrix based supportive polymers and tubular nerve guidance channels. Such polymeric structures provide neurotrophic support from injured nerve stumps, retard the fibrous tissue infiltration and guide regenerating axons to appropriate targets. The development and application of nerve guidance conduits (NGCs) to treat nerve gap injuries offer clinically relevant and feasible solutions. Enhanced understanding of the nerve regeneration processes and advances in NGCs design, polymers and fabrication strategies have led to developing modern NGCs with superior regeneration-conducive capacities. Current review focuses on the advances in surgical and engineering approaches to treat peripheral nerve injuries. We suggest the incorporation of endothelial cell growth promoting cues and factors into the NGC interior for its possible enhancement effects on the axonal regeneration process that may result in substantial functional outcomes.

Adult tissue-derived neural crest-like stem cells: Sources, regulatory networks, and translational potential

Neural crest (NC) cells are a multipotent stem cell population that give rise to a diverse array of cell types in the body, including peripheral neurons, Schwann cells (SC), craniofacial cartilage and bone, smooth muscle cells, and melanocytes. NC formation and differentiation into specific lineages takes place in response to a set of highly regulated signaling and transcriptional events within the neural plate border. Premigratory NC cells initially are contained within the dorsal neural tube from which they subsequently emigrate, migrating to often distant sites in the periphery. Following their migration and differentiation, some NC‐like cells persist in adult tissues in a nascent multipotent state, making them potential candidates for autologous cell therapy. This review discusses the gene regulatory network responsible for NC development and maintenance of multipotency. We summarize the genes and signaling pathways that have been implicated in the differentiation of a postmigratory NC into mature myelinating SC. We elaborate on the signals and transcription factors involved in the acquisition of immature SC fate, axonal sorting of unmyelinated neuronal axons, and finally the path toward mature myelinating SC, which envelope axons within myelin sheaths, facilitating electrical signal propagation. The gene regulatory events guiding development of SC in vivo provides insights into means for differentiating NC‐like cells from adult human tissues into functional SC, which have the potential to provide autologous cell sources for the treatment of demyelinating and neurodegenerative disorders.

BMP-7/Smad expression in dedifferentiated Schwann cells during axonal regeneration and upregulation of endogenous BMP-7 following administration of PTH (1-34)

PURPOSE:

To determine the expression and distribution of bone morphogenetic protein (BMP)-7 and related molecules during peripheral nerve regeneration and to assess whether administration of parathyroid hormone (PTH) drug (1-34) potentiates the intrinsic upregulation of BMP-7/Smad signaling.

METHODS:

The rat sciatic nerves were crushed with an aneurysm clip resulting in axonal degeneration. In the normal nerve, and at 1, 2, 4, and 8 weeks after injury, BMP-7, BMP receptors, p-Smad 1/5/8, and Noggin, the endogenous BMP antagonist, were evaluated. Additionally, the distribution of BMP-7 was assessed by fluorescent double immunostaining. In vitro studies were also performed to examine the effect of BMP-7 and PTH (1-34) administration on rat Schwann cells (SCs).

RESULTS:

Aneurysm clip made reliable animal model of the nerve injury with recovery at 8 weeks after the injury. BMP-7/Smad protein and mRNA were significantly upregulated on axon-SCs units at 1 week after injury, and this upregulated expression was maintained for 4 weeks. Besides, significant upregulation of Noggin's expression was observed on axon-SCs units at 2 weeks after injury. Moreover, fluorescent double immunostaining showed co-localization between expression of BMP-7 and p75NTR during axonal regeneration. In the in vitro study, administration of BMP-7 induced significant proliferation of SCs. Application of PTH (1-34) upregulated BMP-7 on SCs.

DISCUSSION/CONCLUSION:

BMPs were reported to be involved in protection and recovery after injury as well as in neurogenesis. Our current study showed that BMP/Smad signaling molecules were upregulated on dedifferentiated SCs after peripheral nerve injury and that administration of BMP-7 increased SC viability in vitro. These results suggested that axonal regeneration could be induced via upregulation of endogenous BMP-7 on SCs by PTH (1-34) administration.

Advances in stem cell treatment for sciatic nerve injury

INTRODUCTION

The sciatic nerve is one of the peripheral nerves that is most prone to injuries. After injury, the connection between the nervous system and the distal organs is disrupted, and delayed treatment results in distal organ atrophy and total disability. Regardless of great advances in the fields of neurosurgery, biological sciences, and regenerative medicine, total functional recovery is yet to be achieved.

AREAS COVERED

Cell-based therapy for the treatment of peripheral nerve injuries (PNIs) has brought a new perspective to the field of regenerative medicine. Having the ability to differentiate into neural and glial cells, stem cells enhance neural regeneration after PNIs. Augmenting axonal regeneration, remyelination, and muscle mass preservation are the main mechanisms underlying stem cells' beneficial effects on neural regeneration.

EXPERT OPINION

Despite the usefulness of employing stem cells for the treatment of PNIs in pre-clinical settings, further assessments are still needed in order to translate this approach into clinical settings. Mesenchymal stem cells, especially adipose-derived stem cells, with the ability of autologous transplantation, as well as easy harvesting procedures, are speculated to be the most promising source to be used in the treatment of PNIs.

Comparison of phenotypes and transcriptomes of mouse skin-derived precursors and dermal mesenchymal stem cells

Both skin-derived precursors (SKPs) and dermal mesenchymal stem cells (dMSCs) are promising candidates for cellular therapy and regenerative medicine. To date the comparison of phenotypes and transcriptomes of mouse SKPs (mSKPs) and dMSCs has never been reported. Here we characterized and compared the biological properties and transcriptomes of mSKP and dMSCs from the same mouse dermis sample. Firstly, we analyzed mSKPs and dMSCs by use of immunocytochemistry, cell cycle analysis, and CD antigen expression. Then we conducted the osteogenic, adipogenic, and chondrogenic induced differentiation for both cell types. Lastly, we compared their genomic profiles by RNA-sequencing (RNA-Seq), and verified the results of RNA-Seq by quantitative real time reverse transcription PCR (qRT-PCR). The results suggested that mSKPs and dMSCs shared similarities in certain positive stem cells markers expression, but demonstrated difference in Nanog and Oct4 expression. mSKPs and dMSCs demonstrated similar cell cycle distribution and CD antigen expression. Both types of cells could be induced differentiated into osteocytes, adipocytes, and chondrocytes. However, RNA-Seq and qRT-PCR results indicated that mSKPs and dMSCs had distinct transcriptome profiles. The majority of enriched differentially expressed genes (DEGs) from mSKPs was immune-related, while the majority of enriched DEGs from dMSCs was differentiation/development/disease-related. Transcriptome profiles suggested that mSKPs and dMSCs might have potential usage in the relevant morbidity management. These results may indicate a molecular basis for novel stem cell-based therapeutic strategies.

Schwann cells and mesenchymal stem cells in laminin- or fibronectin-aligned matrices and regeneration across a critical size defect of 15 mm in the rat sciatic nerve

OBJECTIVE

Artificial nerve guides are being developed to substitute for autograft repair after peripheral nerve injuries. However, the use of conduits is limited by the length of the gap that needs to be bridged, with the success of regeneration highly compromised in long gaps. Addition of aligned proregenerative cells and extracellular matrix (ECM) components inside the conduit can be a good strategy to achieve artificial grafts that recreate the natural environment offered by a nerve graft. The purpose of this study was to functionalize chitosan devices with different cell types to support regeneration in limiting gaps in the rat peripheral nerve.

METHODS

The authors used chitosan devices combined with proteins of the ECM and cells in a rat model of sciatic nerve injury. Combinations of fibronectin and laminin with mesenchymal stem cells (MSCs) or Schwann cells (SCs) were aligned within tethered collagen-based gels, which were placed inside chitosan tubes that were then used to repair a critical-size gap of 15 mm in the rat sciatic nerve. Electrophysiology and algesimetry tests were performed to analyze functional recovery during the 4 months after injury and repair. Histological analysis was performed at the midlevel and distal level of the tubes to assess the number of regenerated myelinated fibers.

RESULTS

Functional analysis demonstrated that SC-aligned scaffolds resulted in 100% regeneration success in a 15-mm nerve defect in this rat model. In contrast, animals that underwent repair with MSC-aligned constructs had only 90% regeneration success, and those implanted with acellular bridges had only 75% regeneration success.

CONCLUSIONS

These results indicate that the combination of chitosan conduits with ECM-enriched cellular gels represents a good alternative to the use of autografts for repairing long nerve gaps.

Treatment of refractory epilepsy patients with autologous mesenchymal stem cells reduces seizure frequency: An open label study

PURPOSE

Existing anti-epileptic drugs (AED) have limited efficiency in many patients, necessitating the search for alternative approaches such as stem cell therapy. We report the use of autologous patient-derived mesenchymal stem cells (MSC) as a therapeutic agent in symptomatic drug-resistant epilepsy in a Phase I open label clinical trial (registered as NCT02497443).

PATIENTS AND METHODS

The patients received either standard treatment with AED (control group), or AED supplemented with single intravenous administration of undifferentiated autologous MSC (target dose of 1×10⁶cells/kg), followed by a single intrathecal injection of neurally induced autologous MSC (target dose of 0.1×10⁶cells/kg).

RESULTS

MSC injections were well tolerated and did not cause any severe adverse effects. Seizure frequency was designated as the main outcome and evaluated at 1 year time point. 3 out of 10 patients in MSC therapy group achieved remission (no seizures for one year and more), and 5 additional patients became responders to AEDs, while only 2 out of 12 patients became responders in control group (difference significant, P=0.0135).

CONCLUSIONS

MSC possess unique immunomodulatory properties and are a safe and promising candidate for cell therapy in AED resistant epilepsy patients.

Inter-microcarrier transfer and phenotypic stability of stem cell-derived Schwann cells in stirred suspension bioreactor culture

Emerging bioreactor technologies offer an effective way for scaled-up production of large numbers of cells for cell therapy applications. One of the clinical paradigms where cell therapy can be an asset is restorative neurosciences. Nerve repair can benefit from the injections of stem cells and/or Schwann cells, acting as a source for axon myelination, myelin debris clearance, and trophic support. We have adapted microcarrier-based suspension bioreactor culture for Schwann cells (SCs) differentiated from a new stem cell source - skin-derived precursors (SKPs). SKP-derived SCs attach and grow on different types of microcarriers in both static and stirred culture, with Cytodex 3 and CultiSpher-S found most effective. Inter-microcarrier migration of SKP-SCs represents a key mechanism for rapid expansion and colonization in stirred suspension culture. We have shown that microcarrier-expanded SKP-SCs cells express Schwann cell markers p75-NTR, GFAP and S100 and retain their key ability to myelinate axons both in vitro and in vivo. Scaled-up microcarrier-based production of SKP-SCs in suspension bioreactors appears feasible for timely generation of sufficient cell numbers for nerve repair strategies.

Concise Review: Human Dermis as an Autologous Source of Stem Cells for Tissue Engineering and Regenerative Medicine

The exciting potential for regenerating organs from autologous stem cells is on the near horizon, and adult dermis stem cells (DSCs) are particularly appealing because of the ease and relative minimal invasiveness of skin collection. A substantial number of reports have described DSCs and their potential for regenerating tissues from mesenchymal, ectodermal, and endodermal lineages; however, the exact niches of these stem cells in various skin types and their antigenic surface makeup are not yet clearly defined. The multilineage potential of DSCs appears to be similar, despite great variability in isolation and in vitro propagation methods. Despite this great potential, only limited amounts of tissues and clinical applications for organ regeneration have been developed from DSCs. This review summarizes the literature on DSCs regarding their niches and the specific markers they express. The concept of the niches and the differentiation capacity of cells residing in them along particular lineages is discussed. Furthermore, the advantages and disadvantages of widely used methods to demonstrate lineage differentiation are considered. In addition, safety considerations and the most recent advancements in the field of tissue engineering and regeneration using DSCs are discussed. This review concludes with thoughts on how to prospectively approach engineering of tissues and organ regeneration using DSCs. Our expectation is that implementation of the major points highlighted in this review will lead to major advancements in the fields of regenerative medicine and tissue engineering.

SIGNIFICANCE

Autologous dermis-derived stem cells are generating great excitement and efforts in the field of regenerative medicine and tissue engineering. The substantial impact of this review lies in its critical coverage of the available literature and in providing insight regarding niches, characteristics, and isolation methods of stem cells derived from the human dermis. Furthermore, it provides analysis of the current state-of-the-art regenerative approaches using human-derived dermal stem cells, with consideration of current guidelines, to assist translation toward therapeutic use.