Transplants of Encapsulated Rat Choroid Plexus Cells Exert Neuroprotection in a Rodent Model of Huntington's Disease

Cell Encapsulation and 3D Bioprinting for Therapeutic Cell Transplantation

The promise of cell therapy has been augmented by introducing biomaterials, where intricate scaffold shapes are fabricated to accommodate the cells within. In this review, we first discuss cell encapsulation and the promising potential of biomaterials to overcome challenges associated with cell therapy, particularly cellular function and longevity. More specifically, cell therapies in the context of autoimmune disorders, neurodegenerative diseases, and cancer are reviewed from the perspectives of preclinical findings as well as available clinical data. Next, techniques to fabricate cell-biomaterials constructs, focusing on emerging 3D bioprinting technologies, will be reviewed. 3D bioprinting is an advancing field that enables fabricating complex, interconnected, and consistent cell-based constructs capable of scaling up highly reproducible cell-biomaterials platforms with high precision. It is expected that 3D bioprinting devices will expand and become more precise, scalable, and appropriate for clinical manufacturing. Rather than one printer fits all, seeing more application-specific printer types, such as a bioprinter for bone tissue fabrication, which would be different from a bioprinter for skin tissue fabrication, is anticipated in the future.

Experimental approaches for manipulating choroid plexus epithelial cells

Choroid plexus (ChP) epithelial cells are crucial for the function of the blood-cerebrospinal fluid barrier (BCSFB) in the developing and mature brain. The ChP is considered the primary source and regulator of CSF, secreting many important factors that nourish the brain. It also performs CSF clearance functions including removing Amyloid beta and potassium. As such, the ChP is a promising target for gene and drug therapy for neurodevelopmental and neurological disorders in the central nervous system (CNS). This review describes the current successful and emerging experimental approaches for targeting ChP epithelial cells. We highlight methodological strategies to specifically target these cells for gain or loss of function in vivo. We cover both genetic models and viral gene delivery systems. Additionally, several lines of reporters to access the ChP epithelia are reviewed. Finally, we discuss exciting new approaches, such as chemical activation and transplantation of engineered ChP epithelial cells. We elaborate on fundamental functions of the ChP in secretion and clearance and outline experimental approaches paving the way to clinical applications.

Regulation of choroid plexus development and its functions

The choroid plexus (ChP) is an extensively vascularized tissue that protrudes into the brain ventricular system of all vertebrates. This highly specialized structure, consisting of the polarized epithelial sheet and underlying stroma, serves a spectrum of functions within the central nervous system (CNS), most notably the production of cerebrospinal fluid (CSF). The epithelial cells of the ChP have the competence to tightly modulate the biomolecule composition of CSF, which acts as a milieu functionally connecting ChP with other brain structures. This review aims to eloquently summarize the current knowledge about the development of ChP. We describe the mechanisms that control its early specification from roof plate followed by the formation of proliferative regions-cortical hem and rhombic lips-feeding later development of ChP. Next, we summarized the current knowledge on the maturation of ChP and mechanisms that control its morphological and cellular diversity. Furthermore, we attempted to review the currently available battery of molecular markers and mouse strains available for the research of ChP, and identified some technological shortcomings that must be overcome to accelerate the ChP research field. Overall, the central principle of this review is to highlight ChP as an intriguing and surprisingly poorly known structure that is vital for the development and function of the whole CNS. We believe that our summary will increase the interest in further studies of ChP that aim to describe the molecular and cellular principles guiding the development and function of this tissue.

Layer-by-Layer Cell Encapsulation for Drug Delivery: The History, Technique Basis, and Applications

The encapsulation of cells with various polyelectrolytes through layer-by-layer (LbL) has become a popular strategy in cellular function engineering. The technique sprang up in 1990s and obtained tremendous advances in multi-functionalized encapsulation of cells in recent years. This review comprehensively summarized the basis and applications in drug delivery by means of LbL cell encapsulation. To begin with, the concept and brief history of LbL and LbL cell encapsulation were introduced. Next, diverse types of materials, including naturally extracted and chemically synthesized, were exhibited, followed by a complicated basis of LbL assembly, such as interactions within multilayers, charge distribution, and films morphology. Furthermore, the review focused on the protective effects against adverse factors, and bioactive payloads incorporation could be realized via LbL cell encapsulation. Additionally, the payload delivery from cell encapsulation system could be adjusted by environment, redox, biological processes, and functional linkers to release payloads in controlled manners. In short, drug delivery via LbL cell encapsulation, which takes advantage of both cell grafts and drug activities, will be of great importance in basic research of cell science and biotherapy for various diseases.

Choroid plexus and the blood-cerebrospinal fluid barrier in disease

The choroid plexus (CP) forming the blood-cerebrospinal fluid (B-CSF) barrier is among the least studied structures of the central nervous system (CNS) despite its clinical importance. The CP is an epithelio-endothelial convolute comprising a highly vascularized stroma with fenestrated capillaries and a continuous lining of epithelial cells joined by apical tight junctions (TJs) that are crucial in forming the B-CSF barrier. Integrity of the CP is critical for maintaining brain homeostasis and B-CSF barrier permeability. Recent experimental and clinical research has uncovered the significance of the CP in the pathophysiology of various diseases affecting the CNS. The CP is involved in penetration of various pathogens into the CNS, as well as the development of neurodegenerative (e.g., Alzheimer´s disease) and autoimmune diseases (e.g., multiple sclerosis). Moreover, the CP was shown to be important for restoring brain homeostasis following stroke and trauma. In addition, new diagnostic methods and treatment of CP papilloma and carcinoma have recently been developed. This review describes and summarizes the current state of knowledge with regard to the roles of the CP and B-CSF barrier in the pathophysiology of various types of CNS diseases and sets up the foundation for further avenues of research.

Biomaterials for Personalized Cell Therapy

Cell therapy has already had an important impact on healthcare and provided new treatments for previously intractable diseases. Notable examples include mesenchymal stem cells for tissue regeneration, islet transplantation for diabetes treatment, and T cell delivery for cancer immunotherapy. Biomaterials have the potential to extend the therapeutic impact of cell therapies by serving as carriers that provide 3D organization and support cell viability and function. With the growing emphasis on personalized medicine, cell therapies hold great potential for their ability to sense and respond to the biology of an individual patient. These therapies can be further personalized through the use of patient-specific cells or with precision biomaterials to guide cellular activity in response to the needs of each patient. Here, the role of biomaterials for applications in tissue regeneration, therapeutic protein delivery, and cancer immunotherapy is reviewed, with a focus on progress in engineering material properties and functionalities for personalized cell therapies.

Cell encapsulation: Overcoming barriers in cell transplantation in diabetes and beyond

Cell-based therapy is emerging as a promising strategy for treating a wide range of human diseases, such as diabetes, blood disorders, acute liver failure, spinal cord injury, and several types of cancer. Pancreatic islets, blood cells, hepatocytes, and stem cells are among the many cell types currently used for this strategy. The encapsulation of these "therapeutic" cells is under intense investigation to not only prevent immune rejection but also provide a controlled and supportive environment so they can function effectively. Some of the advanced encapsulation systems provide active agents to the cells and enable a complete retrieval of the graft in the case of an adverse body reaction. Here, we review various encapsulation strategies developed in academic and industrial settings, including the state-of-the-art technologies in advanced preclinical phases as well as those undergoing clinical trials, and assess their advantages and challenges. We also emphasize the importance of stimulus-responsive encapsulated cell systems that provide a "smart and live" therapeutic delivery to overcome barriers in cell transplantation as well as their use in patients.

Stem cell therapy for neurological disorders: A focus on aging

Age-related neurological disorders continue to pose a significant societal and economic burden. Aging is a complex phenomenon that affects many aspects of the human body. Specifically, aging can have detrimental effects on the progression of brain diseases and endogenous stem cells. Stem cell therapies possess promising potential to mitigate the neurological symptoms of such diseases. However, aging presents a major obstacle for maximum efficacy of these treatments. In this review, we discuss current preclinical and clinical literature to highlight the interactions between aging, stem cell therapy, and the progression of major neurological disease states such as Parkinson's disease, Huntington's disease, stroke, traumatic brain injury, amyotrophic lateral sclerosis, multiple sclerosis, and multiple system atrophy. We raise important questions to guide future research and advance novel treatment options.

An update on intracerebral stem cell grafts

INTRODUCTION

Primary neurological disorders are notoriously debilitating and deadly, and over the past four decades stem cell therapy has emerged as a promising treatment. Translation of stem cell therapies from the bench to the clinic requires a better understanding of delivery protocols, safety profile, and efficacy in each disease. Areas covered: In this review, benefits and risks of intracerebral stem cell transplantation are presented for consideration. Milestone discoveries in stem cell applications are reviewed to examine the efficacy and safety of intracerebral stem cell transplant therapy for disorders of the central nervous system and inform design of translatable protocols for clinically feasible stem cell-based treatments. Expert commentary: Intracerebral administration, compared to peripheral delivery, is more invasive and carries the risk of open brain surgery. However, direct cell implantation bypasses the blood-brain barrier and reduces the first-pass effect, effectively increasing the therapeutic cell deposition at its intended site of action. These benefits must be weighed with the risk of graft-versus-host immune response. Rigorous clinical trials are underway to assess the safety and efficacy of intracerebral transplants, and if successful will lead to widely available stem cell therapies for neurologic diseases in the coming years.

Transplantation of choroid plexus epithelial cells into contusion-injured spinal cord of rats

Purpose: The effect of the transplantation of choroid plexus epithelial cells (CPECs) on locomotor improvement and tissue repair including axonal extension in spinal cord lesions was examined in rats with spinal cord injury (SCI).

Methods: CPECs were cultured from the choroid plexus of green fluorescent protein (GFP)-transgenic rats, and transplanted directly into the contusion-injured spinal cord lesions of rats of the same strain. Locomotor behaviors were evaluated based on BBB scores every week after transplantation until 4 weeks after transplantation. Histological and immunohistochemical examinations were performed at 2 days, and every week until 5 weeks after transplantation.

Results: Locomotor behaviors evaluated by the BBB score were significantly improved in cell-transplanted rats. Numerous axons grew, with occasional interactions with CPECs, through the astrocyte-devoid areas. These axons exhibited structural characteristics of peripheral nerves. GAP-43-positive axons were found at the border of the lesion 2 days after transplantation. Cavity formation was more reduced in cell-transplanted than control spinal cords. CPECs were found within the spinal cord lesion, and sometimes in association with astrocytes at the border of the lesion until 2 weeks after transplantation.

Conclusion: The transplantation of CPECs enhanced locomotor improvement and tissue recovery, including axonal regeneration, in rats with SCI.

Primary Choroid Plexus Tissue for Use in Cellular Therapy

The choroid plexus (CP) has been explored as a cellular therapeutic due to its broad-ranging secretome and demonstrated longevity in a variety of encapsulation modalities. While the CP organ is normally involved in disease repair processes in the brain, the range of indications that could potentially be ameliorated with exogenous CP therapy is widespread, including diseases of the central nervous system, hearing loss, chronic wounds, and others. The CP can be isolated from animal sources and digested into a highly purified epithelial culture that can withstand encapsulation and transplantation. Its epithelium can adapt to different microenvironments, and depending on culture conditions, can be manipulated into various three-dimensional configurations with distinct gene expression profiles. The cocktail of proteins secreted by the CP can be harvested in culture, and purified forms of these extracts have been evaluated in topical applications to treat poorly healing wounds. When encapsulated, the epithelial clusters can be maintained for extended durations in vitro with minimal impact on potency. A treatment for Parkinson's disease utilizing encapsulated porcine CP has been developed and is currently being evaluated in a Phase I clinical trial. The current chapter serves to summarize recent experience with CP factor delivery, and provides a description of the relevant materials and methods employed in these studies.

Safety and tolerability of silk fibroin hydrogels implanted into the mouse brain

At present, effective therapies to repair the central nervous system do not exist. Biomaterials might represent a new frontier for the development of neurorestorative therapies after brain injury and degeneration. In this study, an in situ gelling silk fibroin hydrogel was developed via the sonication-induced gelation of regenerated silk fibroin solutions. An adequate timeframe for the integration of the biomaterial into the brain tissue was obtained by controlling the intensity and time of sonication. After the intrastriatal injection of silk fibroin the inflammation and cell death in the implantation area were transient. We did not detect considerable cognitive or sensorimotor deficits, either as examined by different behavioral tests or an electrophysiological analysis. The sleep and wakefulness states studied by chronic electroencephalogram recordings and the fitness of thalamocortical projections and the somatosensory cortex explored by evoked potentials were in the range of normality. The methodology used in this study might serve to assess the biological safety of other biomaterials implanted into the rodent brain. Our study highlights the biocompatibility of native silk with brain tissue and extends the current dogma of the innocuousness of this biomaterial for therapeutic applications, which has repercussion in regenerative neuroscience.

STATEMENT OF SIGNIFICANCE

The increasingly use of sophisticated biomaterials to encapsulate stem cells has changed the comprehensive overview of potential strategies for repairing the nervous system. Silk fibroin (SF) meets with most of the standards of a biomaterial suitable to enhance stem cell survival and function. However, a proof-of-principle of the in vivo safety and tolerability of SF implanted into the brain tissue is needed. In this study we have examined the tissue bioresponse and brain function after implantation of SF hydrogels. We have demonstrated the benign coexistence of silk with the complex neuronal circuitry that governs sensorimotor coordination and mechanisms such as learning and memory. Our results have repercussion in the development of advances strategies using this biomaterial in regenerative neuroscience.

A Neuroprotective Sericin Hydrogel As an Effective Neuronal Cell Carrier for the Repair of Ischemic Stroke

Ischemic stroke causes extensive cellular loss that impairs brain functions, resulting in severe disabilities. No effective treatments are currently available for brain tissue regeneration. The need to develop effective therapeutic approaches for treating stroke is compelling. A tissue engineering approach employing a hydrogel carrying both cells and neurotrophic cytokines to damaged regions is an encouraging alternative for neuronal repair. However, this approach is often challenged by low in vivo cell survival rate, and low encapsulation efficiency and loss of cytokines. To address these limitations, we propose to develop a biomaterial that can form a matrix capable of improving in vivo survival of transplanted cells and reducing in vivo loss of cytokines. Here, we report that using sericin, a natural protein from silk, we have fabricated a genipin-cross-linked sericin hydrogel (GSH) with porous structure and mild swelling ratio. The GSH supports the effective attachment and growth of neurons in vitro. Strikingly, our data reveal that sericin protein is intrinsically neurotrophic and neuroprotective, promoting axon extension and branching as well as preventing primary neurons from hypoxia-induced cell death. Notably, these functions are inherited by the GSH's degradation products, which might spare a need of incorporating costly cytokines. We further demonstrate that this neurotrophic effect is dependent on the Lkb1-Nuak1 pathway, while the neuroprotective effect is realized through regulating the Bcl-2/Bax protein ratio. Importantly, when transplanted in vivo, the GSH gives a high cell survival rate and allows the cells to continuously proliferate. Together, this work unmasks the neurotrophic and neuroprotective functions for sericin and provides strong evidence justifying the GSH's suitability as a potential neuronal cell delivery vehicle for ischemic stroke repair.

Construction of a novel inducing system with multi-layered alginate microcapsules to regulate differentiation of neural precursor cells from bone mesenchymal stem cells

Neural precursor cells (NPCs) are a promising cell source for the treatment of nervous system diseases; however, they are limited in their applications due to source-related ethical considerations or legislations. Therefore, a novel approach is necessary to obtain sufficient NPCs. Recently, the usage of bone marrow-derived mesenchymal stem cells (BMSCs) differentiated into neural cells has become a potential method to obtain NPCs. Moreover, growth factors (GFs) are emerging as inducers to evoke the differentiation of BMSCs into NPCs. For example, GFs may activate various signaling pathways related to neural differentiation, such as phosphatidylinositol 3 kinase/protein kinase B, cyclic adenosine monophosphate/protein kinase A, and Janus kinase/signal transducer activator of transcription. However, the utilization of growth factors still has some limitations such as high costs and low rates of neural differentiation. Neuroblastoma cells have been characterized as a potential pool for growth factors. Additionally, basic fibroblast growth factor (bFGF), a type of growth factor, has been demonstrated to be able to increase the differentiation and survival rate of NPCs. For better use of neuroblastoma cells and bFGF, we established a novel system involving multi-layered alginate-polylysine-alginate (APA) microcapsules to encapsulate neuroblastoma cells and bFGF, which may not only provide sufficient growth factors in a sustained manner but also avoid the carcinogenicity caused by neuroblastoma cells. Above all, we hypothesized that neuroblastoma cells and bFGF encapsulated in multilayered alginate microcapsules may efficiently induce the differentiation of BMSCs into NPCs.

Proliferation of cultured mouse choroid plexus epithelial cells

The choroid plexus (ChP) epithelium is a multifunctional tissue found in the ventricles of the brain. The major function of the ChP epithelium is to produce cerebrospinal fluid (CSF) that bathes and nourishes the central nervous system (CNS). In addition to the CSF, ChP epithelial cells (CPECs) produce and secrete numerous neurotrophic factors that support brain homeostasis, such as adult hippocampal neurogenesis. Accordingly, damage and dysfunction to CPECs are thought to accelerate and intensify multiple disease phenotypes, and CPEC regeneration would represent a potential therapeutic approach for these diseases. However, previous reports suggest that CPECs rarely divide, although this has not been extensively studied in response to extrinsic factors. Utilizing a cell-cycle reporter mouse line and live cell imaging, we identified scratch injury and the growth factors insulin-like growth factor 1 (IGF-1) and epidermal growth factor (EGF) as extrinsic cues that promote increased CPEC expansion in vitro. Furthermore, we found that IGF-1 and EGF treatment enhances scratch injury-induced proliferation. Finally, we established whole tissue explant cultures and observed that IGF-1 and EGF promote CPEC division within the intact ChP epithelium. We conclude that although CPECs normally have a slow turnover rate, they expand in response to external stimuli such as injury and/or growth factors, which provides a potential avenue for enhancing ChP function after brain injury or neurodegeneration.

Developments in intracerebral stem cell grafts

The field of stem cell therapy has emerged as a promising research area for brain repair. Optimizing the safety and efficacy of the therapy for clinical trials will require revisiting transplantation protocols. The cell delivery route stands as a key translational item that warrants careful consideration in facilitating the success of stem cell therapy in the clinic. Intracerebral administration, compared to peripheral route, requires an invasive procedure to directly implant stem cells into injured brain. Although invasive, intracerebral transplantation circumvents the prohibitive blood brain barrier in allowing grafted cells when delivered peripherally to penetrate the brain and reach the discreet damaged brain tissues. This review will highlight milestone discoveries in cell therapy for neurological disorders, with emphasis on intracerebral transplantation in relevant animal models and provide insights necessary to optimize the safety and efficacy of cell therapy for the treatment of Parkinson's disease, Huntington's disease, stroke and traumatic brain injury.

Choroid plexus implants rescue Alzheimer's disease-like pathologies by modulating amyloid-β degradation

The choroid plexuses (CP) release numerous biologically active enzymes and neurotrophic factors, and contain a subpopulation of neural progenitor cells providing the capacity to proliferate and differentiate into other types of cells. These characteristics make CP epithelial cells (CPECs) excellent candidates for cell therapy aiming at restoring brain tissue in neurodegenerative illnesses, including Alzheimer's disease (AD). In the present study, using in vitro approaches, we demonstrated that CP were able to diminish amyloid-β (Aβ) levels in cell cultures, reducing Aβ-induced neurotoxicity. For in vivo studies, CPECs were transplanted into the brain of the APP/PS1 murine model of AD that exhibits advanced Aβ accumulation and memory impairment. Brain examination after cell implantation revealed a significant reduction in brain Aβ deposits, hyperphosphorylation of tau, and astrocytic reactivity. Remarkably, the transplantation of CPECs was accompanied by a total behavioral recovery in APP/PS1 mice, improving spatial and non-spatial memory. These findings reinforce the neuroprotective potential of CPECs and the use of cell therapies as useful tools in AD.

Carriers in cell-based therapies for neurological disorders

There is a pressing need for long-term neuroprotective and neuroregenerative therapies to promote full function recovery of injuries in the human nervous system resulting from trauma, stroke or degenerative diseases. Although cell-based therapies are promising in supporting repair and regeneration, direct introduction to the injury site is plagued by problems such as low transplanted cell survival rate, limited graft integration, immunorejection, and tumor formation. Neural tissue engineering offers an integrative and multifaceted approach to tackle these complex neurological disorders. Synergistic therapeutic effects can be obtained from combining customized biomaterial scaffolds with cell-based therapies. Current scaffold-facilitated cell transplantation strategies aim to achieve structural and functional rescue via offering a three-dimensional permissive and instructive environment for sustainable neuroactive factor production for prolonged periods and/or cell replacement at the target site. In this review, we intend to highlight important considerations in biomaterial selection and to review major biodegradable or non-biodegradable scaffolds used for cell transplantation to the central and peripheral nervous system in preclinical and clinical trials. Expanded knowledge in biomaterial properties and their prolonged interaction with transplanted and host cells have greatly expanded the possibilities for designing suitable carrier systems and the potential of cell therapies in the nervous system.

Encapsulated cell therapy for neurodegenerative diseases: from promise to product

Delivering therapeutic molecules, including trophic factor proteins, across the blood brain barrier to the brain parenchyma to treat chronic neurodegenerative diseases remains one of the great challenges in biology. To be effective, delivery needs to occur in a long-term and stable manner at sufficient quantities directly to the target region in a manner that is selective but yet covers enough of the target site to be efficacious. One promising approach uses cellular implants that produce and deliver therapeutic molecules directly to the brain region of interest. Implanted cells can be precisely positioned into the desired region and can be protected from host immunological attack by encapsulating them and by surrounding them within an immunoisolatory, semipermeable capsule. In this approach, cells are enclosed within a semiporous capsule with a perm selective membrane barrier that admits oxygen and required nutrients and releases bioactive cell secretions while restricting passage of larger cytotoxic agents from the host immune defense system. Recent advances in human cell line development have increased the levels of secreted therapeutic molecules from encapsulated cells, and membrane extrusion techniques have led to the first ever clinical demonstrations of long-term survival and function of encapsulated cells in the brain parenchyma. As such, cell encapsulation is capable of providing a targeted, continuous, de novo synthesized source of very high levels of therapeutic molecules that can be distributed over significant portions of the brain.

Secretion of BDNF and GDNF from free and encapsulated choroid plexus epithelial cells

Choroid plexus epithelial cells secrete numerous biologically active neurotrophic factors, which may be beneficial to the transplantation site. Encapsulated cells are often used in tissue transplantation. The present study was conducted to investigate the effect of encapsulation on the secretory function of choroid plexus epithelial cells. Neonatal rat choroid plexus epithelial cells were primarily cultured. After 9 days of culture, the cells were distributed into two groups, and one group of cells was encapsulated in vitro. The initial culture conditions such as cell numbers and medium volumes were the same. Supernatants in the free and encapsulated choroid plexus epithelial cells were collected at the time points of day 1 through day 7. Quantitative determination of the BDNF and GDNF levels was performed by enzyme-linked immunosorbent assay to assess the secretory function of the cells in the two forms. Statistical analyses were performed using a Student t test. P<0.05 was set to indicate statistical significance. A very similar secretion pattern was observed in both groups. In the first 4 days of encapsulation, the release of BDNF and GDNF in the encapsulated cells was significantly lower than that in the free cells, while the difference diminished after day 5. This in vitro study demonstrates that the secretion of BDNF and GDNF in encapsulated choroid plexus epithelial cells is different from that in non-encapsulated cells in the early stage of encapsulation treatment, whereas it is similar in the later stage.

Microencapsulated cell tracking

Microencapsulation of therapeutic cells has been widely pursued to achieve cellular immunoprotection following transplantation. Initial clinical studies have shown the potential of microencapsulation using semi-permeable alginate layers, but much needs to be learned about the optimal delivery route, in vivo pattern of engraftment, and microcapsule stability over time. In parallel with noninvasive imaging techniques for 'naked' (i.e. unencapsulated) cell tracking, microcapsules have now been endowed with contrast agents that can be visualized by (1) H MRI, (19) F MRI, X-ray/computed tomography and ultrasound imaging. By placing the contrast agent formulation in the extracellular space of the hydrogel, large amounts of contrast agents can be incorporated with negligible toxicity. This has led to a new generation of imaging biomaterials that can render cells visible with multiple imaging modalities.

Therapeutic applications of encapsulated cells

The synergy of some promising advances in the fields of cell therapy and biomaterials together with improvements in the fabrication of more refined and tailored microcapsules for drug delivery have triggered the progress of cell encapsulation technology. Cell microencapsulation involves immobilizing the transplanted cells within a biocompatible scaffold surrounded by a membrane in attempt to isolate the cells from the host immune attack and enhance or prolong their function in vivo. This technology represents one strategy which aims to overcome the present difficulties related to local and systemic controlled release of drugs and growth factors as well as to organ graft rejection and thus the requirements for use of immunomodulatory protocols or immunosuppressive drugs. This chapter gives an overview of the current situation of cell encapsulation technology as a controlled drug delivery system, and the essential requirements of the technology, some of the therapeutic applications, the challenges, and the future directions under investigation are highlighted.

Neurological disorders and the potential role for stem cells as a therapy

Introduction Neurological disorders are routinely characterized by loss of cells in response to an injury or a progressive insult. Stem cells could therefore be useful to treat these disorders. Sources of data Pubmed searches of recent literature. Areas of agreement Stem cells exhibit proliferative capacity making them ideally suited for replacing dying cells. However, instead of cell replacement therapy stem cell transplants frequently appear to work via neurotrophic factor release, immunomodulation and upregulation of endogenous stem cells. Areas of controversy and areas timely for developing research Many questions remain with respect to the use of stem cells as a therapy, the answers to which will vary depending on the disorder to be treated and mode of action. Whereas the potential tumorigenic capability of stem cells is a concern, most studies do not support this notion. Further determination of the optimal cell type, and whether to perform allogeneic or autologous transplants warrant investigation before the full potential of stem cells can be realized. In addition, the use of stem cells to develop disease models should not be overlooked.

Targeting the choroid plexus-CSF-brain nexus using peptides identified by phage display

Drug delivery to the central nervous system requires the use of specific portals to enable drug entry into the brain and, as such, there is a growing need to identify processes that can enable drug transfer across both blood-brain and blood-cerebrospinal fluid barriers. Phage display is a powerful combinatorial technique that identifies specific peptides that can confer new activities to inactive particles. Identification of these peptides is directly dependent on the specific screening strategies used for their selection and retrieval. This chapter describes three selection strategies, which can be used to identify peptides that target the choroid plexus (CP) directly or for drug translocation across the CP and into cerebrospinal fluid.

Functional modulation of choroid plexus epithelial clusters in vitro for tissue repair applications

One of the primary obstacles in the restoration or repair of damaged tissues is the temporospatial orchestration of biological and physiological events. Cellular transplantation is an important component of tissue repair as grafted cells can serve as replacement cells or as a source of secreted factors. But few, if any, primary cells can perform more than a single tissue repair function. Epithelial cells, derived from the choroid plexus (CP), are an exception to this rule, as transplanted CP is protective and regenerative in animal models as diverse as CNS degeneration and dermal wound repair. They secrete a myriad of proteins with therapeutic potential as well as matrix and adhesion factors, and contain responsive cytoskeletal components potentially capable of precise manipulation of cellular and extracellular niches. Here we isolated CP from neonatal porcine lateral ventricles and cultured the cells under a variety of conditions to specifically modulate tissue morphology (2D vs. 3D) and protein expression. Using qRT-PCR analysis, transmission electron microscopy, and gene microarray studies we demonstrate a fine level of control over CP epithelial cell clusters opening further opportunities for exploration of the therapeutic potential of this unique tissue source.

Glutamatergic Excitation and GABA Release from a Transplantable Cell Line

The cell line M213-2O CL-4 was derived from cell line M213-2O and further modified to express human glutamate decarboxylase (hGAD-67), the enzyme that synthesizes GABA. Brain transplants of this cell line in animal models of epilepsy have been shown to modulate seizures. However, the mechanisms that underlie such actions are unknown. The purpose of the present study was to characterize this cell line and its responsiveness to several depolarizing conditions, in order to better understand how these cells exert their effects. Intracellular GABA levels were 34-fold higher and GAD activity was 16-fold higher in clone M213-2O CL-4 than in M213-2O. Both cell lines could take up [3H]GABA in vitro, and this uptake was prevented by nipecotic acid. By combining GABA release measurements and calcium imaging in vitro, we found that high extracellular K+, zero Mg2+, or glutamate activated M213-2O CL-4 cells and resulted in GABA release. The response to glutamate appeared to be mediated by AMPA/NMDA-like receptors. High KCl-induced GABA release was prevented when a Ca2+-free Krebs solution was used, suggesting an exocytotic-like mechanism. These results indicate that the cell line M213-2O CL-4 synthesizes, releases, and takes up GABA in vitro, and can be activated by depolarizing stimuli.

Cardiac cell generation from encapsulated embryonic stem cells in static and scalable culture systems

Heart diseases are major causes of morbidity and mortality linked to extensive loss of cardiac cells. Embryonic stem cells (ESCs) give rise to cardiomyocyte-like cells, which may be used in heart cell replacement therapies. Most cardiogenic differentiation protocols involve the culture of ESCs as embryoid bodies (EBs). Stirred-suspension bioreactor cultures of ESC aggregates may be employed for scaling up the production of cardiomyocyte progeny but the wide range of EB sizes and the unknown effects of the hydrodynamic environment on differentiating EBs are some of the major challenges in tightly controlling the differentiation outcome. Here, we explored the cardiogenic potential of mouse ESCs (mESCs) and human ESCs (hESCs) encapsulated in poly-L-lysine (pLL)-coated alginate capsules. Liquefaction of the capsule core led to the formation of single ESC aggregates within each bead and their average size depended on the concentration of seeded ESCs. Encapsulated mESCs were directed along cardiomyogenic lineages in dishes under serum-free conditions with the addition of bone morphogenetic protein 4 (BMP4). Human ESCs in pLL-layered liquid core (LC) alginate beads were also differentiated towards heart cells in serum-containing media. Besides the robust cell proliferation, higher fractions of cells expressing cardiac markers were detected in ESCs encapsulated in LC than in solid beads. Furthermore, we demonstrated for the first time that ESCs encapsulated in pLL-layered LC alginate beads can be coaxed towards heart cells in stirred-suspension bioreactors. Encapsulated ESCs yielded higher fractions of Nkx2.5- and GATA4-positive cells in the bioreactor compared to dish cultures. Differentiated cells formed beating foci that responded to chronotropic agents in an organotypic manner. Our findings warrant further development and implementation of microencapsulation technologies in conjunction with bioreactor cultivation to enable the production of stem cell-derived cardiac cells appropriate for clinical therapies and applications.

Company profile: Tissue regeneration for diabetes and neurological diseases at Living Cell Technologies

Living Cell Technologies’ (LCT’s) cell-based therapeutic for Type 1 diabetes, DIABECELL®, comprises encapsulated porcine insulin-producing cells. DIABECELL is presently in a Phase II clinical trial in New Zealand following positive early results. The cells are implanted into the abdomen to replace the patient’s pancreatic β-islet cells that have been lost as a result of autoimmune disease. LCT is also developing brain choroid plexus cells for the treatment of neurologic diseases. The aim is to enhance the brain’s natural repair mechanism by implanting cells releasing neurotrophins. Choroid plexus cell implants alleviate disease in animal models of Parkinson’s disease, Huntington’s disease and stroke. LCT encapsulates all cells in alginate, permitting implantation without using immunosuppressive drugs.

Secreted Products from the Porcine Choroid Plexus Accelerate the Healing of Cutaneous Wounds

The choroid plexus (CP), located at the blood–brain interface, is partially responsible for maintaining the composition of cerebrospinal fluid. Epithelial cell clusters isolated from the CP secrete numerous biologically active molecules, and are neuroprotective when transplanted in animal models of Huntington's disease and stroke. The transcriptomic and proteomic profiles of CP may extend beyond CNS applications due to an abundance of trophic and regenerative factors, including vascular endothelial growth factor, transforming growth factor-β, and others. We used microarray to investigate the transcriptome of porcine CP epithelium, and then assessed the in vitro and in vivo regenerative capability of secreted CP products in cell monolayers and full-thickness cutaneous wounds. In vitro, CP reduced the void area of fibroblast and keratinocyte scratch cultures by 70% and 33%, respectively, compared to empty capsule controls, which reduced the area by only 35% and 6%, respectively. In vivo, after 10 days of topical application, CP conditioned medium lyophilate dispersed in antibiotic ointment produced a twofold improvement in incision tensile strength compared to ointment containing lyophilized control medium, and an increase in the regeneration of epidermal appendages from roughly 50–150 features per wound. Together, these data identify the CP as a source of secreted regenerative molecules to accelerate and improve the healing of superficial wounds and potentially other similar indications.

Encapsulated living choroid plexus cells: potential long-term treatments for central nervous system disease and trauma

In neurodegenerative disease and in acute brain injury, there is often local up-regulation of neurotrophin production close to the site of the lesion. Treatment by direct injection of neurotrophins and growth factors close to these lesion sites has repeatedly been demonstrated to improve recovery. It has therefore been proposed that transplanting viable neurotrophin-producing cells close to the trauma lesion, or site of degenerative disease, might provide a novel means for continuous delivery of these molecules directly to the site of injury or to a degenerative region. The aim of this paper is to summarize recent published information and present new experimental data that indicate that long-lasting therapeutic implants of choroid plexus (CP) neuroepithelium may be used to treat brain disease. CP produces and secretes numerous biologically active neurotrophic factors (NT). New gene microarray and proteomics data presented here indicate that many other anti-oxidant, anti-toxin and neuronal support proteins are also produced and secreted by CP cells. In the healthy brain, these circulate in the cerebrospinal fluid through the brain and spinal cord, maintaining neuronal networks and associated cells. Recent publications describe how transplanted CP cells and tissue, either free or in an immunoprotected encapsulated form, can effectively deliver therapeutic molecules when placed near the lesion or site of degenerative disease in animal models. Using simple techniques, CP neuroepithelial cell clusters in suspension culture were very durable, remaining viable for 6 months or more in vitro. The cell culture conditions had little effect on the wide range and activity of genes expressed and proteins secreted. Recently, completed experiments show that implanting CP within alginate-poly-ornithine capsules effectively protected these xenogeneic cells from the host immune system and allowed their survival for 6 months or more in the brains of rats, causing no adverse effects. Previously reported evidence demonstrated that CP cells support the survival and differentiation of neuronal cells in vitro and effectively treat acute brain injury and disease in rodents and non-human primates in vivo. The accumulated preclinical data together with the long-term survival of implanted encapsulated cells in vivo provide a sound base for the investigation of these treatments for chronic inherited and established neurodegenerative conditions.

Transplantation of cultured choroid plexus epithelial cells via cerebrospinal fluid shows prominent neuroprotective effects against acute ischemic brain injury in the rat

Choroid plexus (CP) epithelial cells (CPECs) produce cerebrospinal fluid (CSF) to provide the CNS with a specialized microenvironment. Our previous study showed that the conditioned medium of cultured CPECs enhanced the survival and neurite extension of hippocampal neurons. The present study examined the ability of cultured CPECs to protect against ischemic brain injury when transplanted into the CSF. Rats were subjected to a transient occlusion of the middle cerebral artery, followed by an injection of cultured CPECs into the fourth ventricle. The injection markedly reduced neurological deficits and infarction volume within 24h. Other beneficial effects were (1) a reduction in number of apoptotic and inflammatory cells, (2) an up-regulation of the mRNA expression of an anti-apoptotic effecter, cAMP-response element binding protein, and (3) a down-regulation of the production of pro-inflammatory factors such as interleukin-1 beta and inducible nitric oxide synthase. The injected CPECs were located within the ventricles and on the brain's surface, not in the ischemic foci, suggesting that they exert their effects by releasing diffusible neuroprotective factors into the CSF. The transplantation of CPECs via CSF is a potential new strategy for protecting against ischemic brain injury.

Small Agarose Microcapsules with Cell-Enclosing Hollow Core for Cell Therapy: Transplantation of Ifosfamide-Activating Cells to the Mice with Preestablished Subcutaneous Tumor

Cell transplantation after enclosing in microcapsules has been studied as an alternative approach for treatment of wide variety of diseases. In the present study, we examined the feasibility of using agarose microcapsules, having a cell-enclosing hollow core of 100–150 μm in diameter and agarose gel membrane of about 20 μm in thickness, as a device for the methodology. We enclosed cells that had been genetically engineered to express cytochrome P450 2B1, an enzyme that activates the anticancer prodrug ifosfamide. The enclosed cells were shown to express the enzymatic function in the microcapsules in that they suppressed the growth of tumor cells in medium containing ifosfamide. In addition, a more significant regression of preformed tumors was observed in the nude mice implanted with the cell-enclosing microcapsules compared with those implanted with empty capsules after administration of ifosfamide. Preformed tumors shrank by less than 40% in volume in 6 of the 10 recipients implanted with cell-enclosing microcapsules. In contrast, only 1 in 10 of the preformed tumors in the recipient implanted with empty microcapsules shrank by this amount. These results suggest that agarose microcapsules containing cytochrome P450 2B1 enzyme-expressing cells are feasible devices for improving the chemotherapy of tumors. Thus, agarose microcapsule having hollow cores are generally a good candidate as vehicles for cell-encapsulation approaches to cell therapy.

Potential of choroid plexus epithelial cell grafts for neuroprotection in Huntington's disease: what remains before considering clinical trials

The choroid plexuses (CPs) help maintain the extracellular milieu of the brain by modulating chemical exchange between the cerebrospinal fluid and brain parenchyma, surveying the chemical and immunological status of the brain, detoxifying the brain, secreting a nutritive "cocktail" of polypeptides, and participating in repair processes following trauma. Based on recent pre-clinical studies in animal models, a novel therapeutic approach has been suggested that involves transplanting CP for treating acute and chronic brain diseases. To date most studies have focused on rodent and primate models of Huntington's disease (HD) with demonstrations that transplants of CP can prevent the behavioral and anatomical consequences of striatal degeneration. Despite the encouraging results that lend support to the possibility of protecting vulnerable neurons in HD, critical basic science issues remain unexamined that limit the translation of the pre-clinical findings into clinical evaluations of CP transplants for HD. Here we briefly outline the logic behind using this novel cell source for transplantation, the pre-clinical data supporting this concept, and most importantly identify several critical, gating issues that remain prior to moving this approach forward in a meaningful clinical manner.

NF-kappaB activity in endothelial cells is modulated by cell substratum interactions and influences chemokine-mediated adhesion of natural killer cells

Because changes in subendothelial matrix composition are associated with alterations of the endothelial immune phenotype, we sought to understand if cytokine-induced NF-kappaB activity and downstream effects depend on substrate adherence of endothelial cells (EC). We compared the upstream phosphorylation cascade, activation of NF-kappaB, and expression/secretion of downstream effects of EC grown on tissue culture polystyrene plates (TCPS) with EC embedded within collagen-based matrices (MEEC). Adhesion of natural killer (NK) cells was quantified in vitro and in vivo. NF-kappaB subunit p65 nuclear levels were significantly lower and p50 significantly higher in cytokine-stimulated MEEC than in EC-TCPS. Despite similar surface expression of TNF-alpha receptors, MEEC had significantly decreased secretion and expression of IL-6, IL-8, MCP-1, VCAM-1, and ICAM-1. Attenuated fractalkine expression and secretion in MEEC (two to threefold lower than in EC-TCPS; p < 0.0002) correlated with 3.7-fold lower NK cell adhesion to EC (6,335 +/- 420 vs. 1,735 +/- 135 cpm; p < 0.0002). Furthermore, NK cell infiltration into sites of EC implantation in vivo was significantly reduced when EC were embedded within matrix. Matrix embedding enables control of EC substratum interaction. This in turn regulates chemokine and surface molecule expression and secretion, in particular of those compounds within NF-kappaB pathways, chemoattraction of NK cells, local inflammation, and tissue repair.