Embryonic stem cell—derived astrocytes expressing drug-inducible transgenes: differentiation and transplantion into the mouse brain

Derivation of Specific Neural Populations From Pluripotent Cells for Understanding and Treatment of Spinal Cord Injury

Due to the nature of the biological response to traumatic spinal cord injury, there are very limited therapeutic options available to patients. Recent advances in cell transplantation have demonstrated the therapeutic potential of transplanting supportive cell types following spinal cord injury. In particular, pluripotent stem cell derived neural cells are of interest for future investigation. Use of pluripotent stem cells as the source allows many cell types to be produced from a population that can be expanded in vitro. In this review, we will discuss the signaling pathways that have been used to differentiate spinal neural phenotypes from pluripotent stem cells. Additionally, we will highlight methods that have been developed to direct the differentiation of pluripotent stem cells to specific neural fates. Further refinement and elaboration of these techniques might aid in elucidating the multitude of neuronal subtypes endogenous to the spinal cord, as well as produce further therapeutic options for spinal cord injury recovery. Developmental Dynamics 248:78-87, 2019. © 2018 Wiley Periodicals, Inc.

Different Mixed Astrocyte Populations Derived from Embryonic Stem Cells Have Variable Neuronal Growth Support Capacities

Central nervous system injury often leads to functional impairment due, in part, to the formation of an inhibitory glial scar following injury that contributes to poor regeneration. Astrocytes are the major cellular components of the glial scar, which has led to the belief that they are primarily inhibitory following injury. Recent work has challenged this by demonstrating that some astrocytes are required for spinal cord regeneration and astrocytic roles in recovery depend on their phenotype. In this work, two mixed populations containing primarily either fibrous or protoplasmic astrocytes were derived from mouse embryonic stem cells (mESCs). Motoneuron and V2a interneuron growth on live cultures, freeze-lysed cultures, or decellularized extracellular matrix (ECM) from astrocytes were assessed. Both neuronal populations were found to extend significantly longer neurites on protoplasmic-derived substrates than fibrous-derived substrates. Interestingly, neurons extended longer neurites on protoplasmic-derived ECM than fibrous-derived ECM. ECM proteins were compared with in vivo astrocyte expression profiles, and it was found that the ESC-derived ECMs were enriched for astrocyte-specific proteins. Further characterization revealed that protoplasmic ECM had significantly higher levels of axon growth promoting proteins, while fibrous ECM had significantly higher levels of proteins that inhibit axon growth. Supporting this observation, knockdown of spondin-1 improved neurite growth on fibrous ECM, while laminin α5 and γ1 knockdown decreased neurite growth on protoplasmic ECM. These methods allow for scalable production of specific astrocyte subtype-containing populations with different neuronal growth support capacities, and can be used for further studies of the functional importance of astrocyte heterogeneity.

Glia-neuron interactions in neurological diseases: Testing non-cell autonomy in a dish

For the past century, research on neurological disorders has largely focused on the most prominently affected cell types - the neurons. However, with increasing knowledge of the diverse physiological functions of glial cells, their impact on these diseases has become more evident. Thus, many conditions appear to have more complex origins than initially thought. Since neurological pathologies are often sporadic with unknown etiology, animal models are difficult to create and might only reflect a small portion of patients in which a mutation in a gene has been identified. Therefore, reliable in vitro systems to studying these disorders are urgently needed. They might be a pre-requisite for improving our understanding of the disease mechanisms as well as for the development of potential new therapies. In this review, we will briefly summarize the function of different glial cell types in the healthy central nervous system (CNS) and outline their implication in the development or progression of neurological conditions. We will then describe different types of culture systems to model non-cell autonomous interactions in vitro and evaluate advantages and disadvantages. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Stem cells for spinal cord injury: Strategies to inform differentiation and transplantation

The complex pathology of spinal cord injury (SCI), involving a cascade of secondary events and the formation of inhibitory barriers, hampers regeneration across the lesion site and often results in irreversible loss of motor function. The limited regenerative capacity of endogenous cells after SCI has led to a focus on the development of cell therapies that can confer both neuroprotective and neuroregenerative benefits. Stem cells have emerged as a candidate cell source because of their ability to self-renew and differentiate into a multitude of specialized cell types. While ethical and safety concerns impeded the use of stem cells in the past, advances in isolation and differentiation methods have largely mitigated these issues. A confluence of work in stem cell biology, genetics, and developmental neurobiology has informed the directed differentiation of specific spinal cell types. After transplantation, these stem cell-derived populations can replace lost cells, provide trophic support, remyelinate surviving axons, and form relay circuits that contribute to functional recovery. Further refinement of stem cell differentiation and transplantation methods, including combinatorial strategies that involve biomaterial scaffolds and drug delivery, is critical as stem cell-based treatments enter clinical trials. Biotechnol. Bioeng. 2017;114: 245-259. © 2016 Wiley Periodicals, Inc.

Human iPSC for Therapeutic Approaches to the Nervous System: Present and Future Applications

Many central nervous system (CNS) diseases including stroke, spinal cord injury (SCI), and brain tumors are a significant cause of worldwide morbidity/mortality and yet do not have satisfying treatments. Cell-based therapy to restore lost function or to carry new therapeutic genes is a promising new therapeutic approach, particularly after human iPSCs became available. However, efficient generation of footprint-free and xeno-free human iPSC is a prerequisite for their clinical use. In this paper, we will first summarize the current methodology to obtain footprint- and xeno-free human iPSC. We will then review the current iPSC applications in therapeutic approaches for CNS regeneration and their use as vectors to carry proapoptotic genes for brain tumors and review their applications for modelling of neurological diseases and formulating new therapeutic approaches. Available results will be summarized and compared. Finally, we will discuss current limitations precluding iPSC from being used on large scale for clinical applications and provide an overview of future areas of improvement. In conclusion, significant progress has occurred in deriving iPSC suitable for clinical use in the field of neurological diseases. Current efforts to overcome technical challenges, including reducing labour and cost, will hopefully expedite the integration of this technology in the clinical setting.

Finding degrees of separation: experimental approaches for astroglial and oligodendroglial cell isolation and genetic targeting

The study of CNS glial cell function requires experimental methods to detect, purify, and manipulate each cell population with fidelity and specificity. With the identification and cloning of cell- and stage-specific markers, glial cell analysis techniques have grown beyond physical methods of tissue dissociation and cell culture, and become highly specific with immunoselection of cell cultures in vitro and genetic targeting in vivo. The unique plasticity of glial cells offers the potential for cell replacement therapies in neurological disease that utilize neural cells derived from transplanted neural stem and progenitor cells. In this mini-review, we outline general physical and genetic approaches for macroglial cell generation. We summarize cell culture methods to obtain astrocytes and oligodendrocytes and their precursors, from developing and adult tissue, as well as approaches to obtain human neural progenitor cells through the establishment of stem cells. We discuss popular targeting rodent strains designed for cell-specific detection, selection and manipulation of neuroglial cell progenitors and their committed progeny. Based on shared markers between astrocytes and stem cells, we discuss genetically modified mouse strains with overlapping expression, and highlight SOX-expressing strains available for targeting of stem and progenitor cell populations. We also include recently established mouse strains for detection, and tag-assisted RNA and miRNA analysis. This discussion aims to provide a brief overview of the rapidly expanding collection of experimental approaches and genetic resources for the isolation and targeting of macroglial cells, their sources, progeny and gene products to facilitate our understanding of their properties and potential application in pathology.

"Footprint-free" human induced pluripotent stem cell-derived astrocytes for in vivo cell-based therapy

The generation of human induced pluripotent stem cells (hiPSC) from somatic cells has enabled the possibility to provide patient-specific hiPSC for cell-based therapy, drug discovery, and other translational applications. Two major obstacles in using hiPSC for clinical application reside in the risk of genomic modification when they are derived with viral transgenes and risk of teratoma formation if undifferentiated cells are engrafted. In this study, we report the generation of "footprint-free" hiPSC-derived astrocytes. These are efficiently generated, have anatomical and physiological characteristics of fully differentiated astrocytes, maintain homing characteristics typical of stem cells, and do not give rise to teratomas when engrafted in the brain. Astrocytes can be obtained in sufficient numbers, aliquoted, frozen, thawed, and used when needed. Our results show the feasibility of differentiating astrocytes from "footprint-free" iPSC. These are suitable for clinical cell-based therapies as they can be induced from patients' specific cells, do not require viral vectors, and are fully differentiated. "Footprint-free" hiPSC-derived astrocytes represent a new potential source for therapeutic use for cell-based therapy, including treatment of high-grade human gliomas, and drug discovery.

Stemness of the CT-2A Immunocompetent Mouse Brain Tumor Model: Characterization In Vitro

Evidence has pointed to brain tumor stem cells (BTSC) as culprits behind human high-grade glioma (hHGG) resistance to standard therapy. Pre-clinical rodent models are the mainstay for testing of new therapeutic strategies. The typical model involves the intracranial injection of human glioma cells into immunocompromised hosts, hindering the evaluation of tumor-host responses and resulting in non-infiltrative tumors. The CT-2A model is an immunocompetent mouse model with potential to overcome these disadvantages. In this study, we confirmed the highly infiltrative nature of intracranial CT-2A tumors and optimized reproducible injection parameters. We then generated neurospheres and established, for the first time, the stemness of this model. CT-2A expression of the BTSC marker, CD133, increased from 2% in monolayer cells to 31% in fully-formed neurospheres. Investigation of three stem cell markers (Oct4, Nanog and Nestin) revealed a distinct stemness signature with monolayer cells expressing Oct4 and Nestin (no Nanog), and neurospheres expressing all three. Additionally, CT-2A cells were more proliferative and invasive than U87 cells, while CT-2A neurospheres were significantly more proliferative and invasive than either monolayer cells in vitro. Taken together, our results show that this model is a valuable tool for pre-clinical testing of novel therapeutics against hHGG and also affords the opportunity for investigation of BTSC in an immunocompetent setting.

Stem cells as therapeutic vehicles for the treatment of high-grade gliomas

Stem cells have generated great interest in the past decade as potential tools for cell-based treatment of human high-grade gliomas. Thus far, 3 types of stem cells have been tested as vehicles for various therapeutic agents: embryonic, neural, and mesenchymal. The types of therapeutic approaches and/or agents examined in the context of stem cell-based delivery include cytokines, enzyme/prodrug suicide combinations, viral particles, matrix metalloproteinases, and antibodies. Each strategy has specific advantages and disadvantages. Irrespective of the source and/or type of stem cell, there are several areas of concern for their translation to the clinical setting, such as migration in the adult human brain, potential teratogenesis, immune rejection, and regulatory and ethical issues. Nonetheless, a clinical trial is under way using neural stem cell-based delivery of an enzyme/prodrug suicide combination for recurrent high-grade glioma. A proposed future direction could encompass the use of stem cells as vehicles for delivery of agents targeting glioma stem cells, which have been implicated in the resistance of high-grade glioma to treatment. Overall, stem cells are providing an unprecedented opportunity for cell-based approaches in the treatment of high-grade gliomas, which have a persistently dismal prognosis and mandate a continued search for therapeutic options.

Efficient differentiation of human embryonic and induced pluripotent stem cells into functional astrocytes

Human high-grade gliomas (hHGG) remain a therapeutic challenge in neuro-oncology despite current multimodality treatments. We recently demonstrated that murine embryonic stem cell (mESC)-derived astrocytes conditionally expressing proapoptotic genes can successfully be used to induce apoptosis and tumor shrinkage of hHGG tumor in vitro and in an in vivo mouse model. The first step in the translation of these results to the clinical settings, however, requires availability of human embryonic stem cells (hESC)- and/or induced pluripotent cell (hiPSC)-derived astrocytes engineered to express proapoptotic genes. The potential for directed differentiation of hESCs and hiPSCs to functional postmitotic astrocytes is not fully characterized. In this study, we show that once specified to neuro-epithelial lineage, hiPSC could be differentiated to astrocytes with a similar efficiency as hESC. However, our analyses of 2 hESC and 2 hiPSC cell lines showed some variability in differentiation potential into astrocytic lineages. Both the hESC- and hiPSC-derived astrocytes appeared to follow the functional properties of mESC-derived astrocytes, namely, migration and tropism for hHGG. This work provides evidence that hESC- and hiPSC-derived cells are able to generate functionally active astrocytes. These results demonstrate the feasibility of using iPSC-derived astrocytes, a new potential source for therapeutic use for brain tumors and other neurological diseases.

Embryonic stem cell (ESC)-mediated transgene delivery induces growth suppression, apoptosis and radiosensitization, and overcomes temozolomide resistance in malignant gliomas

High-grade gliomas are among the most lethal of all cancers. Despite considerable advances in multimodality treatment, including surgery, radiotherapy and chemotherapy, the overall prognosis for patients with this disease remains dismal. Currently available treatments necessitate the development of more effective tumor-selective therapies. The use of gene therapy for malignant gliomas is promising, as it allows in situ delivery and selectively targets brain tumor cells while sparing the adjacent normal brain tissue. Viral vectors that deliver proapoptotic genes to malignant glioma cells have been investigated. Although tangible results on patients' survival remain to be further documented, significant advances in therapeutic gene transfer strategies have been made. Recently, cell-based gene delivery has been sought as an alternative method. In this paper, we report the proapoptotic effects of embryonic stem cell (ESC)-mediated mda-7/IL-24 delivery to malignant glioma cell lines. Our data show that these are similar to those observed using a viral vector. In addition, acknowledging the heterogeneity of malignant glioma cells and their signaling pathways, we assessed the effects of conventional treatment for high-grade gliomas, ionizing radiation and temozolomide, when combined with ESC-mediated transgene delivery. This combination resulted in synergistic effects on tumor cell death. The mechanisms involved in this beneficial effect included activation of both apoptosis and autophagy. Our in vitro data support the concept that ESC-mediated gene delivery might offer therapeutic advantages over standard approaches to malignant gliomas. Our results corroborate the theory that combined treatments exploiting different signaling pathways are needed to succeed in the treatment of malignant gliomas.

Gene therapy as an adjuvant treatment for malignant gliomas: from bench to bedside

Malignant brain tumors, including high-grade gliomas, are among the most lethal of all cancers. Despite considerable advances, including multi-modality treatments with surgery, radiotherapy, and chemotherapy, the overall prognosis for patients with this disease remains dismal. Currently available treatments necessitate the development of more effective tumor-selective therapies. The use of gene therapy for brain tumor therapy is promising as it can be delivered in situ and selectively targets brain tumor cells while sparing the adjacent normal brain tissue. In this article, we summarize the laboratory and clinical work using viral, cell-based, and synthetic vectors, as well as other strategies focused on potentiate gene delivery. Although tangible results on patients' survival remains to be further documented, significant advances in therapeutic gene transfer strategies have been made. The enthusiasm of this progress needs to be tempered by the realistic assessment of the challenges needed to be overcome. Finally, as the field of gene delivery progresses, advances must be made in identifying genes and proteins key to the treatment of malignant gliomas. Due to the great heterogeneity of malignant glioma cells, only approaches combining different strategies may be ultimately successful in defeating this disease.

In vivo gene delivery by embryonic-stem-cell-derived astrocytes for malignant gliomas

The treatment of malignant gliomas with current therapies remains a challenge in neurooncology. Our recent work showed that embryonic stem cell (ESC)-derived astrocytes conditionally expressing genes can be used to induce apoptosis in malignant glioma cells in vitro. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene has been shown to induce apoptosis in a variety of tumor cells, including gliomas. The aim of this study was to assess the proapoptotic effects of transgenic TRAIL delivered by ESC-derived astrocytes on malignant gliomas in vivo. Malignant glioma A172 cells were used to induce heterotopic xenografts in nude mice. ESC-derived astrocytes conditionally expressing TRAIL were injected into the xenografts. TRAIL expression was documented in the malignant glioma xenografts by reverse transcription PCR and immunohistochemistry after external gene induction. A significant reduction in tumor volume occurred 48 h after a single injection (14%) and double injections (31%) in the experimental groups. Terminal dUTP nick end labeling (TUNEL) revealed abundant apoptotic tumor cells in the experimental groups. Seven days after injection, the tumor had undergone severe necrosis, with only scattered residual tumor cells at the periphery. Death receptor DR4 expression increased significantly in the experimental groups compared with controls. Our data suggest that ESC-derived astrocytes conditionally expressing TRAIL should be considered as vectors to deliver gene therapy for malignant gliomas.

Fluorescence-activated single cell sorting of human embryonic stem cells

Human embryonic stem cells (hESC) are the subject of intense investigation for use in regenerative medicine, in toxicity testing, and as models for the study of human development. Automated cell sorting will enhance the isolation of homogenous pools of differentiated hESCs both for basic studies and for therapeutic applications. Sorting could also be used to deplete undifferentiated, potentially tumourigenic cells. However, hESCs are sensitive to single cell disaggregation and recover poorly when plated at clonal density. Here we report a method for successful semi-automated single cell sorting of hESCs. This method utilizes an ES-specific promoter-transgene construct and automated FACS-based single cell sorting and plating. Clonal recovery in physiologic oxygen (2%) was increased fourfold over room oxygen (21%; p < 0.01). This automated protocol will help to realize proposed hESC strategies that are hampered by low throughput and poor yields.

Apoptosis in human glioblastoma cells produced using embryonic stem cell–derived astrocytes expressing tumor necrosis factor–related apoptosis-inducing ligand

Object

Embryonic stem (ES) cell–derived astrocytes have several theoretical and practical advantages as gene therapy vectors in the treatment of malignant gliomas. The aim of this study was to test the proapoptotic effects of ES cell–derived astrocytes expressing transgenic tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) in human malignant glioma cells.

Methods

Mouse ES cells containing a doxycycline-inducible transgene were engineered with human TRAIL (hTRAIL) and then directed to differentiate into astrocytes. The ES cell-derived–TRAIL-expressing astrocytes were cocultured with human malignant glioma cells. Reverse transcriptase polymerase chain reaction, immunocytochemistry, terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick-end labeling, and flow cytometry were used to quantify results.

In vitro coculture of ES cell–derived astrocytes expressing hTRAIL with A172 human malignant glioma cells after doxycycline induction caused a significant decrease in cell viability from 85 ± 2% at baseline to 8 ± 2% posttreatment (p < 0.001). Labeling with apoptotic markers showed that cell death occurred by means of apoptosis. A significant increase in apoptotic rate (88 ± 3%) from baseline (4 ± 2%) was found in A172 cells after doxycycline induction (p < 0.005). This effect was superior to the apoptotic rate seen after treatment with recombinant TRAIL (57 ± 2%). A decrease in cell viability and an increase in the apoptotic rate were not found in TRAIL-expressing–ES cell-derived astrocytes after induction with doxycycline or in A172 cells exposed to doxycycline alone.

Conclusions

Engineering of transgenic hTRAIL by using ES cell–derived astrocytes induced apoptosis in human malignant glioma cells while sparing nontumor astrocytes. The apoptotic effects of transgenic hTRAIL are greater than those of recombinant hTRAIL. Analysis of these results suggests that hTRAIL-expressing–ES cell-derived astrocytes should be considered in the development of new in vivo strategies to treat malignant human gliomas.

Embryonic stem cell–derived astrocytes: a novel gene therapy vector for brain tumors

Object

For gene therapy strategies currently in clinical trials, viral vectors are used to deliver transgenes directly to normal and tumor cells within the central nervous system (CNS). The use of viral vectors is limited by several factors. The aim of this study was to assess whether embryonic stem cell (ESC)–derived astrocytes expressing a doxycycline-inducible transgene can be used as a vector for gene therapy.

Methods

The authors generated a pure population of ESC-derived astrocytes carrying a transgene, tumor necrosis factor–related apoptosis-inducing ligand (TRAIL), inserted in the chromosome under the control of a highly regulated doxycycline-inducible expression system. Fully differentiated ESC-derived astrocytes were stereotactically transplanted in the mouse brain, and then cell migration and transgene expression were studied.

Results

The ESC-derived astrocytes started to migrate from the transplant site 48 hours after the procedure. They were found to have migrated throughout the brain tissue by 6 weeks. Transplanted ESC-derived astrocytes expressed the TRAIL transgene after doxycycline induction throughout the duration of the experiment. Teratoma formation was not observed in long-term experiments (12 weeks).

Conclusions

These data show that ESC-derived astrocytes can be used as delivery vectors for CNS tumors. This technique might have a major impact on the treatment of patients with malignant gliomas and a wide spectrum of other neurological diseases.