INDEX-db: The Indian Exome Reference Database (Phase I)

Deep sequencing-based genetic mapping has greatly enhanced the ability to catalog variants with plausible disease association. Confirming how these identified variants contribute to specific disease conditions, across human populations, poses the next challenge. Differential selection pressure may impact the frequency of genetic variations, and thus detection of association with disease conditions, across populations. To understand genotype to phenotype correlations, it thus becomes important to first understand the spectrum of genetic variation within a population by creating a reference map. In this study, we report the development of phase I of a new database of genetic variations called INDian EXome database (INDEX-db), from the Indian population, with an aim to establish a centralized database of integrated information. This could be useful for researchers involved in studying disease mechanisms at clinical, genetic, and cellular levels.

Repurposing the Cord Blood Bank for Haplobanking of HLA-Homozygous iPSCs and Their Usefulness to Multiple Populations

Although autologous induced pluripotent stem cells (iPSCs) can potentially be useful for treating patients without immune rejection, in reality it will be extremely expensive and labor-intensive to make iPSCs to realize personalized medicine. An alternative approach is to make use of human leukocyte antigen (HLA) haplotype homozygous donors to provide HLA matched iPSC products to significant numbers of patients. To establish a haplobank of iPSCs, we repurposed the cord blood bank by screening ∼4,200 high resolution HLA typed cord blood samples, and selected those homozygous for the 10 most frequent HLA-A,-B,-DRB1 haplotypes in the Korean population. Following the generation of 10 iPSC lines, we conducted a comprehensive characterization, including morphology, expression of pluripotent markers and cell surface antigens, three-germ layer formation, vector clearance, mycoplasma/microbiological/viral contamination, endotoxin, and short tandem repeat (STR) assays. Various genomic analyses using microarray and comparative genomic hybridization (aCGH)-based single nucleotide polymorphism (SNP) and copy number variation (CNV) were also conducted. These 10 HLA-homozygous iPSC lines match 41.07% of the Korean population. Comparative analysis of HLA population data shows that they are also of use in other Asian populations, such as Japan, with some limited utility in ethnically diverse populations, such as the UK. Taken together, the generation of the 10 most frequent Korean HLA-homozygous iPSC lines serves as a useful pointer for the development of optimal methods for iPSC generation and quality control and indicates the benefits and limitations of collaborative HLA driven selection of donors for future stocking of worldwide iPSC haplobanks. Stem Cells 2018;36:1552-1566.

Cloning and identification of mouse steroid receptor coactivator-1 (mSRC-1), as a coactivator of peroxisome proliferator-activated receptor gamma

Peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear receptor superfamily, is expressed predominantly in adipose tissue. Forced expression of the two isoforms of this receptor, PPARgamma1 and PPARgamma2, in fibroblasts initiates a transcriptional cascade that leads to the development of adipocyte phenotype. Using the yeast two-hybrid system and GAL4-PPARgamma as bait to screen mouse liver cDNA library, we isolated a mouse steroid receptor coactivator (mSRC-1) involved in nuclear hormone receptor transcriptional activity as a mPPARgamma interactive protein. mSRC-1 cDNA we isolated contains an open reading frame of 1447 amino acids and encodes a new member of the basic helix-loop-helix-PAS domain family. We show that the binding of mSRC-1 to mPPARgamma is ligand independent and coexpression of mSRC-1 with mPPARgamma increases the transcriptional activity of mPPARgamma in the presence of mPPARgamma ligand. We have identified the presence of two putative mPPARgamma binding sites in the mSRC-1, one between residues 620 and 789, and the second between residues 1231 and 1447. These two regions exhibit different degrees of binding affinity for mPPARgamma. We also show that mSRC-1 exhibits its own constitutive transcriptional activity in the yeast as well as in mammalian cells. These results suggest that mSRC-1 interacts with PPARgamma and plays a role in the PPARgamma-mediated signaling pathway.

Expression of transcription factors and stem cell factor precedes hepatocyte differentiation in rat pancreas

Multiple foci of morphologically and functionally differentiated hepatocytes are induced in the pancreas of adult rats subjected to a copper depletion-repletion regimen. Differentiation of hepatocytes in pancreas is preceded by irreversible depletion of over 90% of pancreatic acinar cells. Progressive acinar cell loss during 4-6 weeks of copper deficiency results in the proliferation of oval cells, some of which may serve as the hepatocyte precursor or stem cells. Albumin mRNA is detected in oval cells at 5 and 6 weeks by in situ hybridization at which time no morphologically identifiable hepatocytes are evident in the pancreas. Immunocytochemical analysis demonstrated the presence of stem cell factor (SCF) in proliferating oval cells during 6 weeks of copper depletion, and Northern blot analysis revealed the expression of liver-enriched transcription factors in the rat pancreas during this 4-6-week period of copper deficiency. CCAAT/enhancer binding protein alpha (C/EBP alpha) mRNA was detected first at 4 weeks of copper deficiency. By 5 and 6 weeks of copper deficiency, the expression of mRNAs of C/EBP alpha, beta, and delta, and hepatocyte nuclear factor-3 factor (HNF-3 beta) was markedly enhanced. This enhanced expression of liver-enriched transcription factors and the SCF during oval cell proliferation in the pancreas preceding the expression of albumin mRNA and subsequent differentiation of hepatocyte phenotype further supports the identity of these oval cells as hepatocyte precursors or stem cells.

Human-Induced Pluripotent Stem Cells Manufactured Using a Current Good Manufacturing Practice-Compliant Process Differentiate Into Clinically Relevant Cells From Three Germ Layers

The discovery of reprogramming and generation of human-induced pluripotent stem cells (iPSCs) has revolutionized the field of regenerative medicine and opened new opportunities in cell replacement therapies. While generation of iPSCs represents a significant breakthrough, the clinical relevance of iPSCs for cell-based therapies requires generation of high-quality specialized cells through robust and reproducible directed differentiation protocols. We have recently reported manufacturing of human iPSC master cell banks (MCB) under current good manufacturing practices (cGMPs). Here, we describe the clinical potential of human iPSCs generated using this cGMP-compliant process by differentiating them into the cells from all three embryonic germ layers including ectoderm, endoderm, and mesoderm. Most importantly, we have shown that our iPSC manufacturing process and cell culture system is not biased toward a specific lineage. Following controlled induction into a specific differentiation lineage, specialized cells with morphological and cellular characteristics of neural stem cells, definitive endoderm, and cardiomyocytes were developed. We believe that these cGMP-compliant iPSCs have the potential to make various clinically relevant products suitable for cell therapy applications.

Groundwater quality in the alluvial aquifer system of northwest India: New evidence of the extent of anthropogenic and geogenic contamination

Groundwater depletion has been widely studied in northwest India, but water quality concerns are still poorly constrained. In this study, we explore the hydrochemistry of the top 160m of the aquifer system, through detailed field studies in the Bist-Doab region, considering both anthropogenic and geogenic controls. A detailed comparison is made between sites dominated by urban and agricultural landuse. Salinity, nitrate, chloride and lead concentrations are significantly higher in the shallow (0-50m) groundwater system due to surface anthropogenic contaminant loading from agricultural and urban sources. The widespread occurrence of oxic groundwater within the aquifer system means that denitrification potential is limited and also enhances the mobility of selenium and uranium in groundwater. Geogenic trace elements (e.g. As, Se, F), are generally found at concentrations below WHO guideline drinking water values, however elevated U concentrations (50-70μg/L) are found within the deeper part of the aquifer and shallow urban aquifers associated with higher bicarbonate waters. Higher concentration of Se (10-40μg/L) are found exclusively in the shallow groundwater system where Se is mobilised from soils and transported to depth in the shallow aquifer due to the prevailing oxidising aquifer conditions. New evidence from a range of environmental tracers shows elevated concentrations of anthropogenic contaminants in the deeper part of the aquifer (50-160m deep) and demonstrates vulnerability to vertical migration of contaminants. Continued intensive groundwater abstraction from >100m deep means that water quality risks to the deep aquifer system need to be considered together with water quantity constraints.

Detailed Characterization of Human Induced Pluripotent Stem Cells Manufactured for Therapeutic Applications

We have recently described manufacturing of human induced pluripotent stem cells (iPSC) master cell banks (MCB) generated by a clinically compliant process using cord blood as a starting material (Baghbaderani et al. in Stem Cell Reports, 5(4), 647-659, 2015). In this manuscript, we describe the detailed characterization of the two iPSC clones generated using this process, including whole genome sequencing (WGS), microarray, and comparative genomic hybridization (aCGH) single nucleotide polymorphism (SNP) analysis. We compare their profiles with a proposed calibration material and with a reporter subclone and lines made by a similar process from different donors. We believe that iPSCs are likely to be used to make multiple clinical products. We further believe that the lines used as input material will be used at different sites and, given their immortal status, will be used for many years or even decades. Therefore, it will be important to develop assays to monitor the state of the cells and their drift in culture. We suggest that a detailed characterization of the initial status of the cells, a comparison with some calibration material and the development of reporter sublcones will help determine which set of tests will be most useful in monitoring the cells and establishing criteria for discarding a line.

Derivation, Characterization, and Neural Differentiation of Integration-Free Induced Pluripotent Stem Cell Lines from Parkinson's Disease Patients Carrying SNCA, LRRK2, PARK2, and GBA Mutations

We report generation of induced pluripotent stem cell (iPSC) lines from ten Parkinson’s disease (PD) patients carrying SNCA, PARK2, LRRK2, and GBA mutations, and one age-matched control. After validation of pluripotency, long-term genome stability, and integration-free reprogramming, eight of these lines (one of each SNCA, LRRK2 and GBA, four PARK2 lines, and the control) were differentiated into neural stem cells (NSC) and subsequently to dopaminergic cultures. We did not observe significant differences in the timeline of neural induction and NSC derivation between the patient and control line, nor amongst the patient lines, although we report considerable variability in the efficiency of dopaminergic differentiation among patient lines. We performed whole genome expression analyses of the lines at each stage of differentiation (fibroblast, iPSC, NSC, and dopaminergic culture) in an attempt to identify alterations by large-scale evaluation. While gene expression profiling clearly distinguished cells at different stages of differentiation, no mutation-specific clustering or difference was observed, though consistent changes in patient lines were detected in genes associated mitochondrial biology. We further examined gene expression in a stress model (MPTP-induced dopaminergic neuronal death) using two clones from the SNCA triplication line, and detected changes in genes associated with mitophagy. Our data suggested that even a well-characterized line of a monogenic disease may not be sufficient to determine the cause or mechanism of the disease, and highlights the need to use more focused strategies for large-scale data analysis.

Comparative neurotoxicity screening in human iPSC-derived neural stem cells, neurons and astrocytes

Induced pluripotent stem cells (iPSC) and their differentiated derivatives offer a unique source of human primary cells for toxicity screens. Here, we report on the comparative cytotoxicity of 80 compounds (neurotoxicants, developmental neurotoxicants, and environmental compounds) in iPSC as well as isogenic iPSC-derived neural stem cells (NSC), neurons, and astrocytes. All compounds were tested over a 24-h period at 10 and 100 μM, in duplicate, with cytotoxicity measured using the MTT assay. Of the 80 compounds tested, 50 induced significant cytotoxicity in at least one cell type; per cell type, 32, 38, 46, and 41 induced significant cytotoxicity in iPSC, NSC, neurons, and astrocytes, respectively. Four compounds (valinomycin, 3,3',5,5'-tetrabromobisphenol, deltamethrin, and triphenyl phosphate) were cytotoxic in all four cell types. Retesting these compounds at 1, 10, and 100 μM using the same exposure protocol yielded consistent results as compared with the primary screen. Using rotenone, we extended the testing to seven additional iPSC lines of both genders; no substantial difference in the extent of cytotoxicity was detected among the cell lines. Finally, the cytotoxicity assay was simplified by measuring luciferase activity using lineage-specific luciferase reporter iPSC lines which were generated from the parental iPSC line. This article is part of a Special Issue entitled SI: PSC and the brain.

Research using Mesenchymal Stem/Stromal Cells: quality metric towards developing a reference material

Mesenchymal stem/stromal cells (MSCs) have been extensively investigated for their regenerative, immune-modulatory, and wound healing properties. While the laboratory studies have suggested that MSC's have a unique potential for modulating the etiopathology of multiple diseases, the results from clinical trials have not been encouraging or reproducible. One of the explanations for such variability is explained by the "art" of isolating and propagating MSCs. Therefore, establishing more than minimal criteria to define MSC would help understand best protocols to isolate, propagate and deliver MSCs. Developing a calibration standard, a database and a set of functional tests would be a better quality metric for MSCs. In this review, we discuss the importance of selecting a standard, issues associated with coming up with such a standard and how these issues can be mitigated.

Genetic Modification in Human Pluripotent Stem Cells by Homologous Recombination and CRISPR/Cas9 System

Genetic modification is an indispensable tool to study gene function in normal development and disease. The recent breakthrough of creating human induced pluripotent stem cells (iPSCs) by defined factors (Takahashi et al., Cell 131:861-872, 2007) provides a renewable source of patient autologous cells that not only retain identical genetic information but also give rise to many cell types of the body including neurons and glia. Meanwhile, the rapid advancement of genome modification tools such as gene targeting by homologous recombination (Capecchi, Nat Rev Genet 6:507-512, 2005) and genome editing tools such as CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas (CRISPR-associated) system, TALENs (Transcription activator-like effector nucleases), and ZFNs (Zinc finger nucleases) (Wang et al., Cell 153:910-918, 2013; Mali et al., Science 339:823-826, 2013; Hwang et al., Nat Biotechnol 31:227-229, 2013; Friedland et al., Nat Methods 10(8):741-743, 2013; DiCarlo et al., Nucleic Acids Res 41:4336-4343, 2013; Cong et al., Science 339:819-823, 2013) has greatly accelerated the development of human genome manipulation at the molecular level. This chapter describes the protocols for making neural lineage reporter lines using homologous recombination and the CRISPR/Cas system-mediated genome editing, including construction of targeting vectors, guide RNAs, transfection into hPSCs, and selection and verification of successfully targeted clones. This method can be applied to various needs of hPSC genetic engineering at high efficiency and high reliability.

Developing Induced Pluripotent Stem Cell-Based Therapy for the Masses

The discovery of induced pluripotent stem cells and the ability to manufacture them using clinically compliant protocols has the potential to revolutionize the field of regenerative medicine. However, realizing this potential requires the development of processes that are reliable, reproducible, and cost-effective and that at the same time do not compromise the safety of the individuals receiving this therapy. In the present report, we discuss how cost reductions can be obtained using our experience with obtaining approval of biologic agents, autologous therapy, and the recent approval of cord blood banks. Significance: For therapy to be widely available, the cost of manufacturing stem cells must be reduced. The steps proposed in the present report, when implemented, have the potential to reduce these costs significantly.

Banking on iPSC--is it doable and is it worthwhile

The discovery of induced pluripotent stem cells (iPSCs) and concurrent development of protocols for their cell-type specific differentiation have revolutionized studies of diseases and raised the possibility that personalized medicine may be achievable. Realizing the full potential of iPSC will require addressing the challenges inherent in obtaining appropriate cells for millions of individuals while meeting the regulatory requirements of delivering therapy and keeping costs affordable. Critical to making PSC based cell therapy widely accessible is determining which mode of cell collection, storage and distribution, will work. In this manuscript we suggest that moderate sized bank where a diverse set of lines carrying different combinations of commonly present HLA alleles are banked and differentiated cells are made available to matched recipients as need dictates may be a solution. We discuss the issues related to developing such a bank and how it could be constructed and propose a bank of selected HLA phenotypes from carefully screened healthy individuals as a solution to delivering personalized medicine.

Human Induced Pluripotent Stem Cell NEUROG2 Dual Knockin Reporter Lines Generated by the CRISPR/Cas9 System

Human induced pluripotent stem cell (hiPSC) technologies are powerful tools for modeling development and disease, drug screening, and regenerative medicine. Faithful gene targeting in hiPSCs greatly facilitates these applications. We have developed a fast and precise clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) technology-based method and obtained fluorescent protein and antibiotic resistance dual knockin reporters in hiPSC lines for neurogenin2 (NEUROG2), an important proneural transcription factor. Gene targeting efficiency was greatly improved in CRISPR/Cas9-mediated homology directed recombination (∼ 33% correctly targeted clones) compared to conventional targeting protocol (∼ 3%) at the same locus. No off-target events were detected. In addition, taking the advantage of the versatile applications of the CRISPR/Cas9 system, we designed transactivation components to transiently induce NEUROG2 expression, which helps identify transcription factor binding sites and trans-regulation regions of human NEUROG2. The strategy of using CRISPR/Cas9 genome editing coupled with fluorescence-activated cell sorting of neural progenitor cells in a knockin lineage hiPSC reporter platform might be broadly applicable in other stem cell derivatives and subpopulations.

cGMP-Manufactured Human Induced Pluripotent Stem Cells Are Available for Pre-clinical and Clinical Applications

The discovery of induced pluripotent stem cells (iPSCs) and the concurrent development of protocols for their cell-type-specific differentiation have revolutionized our approach to cell therapy. It has now become critical to address the challenges related to the generation of iPSCs under current good manufacturing practice (cGMP) compliant conditions, including tissue sourcing, manufacturing, testing, and storage. Furthermore, regarding the technical challenges, it is very important to keep the costs of manufacturing and testing reasonable and solve logistic hurdles that permit the global distribution of these products. Here we describe our efforts to develop a process for the manufacturing of iPSC master cell banks (MCBs) under cGMPs and announce the availability of such banks.

Mitochondrial alterations by PARKIN in dopaminergic neurons using PARK2 patient-specific and PARK2 knockout isogenic iPSC lines

In this study, we used patient-specific and isogenic PARK2-induced pluripotent stem cells (iPSCs) to show that mutations in PARK2 alter neuronal proliferation. The percentage of TH(+) neurons was decreased in Parkinson's disease (PD) patient-derived neurons carrying various mutations in PARK2 compared with an age-matched control subject. This reduction was accompanied by alterations in mitochondrial:cell volume fraction (mitochondrial volume fraction). The same phenotype was confirmed in isogenic PARK2 null lines. The mitochondrial phenotype was also seen in non-midbrain neurons differentiated from the PARK2 null line, as was the functional phenotype of reduced proliferation in culture. Whole genome expression profiling at various stages of differentiation confirmed the mitochondrial phenotype and identified pathways altered by PARK2 dysfunction that include PD-related genes. Our results are consistent with current model of PARK2 function where damaged mitochondria are targeted for degradation via a PARK2/PINK1-mediated mechanism.

A platform for rapid generation of single and multiplexed reporters in human iPSC lines

Induced pluripotent stem cells (iPSC) are important tools for drug discovery assays and toxicology screens. In this manuscript, we design high efficiency TALEN and ZFN to target two safe harbor sites on chromosome 13 and 19 in a widely available and well-characterized integration-free iPSC line. We show that these sites can be targeted in multiple iPSC lines to generate reporter systems while retaining pluripotent characteristics. We extend this concept to making lineage reporters using a C-terminal targeting strategy to endogenous genes that express in a lineage-specific fashion. Furthermore, we demonstrate that we can develop a master cell line strategy and then use a Cre-recombinase induced cassette exchange strategy to rapidly exchange reporter cassettes to develop new reporter lines in the same isogenic background at high efficiency. Equally important we show that this recombination strategy allows targeting at progenitor cell stages, further increasing the utility of the platform system. The results in concert provide a novel platform for rapidly developing custom single or dual reporter systems for screening assays.

Can cord blood banks transform into induced pluripotent stem cell banks?

The discovery of induced pluripotent stem cells (iPSCs) and the rapid evolution of clinically compliant protocols to generate such lines from a variety of tissue sources has raised the possibility that personalized medicine may be achievable in the near future. Several strategies to deliver iPSCs for iPSC-derived cell-based therapy have been proposed: one such model has been the cell-banking model, using processes developed by the cord blood industry. The cord blood industry has evolved primarily as a banking model in which units of cord blood harvested from discarded placenta are stored either in a public or a private cord blood bank for future use. The consideration of a cord blood--like banking model has been further spurred by the realization that this population of cells is an ideal starting sample to generate pluripotent cells. Spurred by these technological advances, major efforts are underway to develop a current Good Manufacturing Practice--compliant protocol to generate iPSCs from cord blood and to develop a haplobanking strategy. In this article, we discuss the issues that may affect such an effort.

Enabling consistency in pluripotent stem cell-derived products for research and development and clinical applications through material standards

There is a need for physical standards (reference materials) to ensure both reproducibility and consistency in the production of somatic cell types from human pluripotent stem cell (hPSC) sources. We have outlined the need for reference materials (RMs) in relation to the unique properties and concerns surrounding hPSC-derived products and suggest in-house approaches to RM generation relevant to basic research, drug screening, and therapeutic applications. hPSCs have an unparalleled potential as a source of somatic cells for drug screening, disease modeling, and therapeutic application. Undefined variation and product variability after differentiation to the lineage or cell type of interest impede efficient translation and can obscure the evaluation of clinical safety and efficacy. Moreover, in the absence of a consistent population, data generated from in vitro studies could be unreliable and irreproducible. Efforts to devise approaches and tools that facilitate improved consistency of hPSC-derived products, both as development tools and therapeutic products, will aid translation. Standards exist in both written and physical form; however, because many unknown factors persist in the field, premature written standards could inhibit rather than promote innovation and translation. We focused on the derivation of physical standard RMs. We outline the need for RMs and assess the approaches to in-house RM generation for hPSC-derived products, a critical tool for the analysis and control of product variation that can be applied by researchers and developers. We then explore potential routes for the generation of RMs, including both cellular and noncellular materials and novel methods that might provide valuable tools to measure and account for variation. Multiparametric techniques to identify "signatures" for therapeutically relevant cell types, such as neurons and cardiomyocytes that can be derived from hPSCs, would be of significant utility, although physical RMs will be required for clinical purposes.

Concise review: making and using clinically compliant pluripotent stem cell lines

The field of pluripotent stem cells (PSCs) is in a state of dynamic flux driven by significant advances in the derivation of specific phenotypes from embryonic stem cells, breakthroughs in somatic cell nuclear transfer, and dramatic improvements in generating induced PSCs using zero footprint methods. Spurred by these technological advances, companies have begun to plan clinical studies using human PSC derivatives manufactured in current Good Manufacturing Practice-compliant conditions. In the present review, we discuss the challenges in making these biological products, starting from tissue sourcing to the processes involved in manufacture, storage, and distribution. Additional challenges exist to meeting the regulatory requirements and keeping costs affordable. A model is described that has been proposed by the U.S. National Institutes of Health for reducing the costs and permitting flexibility and innovation by individual investigators. This model, combined with small adjustments in the regulatory processes tailored to address the unique properties of PSCs, has the potential of significantly accelerating the implementation of PSC-based cell therapy.

Xenogeneic-free defined conditions for derivation and expansion of human embryonic stem cells with mesenchymal stem cells

The potential applications of human embryonic stem cells (hESCs) in regenerative medicine and developmental research have made stem cell biology one of the most fascinating and rapidly expanding fields of biomedicine. The first clinical trial of hESCs in humans has begun, and the field of stem cell therapy has just entered a new era. Here, we report seven hESC lines (SEES-1, -2, -3, -4, -5, -6, and -7). Four of them were derived and maintained on irradiated human mesenchymal stem cells (hMSCs) grown in xenogeneic-free defined media and substrate. Xenogeneic-free hMSCs isolated from the subcutaneous tissue of extra fingers from individuals with polydactyly showed appropriate potentials as feeder layers in the pluripotency and growth of hESCs. In this report, we describe a comprehensive characterization of these newly derived SEES cell lines. In addition, we developed a scalable culture system for hESCs having high biological safety by using gamma-irradiated serum replacement and pharmaceutical-grade recombinant basic fibroblast growth factor (bFGF, also known as trafermin). This is first report describing the maintenance of hESC pluripotency using pharmaceutical-grade human recombinant bFGF (trafermin) and gamma-irradiated serum replacement. Our defined medium system provides a path to scalability in Good Manufacturing Practice (GMP) settings for the generation of clinically relevant cell types from pluripotent cells for therapeutic applications.

Transfection, selection, and colony-picking of human induced pluripotent stem cells TALEN-targeted with a GFP gene into the AAVS1 safe harbor

Targeted transgene addition can provide persistent gene expression while circumventing the gene silencing and insertional mutagenesis caused by viral vector mediated random integration. This protocol describes a universal and efficient transgene targeted addition platform in human iPSCs based on utilization of validated open-source TALENs and a gene-trap-like donor to deliver transgenes into a safe harbor locus. Importantly, effective gene editing is rate-limited by the delivery efficiency of gene editing vectors. Therefore, this protocol first focuses on preparation of iPSCs for transfection to achieve high nuclear delivery efficiency. When iPSCs are dissociated into single cells using a gentle-cell dissociation reagent and transfected using an optimized program, >50% cells can be induced to take up the large gene editing vectors. Because the AAVS1 locus is located in the intron of an active gene (PPP1R12C), a splicing acceptor (SA)-linked puromycin resistant gene (PAC) was used to select targeted iPSCs while excluding random integration-only and untransfected cells. This strategy greatly increases the chance of obtaining targeted clones, and can be used in other active gene targeting experiments as well. Two weeks after puromycin selection at the dose adjusted for the specific iPSC line, clones are ready to be picked by manual dissection of large, isolated colonies into smaller pieces that are transferred to fresh medium in a smaller well for further expansion and genetic and functional screening. One can follow this protocol to readily obtain multiple GFP reporter iPSC lines that are useful for in vivo and in vitro imaging and cell isolation.

Rescue of an in vitro neuron phenotype identified in Niemann-Pick disease, type C1 induced pluripotent stem cell-derived neurons by modulating the WNT pathway and calcium signaling

Niemann-Pick disease, type C1 (NPC1) is a familial disorder that has devastating consequences on postnatal development with multisystem effects, including neurodegeneration. There is no Food and Drug Administration-approved treatment option for NPC1; however, several potentially therapeutic compounds have been identified in assays using yeast, rodent models, and NPC1 human fibroblasts. Although these discoveries were made in fibroblasts from NPC1 subjects and were in some instances validated in animal models of the disease, testing these drugs on a cell type more relevant for NPC1 neurological disease would greatly facilitate both study of the disease and identification of more relevant therapeutic compounds. Toward this goal, we have generated an induced pluripotent stem cell line from a subject homozygous for the most frequent NPC1 mutation (p.I1061T) and subsequently created a stable line of neural stem cells (NSCs). These NSCs were then used to create neurons as an appropriate disease model. NPC1 neurons display a premature cell death phenotype, and gene expression analysis of these cells suggests dysfunction of important signaling pathways, including calcium and WNT. The clear readout from these cells makes them ideal candidates for high-throughput screening and will be a valuable tool to better understand the development of NPC1 in neural cells, as well as to develop better therapeutic options for NPC1.

Compounds with species and cell type specific toxicity identified in a 2000 compound drug screen of neural stem cells and rat mixed cortical neurons

Human primary neural tissue is a vital component for the quick and simple determination of chemical compound neurotoxicity in vitro. In particular, such tissue would be ideal for high-throughput screens that can be used to identify novel neurotoxic or neurotherapeutic compounds. We have previously established a high-throughput screening platform using human induced pluripotent stem cell (iPSC)-derived neural stem cells (NSCs) and neurons. In this study, we conducted a 2000 compound screen with human NSCs and rat cortical cells to identify compounds that are selectively toxic to each group. Approximately 100 of the tested compounds showed specific toxicity to human NSCs. A secondary screen of a small subset of compounds from the primary screen on human iPSCs, NSC-derived neurons, and fetal astrocytes validated the results from >80% of these compounds with some showing cell specific toxicity. Amongst those compounds were several cardiac glycosides, all of which were selectively toxic to the human cells. As the screen was able to reliably identify neurotoxicants, many with species and cell-type specificity, this study demonstrates the feasibility of this NSC-driven platform for higher-throughput neurotoxicity screens.

Survival and engraftment of dopaminergic neurons manufactured by a Good Manufacturing Practice-compatible process

BACKGROUND AIMS

We have previously reported a Good Manufacturing Practice (GMP)-compatible process for generating authentic dopaminergic neurons in defined media from human pluripotent stem cells and determined the time point at which dopaminergic precursors/neurons (day 14 after neuronal stem cell [NSC] stage) can be frozen, shipped and thawed without compromising their viability and ability to mature in vitro. One important issue we wished to address is whether dopaminergic precursors/neurons manufactured by our GMP-compatible process can be cryopreserved and engrafted in animal Parkinson disease (PD) models.

METHODS

In this study, we evaluated the efficacy of freshly prepared and cryopreserved dopaminergic neurons in the 6-hydroxydopamine-lesioned rat PD model.

RESULTS

We showed functional recovery up to 6 months post-transplantation in rats transplanted with our cells, whether freshly prepared or cryopreserved. In contrast, no motor improvement was observed in two control groups receiving either medium or cells at a slightly earlier stage (day 10 after NSC stage). Histologic analysis at the end point of the study (6 months post-transplantation) showed robust long-term survival of donor-derived tyrosine hydroxylase (TH)(+) dopaminergic neurons in rats transplanted with day 14 dopaminergic neurons. Moreover, TH(+) fibers emanated from the graft core into the surrounding host striatum. Consistent with the behavioral analysis, no or few TH(+) neurons were detected in animals receiving day 10 cells, although human cells were present in the graft. Importantly, no tumors were detected in any grafted rats, but long-term tumorigenic studies will need to determine the safety of our products.

CONCLUSIONS

Dopaminergic neurons manufactured by a GMP-compatible process from human ESC survived and engrafted efficiently in the 6-OHDA PD rat model.

Stable enhanced green fluorescent protein expression after differentiation and transplantation of reporter human induced pluripotent stem cells generated by AAVS1 transcription activator-like effector nucleases

Human induced pluripotent stem (hiPS) cell lines with tissue-specific or ubiquitous reporter genes are extremely useful for optimizing in vitro differentiation conditions as well as for monitoring transplanted cells in vivo. The adeno-associated virus integration site 1 (AAVS1) locus has been used as a "safe harbor" locus for inserting transgenes because of its open chromatin structure, which permits transgene expression without insertional mutagenesis. However, it is not clear whether targeted transgene expression at the AAVS1 locus is always protected from silencing when driven by various promoters, especially after differentiation and transplantation from hiPS cells. In this paper, we describe a pair of transcription activator-like effector nucleases (TALENs) that enable more efficient genome editing than the commercially available zinc finger nuclease at the AAVS1 site. Using these TALENs for targeted gene addition, we find that the cytomegalovirus-immediate early enhancer/chicken β-actin/rabbit β-globin (CAG) promoter is better than cytomegalovirus 7 and elongation factor 1α short promoters in driving strong expression of the transgene. The two independent AAVS1, CAG, and enhanced green fluorescent protein (EGFP) hiPS cell reporter lines that we have developed do not show silencing of EGFP either in undifferentiated hiPS cells or in randomly and lineage-specifically differentiated cells or in teratomas. Transplanting cardiomyocytes from an engineered AAVS1-CAG-EGFP hiPS cell line in a myocardial infarcted mouse model showed persistent expression of the transgene for at least 7 weeks in vivo. Our results show that high-efficiency targeting can be obtained with open-source TALENs and that careful optimization of the reporter and transgene constructs results in stable and persistent expression in vitro and in vivo.

Efficient generation of astrocytes from human pluripotent stem cells in defined conditions

Astrocytes can be generated from various tissue sources including human pluripotent stem cells (PSC). In this manuscript, we describe a chemically defined xeno-free medium culture system for rapidly generating astrocytes from neural stem cells derived from PSC. We show that astrocyte development in vitro, mimics normal development in vivo, and also passes through a CD44(+) astrocyte precursor stage. Astrocytes generated by our method display similar gene expression patterns, morphological characteristics and functional properties to primary astrocytes, and they survive and integrate after xenotransplantation. Whole genome expression profiling of astrocyte differentiation was performed at several time points of differentiation, and the results indicate the importance of known regulators and identify potential novel regulators and stage-specific lineage markers.

Soliciting strategies for developing cell-based reference materials to advance mesenchymal stromal cell research and clinical translation

The mesenchymal stromal cell (MSC) field continues to rapidly progress with a number of clinical trials initiated and completed, with some reported successes in multiple clinical indications, and a growing number of companies established. The field, nevertheless, faces several challenges. Persistent issues include the definition of a MSC and comparability between MSC preparations. This is because of inherent cell heterogeneity, the absence of markers that are unique to MSCs, and the difficulty in precisely defining them by developmental origin. Differences in the properties of MSCs also depend on the site of tissue harvest, phenotypic and genotypic characteristics of the donor and the isolation, and storage and expansion methods used. These differences may be sufficient to ensure that attributes of the final MSC product could differ in potentially significant ways. Since there are currently no gold standards, we propose using a reference material to establish methods of comparability among MSC preparations. We suggest four possible "ruler scenarios" and a method for global distribution. We further suggest that critical to establishing a reference material is the need to define protocols for comparing cells. The main purpose of this article is to solicit input in establishing a consensus-based comparison. A comparative approach will be critical to all stages of translation to better clarify mechanisms of MSC actions, define an optimal cell manufacturing process, ensure best practice clinical investigations, extend the use of an MSC product for new indications, protect an MSC product from imitators, and develop uniform reimbursement policies. Importantly, a reference material may enable a consensus on a practical definition of MSCs.

hESC-derived Olig2+ progenitors generate a subtype of astroglia with protective effects against ischaemic brain injury

Human pluripotent stem cells (hPSCs) have been differentiated to astroglia, but the utilization of hPSC-derived astroglia as cell therapy for neurological diseases has not been well studied. Astroglia are heterogeneous, and not all astroglia are equivalent in promoting neural repair. A prerequisite for cell therapy is to derive defined cell populations with superior therapeutic effects. Here we use an Olig2-GFP human embryonic stem cell (hESC) reporter to demonstrate that hESC-derived Olig2(+) progenitors generate a subtype of previously uncharacterized astroglia (Olig2PC-Astros). These Olig2PC-Astros differ substantially from astroglia differentiated from Olig2-negative hESC-derived neural progenitor cells (NPC-Astros), particularly in their neuroprotective properties. When grafted into brains subjected to global ischaemia, Olig2PC-Astros exhibit superior neuroprotective effects and improved behavioural outcome compared to NPC-Astros. Thus, this new paradigm of human astroglial differentiation is useful for studying the heterogeneity of human astroglia, and the unique Olig2PC-Astros may constitute a new cell therapy for treating cerebral ischaemia and other neurological diseases.

Comparison of the molecular profiles of human embryonic and induced pluripotent stem cells of isogenic origin

Many studies have compared the genetic and epigenetic profiles of human induced pluripotent stem cells (hiPSCs) to human embryonic stem cells (hESCs) and yet the picture remains unclear. To address this, we derived a population of neural precursor cells (NPCs) from the H1 (WA01) hESC line and generated isogenic iPSC lines by reprogramming. The gene expression and methylation profile of three lines were compared to the parental line and intermediate NPC population. We found no gene probe with expression that differed significantly between hESC and iPSC samples under undifferentiated or differentiated conditions. Analysis of the global methylation pattern also showed no significant difference between the two PSC populations. Both undifferentiated populations were distinctly different from the intermediate NPC population in both gene expression and methylation profiles. One point to note is that H1 is a male line and so extrapolation to female lines should be cautioned. However, these data confirm our previous findings that there are no significant differences between hESCs and hiPSCs at the gene expression or methylation level.

RISC in PD: the impact of microRNAs in Parkinson's disease cellular and molecular pathogenesis

Parkinson's disease (PD) is a debilitating neurodegenerative disease characterized primarily by the selective death of dopaminergic (DA) neurons in the substantia nigra pars compacta of the midbrain. Although several genetic forms of PD have been identified, the precise molecular mechanisms underlying DA neuron loss in PD remain elusive. In recent years, microRNAs (miRNAs) have been recognized as potent post-transcriptional regulators of gene expression with fundamental roles in numerous biological processes. Although their role in PD pathogenesis is still a very active area of investigation, several seminal studies have contributed significantly to our understanding of the roles these small non-coding RNAs play in the disease process. Among these are studies which have demonstrated specific miRNAs that target and down-regulate the expression of PD-related genes as well as those demonstrating a reciprocal relationship in which PD-related genes act to regulate miRNA processing machinery. Concurrently, a wealth of knowledge has become available regarding the molecular mechanisms that unify the underlying etiology of genetic and sporadic PD pathogenesis, including dysregulated protein quality control by the ubiquitin-proteasome system and autophagy pathway, activation of programmed cell death, mitochondrial damage and aberrant DA neurodevelopment and maintenance. Following a discussion of the interactions between PD-related genes and miRNAs, this review highlights those studies which have elucidated the roles of these pathways in PD pathogenesis. We highlight the potential of miRNAs to serve a critical regulatory role in the implicated disease pathways, given their capacity to modulate the expression of entire families of related genes. Although few studies have directly linked miRNA regulation of these pathways to PD, a strong foundation for investigation has been laid and this area holds promise to reveal novel therapeutic targets for PD.

Genome wide profiling of dopaminergic neurons derived from human embryonic and induced pluripotent stem cells

Recent advances in human embryonic stem cell (ESC) and induced pluripotent stem cell (iPSC) biology enable generation of dopaminergic neurons for potential therapy and drug screening. However, our current understanding of molecular and cellular signaling that controls human dopaminergic development and function is limited. Here, we report on a whole genome analysis of gene expression during dopaminergic differentiation of human ESC/iPSC using Illumina bead microarrays. We generated a transcriptome data set containing the expression levels of 28,688 unique transcripts by profiling five lines (three ESC and two iPSC lines) at four stages of differentiation: (1) undifferentiated ESC/iPSC, (2) neural stem cells, (3) dopaminergic precursors, and (4) dopaminergic neurons. This data set provides comprehensive information about genes expressed at each stage of differentiation. Our data indicate that distinct pathways are activated during neural and dopaminergic neuronal differentiation. For example, WNT, sonic hedgehog (SHH), and cAMP signaling pathways were found over-represented in dopaminergic populations by gene enrichment and pathway analysis, and their role was confirmed by perturbation analyses using RNAi (small interfering RNA of SHH and WNT) or small molecule [dibutyryl cyclic AMP (dcAMP)]. In summary, whole genome profiling of dopaminergic differentiation enables systematic analysis of genes/pathways, networks, and cellular/molecular processes that control cell fate decisions. Such analyses will serve as the foundation for better understanding of dopaminergic development, function, and development of future stem cell-based therapies.

Functional screening assays with neurons generated from pluripotent stem cell-derived neural stem cells

Rapid and effective drug discovery for neurodegenerative disease is currently impeded by an inability to source primary neural cells for high-throughput and phenotypic screens. This limitation can be addressed through the use of pluripotent stem cells (PSCs), which can be derived from patient-specific samples and differentiated to neural cells for use in identifying novel compounds for the treatment of neurodegenerative diseases. We have developed an efficient protocol to culture pure populations of neurons, as confirmed by gene expression analysis, in the 96-well format necessary for screens. These differentiated neurons were subjected to viability assays to illustrate their potential in future high-throughput screens. We have also shown that organelles such as nuclei and mitochondria could be live-labeled and visualized through fluorescence, suggesting that we should be able to monitor subcellular phenotypic changes. Neurons derived from a green fluorescent protein-expressing reporter line of PSCs were live-imaged to assess markers of neuronal maturation such as neurite length and co-cultured with astrocytes to demonstrate further maturation. These studies confirm that PSC-derived neurons can be used effectively in viability and functional assays and pave the way for high-throughput screens on neurons derived from patients with neurodegenerative disorders.

LULL(ed) into complacency: a perspective on licenses and stem cell translational science

The US has had a very successful model for facilitating the translation of a basic discovery to a commercial application. The success of the model has hinged on providing clarity on ownership of a discovery, facilitating the licensing process, providing adequate incentive to the inventors, and developing a self-sustaining model for reinvestment. In recent years, technological, political, and regulatory changes have put strains on this model and in some cases have hindered progress rather than facilitated it. This is particularly true for the nascent field of regenerative medicine. To illustrate this, I will describe the contributing practices of several different entities, including universities, repositories, patent trolls, and service providers. It is my hope that the scientific community will be motivated to coordinate efforts against these obstacles to translation.

Tumorigenicity as a clinical hurdle for pluripotent stem cell therapies

Human pluripotent stem cells (PSCs) are a leading candidate for cell-based therapies because of their capacity for unlimited self renewal and pluripotent differentiation. These advances have recently culminated in the first-in-human PSC clinical trials by Geron, Advanced Cell Technology and the Kobe Center for Developmental Biology for the treatment of spinal cord injury and macular degeneration. Despite their therapeutic promise, a crucial hurdle for the clinical implementation of human PSCs is their potential to form tumors in vivo. In this Perspective, we present an overview of the mechanisms underlying the tumorigenic risk of human PSC-based therapies and discuss current advances in addressing these challenges.

Pluripotent stem cells in translation: a Food and Drug Administration-National Institutes of Health collaboration

Recently, the U.S. Food and Drug Administration (FDA), the U.S. National Institutes of Health, and the stem cell research community have collaborated on a series of workshops that address moving pluripotent stem cell therapies into the clinic. The first two workshops in the series focused on preclinical science, and a third, future workshop will focus on clinical trials. This summary addresses major points from both of the recent preclinically focused meetings. When entering into a therapeutics developmental program based on pluripotent cells, investigators must make decisions at the very early stages that will have major ramifications during later phases of development. Presentations and discussions from both invited participants and FDA staff described the need to characterize and document the quality, variability, and suitability of the cells and commercial reagents used at every translational stage. This requires consideration of future regulatory requirements, ranging from donor eligibility of the original source material to the late-stage manufacturing protocols. Federal, industrial, and academic participants agreed that planning backward is the best way to anticipate what evidence will be needed to justify human testing of novel therapeutics and to eliminate wasted efforts.

Using human pluripotent stem cell-derived dopaminergic neurons to evaluate candidate Parkinson's disease therapeutic agents in MPP+ and rotenone models

To begin to develop a high-throughput assay system to evaluate potential small-molecule therapy for Parkinson's disease (PD), we have performed a low-throughput assay with a small number of compounds using human pluripotent stem cell-derived dopaminergic neurons. We first evaluated the role of 44 compounds known to work in rodent systems in a 1-methyl-4-phenylpyridinium (MPP(+)) assay in a 96-well format using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay as a readout for neuroprotection. Glial cell-derived neurotrophic factor was used as a positive control because of its well-documented neuroprotective effect on dopaminergic neurons, and two concentrations of each drug were tested. Of 44 compounds screened, 16 showed a neuroprotective effect at one or both dosages tested. A dose-response curve of a subset of the 16 positives was established in the MPP(+) model. In addition, we validated neuroprotective effects of these compounds in a rotenone-induced dopaminergic neuronal cell death, another established model for PD. Our human primary dopaminergic neuron-based assays provide a platform for rapid screening and/or validation of potential neuroprotective agents in PD treatment using patient-specific cells and show the importance of using human cells for such assays.

Assessing iPSC reprogramming methods for their suitability in translational medicine

The discovery of the ability to induce somatic cells to a pluripotent state through the overexpression of specific transcription factors has the potential to transform the ways in which pharmaceutical agents and cellular transplantation therapies are developed. Proper utilization of the technology to generate induced pluripotent stem cells (iPSCs) requires that researchers select the appropriate reprogramming method for generating iPSCs so that the resulting iPSCs can be transitioned towards clinical applications effectively. This article reviews all of the currently available reprogramming techniques with a focus on critiquing them on the basis of their utility in translational medicine.

Steering a new course for stem cell research: NIH's intramural Center for Regenerative Medicine

The phenomenal progress made in stem cell biology in the past few years has infused the field of regenerative medicine with a great deal of scientific enthusiasm. However, along with the excitement of discovery comes a new sense of translational urgency. The prospect of using embryonic and induced pluripotent stem cell tools and technologies to produce cell-based therapies and other treatments is no longer a distant dream; it is a very real opportunity that demands our attention today. As with most new fields, regenerative medicine has experienced some significant growing pains, and we have identified a number of key obstacles to progress. Given our role as the lead U.S. biomedical research agency and the world's largest supporter of medical research, the National Institutes of Health (NIH) has a responsibility to find ways to reduce or remove many of these obstacles and, consequently, has-and continues-to respond to these challenges in a variety of ways. In this brief essay, we will review our progress and highlight a new development: the founding of a Center for Regenerative Medicine on the NIH campus.

Evaluation of cholesterol reduction activity of methyl-β-cyclodextrin using differentiated human neurons and astrocytes

Recent advances in stem cell technology have enabled large-scale production of human cells such as cardiomyocytes, hepatocytes, and neurons for evaluation of pharmacologic effect and toxicity of drug candidates. The assessment of compound efficacy and toxicity using human cells should lower the high clinical attrition rates of drug candidates by reducing the impact of species differences on drug efficacy and toxicity from animal studies. Methyl-β-cyclodextrin (MBCD) has been shown to reduce lysosomal cholesterol accumulation in skin fibroblasts derived from patients with Niemann Pick type C disease and in the NPC1-/- mouse model. However, the compound has never been tested in human differentiated neurons. We have determined the cholesterol reduction effect of MBCD in neurons differentiated from human neural stem cells (NSCs) and commercially available astrocytes. The use of NSCs for producing differentiated neurons in large quantities can significantly reduce the production time and enhance the reproducibility of screening results. The EC(50) values of MBCD on cholesterol reduction in human neurons and astrocytes were 66.9 and 110.7 µM, respectively. The results indicate that human neurons differentiated from the NSCs and human astrocytes are useful tools for evaluating pharmacologic activity and toxicity of drug candidates to predict their clinical efficacy.

Stromal factors SDF1α, sFRP1, and VEGFD induce dopaminergic neuron differentiation of human pluripotent stem cells

Human embryonic stem cell (hESC)-derived dopaminergic (DA) neurons hold potential for treating Parkinson's disease (PD) through cell replacement therapy. Generation of DA neurons from hESCs has been achieved by coculture with the stromal cell line PA6, a source of stromal cell-derived inducing activity (SDIA). However, the factors produced by stromal cells that result in SDIA are largely undefined. We previously reported that medium conditioned by PA6 cells can generate functional DA neurons from NTera2 human embryonal carcinoma stem cells. Here we show that PA6-conditioned medium can induce DA neuronal differentiation in both NTera2 cells and the hESC I6 cell line. To identify the factor(s) responsible for SDIA, we used large-scale microarray analysis of gene expression combined with mass spectrometric analysis of PA6-conditioned medium (CM). The candidate factors, hepatocyte growth factor (HGF), stromal cell-derived factor-1 α (SDF1α), secreted frizzled-related protein 1 (sFRP1), and vascular endothelial growth factor D (VEGFD) were identified, and their concentrations in PA6 CM were established by immunoaffinity capillary electrophoresis. Upon addition of SDF1α, sFRP1, and VEGFD to the culture medium, we observed an increase in the number of cells expressing tyrosine hydroxylase (a marker for DA neurons) and βIII-tubulin (a marker for immature neurons) in both the NTera2 and I6 cell lines. These results indicate that SDF1α, sFRP1, and VEGFD are major components of SDIA and suggest the potential use of these defined factors to elicit DA differentiation of pluripotent human stem cells for therapeutic intervention in PD.

Human neural crest stem cells derived from human ESCs and induced pluripotent stem cells: induction, maintenance, and differentiation into functional schwann cells

The neural crest (NC) is a transient, multipotent, migratory cell population unique to vertebrates that gives rise to diverse cell lineages. Much of our knowledge of NC development comes from studies of organisms such as chicken and zebrafish because human NC is difficult to obtain because of its transient nature and the limited availability of human fetal cells. Here we examined the process of NC induction from human pluripotent stem cells, including human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs). We showed that NC cells could be efficiently induced from hESCs by a combination of growth factors in medium conditioned on stromal cells and that NC stem cells (NCSCs) could be purified by p75 using fluorescence-activated cell sorting (FACS). FACS-isolated NCSCs could be propagated in vitro in five passages and cryopreserved while maintaining NCSC identity characterized by the expression of a panel of NC markers such as p75, Sox9, Sox10, CD44, and HNK1. In vitro-expanded NCSCs were able to differentiate into neurons and glia (Schwann cells) of the peripheral nervous system, as well as mesenchymal derivatives. hESC-derived NCSCs appeared to behave similarly to endogenous embryonic NC cells when injected in chicken embryos. Using a defined medium, we were able to generate and propagate a nearly pure population of Schwann cells that uniformly expressed glial fibrillary acidic protein, S100, and p75. Schwann cells generated by our protocol myelinated rat dorsal root ganglia neurons in vitro. To our knowledge, this is the first report on myelination by hESC- or iPSC-derived Schwann cells.

Concise review: non-cell autonomous reprogramming: a nucleic acid-free approach to induction of pluripotency

The reprogramming of somatic cells to a pluripotent state by the expression of a defined set of exogenous transcription factors represents a significant breakthrough for the use of stem cells in regenerative medicine. It has the potential to make autologous stem cell therapy practical and promote better understanding of the disease processes by generating patient specific stem cells. Several strategies have been used to generate induced pluripotent stem cells (iPSCs) that include nucleic acid and non-nucleic acid-based approaches, with and without epigenetic modifications. The purpose of these different approaches for generating iPSCs, besides understanding the underlying mechanism, is to develop a facile method for reprogramming without genetic alteration, suitable for clinical use. Here, we discuss different strategies for generating iPSCs, with an emphasis on a recent non-cell autonomous approach to reprogram somatic progenitors that regenerate cornea to a pluripotent state through the recruitment of endogenous transcription factors.

Human glial-restricted progenitor transplantation into cervical spinal cord of the SOD1 mouse model of ALS

Cellular abnormalities are not limited to motor neurons in amyotrophic lateral sclerosis (ALS). There are numerous observations of astrocyte dysfunction in both humans with ALS and in SOD1(G93A) rodents, a widely studied ALS model. The present study therapeutically targeted astrocyte replacement in this model via transplantation of human Glial-Restricted Progenitors (hGRPs), lineage-restricted progenitors derived from human fetal neural tissue. Our previous findings demonstrated that transplantation of rodent-derived GRPs into cervical spinal cord ventral gray matter (in order to target therapy to diaphragmatic function) resulted in therapeutic efficacy in the SOD1(G93A) rat. Those findings demonstrated the feasibility and efficacy of transplantation-based astrocyte replacement for ALS, and also show that targeted multi-segmental cell delivery to cervical spinal cord is a promising therapeutic strategy, particularly because of its relevance to addressing respiratory compromise associated with ALS. The present study investigated the safety and in vivo survival, distribution, differentiation, and potential efficacy of hGRPs in the SOD1(G93A) mouse. hGRP transplants robustly survived and migrated in both gray and white matter and differentiated into astrocytes in SOD1(G93A) mice spinal cord, despite ongoing disease progression. However, cervical spinal cord transplants did not result in motor neuron protection or any therapeutic benefits on functional outcome measures. This study provides an in vivo characterization of this glial progenitor cell and provides a foundation for understanding their capacity for survival, integration within host tissues, differentiation into glial subtypes, migration, and lack of toxicity or tumor formation.

Cell-based therapy for neural disorders--anticipating challenges

Neurological syndromes, such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, Huntington's disease, amyotrophic lateral sclerosis, and lysosomal storage disorders, such as Battens disease, are devastating because they result in increasing loss of cognitive and physical function. Sadly, no drugs are currently available to halt their progression. The relative paucity of curative approaches for these and other conditions of the nervous system have led to a widespread evaluation of alternative treatment modalities including cell-based interventions. Several cell types have been tested successfully in animal models where safety and efficacy have been demonstrated. Early clinical trials have also been initiated in humans, and some have shown a degree of success albeit on a more limited scale than in animal experiments. Recent demonstrations that pluripotent stem cells, such as embryonic stem cells and induced pluripotent stem cells, can differentiate into a variety of specific neural phenotypes has stimulated worldwide enthusiasm for developing cell-based intervention of neurological disease. Indeed, several groups are preparing investigational new drug applications to treat disorders as diverse as macular degeneration, lysosomal storage diseases, and Parkinson's disease. It is noteworthy that cell replacement therapies for neurological conditions face key challenges, some of which are unique, because of the development and organization of the nervous system, its metabolism, and connectivity. Choice of the cell (or cells), the process of manufacturing them, defining the delivery pathway, developing and testing in an appropriate preclinical model, selecting a patient population, and visualizing and following or monitoring patients all pose specific issues as related to the central and peripheral nervous systems. In this review, we address a myriad of challenges that are solvable, but require careful planning and attention to the special demands of the human nervous system.