Chemical ablation of tumor-initiating human pluripotent stem cells

Induced pluripotent stem cell-related approaches to generate dopaminergic neurons for Parkinson's disease

The progressive loss of dopaminergic neurons in affected patient brains is one of the pathological features of Parkinson's disease, the second most common human neurodegenerative disease. Although the detailed pathogenesis accounting for dopaminergic neuron degeneration in Parkinson's disease is still unclear, the advancement of stem cell approaches has shown promise for Parkinson's disease research and therapy. The induced pluripotent stem cells have been commonly used to generate dopaminergic neurons, which has provided valuable insights to improve our understanding of Parkinson's disease pathogenesis and contributed to anti-Parkinson's disease therapies. The current review discusses the practical approaches and potential applications of induced pluripotent stem cell techniques for generating and differentiating dopaminergic neurons from induced pluripotent stem cells. The benefits of induced pluripotent stem cell-based research are highlighted. Various dopaminergic neuron differentiation protocols from induced pluripotent stem cells are compared. The emerging three-dimension-based brain organoid models compared with conventional two-dimensional cell culture are evaluated. Finally, limitations, challenges, and future directions of induced pluripotent stem cell-based approaches are analyzed and proposed, which will be significant to the future application of induced pluripotent stem cell-related techniques for Parkinson's disease.

Optical Precise Ablation of Targeted Individual Neurons In Vivo

Targeted cell ablation is a powerful strategy for investigating the function of individual neurons within neuronal networks. Multiphoton ablation technology by a tightly focused femtosecond laser, with its significant advantages of noninvasiveness, high efficiency, and single-cell resolution, has been widely used in the study of neuroscience. However, the firing activity of the ablated neuron and its impact on the surrounding neurons and entire neuronal ensembles are still unclear. In this study, we describe the depolarization process of targeted neuron ablation by a femtosecond laser based on a standard two-photon microscope in vitro and in vivo. The photoporation damages the cell membrane, depolarizes the membrane potential, and thus disables the neuron's ability to fire action potentials. The dysfunctional neuron after laser ablation affects both the responses of surrounding neighbors and the functions of ensemble neurons in vivo. Although abnormal Ca2+ responses in spatially surrounding neurons are observed, the damage effect is confined to the focal volume. The function of the neuronal ensembles that associate with a specific visual stimulation is not influenced by the ablation of an individual member of the ensemble, indicating the redundancy of the ensemble organization. This study thus provides an insight into the targeted neuron ablation as well as the role of an individual neuron in an ensemble.

Scalable Bioreactor-based Suspension Approach to Generate Stem Cell-derived Islets From Healthy Donor-derived iPSCs

BACKGROUND

Induced pluripotent stem cells (iPSCs) offer the potential to generate autologous iPSC-derived islets (iPSC islets), however, remain limited by scalability and product safety.

METHODS

Herein, we report stagewise characterization of cells generated following a bioreactor-based differentiation protocol. Cell characteristics were assessed using flow cytometry, quantitative reverse transcription polymerase chain reaction, patch clamping, functional assessment, and in vivo functional and immunohistochemistry evaluation. Protocol yield and costs are assessed to determine scalability.

RESULTS

Differentiation was capable of generating 90.4% PDX1 + /NKX6.1 + pancreatic progenitors and 100% C-peptide + /NKX6.1 + iPSC islet cells. However, 82.1%, 49.6%, and 0.9% of the cells expressed SOX9 (duct), SLC18A1 (enterochromaffin cells), and CDX2 (gut cells), respectively. Explanted grafts contained mature monohormonal islet-like cells, however, CK19 + ductal tissues persist. Using this protocol, semi-planar differentiation using 150 mm plates achieved 5.72 × 10 4 cells/cm 2 (total 8.3 × 10 6 cells), whereas complete suspension differentiation within 100 mL Vertical-Wheel bioreactors significantly increased cell yield to 1.1 × 10 6 cells/mL (total 105.0 × 10 6 cells), reducing costs by 88.8%.

CONCLUSIONS

This study offers a scalable suspension-based approach for iPSC islet differentiation within Vertical-Wheel bioreactors with thorough characterization of the ensuing product to enable future protocol comparison and evaluation of approaches for off-target cell elimination. Results suggest that bioreactor-based suspension differentiation protocols may facilitate scalability and clinical implementation of iPSC islet therapies.

Research progress of autoimmune diseases based on induced pluripotent stem cells

Autoimmune diseases can damage specific or multiple organs and tissues, influence the quality of life, and even cause disability and death. A 'disease in a dish' can be developed based on patients-derived induced pluripotent stem cells (iPSCs) and iPSCs-derived disease-relevant cell types to provide a platform for pathogenesis research, phenotypical assays, cell therapy, and drug discovery. With rapid progress in molecular biology research methods including genome-sequencing technology, epigenetic analysis, '-omics' analysis and organoid technology, large amount of data represents an opportunity to help in gaining an in-depth understanding of pathological mechanisms and developing novel therapeutic strategies for these diseases. This paper aimed to review the iPSCs-based research on phenotype confirmation, mechanism exploration, drug discovery, and cell therapy for autoimmune diseases, especially multiple sclerosis, inflammatory bowel disease, and type 1 diabetes using iPSCs and iPSCs-derived cells.

Innovations in Stem Cell Therapy for Diabetic Wound Healing

Significance: The global burden of diabetic wounds, particularly diabetic foot ulcers, continues to have large economic and social impact throughout the world. Current strategies are not sufficient to overcome this burden of disease. Finding newer, more advanced regenerative cell and tissue-based strategies to reduce morbidity remains paramount. Recent Advances: Recent advances in stem cell therapies are discussed. We also highlight the practical issues of translating these advancing technologies into the clinical setting. Critical Issues: We discuss the use of somatic and induced pluripotent stem cells and the stromal vascular fraction, as well as innovations, including the use of 3D bioprinting of skin. We also explore related issues of using regenerative techniques in clinical practice, including the current regulatory landscape and translatability of in vivo research. Future Directions: Advances in stem cell manipulation showcase the best therapeutic resources available to enhance mechanisms of wound healing such as angiogenesis, cell proliferation, and collagen synthesis; potential methods include changing the scaffold microenvironment, including relative oxygen tension, and the use of gene modification and nanotechnology. Secretome engineering, particularly the use of extracellular vesicles, may be another potential cell-derived therapeutic that may enable use of cell-free translational therapy.

Optimizing Generation of Stem Cell-Derived Islet Cells

Islet transplantation is a highly effective treatment for select patients with type 1 diabetes. Unfortunately, current use is limited to those with brittle disease due to donor limitations and immunosuppression requirements. Discovery of factors for induction of pluripotent stem cells from adult somatic cells into a malleable state has reinvigorated the possibility of autologous-based regenerative cell therapies. Similarly, recent progress in allogeneic human embryonic stem cell islet products is showing early success in clinical trials. Describing safe and standardized differentiation protocols with clear pathways to optimize yield and minimize off-target growth is needed to efficiently move the field forward. This review discusses current islet differentiation protocols with a detailed break-down of differentiation stages to guide step-wise controlled generation of functional islet products.

Xeno-Free Integrated Platform for Robust Production of Cardiomyocyte Sheets from hiPSCs

Human induced pluripotent stem cells (hiPSCs) can be efficiently differentiated into cardiomyocytes (CMs), which can be used for cardiac disease modeling, for drug screening, and to regenerate damaged myocardium. Implementation of xeno-free culture systems is essential to fully explore the potential of these cells. However, differentiation using xeno-free adhesion matrices often results in low CM yields and lack of functional CM sheets, capable of enduring additional maturation stages. Here, we established a xeno-free CM differentiation platform using TeSR/Synthemax, including a replating step and integrated with two versatile purification/enrichment metabolic approaches. Results showed that the replating step was essential to reestablish a fully integrated, closely-knit CM sheet. In addition, replating contributed to increase the cTnT expression from 65% to 75% and the output from 2.2 to 3.1 CM per hiPSC, comparable with the efficiency observed when using TeSR/Matrigel. In addition, supplementation with PluriSin1 and Glu-Lac+ medium allowed increasing the CM content over 80% without compromising CM sheet integrity or functionality. Thus, this xeno-free differentiation platform is a reliable and robust method to produce hiPSC-derived CMs, increasing the possibility of using these cells safely for a wide range of applications.

Characterization of stem-cell-derived islets during differentiation and after implantation

Recapitulation of embryonic pancreatic development has enabled development of methods for in vitro islet cell differentiation using human pluripotent stem cells (hPSCs), which have the potential to cure diabetes. Advanced methods for optimal generation of stem-cell-derived islets (SC-islets) has enabled successful diabetes reversal in rodents and shown promising early clinical trial outcomes. The main impediment for use of SC-islets is concern about safety because of off-target growth resulting from contaminated residual cells. In this review, we summarize the different endocrine and non-endocrine cell populations that have been described to emerge throughout β cell differentiation and after transplantation. We discuss the most recent approaches to enrich endocrine populations and remove off-target cells. Finally, we discuss the critical quality control and release criteria testing that we anticipate will be required prior to transplantation to ensure product safety.

The Tumorigenic Potential of Human Pluripotent Stem Cells

Human pluripotent stem cells (hPSCs) are currently evaluated for clinical applications due to their proliferation and differentiation capacities, raising the need to both assess and enhance, the safety of hPSC-based treatments. Distinct molecular features contribute to the tumorigenicity of hPSCs, manifested in the formation of teratoma tumors upon transplantation in vivo. Prolonged in vitro culturing of hPSCs can enhance selection for specific genetic aberrations, either at the chromosome or gene level. Some of these aberrations are tightly linked to human tumor pathology and increase the tumorigenic aggressiveness of the abnormal cells. In this perspective, we describe major tumor-associated risk factors entailed in hPSC-based therapy, and present precautionary and safety measures relevant for the development and application of such therapies.

The Impact of Acquired Genetic Abnormalities on the Clinical Translation of Human Pluripotent Stem Cells

Human pluripotent stem cells (hPSC) are known to acquire chromosomal abnormalities, which range from point mutations to large copy number changes, including full chromosome aneuploidy. These aberrations have a wide-ranging influence on the state of cells, in both the undifferentiated and differentiated state. Currently, very little is known on how these abnormalities will impact the clinical translation of hPSC, and particularly their potential to prime cells for oncogenic transformation. A further complication is that many of these abnormalities exist in a mosaic state in culture, which complicates their detection with conventional karyotyping methods. In this review we discuss current knowledge on how these aberrations influence the cell state and how this may impact the future of research and the cells’ clinical potential.

Cell surface markers for immunophenotyping human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cells (hPSC) self-renew and represent a potentially unlimited source for the production of cardiomyocytes (CMs) suitable for studies of human cardiac development, drug discovery, cardiotoxicity testing, and disease modelling and for cell-based therapies. However, most cardiac differentiation protocols yield mixed cultures of atrial-, ventricular-, and pacemaker-like cells at various stages of development, as well as non-CMs. The proportions and maturation states of these cell types result from disparities among differentiation protocols and time of cultivation, as well as hPSC reprogramming inconsistencies and genetic background variations. The reproducible use of hPSC-CMs for research and therapy is therefore limited by issues of cell population heterogeneity and functional states of maturation. A validated method that overcomes issues of cell heterogeneity is immunophenotyping coupled with live cell sorting, an approach that relies on accessible surface markers restricted to the desired cell type(s). Here we review current progress in unravelling heterogeneity in hPSC-cardiac cultures and in the identification of surface markers suitable for defining cardiac identity, subtype specificity, and maturation states.

Cell-Based Therapeutic Approaches for Cystic Fibrosis

Cystic Fibrosis (CF) is a chronic autosomal recessive disease caused by defects in the cystic fibrosis transmembrane conductance regulator gene (CFTR). Cystic Fibrosis affects multiple organs but progressive remodeling of the airways, mucus accumulation, and chronic inflammation in the lung, result in lung disease as the major cause of morbidity and mortality. While advances in management of CF symptoms have increased the life expectancy of this devastating disease, and there is tremendous excitement about the potential of new agents targeting the CFTR molecule itself, there is still no curative treatment. With the recent advances in the identification of endogenous airway progenitor cells and in directed differentiation of pluripotent cell sources, cell-based therapeutic approaches for CF have become a plausible treatment method with the potential to ultimately cure the disease. In this review, we highlight the current state of cell therapy in the CF field focusing on the relevant autologous and allogeneic cell populations under investigation and the challenges associated with their use. In addition, we present advances in induced pluripotent stem (iPS) cell approaches and emerging new genetic engineering methods, which have the capacity to overcome the current limitations hindering cell therapy approaches.

Prevention of tumor risk associated with the reprogramming of human pluripotent stem cells

Human pluripotent embryonic stem cells have two special features: self-renewal and pluripotency. It is important to understand the properties of pluripotent stem cells and reprogrammed stem cells. One of the major problems is the risk of reprogrammed stem cells developing into tumors. To understand the process of differentiation through which stem cells develop into cancer cells, investigators have attempted to identify the key factors that generate tumors in humans. The most effective method for the prevention of tumorigenesis is the exclusion of cancer cells during cell reprogramming. The risk of cancer formation is dependent on mutations of oncogenes and tumor suppressor genes during the conversion of stem cells to cancer cells and on the environmental effects of pluripotent stem cells. Dissecting the processes of epigenetic regulation and chromatin regulation may be helpful for achieving correct cell reprogramming without inducing tumor formation and for developing new drugs for cancer treatment. This review focuses on the risk of tumor formation by human pluripotent stem cells, and on the possible treatment options if it occurs. Potential new techniques that target epigenetic processes and chromatin regulation provide opportunities for human cancer modeling and clinical applications of regenerative medicine.

Elimination of Teratogenic Human Induced Pluripotent Stem Cells by Bee Venom via Calcium-Calpain Pathway

Induced pluripotent stem cells (iPSCs) are regarded as a promising option for cell-based regenerative medicine. To obtain safe and efficient iPSC-based cell products, it is necessary to selectively eliminate the residual iPSCs prior to in vivo implantation due to the risk of teratoma formation. Bee venom (BV) has long been used in traditional Chinese medicine to treat inflammatory diseases and relieve pain, and has been shown to exhibit anti-cancer, anti-mutagenic, anti-nociceptive, and radioprotective activities. However, the potential benefits of BV in iPSC therapy, particularly its anti-teratoma activity, have not been examined. In this study, we found that BV selectively induced cell death in iPSCs, but not in iPSC-derived differentiated cells (iPSCs-Diff). BV rapidly disrupted cell membrane integrity and focal adhesions, followed by induction of apoptosis and necroptosis in iPSCs. We also found that BV remarkably enhanced intracellular calcium levels, calpain activation, and reactive oxygen speciesgeneration in iPSCs. BV treatment before in ovo grafting efficiently prevented iPSC-derived teratoma formation. In contrast, no DNA damage was observed in iPSCs-Diff following BV treatment, further demonstrating the safety of BV for use with iPSCs-Diff. Taken together, these findings show that BV has potent anti-teratoma activity by eliminating residual iPSCs, and can be used for the development of effective and safe iPSC-based cell therapies.

Ethanol extract of Magnoliae cortex (EEMC) limits teratoma formation of pluripotent stem cells by selective elimination of undifferentiated cells through the p53-dependent mitochondrial apoptotic pathway

BACKGROUND

Induced pluripotent stem cells (iPSCs) are regarded as the best potential cell source for cell-based regenerative medicine. To develop a safe and efficient iPSC-based cell therapy, it is very important to avoid possible teratoma formation, which can arise from undifferentiated iPSCs (USCs) remaining among differentiated cell products. Dried bark of Magnolia officinalis (Magnolia cortex, MC) has long been used in traditional medicine to treat gastrointestinal ailments and allergic diseases, and has shown have various pharmacological activities, including anti-bacterial, anti-inflammatory, and anti-cancer effects. However, its effects on iPSCs have not yet been examined.

PURPOSE

In this study, we investigated the selective cytotoxic effects of ethanol extract of MC (EEMC) on undifferentiated iPSCs and elucidated the underlying apoptotic mechanisms in detail. We also investigated the inhibitory effects of EEMC on teratoma formation via in ovo experiments.

RESULTS

We found that EEMC greatly reduced cell growth and induced apoptotic cell death in USCs, but not in differentiated or normal cells. EEMC caused G2/M cell cycle arrest, mitochondrial damage, and caspase activation of USCs, accompanied by p53 accumulation. In p53KO human iPSCs, EEMC had no cytotoxicity, reinforcing that EEMC-mediated apoptosis of USCs is p53-dependent. EEMC did not cause DNA damage in iPSC-derived differentiated cells. In ovo teratoma formation assay revealed that EEMC treatment before injection efficiently eliminated USCs and prevented teratoma formation.

CONCLUSIONS

These results collectively indicate that EEMC has potent anti-teratoma activity, and therefore can be used for the development of safe iPSC-based therapy.

Report of the Key Opinion Leaders Meeting on Stem Cell-derived Beta Cells

Beta cell replacement has the potential to restore euglycemia in patients with insulin-dependent diabetes. Although great progress has been made in establishing allogeneic islet transplantation from deceased donors as the standard of care for those with the most labile diabetes, it is also clear that the deceased donor organ supply cannot possibly treat all those who could benefit from restoration of a normal beta cell mass, especially if immunosuppression were not required. Against this background, the International Pancreas and Islet Transplant Association in collaboration with the Harvard Stem Cell Institute, the Juvenile Diabetes Research Foundation (JDRF), and the Helmsley Foundation held a 2-day Key Opinion Leaders Meeting in Boston in 2016 to bring together experts in generating and transplanting beta cells derived from stem cells. The following summary highlights current technology, recent significant breakthroughs, unmet needs and roadblocks to stem cell-derived beta cell therapies, with the aim of spurring future preclinical collaborative investigations and progress toward the clinical application of stem cell-derived beta cells.

Atorvastatin Inhibits the HIF1α-PPAR Axis, Which Is Essential for Maintaining the Function of Human Induced Pluripotent Stem Cells

We herein report a novel mechanism of action of statin preparations using a new drug discovery method. Milk fat globule-EGF factor 8 protein (MFG-E8) was identified from the secretory component of mouse embryonic fibroblast (MEF) as a cell adhesion-promoting factor effective for screening active cellular agents of human induced pluripotent stem cells (hiPSCs) in vitro using electrochemical impedance. Our analyses showed that atorvastatin did not cause death in myocardial cells differentiated from hiPSCs but reduced the pluripotent cell survival in vitro when using serum- and albumin-free media, and inhibited the ability to form teratomas in mice. This result could have been already the cytopathic effect of atorvastatin, and complete elimination of hiPSCs was confirmed in the xenotransplantation assay. The administration of atorvastatin to hiPSCs caused the expression of hypoxia inducible factor (HIF)1α mRNA to be unchanged at 6 hr and downregulated at 24 hr. In addition, the inhibition of the survival of hiPSCs was confirmed by HIF1α-peroxisome proliferator-activated receptor (PPAR) axis inhibition. These results suggest that the addition of atorvastatin to hiPSC cultures reduces the survival of pluripotent cells by suppressing the HIF1α-PPAR axis. In summary, the HIF1α-PPAR axis has an important role in maintaining the survival of pluripotent hiPSCs.

Genetic and epigenetic factors which modulate differentiation propensity in human pluripotent stem cells

BACKGROUND

Human pluripotent stem cell (hPSC) lines are known to have a bias in their differentiation. This gives individual cell lines a propensity to preferentially differentiate towards one germ layer or cell type over others. Chromosomal aberrations, mitochondrial mutations, genetic diversity and epigenetic variance are the main drivers of this phenomenon, and can lead to a wide range of phenotypes.

OBJECTIVE AND RATIONALE

Our aim is to provide a comprehensive overview of the different factors which influence differentiation propensity. Specifically, we sought to highlight known genetic variances and their mechanisms, in addition to more general observations from larger abnormalities. Furthermore, we wanted to provide an up-to-date list of a growing number of predictive indicators which are able to identify differentiation propensity before the initiation of differentiation. As differentiation propensity can lead to difficulties in both research as well as clinical translation, our thorough overview could be a useful tool.

SEARCH METHODS

Combinations of the following key words were applied as search criteria in the PubMed database: embryonic stem cells, induced pluripotent stem cells, differentiation propensity (also: potential, efficiency, capacity, bias, variability), epigenetics, chromosomal abnormalities, genetic aberrations, X chromosome inactivation, mitochondrial function, mitochondrial metabolism, genetic diversity, reprogramming, predictive marker, residual stem cell, clinic. Only studies in English were included, ranging from 2000 to 2017, with a majority ranging from 2010 to 1017. Further manuscripts were added from cross-references.

OUTCOMES

Differentiation propensity is affected by a wide variety of (epi)genetic factors. These factors clearly lead to a loss of differentiation capacity, preference towards certain cell types and oftentimes, phenotypes which begin to resemble cancer. Broad changes in (epi)genetics, such as aneuploidies or wide-ranging modifications to the epigenetic landscape tend to lead to extensive, less definite changes in differentiation capacity, whereas more specific abnormalities often have precise ramifications in which certain cell types become more preferential. Furthermore, there appears to be a greater, though often less considered, contribution to differentiation propensity by factors such as mitochondria and inherent genetic diversity. Varied differentiation capacity can also lead to potential consequences in the clinical translation of hPSC, including the occurrence of residual undifferentiated stem cells, and the transplantation of potentially transformed cells.

WIDER IMPLICATIONS

As hPSC continue to advance towards the clinic, our understanding of them progresses as well. As a result, the challenges faced become more numerous, but also more clear. If the transition to the clinic is to be achieved with a minimum number of potential setbacks, thorough evaluation of the cells will be an absolute necessity. Altered differentiation propensity represents at least one such hurdle, for which researchers and eventually clinicians will need to find solutions. Already, steps are being taken to tackle the issue, though further research will be required to evaluate any long-term risks it poses.

Islet encapsulation

Review of emerging advances and persisting challenges in the engineering and translation of islet encapsulation technologies.

Mitophagy-driven mitochondrial rejuvenation regulates stem cell fate

Our understanding on how selective mitochondrial autophagy, or mitophagy, can sustain the archetypal properties of stem cells is incomplete. PTEN-induced putative kinase 1 (PINK1) plays a key role in the maintenance of mitochondrial morphology and function and in the selective degradation of damaged mitochondria by mitophagy. Here, using embryonic fibroblasts from PINK1 gene-knockout (KO) mice, we evaluated whether mitophagy is a causal mechanism for the control of cell-fate plasticity and maintenance of pluripotency. Loss of PINK1-dependent mitophagy was sufficient to dramatically decrease the speed and efficiency of induced pluripotent stem cell (iPSC) reprogramming. Mitophagy-deficient iPSC colonies, which were characterized by a mixture of mature and immature mitochondria, seemed unstable, with a strong tendency to spontaneously differentiate and form heterogeneous populations of cells. Although mitophagy-deficient iPSC colonies normally expressed pluripotent markers, functional monitoring of cellular bioenergetics revealed an attenuated glycolysis in mitophagy-deficient iPSC cells. Targeted metabolomics showed a notable alteration in numerous glycolysis- and TCA-related metabolites in mitophagy-deficient iPSC cells, including a significant decrease in the intracellular levels of α-ketoglutarate -a key suppressor of the differentiation path in stem cells. Mitophagy-deficient iPSC colonies exhibited a notably reduced teratoma-initiating capacity, but fully retained their pluripotency and multi-germ layer differentiation capacity in vivo. PINK1-dependent mitophagy pathway is an important mitochondrial switch that determines the efficiency and quality of somatic reprogramming. Mitophagy-driven mitochondrial rejuvenation might contribute to the ability of iPSCs to suppress differentiation by directing bioenergetic transition and metabolome remodeling traits. These findings provide new insights into how mitophagy might influence the stem cell decisions to retain pluripotency or differentiate in tissue regeneration and aging, tumor growth, and regenerative medicine.

Helping Induced hPSCs Clean Up Their Act

Inhibition of the tumorigenic potential of human pluripotent stem cells (hPSCs) remains critically important for safe hPSC-based therapy. In this issue of Cell Chemical Biology, Kuang et al. (2017) reveal that the phospho-D-peptide D-3 efficiently induces death of residual hPSCs, but not of differentiated progenies, through high alkaline phosphatase activity in hPSCs.

Elimination of undifferentiated human embryonic stem cells by cardiac glycosides

An important safety concern in the use of human pluripotent stem cells (hPSCs) is tumorigenic risk, because these cells can form teratomas after an in vivo injection at ectopic sites. Several thousands of undifferentiated hPSCs are sufficient to induce teratomas in a mouse model. Thus, it is critical to remove all residue-undifferentiated hPSCs that have teratoma potential before the clinical application of hPSC-derived cells. In this study, our data demonstrated the cytotoxic effects of cardiac glycosides, such as digoxin, lanatoside C, bufalin, and proscillaridin A, in human embryonic stem cells (hESCs). This phenomenon was not observed in human bone marrow mesenchymal stem cells (hBMMSCs). Most importantly, digoxin and lanatoside C did not affect the stem cells’ differentiation ability. Consistently, the viability of the hESC-derived MSCs, neurons, and endothelium cells was not affected by the digoxin and lanatoside C treatment. Furthermore, the in vivo experiments demonstrated that digoxin and lanatoside C prevented teratoma formation. To the best of our knowledge, this study is the first to describe the cytotoxicity and tumor prevention effects of cardiac glycosides in hESCs. Digoxin and lanatoside C are also the first FDA-approved drugs that demonstrated cytotoxicity in undifferentiated hESCs.

Technical approaches to induce selective cell death of pluripotent stem cells

Despite the recent promising results of clinical trials using human pluripotent stem cell (hPSC)-based cell therapies for age-related macular degeneration (AMD), the risk of teratoma formation resulting from residual undifferentiated hPSCs remains a serious and critical hurdle for broader clinical implementation. To mitigate the tumorigenic risk of hPSC-based cell therapy, a variety of approaches have been examined to ablate the undifferentiated hPSCs based on the unique molecular properties of hPSCs. In the present review, we offer a brief overview of recent attempts at selective elimination of undifferentiated hPSCs to decrease the risk of teratoma formation in hPSC-based cell therapy.

The Nexus of Stem Cell-Derived Beta-Cells and Genome Engineering

Diabetes, type 1 and type 2 (T1D and T2D), are diseases of epidemic proportions, which are complicated and defined by genetics, epigenetics, environment, and lifestyle choices. Current therapies consist of whole pancreas or islet transplantation. However, these approaches require life-time immunosuppression, and are compounded by the paucity of available donors. Pluripotent stem cells have advanced research in the fields of stem cell biology, drug development, disease modeling, and regenerative medicine, and importantly allows for the interrogation of therapeutic interventions. Recent developments in beta-cell differentiation and genomic modifications are now propelling investigations into the mechanisms behind beta-cell failure and autoimmunity, and offer new strategies for reducing the propensity for immunogenicity. This review discusses the derivation of endocrine lineage cells from human pluripotent stem cells for the treatment of diabetes, and how the editing or manipulation of their genomes can transcend many of the remaining challenges of stem cell technologies, leading to superior transplantation and diabetes drug discovery platforms.

A preliminary analysis of volatile metabolites of human induced pluripotent stem cells along the in vitro differentiation

Cellular metabolism of stem cell biology is still an unexplored field. However, considering the amount of information carried by metabolomes, this is a promising field for a fast identification of stem cells itself and during the differentiation process. One of the goals of such application is the identification of residual pluripotent cells before cell transplantation to avoid the occurrence of teratomas. In this paper, we investigated in vitro the volatile compounds (VOCs) released during human induced pluripotent stem cells (hiPSCs) reprogramming. In particular, we studied hiPSCs differentiation to floating and adherent embryoid bodies until early neural progenitor cells. A preliminary Gas Chromatographic/Mass Spectrometer (GC/MS) analysis, based on a single extraction method and chromatographic separation, indicated 17 volatile compounds whose relative abundance is altered in each step of the differentiation process. The pattern of VOCs shown by hiPSCs is well distinct and makes these cells sharply separated from the other steps of differentiations. Similar behaviour has also been observed with an array of metalloporphyrins based gas sensors. The use of electronic sensors to control the process of differentiation of pluripotent stem cells might suggest a novel perspective for a fast and on-line control of differentiation processes.

Cardiomyocyte Differentiation Promotes Cell Survival During Nicotinamide Phosphoribosyltransferase Inhibition Through Increased Maintenance of Cellular Energy Stores

To address concerns regarding the tumorigenic potential of undifferentiated human pluripotent stem cells (hPSC) that may remain after in vitro differentiation and ultimately limit the broad use of hPSC‐derivatives for therapeutics, we recently described a method to selectively eliminate tumorigenic hPSC from their progeny by inhibiting nicotinamide phosphoribosyltransferase (NAMPT). Limited exposure to NAMPT inhibitors selectively removes hPSC from hPSC‐derived cardiomyocytes (hPSC‐CM) and spares a wide range of differentiated cell types; yet, it remains unclear when and how cells acquire resistance to NAMPT inhibition during differentiation. In this study, we examined the effects of NAMPT inhibition among multiple time points of cardiomyocyte differentiation. Overall, these studies show that in vitro cardiomyogenic commitment and continued culturing provides resistance to NAMPT inhibition and cell survival is associated with the ability to maintain cellular ATP pools despite depletion of NAD levels. Unlike cells at earlier stages of differentiation, day 28 hPSC‐CM can survive longer periods of NAMPT inhibition and maintain ATP generation by glycolysis and/or mitochondrial respiration. This is distinct from terminally differentiated fibroblasts, which maintain mitochondrial respiration during NAMPT inhibition. Overall, these results provide new mechanistic insight into how regulation of cellular NAD and energy pools change with hPSC‐CM differentiation and further inform how NAMPT inhibition strategies could be implemented within the context of cardiomyocyte differentiation. Stem Cells Translational Medicine2017;6:1191–1201

Clinical potential of human-induced pluripotent stem cells : Perspectives of induced pluripotent stem cells

The recent establishment of induced pluripotent stem (iPS) cells promises the development of autologous cell therapies for degenerative diseases, without the ethical concerns associated with human embryonic stem (ES) cells. Initially, iPS cells were generated by retroviral transduction of somatic cells with core reprogramming genes. To avoid potential genotoxic effects associated with retroviral transfection, more recently, alternative non-viral gene transfer approaches were developed. Before a potential clinical application of iPS cell-derived therapies can be planned, it must be ensured that the reprogramming to pluripotency is not associated with genome mutagenesis or epigenetic aberrations. This may include direct effects of the reprogramming method or "off-target" effects associated with the reprogramming or the culture conditions. Thus, a rigorous safety testing of iPS or iPS-derived cells is imperative, including long-term studies in model animals. This will include not only rodents but also larger mammalian model species to allow for assessing long-term stability of the transplanted cells, functional integration into the host tissue, and freedom from undifferentiated iPS cells. Determination of the necessary cell dose is also critical; it is assumed that a minimum of 1 billion transplantable cells is required to achieve a therapeutic effect. This will request medium to long-term in vitro cultivation and dozens of cell divisions, bearing the risk of accumulating replication errors. Here, we review the clinical potential of human iPS cells and evaluate which are the most suitable approaches to overcome or minimize risks associated with the application of iPS cell-derived cell therapies.

Transgene Reactivation in Induced Pluripotent Stem Cell Derivatives and Reversion to Pluripotency of Induced Pluripotent Stem Cell-Derived Mesenchymal Stem Cells

Induced pluripotent stem cells (iPSCs) have enormous potential in regenerative medicine and disease modeling. It is now felt that clinical trials should be performed with iPSCs derived with nonintegrative constructs. Numerous studies, however, including those describing disease models, are still being published using cells derived from iPSCs generated with integrative constructs. Our experimental work presents the first evidence of spontaneous transgene reactivation in vitro in several cellular types. Our results show that the transgenes were predominantly silent in parent iPSCs, but in mesenchymal and endothelial iPSC derivatives, the transgenes experienced random upregulation of Nanog and c-Myc. Additionally, we provide evidence of spontaneous secondary reprogramming and reversion to pluripotency in mesenchymal stem cells derived from iPSCs. These findings strongly suggest that the studies, which use cellular products derived from iPSCs generated with retro- or lentiviruses, should be evaluated with consideration of the possibility of transgene reactivation. The in vitro model described here provides insight into the earliest events of culture transformation and suggests the hypothesis that reversion to pluripotency may be responsible for the development of tumors in cell replacement experiments. The main goal of this work, however, is to communicate the possibility of transgene reactivation in retro- or lenti-iPSC derivatives and the associated loss of cellular fidelity in vitro, which may impact the outcomes of disease modeling and related experimentation.

Rescuing macrophage normal function in spinal cord injury with embryonic stem cell conditioned media

Background

Macrophages play an important role in the inflammatory responses involved with spinal cord injury (SCI). We have previously demonstrated that infiltrated bone marrow-derived macrophages (BMDMs) engulf myelin debris, forming myelin-laden macrophages (mye-Mϕ). These mye-Mϕ promote disease progression through their pro-inflammatory phenotype, enhanced neurotoxicity, and impaired phagocytic capacity for apoptotic cells. We thus hypothesize that the excessive accumulation of mye-Mϕ is the root of secondary injury, and that targeting mye-Mϕ represents an efficient strategy to improve the local inflammatory microenvironment in injured spinal cords and to further motor neuron function recovery. In this study, we administer murine embryonic stem cell conditioned media (ESC-M) as a cell-free stem cell based therapy to treat a mouse model of SCI.

Results

We showed that BMDMs, but not microglial cells, engulf myelin debris generated at the injury site. Phagocytosis of myelin debris leads to the formation of mye-Mϕ in the injured spinal cord, which are surrounded by activated microglia cells. These mye-Mϕ are pro-inflammatory and lose the normal macrophage phagocytic capacity for apoptotic cells. We therefore focus on how to trigger lipid efflux from mye-Mϕ and thus restore their function. Using ESC-M as an immune modulating treatment for inflammatory damage after SCI, we rescued mye-Mϕ function and improved functional locomotor recovery. ESC-M treatment on mye-Mϕ resulted in improved exocytosis of internalized lipids and a normal capacity for apoptotic cell phagocytosis. Furthermore, when ESC-M was administered intraperitoneally after SCI, animals exhibited significant improvements in locomotor recovery. Examination of spinal cords of the ESC-M treated mice revealed similar improvements in macrophage function as well as a shift towards a more anti-inflammatory environment at the lesion and parenchyma.

Conclusions

The embryonic stem cell conditioned media can be used as an effective treatment for SCI to resolve inflammation and improve functional recovery while circumventing the complications involved in whole cell transplantation.

The Use of Induced Pluripotent Stem Cells for the Study and Treatment of Liver Diseases

Liver disease is a major global health concern. Liver cirrhosis is one of the leading causes of death in the world and currently the only therapeutic option for end-stage liver disease (e.g., acute liver failure, cirrhosis, chronic hepatitis, cholestatic diseases, metabolic diseases, and malignant neoplasms) is orthotropic liver transplantation. Transplantation of hepatocytes has been proposed and used as an alternative to whole organ transplant to stabilize and prolong the lives of patients in some clinical cases. Although these experimental therapies have demonstrated promising and beneficial results, their routine use remains a challenge due to the shortage of donor livers available for cell isolation, variable quality of those tissues, the potential need for lifelong immunosuppression in the transplant recipient, and high costs. Therefore, new therapeutic strategies and more reliable clinical treatments are urgently needed. Recent and continuous technological advances in the development of stem cells suggest they may be beneficial in this respect. In this review, we summarize the history of stem cell and induced pluripotent stem cell (iPSC) technology in the context of hepatic differentiation and discuss the potential applications the technology may offer for human liver disease modeling and treatment. This includes developing safer drugs and cell-based therapies to improve the outcomes of patients with currently incurable health illnesses. We also review promising advances in other disease areas to highlight how the stem cell technology could be applied to liver diseases in the future. © 2016 by John Wiley & Sons, Inc.

Brief reports: Controlling the survival of human pluripotent stem cells by small molecule-based targeting of topoisomerase II alpha

Pluripotent-specific inhibitors (PluriSIns) make a powerful tool to study the mechanisms controlling the survival of human pluripotent stem cells (hPSCs). Here, we characterize the mechanism of action of PluriSIn#2, a compound that selectively eliminates undifferentiated hPSCs, while sparing various other cell types derived from them. Toxicogenomic analysis predicts this compound to be a topoisomerase inhibitor. Gene expression analyses reveal that one of the human topoisomerase enzymes, topoisomerase II alpha (TOP2A), is uniquely expressed in hPSCs: TOP2A is highly expressed in undifferentiated cells, is downregulated during their differentiation, and its expression depends on the expression of core pluripotency transcription factors. Furthermore, siRNA-based knockdown of TOP2A in undifferentiated hPSCs results in their cell death, revealing that TOP2A expression is required for the survival of these cells. We find that PluriSIn#2 does not directly inhibit TOP2A enzymatic activity, but rather selectively represses its transcription, thereby significantly reducing TOP2A protein levels. As undifferentiated hPSCs require TOP2A activity for their survival, TOP2A inhibition by PluriSIn#2 thus causes their cell death. Therefore, TOP2A dependency can be harnessed for the selective elimination of tumorigenic hPSCs from culture.

PSA-NCAM-negative neural crest cells emerging during neural induction of pluripotent stem cells cause mesodermal tumors and unwanted grafts

Tumorigenic potential of human pluripotent stem cells (hPSCs) is an important issue in clinical applications. Despite many efforts, PSC-derived neural precursor cells (NPCs) have repeatedly induced tumors in animal models even though pluripotent cells were not detected. We found that polysialic acid-neural cell adhesion molecule (PSA-NCAM)⁻ cells among the early NPCs caused tumors, whereas PSA-NCAM⁺ cells were nontumorigenic. Molecular profiling, global gene analysis, and multilineage differentiation of PSA-NCAM⁻ cells confirm that they are multipotent neural crest stem cells (NCSCs) that could differentiate into both ectodermal and mesodermal lineages. Transplantation of PSA-NCAM⁻ cells in a gradient manner mixed with PSA-NCAM⁺ cells proportionally increased mesodermal tumor formation and unwanted grafts such as PERIPHERIN⁺ cells or pigmented cells in the rat brain. Therefore, we suggest that NCSCs are a critical target for tumor prevention in hPSC-derived NPCs, and removal of PSA-NCAM⁻ cells eliminates the tumorigenic potential originating from NCSCs after transplantation.

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PSA-NCAM⁻ cells isolated from neural rosettes are classified as multipotent NCSCs

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NCSCs are a potential target for tumor prevention in hPSC-derived-NPC-based therapy

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Removal of PSA-NCAM⁻ cells prevents the introduction of mesodermal tumor in the CNS

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Removal of PSA-NCAM⁻ cells prevents the introduction of unwanted grafts in the CNS

Inhibition of an NAD⁺ salvage pathway provides efficient and selective toxicity to human pluripotent stem cells

The tumorigenic potential of human pluripotent stem cells (hPSCs) is a major limitation to the widespread use of hPSC derivatives in the clinic. Here, we demonstrate that the small molecule STF-31 is effective at eliminating undifferentiated hPSCs across a broad range of cell culture conditions with important advantages over previously described methods that target metabolic processes. Although STF-31 was originally described as an inhibitor of glucose transporter 1, these data support the reclassification of STF-31 as a specific NAD⁺ salvage pathway inhibitor through the inhibition of nicotinamide phosphoribosyltransferase (NAMPT). These findings demonstrate the importance of an NAD⁺ salvage pathway in hPSC biology and describe how inhibition of NAMPT can effectively eliminate hPSCs from culture. These results will advance and accelerate the development of safe, clinically relevant hPSC-derived cell-based therapies.

Overcoming the hurdles for a reproducible generation of human functionally mature reprogrammed neurons

The advent of cell reprogramming technologies has widely disclosed the possibility to have direct access to human neurons for experimental and biomedical applications. Human pluripotent stem cells can be instructed in vitro to generate specific neuronal cell types as well as different glial cells. Moreover, new approaches of direct neuronal cell reprogramming can strongly accelerate the generation of different neuronal lineages. However, genetic heterogeneity, reprogramming fidelity, and time in culture of the starting cells can still significantly bias their differentiation efficiency and quality of the neuronal progenies. In addition, reprogrammed human neurons exhibit a very slow pace in gaining a full spectrum of functional properties including physiological levels of membrane excitability, sustained and prolonged action potential firing, mature synaptic currents and synaptic plasticity. This delay poses serious limitations for their significance as biological experimental model and screening platform. We will discuss new approaches of neuronal cell differentiation and reprogramming as well as methods to accelerate the maturation and functional activity of the converted human neurons.

Embryonic Stem Cells Promoting Macrophage Survival and Function are Crucial for Teratoma Development

Stem cell therapies have had tremendous potential application for many diseases in recent years. However, the tumorigenic properties of stem cells restrict their potential clinical application; therefore, strategies for reducing the tumorigenic potential of stem cells must be established prior to transplantation. We have demonstrated that syngeneic transplantation of embryonic stem cells (ESCs) provokes an inflammatory response that involves the rapid recruitment of bone marrow-derived macrophages (BMDMs). ESCs are able to prevent mature macrophages from macrophage colony-stimulating factor (M-CSF) withdrawal-induced apoptosis, and thus prolong macrophage lifespan significantly by blocking various apoptotic pathways in an M-CSF-independent manner. ESCs express and secrete IL-34, which may be responsible for ESC-promoted macrophage survival. This anti-apoptotic effect of ESCs involves activation of extracellular signal-regulated kinase (ERK)1/2 and PI3K/Akt pathways and thus, inhibition of ERK1/2 and PI3K/AKT activation decreases ESC-induced macrophage survival. Functionally, ESC-treated macrophages also showed a higher level of phagocytic activity. ESCs further serve to polarize BMDMs into M2-like macrophages that exhibit most tumor-associated macrophage phenotypic and functional features. ESC-educated macrophages produce high levels of arginase-1, Tie-2, and TNF-α, which participate in angiogenesis and contribute to teratoma progression. Our study suggests that induction of M2-like macrophage activation is an important mechanism for teratoma development. Strategies targeting macrophages to inhibit teratoma development would increase the safety of ESC-based therapies, inasmuch as the depletion of macrophages completely inhibits ESC-induced angiogenesis and teratoma development.