Generation of induced pluripotent stem cells from human cord blood using OCT4 and SOX2

DNA hypermethylation in somatic cells correlates with higher reprogramming efficiency

The efficiency of somatic cell reprogramming to pluripotency using defined factors is dramatically affected by the cell type of origin. Here, we show that human keratinocytes, which can be reprogrammed at a higher efficiency than fibroblast [Nat Biotechnol 2008;26:1276-1284], share more genes hypermethylated at CpGs with human embryonic stem cells (ESCs) than other somatic cells frequently used for reprogramming. Moreover, pluripotent cells reprogrammed from keratinocytes (KiPS) are more similar to ESCs than those reprogrammed from fibroblasts (FiPS) in regard to DNA methylation levels, mostly due to the presence of genes that fail to acquire high levels of DNA methylation in FiPS cells. We propose that higher reprogramming efficiency correlates with the hypermethylation of tissue-specific genes rather than with a more permissive pluripotency gene network.

Generation of systemic lupus erythematosus-specific induced pluripotent stem cells from urine

Systemic lupus erythematosus (SLE) is the prototype of complex autoimmune diseases characterized by the production of autoantibodies which results in widespread immunologic abnormalities and immune complex formation. The underlying etiology remains largely unknown. When progressing toward kidney failure, it is becoming a serious public health problem. Kidney transplantation is a feasible therapy, but significant limitations were existed, including shortage of donor organs and lack of funding. To find an alternative proposal for kidney replacement, the induced pluripotent stem cells (iPSCs) technology was adopted. We identified typical SLE patients. Lentiviral transduction of OCT4, SOX2, KLF4, and c-MYC, under feeder conditions, resulted in reprogramming of urine-derived renal tubular cells. We investigated the viability of iPSCs generation from patients with SLE by identification of totipotency and pluripotency. SLE patient renal tubular cells-derived iPSCs exhibited properties of human embryonic stem cells, including morphology, growth properties, alkaline phosphatase, expression of pluripotency, genes and surface markers, and teratoma formation. We demonstrated that generation of SLE-specific iPSCs from urine was not only the first time worldwide, but was feasible and efficient. IPSCs from SLE would provide convenient model to study disease pathogenesis, drugs screening, and gene therapy.

Characterization of pluripotent stem cells

Characterization of pluripotent stem cells is required for the registration of stem cell lines and allows for an impartial and objective comparison of the results obtained when generating multiple lines. It is therefore crucial to establish specific, fast and reliable protocols to detect the hallmarks of pluripotency. Such protocols should include immunocytochemistry (takes 2 d), identification of the three germ layers in in vitro-derived embryoid bodies by immunocytochemistry (immunodetection takes 3 d) and detection of differentiation markers in in vivo-generated teratomas by immunohistochemistry (differentiation marker detection takes 4 d). Standardization of the immunodetection protocols used ensures minimum variations owing to the source, the animal species, the endogenous fluorescence or the inability to collect large amounts of cells, thereby yielding results as fast as possible without loss of quality. This protocol provides a description of all the immunodetection procedures necessary to characterize mouse and human stem cell lines in different circumstances.

Shared gene regulation during human somatic cell reprogramming

Human induced pluripotent stem (iPS) cells have the ability to differentiate into all somatic cells and to maintain unlimited self-renewal. Therefore, they have great potential in both basic research and clinical therapy for many diseases. To identify potentially universal mechanisms of human somatic cell reprogramming, we studied gene expression changes in three types of cells undergoing reprogramming. The set of 570 genes commonly regulated during induction of iPS cells includes known embryonic stem (ES) cell markers and pluripotency related genes. We also identified novel genes and biological categories which may be related to somatic cell reprogramming. For example, some of the down-regulated genes are predicted targets of the pluripotency microRNA cluster miR302/367, and the proteins from these putative target genes interact with the stem cell pluripotency factor POU5F1 according to our network analysis. Our results identified candidate gene sets to guide research on the mechanisms operating during somatic cell reprogramming.

Conversion of human fibroblasts to angioblast-like progenitor cells

Lineage conversion of one somatic cell type into another constitutes an attractive approach for research and clinical use. Lineage conversion can proceed in a direct manner, in the absence of proliferation and multipotent progenitor generation, or in an indirect manner, by the generation of expandable multipotent progenitor states. Here we report on the development of a combined reprogramming methodology that, transitioning through a plastic intermediate state, allows for the generation of human mesodermal progenitor cells while circumventing the traditional hallmarks of pluripotency. Converted mesodermal progenitor cells demonstrated bi-potent differentiation potential and were able to generate endothelial and smooth muscle lineages. Importantly, human fibroblasts can be converted into angioblast-like progenitor cells by non-integrative approaches. Differentiated angioblast-like cells exhibit neo-angiogenesis and anastomosis in vivo. The methodology for indirect lineage conversion to angioblast-like cells described here adds to the armamentarium of reprogramming approaches aimed at the clinical treatment of ischemic pathologies.

Intrapatient variations in type 1 diabetes-specific iPS cell differentiation into insulin-producing cells

Nuclear reprogramming of adult somatic tissue enables embryo-independent generation of autologous, patient-specific induced pluripotent stem (iPS) cells. Exploiting this emergent regenerative platform for individualized medicine applications requires the establishment of bioequivalence criteria across derived pluripotent lines and lineage-specified derivatives. Here, from individual patients with type 1 diabetes (T1D) multiple human iPS clones were produced and prospectively screened using a battery of developmental markers to assess respective differentiation propensity and proficiency in yielding functional insulin (INS)-producing progeny. Global gene expression profiles, pluripotency expression patterns, and the capacity to differentiate into SOX17- and FOXA2-positive definitive endoderm (DE)-like cells were comparable among individual iPS clones. However, notable intrapatient variation was evident upon further guided differentiation into HNF4α- and HNF1β-expressing primitive gut tube, and INS- and glucagon (GCG)-expressing islet-like cells. Differential dynamics of pluripotency-associated genes and pancreatic lineage-specifying genes underlined clonal variance. Successful generation of glucose-responsive INS-producing cells required silencing of stemness programs as well as the induction of stage-specific pancreatic transcription factors. Thus, comprehensive fingerprinting of individual clones is mandatory to secure homogenous pools amenable for diagnostic and therapeutic applications of iPS cells from patients with T1D.

Disease modelling using induced pluripotent stem cells: status and prospects

The ability to convert human somatic cells into induced pluripotent stem cells (iPSCs) is allowing the production of custom-tailored cells for drug discovery and for the study of disease phenotypes at the cellular and molecular level. IPSCs have been derived from patients suffering from a large variety of disorders with different severities. In many cases, disease related phenotypes have been observed in iPSCs or their lineage-specific progeny. Several proof of concept studies have demonstrated that these phenotypes can be reversed in vitro using approved drugs. However, several challenges must be overcome to take full advantage of this technology. Here, we highlight recent advances in the field and discuss the main challenges associated with this technology as it applies to disease modelling.

Generation of human induced pluripotent stem cells from urine samples

Human induced pluripotent stem cells (iPSCs) have been generated with varied efficiencies from multiple tissues. Yet, acquiring donor cells is, in most instances, an invasive procedure that requires laborious isolation. Here we present a detailed protocol for generating human iPSCs from exfoliated renal epithelial cells present in urine. This method is advantageous in many circumstances, as the isolation of urinary cells is simple (30 ml of urine are sufficient), cost-effective and universal (can be applied to any age, gender and race). Moreover, the entire procedure is reasonably quick--around 2 weeks for the urinary cell culture and 3-4 weeks for the reprogramming--and the yield of iPSC colonies is generally high--up to 4% using retroviral delivery of exogenous factors. Urinary iPSCs (UiPSCs) also show excellent differentiation potential, and thus represent a good choice for producing pluripotent cells from normal individuals or patients with genetic diseases, including those affecting the kidney.

Neuronopathic Gaucher's disease: induced pluripotent stem cells for disease modelling and testing chaperone activity of small compounds

Gaucher's disease (GD) is caused by mutations in the GBA1 gene, which encodes acid-β-glucosidase, an enzyme involved in the degradation of complex sphingolipids. While the non-neuronopathic aspects of the disease can be treated with enzyme replacement therapy (ERT), the early-onset neuronopathic form currently lacks therapeutic options and is lethal. We have developed an induced pluripotent stem cell (iPSc) model of neuronopathic GD. Dermal fibroblasts of a patient with a P.[LEU444PRO];[GLY202ARG] genotype were transfected with a loxP-flanked polycistronic reprogramming cassette consisting of Oct4, Sox2, Klf4 and c-Myc and iPSc lines derived. A non-integrative lentiviral vector expressing Cre recombinase was used to eliminate the reprogramming cassette from the reprogrammed cells. Our GD iPSc express pluripotent markers, differentiate into the three germ layers, form teratomas, have a normal karyotype and show the same mutations and low acid-β-glucosidase activity as the original fibroblasts they were derived from. We have differentiated them efficiently into neurons and also into macrophages without observing deleterious effects of the mutations on the differentiation process. Using our system as a platform to test chemical compounds capable of increasing acid-β-glucosidase activity, we confirm that two nojirimycin analogues can rescue protein levels and enzyme activity in the cells affected by the disease.

A poor imitation of a natural process: a call to reconsider the iPSC engineering technique

Reprogramming somatic cells into a pluripotent state is expected to initiate a new era in medicine. Because the precise underlying mechanism of reprogramming remains unclear, many efforts have been made to optimize induced pluripotent stem cell (iPSC) engineering. However, satisfactory results have not yet been attained. In this review, we focus on recent roadblocks in iPSC reprogramming engineering, such as the inefficiency of the process, tumorigenicity and heterogeneity of the generation. We conclude that cell reprogramming is a naturally occurring phenomenon rather than a biological technique. We will only be able to mimic the natural process of reprogramming when we fully understand its underlying mechanism. Finally, we highlight the alternative method of direct conversion, which avoids the use of iPSCs to generate cell materials for patient-specific cell therapy.

The Role of HLA in Cord Blood Transplantation

In recent years, umbilical cord blood (CB), a rich source of hematopoietic stem cells (HSC), has been used successfully as an alternative HSC source to treat a variety of hematologic, immunologic, genetic, and oncologic disorders. CB has several advantages, including prompt availability of the transplant, decrease of graft versus host disease (GVHD) and better long-term immune recovery, resulting in a similar long-term survival. Studies have shown that some degree of HLA mismatches is acceptable. This review is intended to outline the main aspects of HLA matching in different settings (related, pediatric, adult, or double-unit HSCT), its effect on transplantation outcome and the role of HLA in donor selection.

Using microRNAs to enhance the generation of induced pluripotent stem cells

Somatic cells reprogrammed to acquire an ES-like state are termed iPS cells. In this unit, a protocol to use microRNAs as enhancers to increase the reprogramming efficiency is described. Mouse embryonic fibroblasts (MEFs) are isolated from E13.5 mouse embryos and seeded for reprogramming by defined factors. microRNA mimics are transfected into MEFs at two time points during this process to enhance the overall reprogramming efficiency. Two standard protocols for characterization of these miR-iPSCs, embryoid body formation and teratoma formation, are also provided. By using this method, the investigators can obtain a significantly higher number of bona-fide iPSC colonies and miR-iPSCs can be derived at a faster rate than with non-treated cells.

Organ engineering--combining stem cells, biomaterials, and bioreactors to produce bioengineered organs for transplantation

Often the only treatment available for patients suffering from diseased and injured organs is whole organ transplant. However, there is a severe shortage of donor organs for transplantation. The goal of organ engineering is to construct biological substitutes that will restore and maintain normal function in diseased and injured tissues. Recent progress in stem cell biology, biomaterials, and processes such as organ decellularization and electrospinning has resulted in the generation of bioengineered blood vessels, heart valves, livers, kidneys, bladders, and airways. Future advances that may have a significant impact for the field include safe methods to reprogram a patient's own cells to directly differentiate into functional replacement cell types. The subsequent combination of these cells with natural, synthetic and/or decellularized organ materials to generate functional tissue substitutes is a real possibility. This essay reviews the current progress, developments, and challenges facing researchers in their goal to create replacement tissues and organs for patients.

Prospects and challenges of reprogrammed cells in hematology and oncology

Induced pluripotent stem cells (iPSCs) have emerged as a promising basis for modeling pediatric genetic disorders, allowing the derivation, study, and genetic correction of disease and patient-specific cell lines in vitro. Similar to embryonic stem cells (ESCs), iPSCs are capable of unlimited in vitro expansion and derivation of many cell types, including hematopoietic stem cells (HSCs). These may not only allow large scale screenings to develop therapeutic compounds, but also help to overcome cross-species barriers of genetically engineered animal models, which do not adequately recapitulate the associated human phenotype. Here, we review the current state and emerging developments of iPSC research, which can be exploited as a tool in modeling pediatric hematopoietic disorders and could lead to new clinical applications in gene and cell therapies.

Reprogramming and the mammalian germline: the Weismann barrier revisited

The germline represents a unique cell type that can transmit genetic material to the next generation. During early embryonic development, somatic cells give rise to a small population of cells known as germ cells, which eventually differentiate into mature gametes. Germ cells undergo a process of removing and resetting relevant epigenetic information, mainly by DNA demethylation. This extensive epigenetic reprogramming leads to the conversion of germ cells into immortal cells that can pass on the genome to the next generation. In the absence of germline-specific reprogramming, germ cells would preserve the old, parental epigenetic memory, which would prevent the transfer of heritable information to the offspring. On the contrary, somatic cells cannot reset epigenetic information by preserving the full methylation pattern on imprinting genes. In this review, we focus on the capacity of germ cells and somatic cells (soma) to transfer genetic information to the next generation, and thus revisit the Weismann theory of heredity.

Growth factor-activated stem cell circuits and stromal signals cooperatively accelerate non-integrated iPSC reprogramming of human myeloid progenitors

Nonviral conversion of skin or blood cells into clinically useful human induced pluripotent stem cells (hiPSC) occurs in only rare fractions (∼0.001%–0.5%) of donor cells transfected with non-integrating reprogramming factors. Pluripotency induction of developmentally immature stem-progenitors is generally more efficient than differentiated somatic cell targets. However, the nature of augmented progenitor reprogramming remains obscure, and its potential has not been fully explored for improving the extremely slow pace of non-integrated reprogramming. Here, we report highly optimized four-factor reprogramming of lineage-committed cord blood (CB) myeloid progenitors with bulk efficiencies of ∼50% in purified episome-expressing cells. Lineage-committed CD33⁺CD45⁺CD34⁻ myeloid cells and not primitive hematopoietic stem-progenitors were the main targets of a rapid and nearly complete non-integrated reprogramming. The efficient conversion of mature myeloid populations into NANOG⁺TRA-1-81⁺ hiPSC was mediated by synergies between hematopoietic growth factor (GF), stromal activation signals, and episomal Yamanaka factor expression. Using a modular bioinformatics approach, we demonstrated that efficient myeloid reprogramming correlated not to increased proliferation or endogenous Core factor expressions, but to poised expression of GF-activated transcriptional circuits that commonly regulate plasticity in both hematopoietic progenitors and embryonic stem cells (ESC). Factor-driven conversion of myeloid progenitors to a high-fidelity pluripotent state was further accelerated by soluble and contact-dependent stromal signals that included an implied and unexpected role for Toll receptor-NFκB signaling. These data provide a paradigm for understanding the augmented reprogramming capacity of somatic progenitors, and reveal that efficient induced pluripotency in other cell types may also require extrinsic activation of a molecular framework that commonly regulates self-renewal and differentiation in both hematopoietic progenitors and ESC.

The gene expression profiles of induced pluripotent stem cells (iPSCs) generated by a non-integrating method are more similar to embryonic stem cells than those of iPSCs generated by an integrating method

Induced pluripotent stem cells (iPSCs) obtained by the ectopic expression of defined transcription factors have tremendous promise and therapeutic potential for regenerative medicine. Many studies have highlighted important differences between iPSCs and embryonic stem cells (ESCs). In this work, we used meta-analysis to compare the global transcriptional profiles of human iPSCs from various cellular origins and induced by different methods. The induction strategy affected the quality of iPSCs in terms of transcriptional signatures. The iPSCs generated by non-integrating methods were closer to ESCs in terms of transcriptional distance than iPSCs generated by integrating methods. Several pathways that could be potentially useful for studying the molecular mechanisms underlying transcription factor-mediated reprogramming leading to pluripotency were also identified. These pathways were mostly associated with the maintenance of ESC pluripotency and cancer regulation. Numerous genes that are up-regulated during the induction of reprogramming also have an important role in the success of human preimplantation embryonic development. Our results indicate that hiPSCs maintain their pluripotency through mechanisms similar to those of hESCs.

Cord blood-derived neuronal cells by ectopic expression of Sox2 and c-Myc

The finding that certain somatic cells can be directly converted into cells of other lineages by the delivery of specific sets of transcription factors paves the way to novel therapeutic applications. Here we show that human cord blood (CB) CD133(+) cells lose their hematopoietic signature and are converted into CB-induced neuronal-like cells (CB-iNCs) by the ectopic expression of the transcription factor Sox2, a process that is further augmented by the combination of Sox2 and c-Myc. Gene-expression analysis, immunophenotyping, and electrophysiological analysis show that CB-iNCs acquire a distinct neuronal phenotype characterized by the expression of multiple neuronal markers. CB-iNCs show the ability to fire action potentials after in vitro maturation as well as after in vivo transplantation into the mouse hippocampus. This system highlights the potential of CB cells and offers an alternative means to the study of cellular plasticity, possibly in the context of drug screening research and of future cell-replacement therapies.

Donor-dependent variations in hepatic differentiation from human-induced pluripotent stem cells

Hepatocytes generated from human induced pluripotent stem cells (hiPSCs) are unprecedented resources for pharmaceuticals and cell therapy. However, the in vitro directed differentiation of human pluripotent stem cells into mature hepatocytes remains challenging. Little attention has so far been paid to variations among hiPSC lines in terms of their hepatic differentiation. In the current study, we developed an improved hepatic differentiation protocol and compared 28 hiPSC lines originated from various somatic cells and derived using retroviruses, Sendai viruses, or episomal plasmids. This comparison indicated that the origins, but not the derivation methods, may be a major determinant of variation in hepatic differentiation. The hiPSC clones derived from peripheral blood cells consistently showed good differentiation efficiency, whereas many hiPSC clones from adult dermal fibroblasts showed poor differentiation. However, when we compared hiPSCs from peripheral blood and dermal fibroblasts from the same individuals, we found that variations in hepatic differentiation were largely attributable to donor differences, rather than to the types of the original cells. These data underscore the importance of donor differences when comparing the differentiation propensities of hiPSC clones.

Progress and bottleneck in induced pluripotency

With their capability to undergo unlimited self-renewal and to differentiate into all cell types in the body, induced pluripotent stem cells (iPSCs), reprogrammed from somatic cells of individual patients with defined factors, have unlimited potential in cell therapy and in modeling complex human diseases. Significant progress has been achieved to improve the safety of iPSCs and the reprogramming efficiency. To avoid the cancer risk and spontaneous reactivation of the reprogramming factors associated with the random integration of viral vectors into the genome, several approaches have been established to deliver the reprogramming factors into the somatic cells without inducing genetic modification. In addition, a panel of small molecule compounds, many of which targeting the epigenetic machinery, have been identified to increase the reprogramming efficiency. Despite these progresses, recent studies have identified genetic and epigenetic abnormalities of iPSCs as well as the immunogenicity of some cells derived from iPSCs. In addition, due to the oncogenic potential of the reprogramming factors and the reprogramming-induced DNA damage, the critical tumor suppressor pathways such as p53 and ARF are activated to act as the checkpoints that suppress induced pluripotency. The inactivation of these tumor suppression pathways even transiently during reprogramming processes could have significant adverse impact on the genome integrity. These safety concerns must be resolved to improve the feasibility of the clinic development of iPSCs into human cell therapy.

The molecular circuitry underlying pluripotency in embryonic stem cells

Cells in the pluripotent state have the ability to self-renew indefinitely and to differentiate to all the cells of the embryo. These cells provide an in vitro window into development, including human development, as well as holding extraordinary promise for cell-based therapies in regenerative medicine. The recent demonstration that somatic cells can be reprogrammed to the pluripotent state has raised the possibility of patient and disease-specific induced pluripotent cells. In this article, we review the molecular underpinning of pluripotency. We focus on the transcriptional and signaling networks that underlie the state of pluripotency and control differentiation. In general, the action of each of the molecular components and pathways is dose and context dependent highlighting the need for a systems approach to understanding pluripotency.

Generation of mature hematopoietic cells from human pluripotent stem cells

A number of malignant and non-malignant hematological disorders are associated with the abnormal production of mature blood cells or primitive hematopoietic precursors. Their capacity for continuous self-renewal without loss of pluripotency and the ability to differentiate into adult cell types from all three primitive germ layers make human embryonic stem cells and induced pluripotent stem cells (hiPSCs) attractive complementary cell sources for large-scale production of transfusable mature blood cell components in cell replacement therapies. The generation of patient-specific hematopoietic stem/precursor cells from iPSCs by the regulated manipulation of various factors involved in reprograming to ensure complete pluripotency, and developing innovative differentiation strategies for generating unlimited supply of clinically safe, transplantable, HLA-matched cells from hiPSCs to outnumber the inadequate source of hematopoietic stem cells obtained from cord blood, bone marrow and peripheral blood, would have a major impact on the field of regenerative and personalized medicine leading to translation of these results from bench to bedside.

Promise and challenges of human iPSC-based hematologic disease modeling and treatment

Postnatal hematopoietic stem cells (HSCs) from umbilical cord blood and adult marrow/blood have been successfully used for treating various human diseases in the past several decades. However, the availability of optimal numbers of HSCs from autologous patients or allogeneic donors with adequate match remains a great barrier to improve and extend HSC and marrow transplantation to more needing patients. In addition, the inability to expand functional human HSCs to sufficient quantity in the laboratory has hindered our research and understanding of human HSCs and hematopoiesis. Recent development in reprogramming technology has provided patient-specific pluripotent stem cells (iPSCs) as a powerful enabling tool for modeling disease and developing therapeutics. Studies have demonstrated the potential of human iPSCs, which can be expanded exponentially and amenable for genome engineering, for using in modeling both inherited and acquired blood diseases. Proof-of-principle studies have also shown the feasibility of iPSCs in gene and cell therapy. Here, we review the recent development in iPSC-based blood disease modeling, and discuss the unsolved issues and challenges in this new and promising field.

Generation of induced pluripotent stem cells from human renal proximal tubular cells with only two transcription factors, OCT4 and SOX2

The tubular epithelium of the kidney is susceptible to injury from a number of different causes, including inflammatory and immune disorders, oxidative stress, and nephrotoxins, among others. Primary renal epithelial cells remain one of the few tools for studying the biochemical and physiological characteristics of the renal tubular system. Nevertheless, differentiated primary cells are not suitable for recapitulation of disease properties that might arise during embryonic kidney formation and further maturation. Thus, cellular systems resembling kidney characteristics are in urgent need to model disease as well as to establish reliable drug-testing platforms. Induced pluripotent stem cells (iPSCs) bear the capacity to differentiate into every cell lineage comprising the adult organism. Thus, iPSCs bring the possibility for recapitulating embryonic development by directed differentiation into specific lineages. iPSC differentiation ultimately allows for both disease modeling in vitro and the production of cellular products with potential for regenerative medicine. Here, we describe the rapid, reproducible, and highly efficient generation of iPSCs derived from endogenous kidney tubular renal epithelial cells with only two transcriptional factors, OCT4 and SOX2. Kidney-derived iPSCs may provide a reliable cellular platform for the development of kidney differentiation protocols allowing drug discovery studies and the study of kidney pathology.

Residual expression of the reprogramming factors prevents differentiation of iPSC generated from human fibroblasts and cord blood CD34+ progenitors

Human induced pluripotent stem cells (hiPSC) have been generated from different tissues, with the age of the donor, tissue source and specific cell type influencing the reprogramming process. Reprogramming hematopoietic progenitors to hiPSC may provide a very useful cellular system for modelling blood diseases. We report the generation and complete characterization of hiPSCs from human neonatal fibroblasts and cord blood (CB)-derived CD34+ hematopoietic progenitors using a single polycistronic lentiviral vector containing an excisable cassette encoding the four reprogramming factors Oct4, Klf4, Sox2 and c-myc (OKSM). The ectopic expression of OKSM was fully silenced upon reprogramming in some hiPSC clones and was not reactivated upon differentiation, whereas other hiPSC clones failed to silence the transgene expression, independently of the cell type/tissue origin. When hiPSC were induced to differentiate towards hematopoietic and neural lineages those hiPSC which had silenced OKSM ectopic expression displayed good hematopoietic and early neuroectoderm differentiation potential. In contrast, those hiPSC which failed to switch off OKSM expression were unable to differentiate towards either lineage, suggesting that the residual expression of the reprogramming factors functions as a developmental brake impairing hiPSC differentiation. Successful adenovirus-based Cre-mediated excision of the provirus OKSM cassette in CB-derived CD34+ hiPSC with residual transgene expression resulted in transgene-free hiPSC clones with significantly improved differentiation capacity. Overall, our findings confirm that residual expression of reprogramming factors impairs hiPSC differentiation.

Muse cells and induced pluripotent stem cell: implication of the elite model

Induced pluripotent stem (iPS) cells have attracted a great deal attention as a new pluripotent stem cell type that can be generated from somatic cells, such as fibroblasts, by introducing the transcription factors Oct3/4, Sox2, Klf4, and c-Myc. The mechanism of generation, however, is not fully understood. Two mechanistic theories have been proposed; the stochastic model purports that every cell type has the potential to be reprogrammed to become an iPS cell and the elite model proposes that iPS cell generation occurs only from a subset of cells. Some reports have provided theoretical support for the stochastic model, but a recent publication demonstrated findings that support the elite model, and thus the mechanism of iPS cell generation remains under debate. To enhance our understanding of iPS cells, it is necessary to clarify the properties of the original cell source, i.e., the components of the original populations and the potential of each population to become iPS cells. In this review, we discuss the two theories and their implications in iPS cell research.

Delineating nuclear reprogramming

Nuclear reprogramming is described as a molecular switch, triggered by the conversion of one cell type to another. Several key experiments in the past century have provided insight into the field of nuclear reprogramming. Previously deemed impossible, this research area is now brimming with new findings and developments. In this review, we aim to give a historical perspective on how the notion of nuclear reprogramming was established, describing main experiments that were performed, including (1) somatic cell nuclear transfer, (2) exposure to cell extracts and cell fusion, and (3) transcription factor induced lineage switch. Ultimately, we focus on (4) transcription factor induced pluripotency, as initiated by a landmark discovery in 2006, where the process of converting somatic cells to a pluripotent state was narrowed down to four transcription factors. The conception that somatic cells possess the capacity to revert to an immature status brings about huge clinical implications including personalized therapy, drug screening and disease modeling. Although this technology has potential to revolutionize the medical field, it is still impeded by technical and biological obstacles. This review describes the effervescent changes in this field, addresses bottlenecks hindering its advancement and in conclusion, applies the latest findings to overcome these issues.

Human umbilical cord is a unique and safe source of various types of stem cells suitable for treatment of hematological diseases and for regenerative medicine

Cord blood (CB) is a rich source of hematopoietic stem cells (HSCs) and for this reason CB transplantation has been used successfully for the treatment of some malignant and nonmalignant diseases. However, this technique is limited by the relatively low number of HSCs present in each CB unit and by the delayed engraftment of platelets and neutrophils. To bypass these obstacles efforts have been made to develop strategies to expand CB HSCs in vitro for transplantation. CB is also an important source of other stem cells, including endothelial progenitors, mesenchymal stem cells (MSCs), very small embryonic/epiblast-like (VSEL) stem cells, and unrestricted somatic stem cells (USSC), potentially suitable for use in regenerative medicine. For some of these stem cell populations, such as MSCs, clinical studies have been started and for other stem cell populations potential clinical applications have been identified and clinical studies will follow. In addition to CB, other parts of umbilical cord, such as the Wharton's jelly, or tissues strictly linked such as the placenta are also rich sources of stem cells.

Potential uses of cord blood in cardiac surgery

Despite advances in the fields of prevention, medical intervention and surgical therapy, cardiovascular disease remains a major public healthcare issue. A promising area of research is the potential application of regenerative therapies with pluripotential stem cells to reduce the burden of heart disease and its sequelae. Umbilical cord blood, a rich source of multiple populations of nonembryonic stem cells, will be a valuable resource and has the potential to advance therapeutic options for patients with acquired and congenital heart disease.

Establishment and optimal culture conditions of microrna-induced pluripotent stem cells generated from HEK293 cells via transfection of microrna-302s expression vector

Induced pluripotent stem cells (iPSCs) have been directly generated from fibroblast cultures though retrovirus- or lentivirus-mediated ectopic overexpression of only a few defined transcriptional factors. This remarkable achievement has greatly enhanced our ability to explore the causes of, and potential cures for, many genetic diseases, and strengthened the promise of regenerative medicine. In fact, to date, many kinds of somatic cells from different tissues have exhibited a capacity for reprogramming toward an embryonic stem cell-like state, but major bottlenecks in iPSC derivation and therapeutic use remain, including low reprogramming efficiencies and the tumorigenesis of the generated iPSC. Here, we successfully generated miR-302s-induced pluripotent stem cells (mirPS cells) from human embryonic kidney (HEK) 293 cells via transfection of the miR-302s expression vector. We also determined the optimal culture conditions to generate mirPS on feeder cells, which included the use of serum-free N2B27 medium. The mirPS cells generated by our improved conditions showed the expression of pluripotent marker genes such as OCT3/4, NANOG, and SOX2 under growth conditions via reverse transcription-PCR, whereas no expression of these genes was observed in HEK293 cells. On the other hand, under differentiation conditions, mirPS cells formed ball-shaped structures (embryoid bodies), and showed the ability to differentiate into three germ layers (ectoderm, mesoderm, and endoderm) in vitro. The results suggested that our generated mirPS cells are actually functional as a cell resource to apply to regenerative medicine, and mirPS cells are suitable materials to clarify the mechanism underlying the reprogramming from somatic cells.

Stem cell gene expression in MRPS18-2-immortalized rat embryonic fibroblasts

We have recently found that primary rat embryonic fibroblasts (REFs) could be immortalized by overexpression of the human mitochondrial ribosomal protein MRPS18-2 (S18-2). A derived cell line, designated 18IM, expressed the embryonic stem cell markers SSEA-1 and Sox2. Upon inoculation into severe combined immunodeficiency mice, 18IM cells differentiated to express pan-keratin. They were not tumorigenic. Here we report the gene profiling of 18IM, compared with REF cells. Pathways involved in oxidative phosphorylation, ubiquinone (Coenzyme Q 10) biosynthesis, fatty acid elongation in mitochondria, PI3K/AKT signaling, a characteristic of rapidly proliferating cells, were upregulated in 18IM. Genes involved in the transcription/translation machinery and redox reactions, like elongation factors, ATP synthases, NADH dehydrogenases, mitogen activated kinases were upregulated as well. 18IM cells produced more pyruvate, indicating enhanced ATP synthesis. The expression of Oct4, Sox2, and Nanog that can contribute to the experimental induction of pluripotency in primary fibroblasts was also elevated, in contrast to Klf4 and C-myc that were downregulated. Subsequently, three new immortalized cell lines were produced by S18-2 overexpression in order to check the representativeness of 18IM. All of them showed anchorage-independent growth pattern. Two of three clones lost vimentin and smooth muscle actin, and expressed Sox2 and Oct4. We suggest that S18-2 is involved in the developmental regulation.

Derivation of induced pluripotent stem cells from human peripheral circulating T cells

This unit describes a protocol for the generation of induced pluripotent stem (iPS) cells from human peripheral circulating T cells. Initially, human dermal fibroblasts and retroviral vectors were used to generate human iPS cells. Invasive approaches, such as skin biopsy, and genomic insertion of transgenes into the host genome are not appropriate for routine clinical application. Peripheral circulating T cells are readily available from blood samples of patients and healthy volunteers. For the efficient generation of human iPS cells, efficient introduction of the transgene into host cells is necessary. Using a combination of activated T cell culture and Sendai virus allows for the easy and efficient introduction of transgenes into activated T cells and the generation of human iPS cells without genomic integration of extrinsic genes. The T cell-derived iPS (TiPS) cells exhibit monoclonal T cell receptor (TCR) rearrangement in their genome, a hallmark of mature terminally differentiated T cells.

Generation of induced pluripotent stem cells from somatic cells

The technology for generation of induced pluripotent stem cell (iPSC) from somatic cells emerged to circumvent the ethical and immunological limitations of embryonic stem cell (ESC). The recent progress of iPSC technology offers an unprecedented tool for regenerative medicine; however, integrating viral-driven iPSCs prohibits clinical applications by their genetic alterations and tumorigenicity. Various approaches including nonintegrating, nonviral, and nongenetic methods have been developed for generating clinically compatible iPSCs. In addition, approaches for using more clinically convenient or compatible source cells replacing fibroblasts have been actively pursued. While iPSC and ESC closely resemble in genomic, cell biologic, and phenotypic characteristics, these two pluripotent stem cells are not identical in terms of differentiation capacity and epigenetic features. In this chapter, we deal with the current techniques of generating iPSCs and their various characteristics.

Reprogramming of somatic cells

Reprogramming of adult somatic cells into pluripotent stem cells may provide an attractive source of stem cells for regenerative medicine. It has emerged as an invaluable method for generating patient-specific stem cells of any cell lineage without the use of embryonic stem cells. A revolutionary study in 2006 showed that it is possible to convert adult somatic cells directly into pluripotent stem cells by using a limited number of pluripotent transcription factors and is called as iPS cells. Currently, both genomic integrating viral and nonintegrating nonviral methods are used to generate iPS cells. However, the viral-based technology poses increased risk of safety, and more studies are now focused on nonviral-based technology to obtain autologous stem cells for clinical therapy. In this review, the pros and cons of the present iPS cell technology and the future direction for the successful translation of this technology into the clinic are discussed.

Induced pluripotent stem cells and personalized medicine: current progress and future perspectives

Generation of induced pluripotent stem cells (iPSCs) has revolutionized the field of regenerative medicine by providing researchers with a unique tool to derive disease-specific stem cells for study. iPSCs can self-renew and can differentiate into many cell types, offering a potentially unlimited source of cells for targeted differentiation into somatic effector cells. Hence, iPSCs are likely to be invaluable for therapeutic applications and disease-related research. In this review, we summarize the recent progress of iPSC generation that has been made with an emphasis on both basic and clinical applications including disease modeling, drug toxicity screening/drug discovery and cell replacement therapy.

Immunological applications of stem cells in type 1 diabetes

Current approaches aiming to cure type 1 diabetes (T1D) have made a negligible number of patients insulin-independent. In this review, we revisit the role of stem cell (SC)-based applications in curing T1D. The optimal therapeutic approach for T1D should ideally preserve the remaining β-cells, restore β-cell function, and protect the replaced insulin-producing cells from autoimmunity. SCs possess immunological and regenerative properties that could be harnessed to improve the treatment of T1D; indeed, SCs may reestablish peripheral tolerance toward β-cells through reshaping of the immune response and inhibition of autoreactive T-cell function. Furthermore, SC-derived insulin-producing cells are capable of engrafting and reversing hyperglycemia in mice. Bone marrow mesenchymal SCs display a hypoimmunogenic phenotype as well as a broad range of immunomodulatory capabilities, they have been shown to cure newly diabetic nonobese diabetic (NOD) mice, and they are currently undergoing evaluation in two clinical trials. Cord blood SCs have been shown to facilitate the generation of regulatory T cells, thereby reverting hyperglycemia in NOD mice. T1D patients treated with cord blood SCs also did not show any adverse reaction in the absence of major effects on glycometabolic control. Although hematopoietic SCs rarely revert hyperglycemia in NOD mice, they exhibit profound immunomodulatory properties in humans; newly hyperglycemic T1D patients have been successfully reverted to normoglycemia with autologous nonmyeloablative hematopoietic SC transplantation. Finally, embryonic SCs also offer exciting prospects because they are able to generate glucose-responsive insulin-producing cells. Easy enthusiasm should be mitigated mainly because of the potential oncogenicity of SCs.

Modeling neurological disorders by human induced pluripotent stem cells

Studies of human brain development are critical as research on neurological disorders have been progressively advanced. However, understanding the process of neurogenesis through analysis of the early embryo is complicated and limited by a number of factors, including the complexity of the embryos, availability, and ethical constrains. The emerging of human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) has shed light of a new approach to study both early development and disease pathology. The cells behave as precursors of all embryonic lineages; thus, they allow tracing the history from the root to individual branches of the cell lineage tree. Systems for neural differentiation of hESCs and iPSCs have provided an experimental model that can be used to augment in vitro studies of in vivo brain development. Interestingly, iPSCs derived from patients, containing donor genetic background, have offered a breakthrough approach to study human genetics of neurodegenerative diseases. This paper summarizes the recent reports of the development of iPSCs from patients who suffer from neurological diseases and evaluates the feasibility of iPSCs as a disease model. The benefits and obstacles of iPSC technology are highlighted in order to raising the cautions of misinterpretation prior to further clinical translations.

Efficient reprogramming of human cord blood CD34+ cells into induced pluripotent stem cells with OCT4 and SOX2 alone

The reprogramming of cord blood (CB) cells into induced pluripotent stem cells (iPSCs) has potential applications in regenerative medicine by converting CB banks into iPSC banks for allogeneic cell replacement therapy. Therefore, further investigation into novel approaches for efficient reprogramming is necessary. Here, we show that the lentiviral expression of OCT4 together with SOX2 (OS) driven by a strong spleen focus-forming virus (SFFV) promoter in a single vector can convert 2% of CB CD34(+) cells into iPSCs without additional reprogramming factors. Reprogramming efficiency was found to be critically dependent upon expression levels of OS. To generate transgene-free iPSCs, we developed an improved episomal vector with a woodchuck post-transcriptional regulatory element (Wpre) that increases transgene expression by 50%. With this vector, we successfully generated transgene-free iPSCs using OS alone. In conclusion, high-level expression of OS alone is sufficient for efficient reprogramming of CB CD34(+) cells into iPSCs. This report is the first to describe the generation of transgene-free iPSCs with the use of OCT4 and SOX2 alone. These findings have important implications for the clinical applications of iPSCs.

Induced pluripotent stem cells from GMP-grade hematopoietic progenitor cells and mononuclear myeloid cells

Introduction

The induced pluripotent stem cell (iPSC) technology allows generation of patient-specific pluripotent stem cells, thereby providing a novel cell-therapy platform for severe degenerative diseases. One of the key issues for clinical-grade iPSC derivation is the accessibility of donor cells used for reprogramming.

Methods

We examined the feasibility of reprogramming mobilized GMP-grade hematopoietic progenitor cells (HPCs) and peripheral blood mononuclear cells (PBMCs) and tested the pluripotency of derived iPS clones.

Results

Ectopic expression of OCT4, SOX2, KLF4, and c-MYC in HPCs and PBMCs resulted in rapid iPSC derivation. Long-term time-lapse imaging revealed efficient iPSC growth under serum- and feeder-free conditions with frequent mitotic events. HPC- and PBMC-derived iPS cells expressed pluripotency-associated markers, including SSEA-4, TRA-1-60, and NANOG. The global gene-expression profiles demonstrated the induction of endogenous pluripotent genes, such as LIN28, TERT, DPPA4, and PODXL, in derived iPSCs. iPSC clones from blood and other cell sources showed similar ultrastructural morphologies and genome-wide gene-expression profiles. On spontaneous and guided differentiation, HPC- and PBMC-derived iPSCs were differentiated into cells of three germ layers, including insulin-producing cells through endodermal lineage, verifying the pluripotency of the blood-derived iPSC clones.

Conclusions

Because the use of blood cells allows minimally invasive tissue procurement under GMP conditions and rapid cellular reprogramming, mobilized HPCs and unmobilized PBMCs would be ideal somatic cell sources for clinical-grade iPSC derivation, especially from diabetes patients complicated by slow-healing wounds.

Complete meiosis from human induced pluripotent stem cells

Gamete failure-derived infertility affects millions of people worldwide; for many patients, gamete donation by unrelated donors is the only available treatment. Embryonic stem cells (ESCs) can differentiate in vitro into germ-like cells, but they are genetically unrelated to the patient. Using an in vitro protocol that aims at recapitulating development, we have achieved, for the first time, complete differentiation of human induced pluripotent stem cells (hiPSCs) to postmeiotic cells. Unlike previous reports using human ESCs, postmeiotic cells arose without the over-expression of germline related transcription factors. Moreover, we consistently obtained haploid cells from hiPSCs of different origin (keratinocytes and cord blood), produced with a different number of transcription factors, and of both genetic sexes, suggesting the independence of our approach from the epigenetic memory of the reprogrammed somatic cells. Our work brings us closer to the production of personalized human gametes in vitro.

Induced pluripotent stem cells--opportunities for disease modelling and drug discovery

The ability to generate induced pluripotent stem cells (iPSCs) from patients, and an increasingly refined capacity to differentiate these iPSCs into disease-relevant cell types, promises a new paradigm in drug development - one that positions human disease pathophysiology at the core of preclinical drug discovery. Disease models derived from iPSCs that manifest cellular disease phenotypes have been established for several monogenic diseases, but iPSCs can likewise be used for phenotype-based drug screens in complex diseases for which the underlying genetic mechanism is unknown. Here, we highlight recent advances as well as limitations in the use of iPSC technology for modelling a 'disease in a dish' and for testing compounds against human disease phenotypes in vitro. We discuss how iPSCs are being exploited to illuminate disease pathophysiology, identify novel drug targets and enhance the probability of clinical success of new drugs.

Induced pluripotent stem cells: opportunities and challenges

Somatic cells have been reprogrammed into pluripotent stem cells by introducing a combination of several transcription factors, such as Oct3/4, Sox2, Klf4 and c-Myc. Induced pluripotent stem (iPS) cells from a patient's somatic cells could be a useful source for drug discovery and cell transplantation therapies. However, most human iPS cells are made by viral vectors, such as retrovirus and lentivirus, which integrate the reprogramming factors into the host genomes and may increase the risk of tumour formation. Several non-integration methods have been reported to overcome the safety concern associated with the generation of iPS cells, such as transient expression of the reprogramming factors using adenovirus vectors or plasmids, and direct delivery of reprogramming proteins. Although these transient expression methods could avoid genomic alteration of iPS cells, they are inefficient. Several studies of gene expression, epigenetic modification and differentiation revealed the insufficient reprogramming of iPS cells, thus suggesting the need for improvement of the reprogramming procedure not only in quantity but also in quality. This report will summarize the current knowledge of iPS generation and discuss future reprogramming methods for medical application.

Stem Cell Therapy: A New Treatment for Burns?

Stem cell therapy has emerged as a promising new approach in almost every medicine specialty. This vast, heterogeneous family of cells are now both naturally (embryonic and adult stem cells) or artificially obtained (induced pluripotent stem cells or iPSCs) and their fates have become increasingly controllable, thanks to ongoing research in this passionate new field. We are at the beginning of a new era in medicine, with multiple applications for stem cell therapy, not only as a monotherapy, but also as an adjunct to other strategies, such as organ transplantation or standard drug treatment. Regrettably, serious preclinical concerns remain and differentiation, cell fusion, senescence and signalling crosstalk with growth factors and biomaterials are still challenges for this promising multidisciplinary therapeutic modality. Severe burns have several indications for stem cell therapy, including enhancement of wound healing, replacement of damaged skin and perfect skin regeneration - incorporating skin appendages and reduced fibrosis -, as well as systemic effects, such as inflammation, hypermetabolism and immunosuppression. The aim of this review is to describe well established characteristics of stem cells and to delineate new advances in the stem cell field, in the context of burn injury and wound healing.

Induced pluripotent stem cells: emerging techniques for nuclear reprogramming

Introduction of four transcription factors, Oct3/4, Sox2, Klf4, and c-Myc, can successfully reprogram somatic cells into embryonic stem (ES)-like cells. These cells, which are referred to as induced pluripotent stem (iPS) cells, closely resemble embryonic stem cells in genomic, cell biologic, and phenotypic characteristics, and the creation of these special cells was a major triumph in cell biology. In contrast to pluripotent stem cells generated by somatic cell nuclear-transfer (SCNT) or ES cells derived from the inner cell mass (ICM) of the blastocyst, direct reprogramming provides a convenient and reliable means of generating pluripotent stem cells. iPS cells have already shown incredible potential for research and for therapeutic applications in regenerative medicine within just a few years of their discovery. In this review, current techniques of generating iPS cells and mechanisms of nuclear reprogramming are reviewed, and the potential for therapeutic applications is discussed.

Use of mouse hematopoietic stem and progenitor cells to treat acute kidney injury

New and effective treatment for acute kidney injury remains a challenge. Here, we induced mouse hematopoietic stem and progenitor cells (HSPC) to differentiate into cells that partially resemble a renal cell phenotype and tested their therapeutic potential. We sequentially treated HSPC with a combination of protein factors for 1 wk to generate a large number of cells that expressed renal developmentally regulated genes and protein. Cell fate conversion was associated with increased histone acetylation on promoters of renal-related genes. Further treatment of the cells with a histone deacetylase inhibitor improved the efficiency of cell conversion by sixfold. Treated cells formed tubular structures in three-dimensional cultures and were integrated into tubules of embryonic kidney organ cultures. When injected under the renal capsule, they integrated into renal tubules of postischemic kidneys and expressed the epithelial marker E-cadherin. No teratoma formation was detected 2 and 6 mo after cell injection, supporting the safety of using these cells. Furthermore, intravenous injection of the cells into mice with renal ischemic injury improved kidney function and morphology by increasing endogenous renal repair and decreasing tubular cell death. The cells produced biologically effective concentrations of renotrophic factors including VEGF, IGF-1, and HGF to stimulate epithelial proliferation and tubular repair. Our study indicates that hematopoietic stem and progenitor cells can be converted to a large number of renal-like cells within a short period for potential treatment of acute kidney injury.