Adaptation to culture of human embryonic stem cells and oncogenesis in vivo

The application of human embryonic stem cells (HESCs) to provide differentiated cells for regenerative medicine will require the continuous maintenance of the undifferentiated stem cells for long periods in culture. However, chromosomal stability during extended passaging cannot be guaranteed, as recent cytogenetic studies of HESCs have shown karyotypic aberrations. The observed karyotypic aberrations probably reflect the progressive adaptation of self-renewing cells to their culture conditions. Genetic change that increases the capacity of cells to proliferate has obvious parallels with malignant transformation, and we propose that the changes observed in HESCs in culture reflect tumorigenic events that occur in vivo, particularly in testicular germ cell tumors. Further supporting a link between culture adaptation and malignancy, we have observed the formation of a chromosomal homogeneous staining region in one HESC line, a genetic feature almost a hallmark of cancer cells. Identifying the genes critical for culture adaptation may thus reveal key players for both stem cell maintenance in vitro and germ cell tumorigenesis in vivo.     

Epigenetic memory and preferential lineage-specific differentiation in induced pluripotent stem cells derived from human pancreatic islet beta cells

Human induced pluripotent stem cells (HiPSCs) appear to be highly similar to human embryonic stem cells (HESCs). Using two genetic lineage-tracing systems, we demonstrate the generation of iPSC lines from human pancreatic islet beta cells. These reprogrammed cells acquired markers of pluripotent cells and differentiated into the three embryonic germ layers. However, the beta cell-derived iPSCs (BiPSCs) maintained open chromatin structure at key beta-cell genes, together with?a unique DNA methylation signature that distinguishes them from other PSCs. BiPSCs also demonstrated an increased ability to differentiate into insulin-producing cells both in?vitro and in?vivo, compared with ESCs and isogenic non-beta iPSCs. Our results suggest that the epigenetic memory may predispose?BiPSCs to differentiate more readily into insulin producing cells. These findings demonstrate that HiPSC phenotype may be influenced by their cells of origin, and suggest that their skewed differentiation potential may be advantageous for cell replacement therapy.     

Generating pluripotent stem cells: Differential epigenetic changes during cellular reprogramming

Pluripotent stem cells hold enomous potential for therapuetic applications in tissue replacement therapy. Reprogramming somatic cells from a patient donor to generate pluripotent stem cells involves both ethical concerns inherent in the use of embryonic and oocyte-derived stem cells, as well as issues of histocompatibility. Among the various pluripotent stem cells, induced pluripotent stem cells (iPSC)-derived by ectopic expression of four reprogramming factors in donor somatic cells-are superior in terms of ethical use, histocompatibility, and derivation method. However, iPSC also show genetic and epigenetic differences that limit their differentiation potential, functionality, safety, and potential clinical utility. Here, we discuss the unique characteristics of iPSC and approaches that are being taken to overcome these limitations.     

The prospect of pluripotent stem cell-based therapy

Human embryonic stem cells (hESC) are able to maintain pluripotency in culture, to proliferate indefinitely and to differentiate into all somatic cell types. Due to these unique properties, hESC may become an exceptional source of tissues for transplantation and have a great potential for the therapy of incurable diseases. Here, we review new developments in the area of embryonic stem cells and discuss major challenges — standardization of protocols for cell derivation and cultivation, identification of specific molecular markers, development of new approaches for directed differentiation, etc. — which remain to be settled, prior to safe and successful clinical application of stem cells. We appraise several potential approaches in hESC-based therapy including derivation of autologous cells via therapeutic cloning (1), generation of immune tolerance to allogenic donor cells via hematopoetic chimerism (2), and development of the banks of hESC lines compatible with the main antigens and exhibiting equivalent pluripotency (3). In addition, we discuss briefly induced pluripotent cells, which are derived via genetic modification of autologous somatic cells and are analogous to ESC. Our analysis demonstrates that uncontrollable differentiation in vivo and teratogenic potential of hESC are critical limitations of their application in clinical practice. Therefore, the major approach in hESC therapy is derivation of a specific differentiated progeny, which has lower proliferative potential and immune privilege, yet poses fewer risks for organism. The review demonstrates that cell therapy is far more complex and resource-consuming process as compared with drug-based medicine and consequently pluripotent stem cell biology and technology still requires further investigation and development before these cells can be used in clinical practice.     

From stem cells to red blood cells:how far away from the clinical application?

The generation of red blood cells(RBCs)from stem cells provides a solution for deficiencies in blood transfusion.Currently,primary hematopoietic stem cells,embryonic stem cells and induced pluripotent stem cells have shown the potential to produce fully mature RBCs.Here,we discuss the advantages,induction protocols,progress and possible clinical applications of stem cells in RBC production.     

Embryonic stem cells and retinal repair

In this review we examine the potential of embryonic stem cells (ESCs) for use in the treatment of retinal diseases involving photoreceptors and retinal pigment epithelium (RPE). We outline the ontogenesis of target retinal cell types (RPE, rods and cones) and discuss how an understanding of developmental processes can inform our manipulation of ESCs in vitro. Due to their potential for cellular therapy, special emphasis is placed upon the derivation and culture of human embryonic stem cells (HESCs) and their differentiation towards a retinal phenotype. In terms of achieving this goal, we suggest that much of the success to date reflects permissive in vitro environments provided by established protocols for HESC derivation, propagation and neural differentiation. In addition, we summarise key factors that may be important for enhancing efficiency of retinal cell-type derivation from HESCs. The retina is an amenable component of the central nervous system (CNS) and as such, diseases of this structure provide a realistic target for the application of HESC-derived cellular therapy to the CNS. In order to further this goal, the second component of our review focuses on the cellular and molecular cues within retinal environments that may influence the survival and behaviour of transplanted cells. Our analysis considers both the potential barriers to transplant integration in the retina itself together with the remodelling in host visual centres that is known to accompany retinal dystrophy.     

Overlapping Genes May Control Reprogramming of Mouse Somatic Cells into Induced Pluripotent Stem Cells (iPSCs) and Breast Cancer Stem Cells

Recent findings suggest the possibility that tumors originate from cancer cells with stem cell properties. The cancer stem cell (CSC) hypothesis provides an explanation for why existing cancer therapies often fail in eradicating highly malignant tumors and end with tumor recurrence. Although normal stem cells and CSCs both share the capacity for self-renewal and multi-lineage differentiation, suggesting that CSC may be derived from normal SCs, the cellular origin of transformation of CSCs is debatable. Research suggests that the tightly controlled balance of self-renewal and differentiation that characterizes normal stem cell function is dis-regulated in cancer. Additionally, recent evidence has linked an embryonic stem cell (ESC)-like gene signature with poorly differentiated high-grade tumors, suggesting that regulatory pathways controlling pluripotency may in part contribute to the somatic CSC phenotype. Here, we introduce expression profile bioinformatic analyses of mouse breast cells with CSC properties, mouse embryonic stem (mES) and induced pluripotent stem (iPS) cells with an emphasis on how study of pluripotent stem cells may contribute to the identification of genes and pathways that facilitate events associated with oncogenesis. Global gene expression analysis from CSCs and induced pluripotent stem cell lines represent an ideal model to study cancer initiation and progression and provide insight into the origin cancer stem cells. Additionally, insight into the genetic and epigenomic mechanisms regulating the balance between self-renewal and differentiation of somatic stem cells and cancer may help to determine whether different strategies used to generate iPSCs are potentially safe for therapeutic use.     

利用化学小分子实现人胚胎干细胞多能性状态的转化

小鼠胚胎干细胞（Embryonic Stem Cells,ESCs）具有两种不同的多能性状态-原始态多能性（naive pluripotency）和始发态多能性（primed pluripotency）,这两种多能性干细胞在形态、自我更新维持条件、基因表达、表观遗传学特征以及单克隆形成率等方面都存在明显差别。传统条件下分离和培养的人胚胎干细胞（human Embryonic Stem Cells,h ESCs）生物学特征更接近始发态多能性状态,需依赖转基因操作才能获得和维持原始态多能性状态。本研究通过在培养体系中添加化学小分子成功地将已建系的始发态多能性h ESCs转化为原始态多能性干细胞,转化后h ESCs呈紧密、圆形、隆起的三维克隆结构,具有两条活化的X染色体,单克隆形成率提高,基因表达更接近原始态多能性特征。结果提示h ESCs也存在两种多能性状态,不同的体外培养环境可获得具备不同多能性特征的h ESCs。原始态多能性状态的获得使h ESCs在基因治疗、器官再生等领域具有广阔的应用前景,而仅改变培养条件,不依赖基因操作的培养方式大大提高了原始态多能性干细胞应用的安全性。     

Complement-dependent control of teratoma formation by embryonic stem cells

The fetus has pluripotent stem cells that when transferred to mature individuals can generate tumors. However, for reasons yet unknown, tumors form rarely in the fetus and/or the mother during normal gestation. We questioned whether the complement system might protect against tumor formation by pluripotent stem cells. Murine embryonic stem cells were notably more susceptible than cardiomyocytes differentiated from those cells to lysis by complement in heterologous and homologous sera. Treatment of embryonic stem cells with heterologous serum averted tumor formation after residual cells were transplanted into mice. Confirming the importance of homologous complement in preventing formation of tumors, untreated embryonic stem cells formed tumors more quickly in C3-deficient than in wild-type mice. Susceptibility of embryonic stem cells to complement required an intact alternative pathway and was owed at least in part to a relative deficiency of sialic acid on cell surfaces compared with differentiated cells. Susceptibility to complement and resistance to tumors was inversely related to the number of cells transferred. These findings show that formation of tumors from embryonic stem cells is controlled in part by the alternative pathway of complement and suggest that susceptibility to complement might represent a general property of pluripotent stem cells that can be exploited to prevent tumor formation.     

The tumorigenic potential of pluripotent stem cells: What can we do to minimize it?

Human pluripotent stem cells (hPSCs) have the potential to fundamentally change the way that we go about treating and understanding human disease. Despite this extraordinary potential, these cells also have an innate capability to form tumors in immunocompromised individuals when they are introduced in their pluripotent state. Although current therapeutic strategies involve transplantation of only differentiated hPSC derivatives, there is still a concern that transplanted cell populations could contain a small percentage of cells that are not fully differentiated. In addition, these cells have been frequently reported to acquire genetic alterations that, in some cases, are associated with certain types of human cancers. Here, we try to separate the panic from reality and rationally evaluate the true tumorigenic potential of these cells. We also discuss a recent study examining the effect of culture conditions on the genetic integrity of hPSCs. Finally, we present a set of sensible guidelines for minimizing the tumorigenic potential of hPSC‐derived cells. © 2016 The Authors. Inside the Cell published by Wiley Periodicals, Inc.