Nonclinical safety strategies for stem cell therapies

Recent breakthroughs in stem cell biology, especially the development of the induced pluripotent stem cell techniques, have generated tremendous enthusiasm and efforts to explore the therapeutic potential of stem cells in regenerative medicine. Stem cell therapies are being considered for the treatment of degenerative diseases, inflammatory conditions, cancer and repair of damaged tissue. The safety of a stem cell therapy depends on many factors including the type of cell therapy, the differentiation status and proliferation capacity of the cells, the route of administration, the intended clinical location, long term survival of the product and/or engraftment, the need for repeated administration, the disease to be treated and the age of the population. Understanding the product profile of the intended therapy is crucial to the development of the nonclinical safety study design.     

神经退行性或损伤性疾病防治的新视点——干细胞药物

干细胞药物是指可以通过调节生物体内干细胞的增殖与分化,来防治由于细胞缺失或损伤而引起疾病的一类治疗和预防药物。近年来发现:运用中药、生长因子和小分子化合物均可调节生物体内干细胞的增殖与分化;而神经系统退行性或损伤性疾病:包括帕金森病(PD)、阿尔采末病(AD)、亨廷顿病(HD)、药物滥用、抑郁症以及脑卒中等,均是由于神经细胞的缺失或损伤而引发的疾病。运用药物来调节自身神经干细胞的增殖与定向分化潜能,以重建受损的功能细胞,恢复其生物学功能,既解决了成体神经干细胞的来源困难和胚胎干细胞的伦理困惑问题,也避免了细胞移植的免疫排斥和手术后遗症问题。为细胞丢失或损伤性疾病的防治提供了崭新的视点和思路。     

Electrospun scaffolds for stem cell engineering

Stem cells interact with and respond to a myriad of signals emanating from their extracellular microenvironment. The ability to harness the regenerative potential of stem cells via a synthetic matrix has promising implications for regenerative medicine. Electrospun fibrous scaffolds can be prepared with high degree of control over their structure creating highly porous meshes of ultrafine fibers that resemble the extracellular matrix topography, and are amenable to various functional modifications targeted towards enhancing stem cell survival and proliferation, directing specific stem cell fates, or promoting tissue organization. The feasibility of using such a scaffold platform to present integrated topographical and biochemical signals that are essential to stem cell manipulation has been demonstrated. Future application of this versatile scaffold platform to human embryonic and induced pluripotent stem cells for functional tissue repair and regeneration will further expand its potential for regenerative therapies.     

Growth factor and small molecule influence on urological tissue regeneration utilizing cell seeded scaffolds

Regenerative medicine strategies combine various attributes from multiple disciplines including stem cell biology, chemistry, materials science and medicine. The junction at which these disciplines intersect provides a means to address unmet medical needs in an assortment of pathologies with the goal of creating sustainable, functional replacement tissues. Tissue damage caused by trauma for example, requires rapid responses in order to mitigate further tissue deterioration. Cell/scaffold composites have been utilized to initiate and stabilize regenerative responses in vivo with the hope that functional tissue can be attained. Along with the gross reconfiguration of regenerating tissues, small molecules and growth factors also play a pivotal role in tissue regeneration. Several regenerative studies targeting a variety of urological tissues demonstrate the utility of these small molecules or growth factors in an in vivo setting.     

细胞治疗帕金森病的研究进展

帕金森病（PD）是一种以黑质多巴胺能神经元丢失为主要病理特征的神经退行性疾病,其病因不清且发病 机制复杂。目前药物和手术治疗还难以根治PD。细胞治疗为PD治疗提供了新的策略,通过移植胎儿腹侧中脑组织 至患者纹状体,可使患者运动功能得到一定程度的恢复,证实细胞移植具有治疗PD的作用;干细胞,包括多能干细 胞、神经干细胞和间充质干细胞通过定向分化为多巴胺能神经元,为临床应用提供了可再生的细胞来源,进一步拓 展了细胞治疗的前景;诱导神经元治疗PD避免了建立体外干细胞库的高成本,有望实现神经元原位再生。就基于 不同细胞来源的PD细胞移植治疗研究进展进行综述,以期为再生医学治疗PD提供新的方向。     

Genetic modification of stem cells for improved therapy of the infarcted myocardium

The conventional treatment modalities for ischemic heart disease only provide symptomatic relief to the patient without repairing and regenerating the damaged myocardium. Stem cell transplantation has emerged as a promising alternative therapeutic approach for cardiovascular diseases. Stem cells possess the potential of differentiation to adopt morphofunctional cardiac and vasculogenic phenotypes to repopulate the scar tissue and restore regional blood flow in the ischemic myocardium. These beneficial therapeutic effects make stem cell transplantation the method of choice for the treatment of ischemic heart disease. The efficacy of stem cell transplantation may be augmented by genetic manipulation of the cells prior to transplantation. Not only will insertion of therapeutic transgene(s) into the stem cells support the survival and differentiation of cells in the unfavorable microenvironment of the ischemic myocardium, but also the genetically manipulated stem cells will serve as a source of the transgene expression product in the heart for therapeutic benefits. We provide an overview of the extensively studied stem cell types for cardiac regeneration, the various methods in which these cells have been genetically manipulated and rationale of genetic modification of stem cells for use in regenerative cardiovascular therapeutics.     

Micromechanical control of cell and tissue development: implications for tissue engineering

Tissue engineering approaches for repair of diseased or lost organs will require the development of new biomaterials that guide cell behavior and seamlessly integrate with living tissues. Previous approaches to engineer artificial tissues have focused largely on optimization of scaffold polymer chemistry and selection of appropriate biochemical additives (e.g., growth factors, adhesive ligands) to provide effective developmental control. However, recent work has shown that micromechanical forces and local variations of extracellular matrix (ECM) elasticity at the microscale regulate cell and tissue development both in vitro and in vivo. The micromechanical properties of the host tissue microenvironment also play a critical role in control of stem cell lineage switching. Here we discuss how new understanding of the fundamental role that mechanical forces play in tissue development might be leveraged to facilitate the development of new types of biomimetic materials for regenerative medicine, with a focus on the design of injectable materials that can target to injury sites, recruit stem cells and direct cellular self-assembly to regenerate functional tissues and organs in situ.     

Stem cells as a novel tool for drug screening and treatment of degenerative diseases

Degenerative diseases similarly as acute tissue injuries lead to massive cell loss and may cause organ failure of vital organs (e.g., heart, central nervous system). Therefore, they belong to a group of disorders that may significantly benefit from stem cells (SCs)-based therapies. Several stem and progenitor cell populations have already been described as valuable tools for developing therapeutic strategies in regenerative medicine. In particular, pluripotent stem cells (PSCs), including adult-tissue-derived PSCs, neonatal-tissue-derived SCs, embryonic stem cells (ESCs), and recently described induced pluripotent stem cells (iPSCs), are the focus of particular attention because of their capacity to differentiate into all the cell lineages. Although PSCs are predominantly envisioned to be applied for organ regeneration, they may be also successfully employed in drug screening and disease modeling. In particular, adult PSCs and iPSCs derived from patient tissues may not only be a source of cells for autologous therapies but also for individual customized in vitro drug testing and studies on the molecular mechanisms of disease. In this review, we will focus on the potential applications of SCs, especially PSCs i) in regenerative medicine therapies, ii) in studying mechanisms of disease, as well as iii) in drug screening and toxicology tests that are crucial in new drug development. In particular, we will discuss the application of SCs in developing new therapeutic approaches to treat degenerative diseases of the neural system and heart. The advantage of adult PSCs in all the above-mentioned settings is that they can be directly harvested from patient tissues and used not only as a safe non-immunogenic source of cells for therapy but also as tools for personalized drug screening and pharmacological therapies.     

Regenerative and immunomodulatory potential of mesenchymal stem cells

In the past few years, mesenchymal stem cells (MSCs) have come into the limelight because of their multi-lineage stem cell potential, which retains some aspects of embryonic stem cells, and because of their characteristic immunoregulatory functions exerted on different immune effector cells. The regenerative and immunomodulatory potential of MSCs has been used to support hemopoietic stem cell engraftment; to repair or regenerate damaged or mutated tissues, such as bone, cartilage, myocardial or hepatic tissues; to interfere with neoplastic cell growth by transfecting MSCs with anti-neoplastic molecules; and to modulate autoimmune reactions such as collagenopathies, multiple sclerosis and graft versus host disease. Thus, MSCs appear to be a very promising tool for regenerative and immunoregulatory cell therapy.     

Regenerative inductive therapy based on DDS technology of protein and gene

Recent development of biomedical engineering including biomaterials and drug delivery system (DDS) as well as basic biology and medicine has enabled cells to induce regeneration repairing of defective tissues as well as substitute the biological functions of damaged organs. For successful tissue regeneration, it is undoubtedly indispensable to give cells a local environment which allows cells to efficiently promote their proliferation and differentiation and consequently induce cell-based tissue regeneration. Tissue engineering is one of the biomedical forms to create this regeneration environment of cells. The tissue and organ repairing based on their regeneration induction has been realized by combining cells with the tissue engineering technology or methodology in a surgical or internally medical manner. This paper overviews the present status and future direction of tissue engineering for regenerative inductive therapy, briefly explaining the key technology of tissue engineering, especially DDS of growth factor and gene.     

Regenerative inductive therapy based on DDS technology of protein and gene

Recent development of biomedical engineering including biomaterials and drug delivery system (DDS) as well as basic biology and medicine has enabled cells to induce regeneration repairing of defective tissues as well as substitute the biological functions of damaged organs. For successful tissue regeneration, it is undoubtedly indispensable to give cells a local environment which allows cells to efficiently promote their proliferation and differentiation and consequently induce cell-based tissue regeneration. Tissue engineering is one of the biomedical forms to create this regeneration environment of cells. The tissue and organ repairing based on their regeneration induction has been realized by combining cells with the tissue engineering technology or methodology in a surgical or internally medical manner. This paper overviews the present status and future direction of tissue engineering for regenerative inductive therapy, briefly explaining the key technology of tissue engineering, especially DDS of growth factor and gene.     

间充质干细胞成骨和成脂分化调控机制研究

间充质干细胞（MSCs）是人体内参与免疫平衡、维持组织器官的稳态和功能以及组织损伤修复的一类重要成体干细胞。MSCs具有自我更新能力和多向分化潜能,国际干细胞协会将MSCs向脂肪、成骨等细胞分化的能力作为其重要的检测标准。作为骨细胞和脂肪细胞的共同来源,MSCs在成骨和成脂分化之间相互协调和相互竞争,并在多种调控因素作用下保持着微妙的平衡。对MSCs成骨、成脂分化的信号通路、调控因素进行分析,并对其分化诱导方法以及鉴定方法进行总结,以期为MSCs基础研究及临床应用提供参考依据。     

Regeneration of cartilage and bone by defined subsets of mesenchymal stromal cells--potential and pitfalls

Mesenchymal stromal cells, also referred to as mesenchymal stem cells, can be obtained from various tissues. Today the main source for isolation of mesenchymal stromal cells in mammals is the bone marrow. Mesenchymal stromal cells play an important role in tissue formation and organogenesis during embryonic development. Moreover, they provide the cellular and humoral basis for many processes of tissue regeneration and wound healing in infancy, adolescence and adulthood as well. There is increasing evidence that mesenchymal stromal cells from bone marrow and other sources including term placenta or adipose tissue are not a homogenous cell population. Only a restricted number of appropriate stem cells markers have been explored so far. But routine preparations of mesenchymal stromal cells contain phenotypically and functionally distinct subsets of stromal cells. Knowledge on the phenotypical characteristics and the functional consequences of such subsets will not only extend our understanding of stem cell biology, but might allow to develop improved regimen for regenerative medicine and wound healing and novel protocols for tissue engineering as well. In this review we will discuss novel strategies for regenerative medicine by specific selection or separation of subsets of mesenchymal stromal cells in the context of osteogenesis and bone regeneration. Mesenchymal stromal cells, which express the specific cell adhesion molecule CD146, also known as MCAM or MUC18, are prone for bone repair. Other cell surface proteins may allow the selection of chondrogenic, myogenic, adipogenic or other pre-determined subsets of mesenchymal stromal cells for improved regenerative applications as well.     

Therapeutic potential of stem cells in diabetes

Stem cells possess the ability to self-renew by symmetric divisions and, under certain circumstances, differentiate to a committed lineage by asymmetric cell divisions. Depending on the origin, stem cells are classified as either embryonic or adult. Embryonic stem cells are obtained from the inner cell mass of the blastocyst, a structure that appears during embryonic development at day 6 in humans and day 3.5 in mice. Adult stem cells are present within tissues of adult organisms and are responsible for cell turnover or repopulation of tissues under normal or exceptional circumstances. Taken together, stem cells might represent a potential source of tissues for cell therapy protocols, and diabetes is a candidate disease that may benefit from cell replacement protocols. The pathology of type 1 diabetes is caused by the autoimmune destruction or malfunction of pancreatic beta cells, and consequently, a lack of insulin. The absence of insulin is life-threatening, thus requiring diabetic patients to take daily hormone injections from exogenous sources; however, insulin injections do not adequately mimic beta cell function. This results in the development of diabetic complications such as neuropathy, nephropathy, retinopathy and diverse cardiovascular disorders. This chapter intends to summarize the possibilities opened by embryonic and adult stem cells in regenerative medicine for the cure of diabetes.     

Morphological and cytofluorimetric analysis of adult mesenchymal stem cells expanded ex vivo from periodontal ligament

Many adult tissues contain a population of stem cells that have the ability of regeneration after trauma, disease or aging. Recently, there has been great interest in mesenchymal stem cells and their roles in maintaining the physiological structure of tissues, and their studies have been considered very important and intriguing, after having shown that this cell population can be expanded ex vivo to regenerate tissues not only of the mesenchymal lineage, such as intervertebral disc cartilage, bone, tooth-associated tissue, cardiomyocytes, but also to differentiate into cells derived from other embryonic layers, including neurons. Currently, different efforts have been focused on the identification of odontogenic progenitors from oral tissues. In this study we isolated and characterized a population of homogeneous human mesenchymal stem cells proliferating in culture with an attached well-spread morphology derived from periodontal ligament, a tissue of ectomesenchymal origin, with the ability to form a specialized joint between alveolar bone and tooth. The adherent cells were harvested and expanded ex vivo under specific conditions and analysed by FACScan flow cytometer and morphological analysis was carried out by light, scanning and transmission electron microscopy. Our results displayed highly evident cells with a fibroblast-like morphology and a secretory apparatus, probably indicating that the enhanced function of the secretory apparatus of the mesenchymal stem cells may be associated with the secretion of molecules that are required to survive and proliferate. Moreover, the presence in periodontal ligament of CD90, CD29, CD44,CD166, CD 105, CD13 positive cells, antigens that are also identified as stromal precursors of the bone marrow, indicate that the periodontal ligament may turn out to be a new efficient source of the cells with intrinsic capacity to self-renewal, high ability to proliferate and differentiate, that can be utilized for a new approach to regenerative medicine and tissue engineering.     

Adult mesenchymal stem cells in dental research: a new approach for tissue engineering

Many adult tissues contain a population of stem cells that have the ability to regenerate after trauma, disease or aging. Recently, there has been great interest in mesenchymal stem cells and their roles in maintaining the physiological structure of tissues. The studies on stem cells are thought to be very important and, in fact, it has been shown that this cell population can be expanded ex vivo to regenerate tissues not only of the mesenchymal lineage, such as intervertebral disc cartilage, bone and tooth-associated tissues, but also other types of tissues. Several studies have focused on the identification of odontogenic progenitors from oral tissues, and it has been shown that the mesenchymal stem cells obtained from periodontal ligament and dental pulp could have similar morphological and phenotypical features of the bone marrow mesenchymal cells. In fact a population of homogeneous human mesenchymal stem cells derived from periodontal ligament and dental pulp, and proliferating in culture with a well-spread morphology, can be recovered and characterized. Since these cells are considered as candidates for regenerative medicine, the knowledge of the cell differentiation mechanisms is imperative for the development of predictable techniques in implant dentistry, oral surgery and maxillo-facial reconstruction. Thus, future research efforts might be focused on the potential use of this cell population in tissue engineering. Further studies will be carried out to elucidate the molecular mechanisms involved in their maintenance and differentiation in vitro and in vivo.     

Biomaterials for stem cell differentiation

The promise of cellular therapy lies in the repair of damaged organs and tissues in vivo as well as generating tissue constructs in vitro for subsequent transplantation. Unfortunately, the lack of available donor cell sources limits its ultimate clinical applicability. Stem cells are a natural choice for cell therapy due to their pluripotent nature and self-renewal capacity. Creating reserves of undifferentiated stem cells and subsequently driving their differentiation to a lineage of choice in an efficient and scalable manner is critical for the ultimate clinical success of cellular therapeutics. In recent years, a variety of biomaterials have been incorporated in stem cell cultures, primarily to provide a conducive microenvironment for their growth and differentiation and to ultimately mimic the stem cell niche. In this review, we examine applications of natural and synthetic materials, their modifications as well as various culture conditions for maintenance and lineage-specific differentiation of embryonic and adult stem cells.     

Chemical biology in stem cell research

Stem cells are offering a considerable range of prospects to the biomedical research including novel platforms for disease models and drug discovery tools to cell transplantation and regenerative therapies. However, there are several obstacles to overcome to bring these potentials into reality. First, robust methods to maintain stem cells in the pluripotent state should be established and factors that are required to direct stem cell fate into a particular lineage should be elucidated. Second, both allogeneic rejection following transplantation and limited cell availability issues must be circumvented. These challenges are being addressed, at least in part, through the identification of a group of chemicals (small molecules) that possess novel activities on stem cell biology. For example, small molecules can be used both in vitro and/or in vivo as tools to promote proliferation of stem cells (self-renewal), to direct stem cells to a lineage specific patterns (differentiation), or to reprogram somatic cells to a more undifferentiated state (de-differentiation or reprogramming). These molecules, in turn, have provided new insights into the signaling mechanisms that regulate stem cell biology, and may eventually lead to effective therapies in regenerative medicine. In this review, we will introduce recent findings with regards to small molecules and their impact on stem cell self-renewal and differentiation.     

Antisense Makes Sense in Engineered Regenerative Medicine

The use of antisense strategies such as ribozymes, oligodeoxynucleotides (ODNs) and small interfering RNA (siRNA) in gene therapy, in conjunction with the use of stem cells and tissue engineering, has opened up possibilities in curing degenerative diseases and injuries to non-regenerating organs and tissues. With their unique ability to down-regulate or silence gene expression, antisense oligonucleotides are uniquely suited in turning down the production of pathogenic or undesirable proteins and cytokines. Here, we review the antisense strategies and their applications in regenerative medicine with a focus on their efficacies in promoting cell viability, regulating cell functionalities as well as shaping an optimal microenvironment for therapeutic purposes. Chunming Wang, and Yongchang Yao contributed equally.