Transplantation of 3D scaffolds seeded with human embryonic stem cells: biological features of surrogate tissue and teratoma-forming potential

Embryonic stem cell-derived extracellular vesicles promote the recovery of kidney injury

BACKGROUND

Embryonic stem cell-derived extracellular vesicles (ESC-EVs) possess therapeutic potential for a variety of diseases and are considered as an alternative of ES cells. Acute kidney injury (AKI) is a common acute and severe disease in clinical practice, which seriously threatens human life and health. However, the roles and mechanisms of ESC-EVs on AKI remain unclear.

METHODS

In this study, we evaluated the effects of ESC-EVs on physiological repair and pathological repair using murine ischemia-reperfusion injury-induced AKI model, the potential mechanisms of which were next investigated. EVs were isolated from ESCs and EVs derived from mouse fibroblasts as therapeutic controls. We then investigated whether ESC-EVs can restore the structure and function of the damaged kidney by promoting physiological repair and inhibiting the pathological repair process after AKI in vivo and in vitro.

RESULTS

We found that ESC-EVs significantly promoted the recovery of the structure and function of the damaged kidney. ESC-EVs increased the proliferation of renal tubular epithelial cells, facilitated renal angiogenesis, inhibited the progression of renal fibrosis, and rescued DNA damage caused by ischemia and reperfusion after AKI. Finally, we found that ESC-EVs play a therapeutic effect by activating Sox9+ cells.

CONCLUSIONS

ESC-EVs significantly promote the physiological repair and inhibit the pathological repair after AKI, enabling restoration of the structure and function of the damaged kidney. This strategy might emerge as a novel therapeutic strategy for ESC clinical application.

A Hepatic Scaffold from Decellularized Liver Tissue: Food for Thought

Allogeneic liver transplantation is still deemed the gold standard solution for end-stage organ failure; however, donor organ shortages have led to extended waiting lists for organ transplants. In order to overcome the lack of donors, the development of new therapeutic options is mandatory. In the last several years, organ bioengineering has been extensively explored to provide transplantable tissues or whole organs with the final goal of creating a three-dimensional growth microenvironment mimicking the native structure. It has been frequently reported that an extracellular matrix-based scaffold offers a structural support and important biological molecules that could help cellular proliferation during the recellularization process. The aim of the present review is to underline the recent developments in cell-on-scaffold technology for liver bioengineering, taking into account: (1) biological and synthetic scaffolds; (2) animal and human tissue decellularization; (3) scaffold recellularization; (4) 3D bioprinting; and (5) organoid technology. Future possible clinical applications in regenerative medicine for liver tissue engineering and for drug testing were underlined and dissected.

A novel method to reconstruct epithelial tissue using high-purity keratinocyte lineage cells induced from human embryonic stem cells

The treatment of oral mucosa defect such as autologous oral mucosa caused by resection of oral mucosa carcinoma is still not ideal in clinical practice. However, Tissue engineering gives us the possibility to solve this problem. As we all know, Human embryonic stem cells (hESCs) have the ability to give rise to various cell types. We can take advantage of the totipotency of human embryonic stem cells to acquire keratinocytes. Directing the epithelial differentiation of hESCs can provide seed cells for the construction of epithelium tissue by tissue engineering. But, how to get high purity keratinocytes by induced stem cells then Applied to tissue engineering mucosa is an important challenge. We described a novel method to directly induce hESCs to differentiate into keratinocytes. Retinoic acid, ascorbic acid, and bone morphogenetic protein induced hESCs to differentiate into cells that highly expressed cytokeratin (CK)14. Our findings suggest that the retinoic acid, ascorbic acid and bone morphogenetic proteins induced hESCs to form high purity keratinocyte cell populations. In addition, we found that the highly pure keratinocyte populations reconstructed artificial tissue resembling epithelial tissue when inoculated in vitro on a biological scaffold.

Looking into the Future: Toward Advanced 3D Biomaterials for Stem-Cell-Based Regenerative Medicine

Stem-cell-based therapies have the potential to provide novel solutions for the treatment of a variety of diseases, but the main obstacles to such therapies lie in the uncontrolled differentiation and functional engraftment of implanted tissues. The physicochemical microenvironment controls the self-renewal and differentiation of stem cells, and the key step in mimicking the stem cell microenvironment is to construct a more physiologically relevant 3D culture system. Material-based 3D assemblies of stem cells facilitate the cellular interactions that promote morphogenesis and tissue organization in a similar manner to that which occurs during embryogenesis. Both natural and artificial materials can be used to create 3D scaffolds, and synthetic organic and inorganic porous materials are the two main kinds of artificial materials. Nanotechnology provides new opportunities to design novel advanced materials with special physicochemical properties for 3D stem cell culture and transplantation. Herein, the advances and advantages of 3D scaffold materials, especially with respect to stem-cell-based therapies, are first outlined. Second, the stem cell biology in 3D scaffold materials is reviewed. Third, the progress and basic principles of developing 3D scaffold materials for clinical applications in tissue engineering and regenerative medicine are reviewed.

[Tubular gastric elongation surgery for high esophageal-gastric anastomosis after resection of esophageal cancer: analysis of 5 cases]

OBJECTIVE

To summarize our experience with tubular gastric elongation surgery for management of insufficient gastric length for high esophageal-gastric anastomosis following esophageal carcinoma resection.

METHODS

From September, 2015 to October 2016, 5 patients with esophageal cancer were treated in our department, including two with cervical esophageal cancer and 3 with thoracic esophageal cancer. The patients with cervical esophageal cancer underwent pharyngeal resection, total laryngectomy, esophageal varus extubation and gastric oropharyngeal anastomosis, and the patients with thoracic esophageal cancer underwent esophageal cancer resection with incisions on the left neck, the right chest and the median abdomen. During the surgery, the length of the stomach was found insufficient to allow routine oropharyngeal anastomosis, and tubular gastric elongation was conducted to extend the tubular stomach to enable successful completion of the surgery.

RESULTS

All the patients recovered smoothly after the surgery and were discharged after 2-3 weeks.

CONCLUSIONS

Tubular gastric elongation surgery can be a good choice for high esophageal-gastric anastomosis after resection of esophageal cancer in cases of insufficient tubular stomach length or high tension at the anastomosis.

Decellularized Matrices As Cell-Instructive Scaffolds to Guide Tissue-Specific Regeneration

Decellularized scaffolds are promising clinically translational biomaterials that can be applied to direct cell responses and promote tissue regeneration. Bioscaffolds derived from the extracellular matrix (ECM) of decellularized tissues can naturally mimic the complex extracellular microenvironment through the retention of compositional, biomechanical, and structural properties specific to the native ECM. Increasingly, studies have investigated the use of ECM-derived scaffolds as instructive substrates to recapitulate properties of the stem cell niche and guide cell proliferation, paracrine factor production, and differentiation in a tissue-specific manner. Here, we review the application of decellularized tissue scaffolds as instructive matrices for stem or progenitor cells, with a focus on the mechanisms through which ECM-derived scaffolds can mediate cell behavior to promote tissue-specific regeneration. We conclude that although additional preclinical studies are required, ECM-derived scaffolds are a promising platform to guide cell behavior and may have widespread clinical applications in the field of regenerative medicine.

Artificial Bone via Bone Tissue Engineering: Current Scenario and Challenges

Bone provides mechanical support, and flexibility to the body as a structural frame work along with mineral storage, homeostasis, and blood pH regulation. The repair and/or replacement of injured or defective bone with healthy bone or bone substitute is a critical problem in orthopedic treatment. Recent advances in tissue engineering have shown promising results in developing bone material capable of substituting the conventional autogenic or allogenic bone transplants. In the present review, we have discussed natural and synthetic scaffold materials such as metal and metal alloys, ceramics, polymers, etc. which are widely being used along with their cellular counterparts such as stem cells in bone tissue engineering with their pros and cons.

New advances in liver decellularization and recellularization: innovative and critical technologies

Techniques for producing decellularized scaffolds for use in liver tissue engineering are emerging as promising methods for tissue reconstruction. In this article, the authors present an overview of liver decellularization methods developed and applied in recent years. These include the widespread use of various perfusion methods for the generation of a 3D scaffold, which may function as a template for either cell recellularization or direct biological application. The authors evaluate methods for scaffold production and explore some factors that may affect the decellularization process. In addition to tissue engineering, this overview includes a description of other potential applications for a decellularized liver scaffold. The authors also introduce the concept of fabrication of fragile biomaterial architecture and finally review the cell types applied to liver scaffold engineering.

Biology-inspired microphysiological system approaches to solve the prediction dilemma of substance testing

The recent advent of microphysiological systems - microfluidic biomimetic devices that aspire to emulate the biology of human tissues, organs and circulation in vitro - is envisaged to enable a global paradigm shift in drug development. An extraordinary US governmental initiative and various dedicated research programs in Europe and Asia have led recently to the first cutting-edge achievements of human single-organ and multi-organ engineering based on microphysiological systems. The expectation is that test systems established on this basis would model various disease stages, and predict toxicity, immunogenicity, ADME profiles and treatment efficacy prior to clinical testing. Consequently, this technology could significantly affect the way drug substances are developed in the future. Furthermore, microphysiological system-based assays may revolutionize our current global programs of prioritization of hazard characterization for any new substances to be used, for example, in agriculture, food, ecosystems or cosmetics, thus, replacing laboratory animal models used currently. Thirty-six experts from academia, industry and regulatory bodies present here the results of an intensive workshop (held in June 2015, Berlin, Germany). They review the status quo of microphysiological systems available today against industry needs, and assess the broad variety of approaches with fit-for-purpose potential in the drug development cycle. Feasible technical solutions to reach the next levels of human biology in vitro are proposed. Furthermore, key organ-on-a-chip case studies, as well as various national and international programs are highlighted. Finally, a roadmap into the future is outlined, to allow for more predictive and regulatory-accepted substance testing on a global scale.

Current Cell-Based Strategies for Whole Kidney Regeneration

Chronic kidney diseases affect thousands of people worldwide. Although hemodialysis alleviates the situation by filtering the patient's blood, it does not replace other kidney functions such as hormone release or homeostasis regulation. Consequently, orthotopic transplantation of donor organs is the ultimate treatment for patients suffering from end-stage renal failure. Unfortunately, the number of patients on the waiting list far exceeds the number of donors. In addition, recipients must remain on immunosuppressive medications for the remainder of their lives, which increases the risk of morbidity due to their weakened immune system. Despite recent advancements in whole organ transplantation, 40% of recipients will face rejection of implanted organs with a life expectancy of only 10 years. Bioengineered patient-specific kidneys could be an inexhaustible source of healthy kidneys without the risk of immune rejection. The purpose of this article is to review the pros and cons of several bioengineering strategies used in recent years and their unresolved issues. These strategies include repopulation of natural scaffolds with a patient's cells, de-novo generation of kidneys using patient-induced pluripotent stem cells combined with stepwise differentiation, and the creation of a patient's kidney in the embryos of other mammalian species.

Kidney bioengineering in regenerative medicine: An emerging therapy for kidney disease

The prevalence of end-stage renal disease is emerging as a serious worldwide public health problem because of the shortage of donor organs and the need to take lifelong immunosuppressive medication in patients who receive a transplanted kidney. Recently, tissue bioengineering of decellularization and recellularization scaffolds has emerged as a novel strategy for organ regeneration, and we review the critical technologies supporting these methods. We present a summary of factors associated with experimental protocols that may shed light on the future development of kidney bioengineering and we discuss the cell sources and bioreactor techniques applied to the recellularization process. Finally, we review some artificial renal engineering technologies and their future prospects, such as kidney on a chip and the application of three-dimensional and four-dimensional printing in kidney tissue engineering.

Surface modification of uniaxial cyclic strain cell culture platform with temperature-responsive polymer for cell sheet detachment

Current cell sheet-based blood vessels lack biomimetic structure and require excessively long culture times that may compromise smooth muscle cell phenotype. We modified a commercially available product for uniaxial cell sheet conditioning with thermoresponsive copolymers. Thus, culture of detachable conditioned cell sheets is shortened while retaining structural integrity and contractility.

Efficient generation of human embryonic stem cell-derived cardiac progenitors based on tissue-specific enhanced green fluorescence protein expression

Cardiac progenitor cells (CPCs) are committed to the cardiac lineage but retain their proliferative capacity before becoming quiescent mature cardiomyocytes (CMs). In medical therapy and research, the use of human pluripotent stem cell-derived CPCs would have several advantages compared with mature CMs, as the progenitors show better engraftment into existing heart tissues, and provide unique potential for cardiovascular developmental as well as for pharmacological studies. Here, we demonstrate that the CAG promoter-driven enhanced green fluorescence protein (EGFP) reporter system enables the identification and isolation of embryonic stem cell-derived CPCs. Tracing of CPCs during differentiation confirmed up-regulation of surface markers, previously described to identify cardiac precursors and early CMs. Isolated CPCs express cardiac lineage-specific transcripts, still have proliferating capacity, and can be re-aggregated into embryoid body-like structures (CAG-EGFP(high) rEBs). Expression of troponin T and NKX2.5 mRNA is up-regulated in long-term cultured CAG-EGFP(high) rEBs, in which more than 90% of the cells become Troponin I positive mature CMs. Moreover, about one third of the CAG-EGFP(high) rEBs show spontaneous contractions. The method described here provides a powerful tool to generate expandable cultures of pure human CPCs that can be used for exploring early markers of the cardiac lineage, as well as for drug screening or tissue engineering applications.

Nondestructive monitoring of tissue-engineered constructs

Abstract Tissue engineering as a multidisciplinary field enables the development of living substitutes to replace, maintain, or restore diseased tissue and organs. Since the term was introduced in medicine in 1987, tissue engineering strategies have experienced significant progress. However, up to now, only a few substitutes were able to overcome the gap from bench to bedside and have been successfully approved for clinical use. Substantial donor variability makes it difficult to predict the quality of tissue-engineered constructs. It is essential to collect sufficient data to ensure that poor or immature constructs are not implanted into patients. The fulfillment of certain quality requirements, such as mechanical and structural properties, is crucial for a successful implantation. There is a clear need for new nondestructive and real-time online monitoring and evaluation methods for tissue-engineered constructs, which are applicable on the biomaterial, tissue, cellular, and subcellular levels. This paper reviews current established nondestructive techniques for implant monitoring including biochemical methods and noninvasive imaging.

Stem cells with decellularized liver scaffolds in liver regeneration and their potential clinical applications

End-stage hepatic failure is a potentially life-threatening condition for which orthotopic liver transplantation (OLT) is the only effective treatment. However, a shortage of available donor organs for transplantation each year results in the death of many patients waiting for liver transplantation. Cell-based therapies and hepatic tissue engineering have been considered as alternatives to liver transplantation. However, primary hepatocyte transplantation has rarely produced therapeutic effects because mature hepatocytes cannot be effectively expanded in vitro, and the availability of hepatocytes is often limited by shortages of donor organs. Decellularization is an attractive technique for scaffold preparation in stem cell-based liver engineering, as the resulting material can potentially retain the liver architecture, native vessel network and specific extracellular matrix (ECM). Thus, the reconstruction of functional and practical liver tissue using decellularized scaffolds becomes possible. This review focuses on the current understanding of liver tissue engineering, whole-organ liver decellularization techniques, cell sources for recellularization and potential clinical applications and challenges.

Teratoma formation: a tool for monitoring pluripotency in stem cell research

This unit describes protocols for evaluating the pluripotency of embryonic and induced pluripotent stem cells using a teratoma formation assay. Cells are prepared for injection and transplanted into immunodeficient mice at the gastrocnemius muscle, a site well suited for teratoma growth and surgical access. Teratomas that form from the cell transplants are explanted, fixed in paraformaldehyde, and embedded in paraffin. These preserved samples are sectioned, stained, and analyzed. Pluripotency of a cell line is confirmed by whether the teratoma contains tissues derived from each of the embryonic germ layers: endoderm, mesoderm, and ectoderm. Alternatively, explanted and fixed teratomas can be cryopreserved for immunohistochemistry, which allows for more detailed identification of specific tissue types present in the samples.

Engineering myocardial tissue patches with hierarchical structure-function

Complex hierarchical organization is a hallmark of tissues and their subsequent integration into organs. A major challenge in tissue engineering is to generate arrays of cells with defined structural organization that display appropriate functional properties. Given what is known about cellular responses to physiochemical cues from the surrounding environment, we can build tissue structures that mimic these microenvironments and validate these platforms using both experimental and computational approaches. Tissue generation encompasses many methods and tissue types, but here we review layering cell sheets to create scaffold-less myocardial patches. We discuss surgical criteria that can drive the design of myocardial cell sheets and the methods used to fabricate, mechanically condition, and functionally test them. We also focus on how computational and experimental approaches could be integrated to optimize tissue mechanical properties by using measurements of biomechanical properties and tissue anisotropy to create predictive computational models. Tissue anisotropy and dynamic mechanical stimuli affect cell phenotype in terms of protein expression and secretion, which in turn, leads to compositional and structural changes that ultimately impact tissue function. Therefore, a combinatorial approach of design, fabrication, testing, and modeling can be carried out iteratively to optimize engineered tissue function.

Promoting the recovery of injured liver with poly (3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) scaffolds loaded with umbilical cord-derived mesenchymal stem cells

Cell-based therapies are major focus of current research for treatment of liver diseases. In this study, mesenchymal stem cells were isolated from human umbilical cord Wharton's jelly (WJ-MSCs). Results confirmed that WJ-MSCs isolated in this study could express the typical MSC-specific markers and be induced to differentiate into adipocytes, osteoblasts, and chondrocytes. They could also be induced to differentiate into hepatocyte-like cells. Poly (3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (PHBVHHx) is a new member of polyhydroxyalkanoate family and biodegradable polyester produced by bacteria. PHBVHHx scaffolds showed much higher cell attachment and viability than the other polymers tested. PHBVHHx scaffolds loaded with WJ-MSCs were transplanted into liver-injured mice. Liver morphology improved after 30 days of transplantation and looked similar to normal liver. Concentrations of serum alanine aminotransferase and total bilirubin were significantly lower, and albumin was significantly higher on days 14 and 30 in the WJ-MSCs+scaffold group than in the carbon tetrachloride (CCl4) group. Hematoxylin-eosin staining showed that liver had similar structure of normal liver lobules and similar size and shape of normal hepatic cells, and Masson staining demonstrated that liver had less blue staining for collagen after 30 days of transplantation. Real-time reverse transcription-polymerase chain reaction (RT-PCR) showed that the expression of the bile duct epithelial cell gene CK-19 in mouse liver is significantly lower on days 14 and 30 in the WJ-MSCs+scaffold group than in the CCl4 group. Real-time RT-PCR, immunocytochemistry, and periodic acid-Schiff staining showed that WJ-MSCs in scaffolds differentiated into hepatocyte-like cells on days 14 and 30 in the WJ-MSCs+scaffold group. Real-time RT-PCR also demonstrated that WJ-MSCs in scaffolds expressed endothelial cell genes Flk-1, vWF, and VE-cadherin on days 14 and 30 in the WJ-MSCs+scaffold group, indicating that WJ-MSCs also differentiated into endothelial-like cells. These results demonstrated that PHBVHHx scaffolds loaded with WJ-MSCs significantly promoted the recovery of injured liver and could be further studied for liver tissue engineering.

Regenerative therapy and tissue engineering for the treatment of end-stage cardiac failure: new developments and challenges

Regeneration of myocardium through regenerative therapy and tissue engineering is appearing as a prospective treatment modality for patients with end-stage heart failure. Focusing on this area, this review highlights the new developments and challenges in the regeneration of myocardial tissue. The role of various cell sources, calcium ion and cytokine on the functional performance of regenerative therapy is discussed. The evolution of tissue engineering and the role of tissue matrix/scaffold, cell adhesion and vascularisation on tissue engineering of cardiac tissue implant are also discussed.

Thermogel nanofiber induces human endometrial-derived stromal cells to neural differentiation: In vitro and in vivo studies in rat

Spinal cord injury (SCI) in humans remains a devastating and incurable disorder. The use of Matrigel, a hydrogel-mimicking extracellular matrix, has been suggested as a scaffold for spinal cord regeneration. Human endometrial-derived stromal cells (hEnSCs) are abundant and available in adult stem cells with low immunological incompatibility, which could be considered for cell replacement therapy. The purpose of this study was to investigate the role of Matrigel in neural differentiation of hEnSCs in vitro and assess the supportive effects of this hydrogel in an animal model of SCI. hEnSCs were isolated and encapsulated into nanofibrous thermogel and cell viability and cell membrane damage were assessed. Encapsulated hEnSCs into Matrigel were treated with neural differentiation medium for 21 days, and then neural genes and protein markers were analyzed using real time-PCR and immunocytochemistry. Matrigel was implanted into rats with SCI and followed for 42 days using a behavioral test. Our study revealed a higher cell viability and neural differentiation in the level of genes and proteins as well as lower cell membrane damage. Substantial recoveries of motor function were observed in animals receiving the Matrigel treatment. The treatment with Matrigel, nanofibrous scaffold, produced beneficial effects on functional recovery following SCI in rats, possibly via assimilation to cytoskeleton fiber, high surface/volume ratio, spatial interconnectivity and containing some adhesive molecules and growth factors, enhancement of anti-inflammation, anti-astrogliosis, neuronal extension, and neuronal regeneration effects.

The effect of Noggin supplementation in Matrigel nanofiber-based cell culture system for derivation of neural-like cells from human endometrial-derived stromal cells

A very important obstacle in axonal regeneration after spinal cord injury is astroglial scaring. Noggin as bone morphogenic protein inhibitor plays a critical role in decreasing GFAP(+) cells and reducing the number of astrocytes in the site of injury. Human endometrial-derived stromal cells (hEnSCs) were isolated and cultured in two different neural inductive mediums consisting of neural progenitor maintenance medium (NPMM)/BDNF or NPMM/BDNF/Noggin in Matrigel 3D cell culture. Neural expression markers were investigated at the mRNA and protein level by real-time PCR and immunocytochemistry, respectively. The results showed that Noggin supplementation was able to increase the expression of Nestin, Tuj-1, and NF, whereas the expressions of GFAP, Bcl2, and Olig2 were decreased. In addition, DAPI staining demonstrated that lighter blue chromatin agreed with our observation of lower level of Bcl2 expression in the Noggin protocol in which over-expression of Bcl2 gene did not induce higher neurogenesis in poor Noggin medium. Our findings clearly demonstrated the neural differentiation potential of hEnSC in Matrigel and also Noggin supplementation was able to inhibit astrocyte formation.

Cancer research by means of tissue engineering--is there a rationale?

Tissue engineering (TE) has evoked new hopes for the cure of organ failure and tissue loss by creating functional substitutes in the laboratory. Besides various innovations in the context of Regenerative Medicine (RM), TE also provided new technology platforms to study mechanisms of angiogenesis and tumour cell growth as well as potentially tumour cell spreading in cancer research. Recent advances in stem cell technology--including embryonic and adult stem cells and induced pluripotent stem cells--clearly show the need to better understand all relevant mechanisms to control cell growth when such techniques will be administered to patients. Such TE-Cancer research models allow us to investigate the interactions that occur when replicating physiological and pathological conditions during the initial phases of replication, morphogenesis, differentiation and growth under variable given conditions. Tissue microenvironment has been extensively studied in many areas of TE and it plays a crucial role in cell signalling and regulation of normal and malignant cell functions. This article is intended to give an overview on some of the most recent developments and possible applications of TE and RM methods with regard to the improvement of cancer research with TE platforms. The synthesis of TE with innovative methods of molecular biology and stem-cell technology may help investigate and potentially modulate principal phenomena of tumour growth and spreading, as well as tumour-related angiogenesis. In the future, these models have the potential to investigate the optimal materials, culture conditions and material structure to propagate tumour growth.

Substrates and supplements for hESCs: a critical review

BACKGROUND

Different laboratories around the world have succeeded in establishing human embryonic stem cell (hESC) lines. However, culture conditions vary considerably among the protocols used and the vast majority of the lines at some stage of their creation have been in contact with an animal derived component. One of the main problems to be overcome for the generation of a clinical-grade hESC line is the choice of a substrate and medium that allows derivation and culture, where animal derived components are kept to a minimum or completely excluded.

MATERIALS AND METHODS

The following review describes past and more recent achievements in the creation and culturing of hESC. It describes protocols, giving special attention to the matrices and supplements used for derivation, maintainance and cryostorage, considering whether they included defined, undefined and/or animal-derived components in their formulations.

CONCLUSION

This information shall be useful for the creation and choice of new substrates and supplements for future research in the field of hESC for therapeutic purposes.

Generation and applications of human pluripotent stem cells induced into neural lineages and neural tissues

Human pluripotent stem cells (hPSCs) represent a new and exciting field in modern medicine, now the focus of many researchers and media outlets. The hype is well-earned because of the potential of stem cells to contribute to disease modeling, drug screening, and even therapeutic approaches. In this review, we focus first on neural differentiation of these cells. In a second part we compare the various cell types available and their advantages for in vitro modeling. Then we provide a “state-of-the-art” report about two major biomedical applications: (1) the drug and toxicity screening and (2) the neural tissue replacement. Finally, we made an overview about current biomedical research using differentiated hPSCs.

Whole-organ tissue engineering: decellularization and recellularization of three-dimensional matrix scaffolds

The definitive treatment for end-stage organ failure is orthotopic transplantation. However, the demand for transplantation far exceeds the number of available donor organs. A promising tissue-engineering/regenerative-medicine approach for functional organ replacement has emerged in recent years. Decellularization of donor organs such as heart, liver, and lung can provide an acellular, naturally occurring three-dimensional biologic scaffold material that can then be seeded with selected cell populations. Preliminary studies in animal models have provided encouraging results for the proof of concept. However, significant challenges for three-dimensional organ engineering approach remain. This manuscript describes the fundamental concepts of whole-organ engineering, including characterization of the extracellular matrix as a scaffold, methods for decellularization of vascular organs, potential cells to reseed such a scaffold, techniques for the recellularization process and important aspects regarding bioreactor design to support this approach. Critical challenges and future directions are also discussed.

Mesenchymal differentiation propensity of a human embryonic stem cell line

OBJECTIVES

To characterize basal differentiation tendencies of a human embryonic stem (hES) cell line, KCL-002.

MATERIALS AND METHODS

In vitro specification and differentiation of hES cells were carried out using embryoid body (EB) cultures and tests of pluripotency and in vivo differentiation were performed by teratoma assays in SCID mice. Real-time PCR, immunohistochemistry, flow cytometry and histological analyses were used to identify expression of genes and proteins associated with the ectodermal, endodermal and mesodermal germ layers.

RESULTS

Undifferentiated KCL-002 cells expressed characteristic markers of pluripotent stem cells such as Nanog, Sox-2, Oct-4 and TRA 1-60. When differentiated in vitro as EB cultures, expression of pluripotency, endodermal and ectodermal markers decreased rapidly. In contrast, mesodermal and mesenchymal markers such as VEGFR-2, α-actin and vimentin increased during EB differentiation as shown by qPCR, immunostaining and flow cytometric analyses. Teratoma formation in SCID mice demonstrated the potential to form all germ layers in vivo with a greater proportion of the tumours containing mesenchymal derivatives.

CONCLUSIONS

The data presented suggest that the KCL-002 hES cell line is pluripotent and harbours a bias in basal differentiation tendencies towards mesodermal and mesenchymal lineage cells. Characterizing innate differentiation propensities of hES cell lines is important for understanding heterogeneity between different cell lines and for further studies aimed at deriving specific lineages from hES cells.

Neural tissue engineering using embryonic and induced pluripotent stem cells

With the recent start of the first clinical trial evaluating a human embryonic stem cell-derived therapy for the treatment of acute spinal cord injury, it is important to review the current literature examining the use of embryonic stem cells for neural tissue engineering applications with a focus on diseases and disorders that affect the central nervous system. Embryonic stem cells exhibit pluripotency and thus can differentiate into any cell type found in the body, including those found in the nervous system. A range of studies have investigated how to direct the differentiation of embryonic cells into specific neural phenotypes using a variety of cues to achieve the goal of replacing diseased or damaged neural tissue. Additionally, the recent development of induced pluripotent stem cells provides an intriguing alternative to the use of human embryonic stem cell lines for these applications. This review will discuss relevant studies that have used embryonic stem cells to replicate the tissue found in the central nervous system as well as evaluate the potential of induced pluripotent stem cells for the aforementioned applications.

Concise review: adipose-derived stromal cells for skeletal regenerative medicine

As the average age of the population grows, the incidence of osteoporosis and skeletal diseases continues to rise. Current treatment options for skeletal repair include immobilization, rigid fixation, alloplastic materials, and bone grafts, all which have significant limitations, especially in the elderly. Adipose-derived stromal cells (ASCs) represent a readily available abundant supply of mesenchymal stem cells, which demonstrate the ability to undergo osteogenesis in vitro and in vivo, making ASCs a promising source of skeletal progenitor cells. Current protocols allow for the harvest of over one million cells from only 15 ml of lipoaspirate. Despite the clinical use of ASCs to treat systemic inflammatory diseases, no large human clinical trials exist using ASCs for skeletal tissue engineering. The aim of this review is to define ASCs, to describe the isolation procedure of ASCs, to review the basic biology of their osteogenic differentiation, discuss cell types and scaffolds available for bone tissue engineering, and finally, to explore imaging of ASCs and their potential future role in human skeletal tissue engineering efforts.

3D PLGA scaffolds improve differentiation and function of bone marrow mesenchymal stem cell-derived hepatocytes

Liver tissue engineering with hepatic stem cells provides a promising alternative to liver transplantation in patients with acute and chronic hepatic failure. In this study, a three-dimensional (3D) bioscaffold was introduced for differentiation of rat bone marrow mesenchymal stem cells (BMSCs) into hepatocytes. For hepatocyte differentiation, third passage BMSCs isolated from normal adult F344 rats were seeded into collagen-coated poly(lactic-co-glycolic acid) (C-PLGA) 3D scaffolds with hepatocyte differentiation medium for 3 weeks. Hepatogenesis in scaffolds was characterized by reverse transcript PCR, western blot, confocal laser scanning microscopy (CLSM), periodic acid-Schiff staining, histochemistry, and biochemical assays with hepatic-specific genes and markers. A monolayer culture system was used as a control differentiation group. The results showed that isolated cells possessed the basic features of BMSCs. Differentiated hepatocyte-like cells in C-PLGA scaffolds expressed hepatocyte-specific markers [eg, albumin (ALB), alpha-fetoprotein, cytokeratin 18, hepatocyte nuclear factor 4alpha, and cytochrome P450] at mRNA and protein levels. Most markers were expressed in C-PLGA group 1 week earlier than in the control group. Results of biocompatibility indicated that the differentiated hepatocyte-like cells grew more stably in C-PLGA scaffolds than that in controls during a 3-week differentiation period. The significantly higher metabolic functions in hepatocyte-like cells in the C-PLGA scaffold group further demonstrated the important role of the scaffold.

CONCLUSION

As the phenomenon of transdifferentiation is uncommon, our successful transdifferentiation rates of BMSCs to mature hepatocytes prove the superiority of the C-PLGA scaffold in providing a suitable environment for such a differentiation. This material can possibly be used as a bioscaffold for liver tissue engineering in future clinical therapeutic applications.

In vivo bone formation by progeny of human embryonic stem cells

The derivation of osteogenic cells from human embryonic stem cells (hESCs) or from induced pluripotent stem cells for bone regeneration would be a welcome alternative to the use of adult stem cells. In an attempt to promote hESC osteogenic differentiation, cells of the HSF-6 line were cultured in differentiating conditions in vitro for prolonged periods of time ranging from 7 to 14.5 weeks, followed by in vivo transplantation into immunocompromised mice in conjunction with hydroxyapatite/tricalcium phosphate ceramic powder. Twelve different medium compositions were tested, along with a number of other variables in culture parameters. In differentiating conditions, HSF-6-derived cells demonstrated an array of diverse phenotypes reminiscent of multiple tissues, but after a few passages, acquired a more uniform, fibroblast-like morphology. Eight to 16 weeks post-transplantation, a group of transplants revealed the formation of histologically proven bone of human origin, including broad areas of multiple intertwining trabeculae, which represents by far the most extensive in vivo bone formation by the hESC-derived cells described to date. Knockout-Dulbecco's modified Eagle's medium-based media with fetal bovine serum, dexamethasone, and ascorbate promoted more frequent bone formation, while media based on α-modified minimum essential medium promoted teratoma formation in 12- to 20-week-old transplants. Transcription levels of pluripotency-related (octamer binding protein 4, Nanog), osteogenesis-related (collagen type I, Runx2, alkaline phosphatase, and bone sialoprotein), and chondrogenesis-related (collagen types II and X, and aggrecan) genes were not predictive of either bone or teratoma formation. The most extensive bone was formed by the strains that, following 4 passages in monolayer conditions, were cultured for 23 to 25 extra days on the surface of hydroxyapatite/tricalcium phosphate particles, suggesting that coculturing of hESC-derived cells with osteoconductive material may increase their osteogenic potential. While none of the conditions tested in this study, and elsewhere, ensured consistent bone formation by hESC-derived cells, our results may elucidate further directions toward the construction of bone on the basis of hESCs or an individual's own induced pluripotent stem cells.

Inosculation: connecting the life-sustaining pipelines

Recent progress in engineering microvascular networks in vitro and in vivo offers exciting opportunities to create tissue constructs with preformed blood vessels, which are rapidly blood perfused by developing interconnections to the preexisting blood vessels of the host tissue after implantation. This process, termed as inosculation, is well known from the revascularization of various tissue grafts, such as transplanted skin, nerves, or bone. It is characterized by the close interaction of the implant's preformed microvascular network and the host microvasculature. The sprouting angiogenic activity of both counterparts determines whether inosculation takes place internally within the implant or externally within the surrounding host tissue. Successful inosculation involves vascular remodeling as well as infiltration of inflammatory cells and stem cells. With the use of sophisticated in vitro and in vivo models, more detailed analysis of regulatory mechanisms of inosculation will help to develop novel strategies, aiming at further accelerating the establishment of a life-sustaining blood supply to implanted tissue constructs.

Modeling the adhesion of human embryonic stem cells to poly(lactic-co-glycolic acid) surfaces in a 3D environment

Human embryonic stem cells (hESCs) have previously been cultured on three dimensional (3D) biodegradable polymer scaffolds. Although complex structures were formed from the hESCs, very little is known about the mechanism of adhesion of these cells to the surfaces of the scaffolds. In this study, we achieved the efficient adhesion of pluripotent hESCs to 3D poly(lactic-co-glycolic acid) (PLGA) scaffolds based on our data from a novel two dimensional (2D) model that imitates the surface properties of the scaffolds. In the 2D model, single cell preparations of pluripotent hESCs adhered efficiently and predominantly to PLGA surfaces coated with laminin in comparison to collagen I, collagen IV, or fibronectin-coated surfaces. Flow cytometry analysis revealed that almost all of the pluripotent single cells expressed the integrin alpha 6, with a small percentage also expressing alpha 3ss1, which facilitates adhesion to laminin. This data was then translated into the 3D environment, with the efficient binding of single pluripotent hESCs to PLGA scaffolds coated with laminin. The utility of this system was shown by the directed differentiation of single hESCs seeded within laminin-coated scaffolds toward the endoderm lineage.

Three-dimensional epithelial tissues generated from human embryonic stem cells

The use of pluripotent human embryonic stem (hES) cells for tissue engineering may provide advantages over traditional sources of progenitor cells because of their ability to give rise to multiple cell types and their unlimited expansion potential. We derived cell populations with properties of ectodermal and mesenchymal cells in two-dimensional culture and incorporated these divergent cell populations into three-dimensional (3D) epithelial tissues. When grown in specific media and substrate conditions, two-dimensional cultures were enriched in cells (EDK1) with mesenchymal morphology and surface markers. Cells with a distinct epithelial morphology (HDE1) that expressed cytokeratin 12 and beta-catenin at cell junctions became the predominant cell type when EDK1 were grown on surfaces enriched in keratinocyte-derived extracellular matrix proteins. When these cells were incorporated into the stromal and epithelial tissue compartments of 3D tissues, they generated multilayer epithelia similar to those generated with foreskin-derived epithelium and fibroblasts. Three-dimensional tissues demonstrated stromal cells with morphologic features of mature fibroblasts, type IV collagen deposition in the basement membrane, and a stratified epithelium that expressed cytokeratin 12. By deriving two distinct cell lineages from a common hES cell source to fabricate complex tissues, it is possible to explore environmental cues that will direct hES-derived cells toward optimal tissue form and function.

Role of bioinspired polymers in determination of pluripotent stem cell fate

Human pluripotent stem cells, including embryonic and induced pluripotent stem cells, hold enormous potential for the treatment of many diseases, owing to their ability to generate cell types useful for therapeutic applications. Currently, many stem cell culture propagation and differentiation systems incorporate animal-derived components for promoting self-renewal and differentiation. However, use of these components is labor intensive, carries the risk of xenogeneic contamination and yields compromised experimental results that are difficult to duplicate. From a biomaterials perspective, the generation of an animal- and cell-free biomimetic microenvironment that provides the appropriate physical and chemical cues for stem cell self-renewal or differentiation into specialized cell types would be ideal. This review presents the use of natural and synthetic polymers that support propagation and differentiation of stem cells, in an attempt to obtain a clear understanding of the factors responsible for the determination of stem cell fate.

In vivo biocompatibility and vascularization of biodegradable porous polyurethane scaffolds for tissue engineering

Scaffolds for tissue engineering should be biocompatible and stimulate rapid blood vessel ingrowth. Herein, we analyzed in vivo the biocompatibility and vascularization of three novel types of biodegradable porous polyurethane scaffolds. The polyurethane scaffolds, i.e., PU-S, PU-M and PU-F, were implanted into dorsal skinfold chambers of BALB/c mice. Using intravital fluorescence microscopy we analyzed vascularization of the implants and venular leukocyte-endothelial cell interaction in the surrounding host tissue over a 14 day period. Incorporation of the scaffolds was analyzed by histology, and a WST-1 assay was performed to evaluate their cell biocompatibility in vitro. Our results indicate that none of the polyurethane scaffolds was cytotoxic. Accordingly, rolling and adherent leukocytes in venules of the dorsal skinfold chamber were found in a physiological range after scaffold implantation and did not significantly differ between the groups, indicating a good in vivo biocompatibility. However, the three scaffolds induced a weak angiogenic response with a microvessel density of only approximately 47-60 and approximately 3-10cm/cm(2) in the border and centre zones of the scaffolds at day 14 after implantation. Histology demonstrated that the scaffolds were incorporated in a granulation tissue, which exhibited only a few blood vessels and inflammatory cells. In conclusion, PU-S, PU-M and PU-F scaffolds may be used to generate tissue constructs which do not induce a strong inflammatory reaction after implantation into patients. However, the scaffolds should be further modified or conditioned in order to accelerate and improve the process of vascularization.

Cell-based therapies for skeletal regenerative medicine

Skeletal deficits represent a substantial biomedical burden on the US healthcare system. Current strategies for reconstructing bony defects are fraught with inadequacies. Cell-based therapies for skeletal regeneration offer a paradigm shift that may provide alternative solutions. Substantial work has identified a host of cellular sources that possess the potential for osteogenic differentiation. Significant efforts have been devoted toward characterizing the role of postnatal cellular sources that are relatively abundant and easily accessible. Among these, the potential of using adipose-derived stromal cells for skeletal regeneration has garnered much interest. Integral to these efforts directed at characterizing cellular sources are studies that seek to understand the factors that initiate and regulate osteogenic differentiation of progenitor cells. Specifically, focus has been directed on elucidating the role of bone morphogenetic protein and fibroblast growth factor signaling in regulating osteogenic differentiation of osteoprogenitor cells. Concurrent studies in the field of scaffold design have also helped to advance the potential for cell-based therapies.

A roadmap to safe, efficient, and stable lentivirus-mediated gene therapy with hematopoietic cell transplantation

Hematopoietic stem cells comprise a prominent target for gene therapy aimed at treating various genetic and acquired disorders. A number of limitations associated with hematopoietic cell transplantation can be circumvented by the use of cells stably modified by retroviral gene transfer. Oncoretroviral and lentiviral vectors offer means for generating efficient and stable transgene expression. This review summarizes the state of the field today in terms of vector development and clinical experimentation. In particular, concerns with the safety of retroviral vectors intended for clinical gene transfer, applicability of preclinical data in directing clinical trial design, and recent research aimed at resolving some of these issues are addressed. Finally, this review underlines the specific advantages offered by lentiviral gene-transfer vectors for gene therapy in stem cells.