Generation of pancreatic insulin-producing cells from rhesus monkey induced pluripotent stem cells

The adult environment promotes the transcriptional maturation of human iPSC-derived muscle grafts

Pluripotent stem cell (PSC)-based cell therapy is an attractive option for the treatment of multiple human disorders, including muscular dystrophies. While in vitro differentiating PSCs can generate large numbers of human lineage-specific tissue, multiple studies evidenced that these cell populations mostly display embryonic/fetal features. We previously demonstrated that transplantation of PSC-derived myogenic progenitors provides long-term engraftment and functional improvement in several dystrophic mouse models, but it remained unknown whether donor-derived myofibers mature to match adult tissue. Here, we transplanted iPAX7 myogenic progenitors into muscles of non-dystrophic and dystrophic mice and compared the transcriptional landscape of human grafts with respective in vitro-differentiated iPAX7 myotubes as well as human skeletal muscle biospecimens. Pairing bulk RNA sequencing with computational deconvolution of human reads, we were able to pinpoint key myogenic changes that occur during the in vitro-to-in vivo transition, confirm developmental maturity, and consequently evaluate their applicability for cell-based therapies.

Current state of stem cell research in non-human primates: an overview

The remarkable similarity between non-human primates (NHPs) and humans establishes them as essential models for understanding human biology and diseases, as well as for developing novel therapeutic strategies, thereby providing more comprehensive reference data for clinical treatment. Pluripotent stem cells such as embryonic stem cells and induced pluripotent stem cells provide unprecedented opportunities for cell therapies against intractable diseases and injuries. As continue to harness the potential of these biotechnological therapies, NHPs are increasingly being employed in preclinical trials, serving as a pivotal tool to evaluate the safety and efficacy of these interventions. Here, we review the recent advancements in the fundamental research of stem cells and the progress made in studies involving NHPs.

In vitro generation of transplantable insulin-producing cells from canine adipose-derived mesenchymal stem cells

Canine mesenchymal stem cells (cMSCs) have potential applications for regenerative therapy, including the generation of insulin-producing cells (IPCs) for studying and treating diabetes. In this study, we established a useful protocol for generating IPCs from canine adipose mesenchymal stem cells (cAD-MSCs). Subsequently, in vitro preservation of pluronic F127-coated alginate (ALGPA)-encapsulated cAD-MSC-derived IPCs was performed to verify ready-to-use IPCs. IPCs were induced from cAD-MSCs with the modulated three-stepwise protocol. The first step of definitive endoderm (DE) induction showed that the cooperation of Chir99021 and Activin A created the effective production of Sox17-expressed DE cells. The second step for pancreatic endocrine (PE) progenitor induction from DE indicated that the treatment with taurine, retinoic acid, FGF2, EGF, TGFβ inhibitor, dorsomorphin, nicotinamide, and DAPT showed the significant upregulation of the pancreatic endocrine precursor markers Pdx1 and Ngn3. The last step of IPC production, the combination of taurine, nicotinamide, Glp-1, forskolin, PI3K inhibitor, and TGFβ inhibitor, yielded efficiently functional IPCs from PE precursors. Afterward, the maintenance of ALGPA-encapsulated cAD-MSC-derived IPCs with VSCBIC-1, a specialized medium, enhanced IPC properties. Conclusion, the modulated three-stepwise protocol generates the functional IPCs. Together, the encapsulation of cAD-MSC-derived IPCs and the cultivation with VSCBIC-1 enrich the maturation of generated IPCs.

Recent Advances in the Generation of β-Cells from Induced Pluripotent Stem Cells as a Potential Cure for Diabetes Mellitus

Diabetes mellitus (DM) is a group of metabolic disorders characterized by high blood glucose levels due to insufficient insulin secretion, insulin action, or both. The present-day solution to diabetes mellitus includes regular administration of insulin, which brings about many medical complications in diabetic patients. Although islet transplantation from cadaveric subjects was proposed to be a permanent cure, the increased risk of infections, the need for immunosuppressive drugs, and their unavailability had restricted its use. To overcome this, the generation of renewable and transplantable β-cells derived from autologous induced pluripotent stem cells (iPSCs) has gained enormous interest as a potential therapeutic strategy to treat diabetes mellitus permanently. To date, extensive research has been undertaken to derive transplantable insulin-producing β-cells (iβ-cells) from iPSCs in vitro by recapitulating the in vivo developmental process of the pancreas. This in vivo developmental process relies on transcription factors, signaling molecules, growth factors, and culture microenvironment. This review highlights the various factors facilitating the generation of mature β-cells from iPSCs. Moreover, this review also describes the generation of pancreatic progenitors and β-cells from diabetic patient-specific iPSCs, exploring the potential of the diabetes disease model and drug discovery. In addition, the applications of genome editing strategies have also been discussed to achieve patient-specific diabetes cell therapy. Last, we have discussed the current challenges and prospects of iPSC-derived β-cells to improve the relative efficacy of the available treatment of diabetes mellitus.

Generation of high yield insulin-producing cells (IPCs) from various sources of stem cells

Type 1 diabetes mellitus occurs when beta cell mass is reduced to less than 20% of the normal level due to immune system destruction of beta cell resulting in an inability to secrete enough insulin. The prevalence of diabetes is expanding according to the American Diabetes Association and the World Health Organization (WHO), foretold to exceed 350 million by 2030. The current treatment does not cure many of the serious complications associated with the disease such as neuropathy, nephropathy, dyslipidemia, retinopathy and cardiovascular disease. Whole pancreas or isolated pancreatic islet transplantation as an alternative therapy can prevent or reduce some of the complications of diabetes. However, the shortage of matched organ or islets cells donor and alloimmune responses limit this therapeutic strategy. Recently, several reports have raised extremely promising results to use different sources of stem cells to differentiate insulin-producing cells and focus on the expansion of these alternative sources. Stem cells, due to their potential for multiple differentiation and self-renewal can differentiate into all cell types, including insulin-producing cells (IPCs). Generation of new beta cells can be achieved from various stem cell sources, including embryonic stem cells (ESCs), adult stem cells, such as mesenchymal stem cells (MSCs) and induced pluripotent stem cells (iPSCs). Thus, this chapter discusses on the assistance of cellular reprogramming of various stem cells as candidates for the generation of IPCs using transcription factors/miRNA, cytokines/small molecules and tissue engineering.

Electrospun Nanofibers for Diabetes: Tissue Engineering and Cell-Based Therapies

Diabetes mellitus is an autoimmune disease which causes loss of insulin secretion producing hyperglycemia by promoting progressive destruction of pancreatic β cells. An ideal therapeutic approach to manage diabetes mellitus is pancreatic β cells replacement. The aim of this review article was to evaluate the role of nanofibrous scaffolds and stem cells in the treatment of diabetes mellitus. Various studies have pointed out that application of electrospun biomaterials has considerably attracted researchers in the field of tissue engineering. The principles of cell therapy for diabetes have been reviewed in the first part of this article, while the usability of tissue engineering as a new therapeutic approach is discussed in the second part.

Feasibility of Induced Pluripotent Stem Cell Therapies for Treatment of Type 1 Diabetes

IMPACT STATEMENT

This review of iPSCs to treat T1D provides a current assessment of the challenges and potential for this proposed new therapy.

Differentiation of nonhuman primate pluripotent stem cells into functional keratinocytes

BACKGROUND

Epidermal grafting using cells derived from pluripotent stem cells will change the face of this side of regenerative cutaneous medicine. To date, the safety of the graft would be the major unmet deal in order to implement long-term skin grafting. In this context, experiments on large animals appear unavoidable to assess this question and possible rejection. Cellular tools for large animal models should be constructed.

METHODS

In this study, we generated monkey pluripotent stem cell-derived keratinocytes and evaluated their capacities to reconstruct an epidermis, in vitro as well as in vivo.

RESULTS

Monkey pluripotent stem cells were differentiated efficiently into keratinocytes able to reconstruct fully epidermis presenting a low level of major histocompatibility complex class-I antigens, opening the way for autologous or allogeneic epidermal long-term grafting.

CONCLUSIONS

Functional keratinocytes generated from nonhuman primate embryonic stem cells and induced pluripotent stem cells reproduce an in-vitro and in-vivo stratified epidermis. These monkey skin grafts will be considered to model autologous or allogeneic epidermal grafting using either embryonic stem cells or induced pluripotent stem cells. This graft model will allow us to further investigate the safety, efficacy and immunogenicity of nonhuman primate PSC-derived epidermis in the perspective of human skin cell therapy.

Human umbilical cord Wharton jelly cells promote extra-pancreatic insulin formation and repair of renal damage in STZ-induced diabetic mice

BACKGROUND

We evaluated the therapeutic effect and fate of high doses of human umbilical cord Wharton jelly cells (hUCWJCs) after IP administration to streptozotocin (STZ)-induced diabetic mice.

METHODS

Type 1 diabetes (T1D) was induced in Kunming mice via IP injection of STZ. hUCWJCs were labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI). Diabetic animals with sustained hyperglycemia for at least 2 weeks were administered 1 × 10⁷ Dil-hUCWJCs via intraperitoneal injection. Insulin, glucagon and PDX-1 were detected by immunofluorescence with confocal microscopy. Serum mouse and human C-peptide was assayed in blood collected via intracardiac puncture. Specific β-cell differentiation markers and human DNA were assessed using qPCR performed with 200 ng of target DNA.

RESULTS

hUCWJCs migrated to the STZ-damaged organs and contributed to lower blood glucose levels in 30% of the treated mice. Confocal microscopy revealed the presence of resident insulin-positive cells in the liver and kidneys. hUCWJC-treated mice with restored hyperglycemia also showed increased serum mouse C-peptide levels. The qPCR results, particularly in the liver, revealed that after transplantation hUCWJCs upregulated genes of endocrine precursors but failed to express endocrine stage markers. Mice with restored hyperglycemia had reduced urinary volume and lacked glomerular hypertrophy, exhibiting a morphology resembling that of normal glomeruli. Moreover, we also verified that one of the possible mechanisms by which hUCWJCs exert immunosuppressive effects is through down-regulation of the cell surface receptor HLA-1.

CONCLUSIONS

We confirmed the potential of IP administration of hUCWJCs and the capability of these cells to migrate to damaged tissues and promote insulin secretion from non-pancreatic local cells and to improve renal damage. These findings confer unique therapeutic properties to hUCWJCs, suggesting a promising future in the treatment of diabetes mellitus.

Effective endothelial cell and human pluripotent stem cell interactions generate functional insulin-producing beta cells

AIMS/HYPOTHESIS

Endothelial cells (ECs) play an essential role in pancreatic organogenesis. We hypothesise that effective in vitro interactions between human microvascular endothelial cells (HMECs) and human pluripotent stem cells (hPSCs) results in the generation of functional pancreatic beta cells.

METHODS

Embryoid bodies (EBs) derived from hPSCs were cultured alone (controls) or with ECs in collagen gels. Subsequently, cells were analysed for pancreatic beta cell markers, and then isolated and expanded. Insulin secretion in response to glucose was evaluated in vitro by static and dynamic (perifusion) assays, and in vivo by EB transplantation into immunodeficient mice.

RESULTS

Co-cultured EBs had a higher expression of mature beta cells markers and enhanced insulin secretion in vitro, compared with controls. In mice, transplanted EBs had higher levels of human C-peptide secretion with a significant reduction in hyperglycaemia after the selective destruction of native pancreatic beta cells. In addition, there was significant in vitro upregulation of bone morphogenetic proteins 2 and 4 (BMP-2, 4) in co-cultured cells, compared with controls.

CONCLUSIONS/INTERPRETATION

ECs provide essential signalling in vitro, such as activation of the BMP pathway, for derivation of functional insulin-producing beta cells from hPSCs.

In vitro models of cancer stem cells and clinical applications

Cancer cells, stem cells and cancer stem cells have for a long time played a significant role in the biomedical sciences. Though cancer therapy is more effective than it was a few years ago, the truth is that still none of the current non-surgical treatments can cure cancer effectively. The reason could be due to the subpopulation called “cancer stem cells” (CSCs), being defined as those cells within a tumour that have properties of stem cells: self-renewal and the ability for differentiation into multiple cell types that occur in tumours.

The phenomenon of CSCs is based on their resistance to many of the current cancer therapies, which results in tumour relapse. Although further investigation regarding CSCs is still needed, there is already evidence that these cells may play an important role in the prognosis of cancer, progression and therapeutic strategy. Therefore, long-term patient survival may depend on the elimination of CSCs. Consequently, isolation of pure CSC populations or reprogramming of cancer cells into CSCs, from cancer cell lines or primary tumours, would be a useful tool to gain an in-depth knowledge about heterogeneity and plasticity of CSC phenotypes and therefore carcinogenesis. Herein, we will discuss current CSC models, methods used to characterize CSCs, candidate markers, characteristic signalling pathways and clinical applications of CSCs. Some examples of CSC-specific treatments that are currently in early clinical phases will also be presented in this review.

Recent Advances in Disease Modeling and Drug Discovery for Diabetes Mellitus Using Induced Pluripotent Stem Cells

Diabetes mellitus (DM) is a widespread metabolic disease with a progressive incidence of morbidity and mortality worldwide. Despite extensive research, treatment options for diabetic patients remains limited. Although significant challenges remain, induced pluripotent stem cells (iPSCs) have the capacity to differentiate into any cell type, including insulin-secreting pancreatic β cells, highlighting its potential as a treatment option for DM. Several iPSC lines have recently been derived from both diabetic and healthy donors. Using different reprogramming techniques, iPSCs were differentiated into insulin-secreting pancreatic βcells. Furthermore, diabetes patient-derived iPSCs (DiPSCs) are increasingly being used as a platform to perform cell-based drug screening in order to develop DiPSC-based cell therapies against DM. Toxicity and teratogenicity assays based on iPSC-derived cells can also provide additional information on safety before advancing drugs to clinical trials. In this review, we summarize recent advances in the development of techniques for differentiation of iPSCs or DiPSCs into insulin-secreting pancreatic β cells, their applications in drug screening, and their role in complementing and replacing animal testing in clinical use. Advances in iPSC technologies will provide new knowledge needed to develop patient-specific iPSC-based diabetic therapies.

Advances and challenges in the differentiation of pluripotent stem cells into pancreatic β cells

Pluripotent stem cells (PSCs) are able to differentiate into several cell types, including pancreatic β cells. Differentiation of pancreatic β cells depends on certain transcription factors, which function in a coordinated way during pancreas development. The existing protocols for in vitro differentiation produce pancreatic β cells, which are not highly responsive to glucose stimulation except after their transplantation into immune-compromised mice and allowing several weeks for further differentiation to ensure the maturation of these cells in vivo. Thus, although the substantial improvement that has been made for the differentiation of induced PSCs and embryonic stem cells toward pancreatic β cells, several challenges still hindering their full generation. Here, we summarize recent advances in the differentiation of PSCs into pancreatic β cells and discuss the challenges facing their differentiation as well as the different applications of these potential PSC-derived β cells.

Pluripotent stem cells as a potential tool for disease modelling and cell therapy in diabetes

Diabetes mellitus is the most prevailing disease with progressive incidence worldwide. To date, the pathogenesis of diabetes is far to be understood, and there is no permanent treatment available for diabetes. One of the promising approaches to understand and cure diabetes is to use pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced PCSs (iPSCs). ESCs and iPSCs have a great potential to differentiate into all cell types, and they have a high ability to differentiate into insulin-secreting β cells. Obtaining PSCs genetically identical to the patient presenting with diabetes has been a longstanding dream for the in vitro modeling of disease and ultimately cell therapy. For several years, somatic cell nuclear transfer (SCNT) was the method of choice to generate patient-specific ESC lines. However, this technology faces ethical and practical concerns. Interestingly, the recently established iPSC technology overcomes the major problems of other stem cell types including the lack of ethical concern and no risk of immune rejection. Several iPSC lines have been recently generated from patients with different types of diabetes, and most of these cell lines are able to differentiate into insulin-secreting β cells. In this review, we summarize recent advances in the differentiation of pancreatic β cells from PSCs, and describe the challenges for their clinical use in diabetes cell therapy. Furthermore, we discuss the potential use of patient-specific PSCs as an in vitro model, providing new insights into the pathophysiology of diabetes.

From Beta cell replacement to beta cell regeneration: implications for antidiabetic therapy

Diabetes is affecting more than 25.8 million people in the United States, causing huge burden on the health care system and economy. Insulin injection, which is the predominant treatment for diabetes, is incapable of replenishing the lost insulin-producing beta cell in patients. Restoring beta cell mass through replacement therapy such as islet transplantation or beta cell regeneration through in vitro and in vivo strategies has attracted particular attentions in the field due to its potential to cure diabetes. In the aspect of islet transplantation, gene therapy, stem cell therapy, and more biocompatible immunosuppressive drugs have been tested in various preclinical animal models to improve the longevity and function of human islets against the posttransplantation challenges. In the islet regeneration aspect, insulin-producing cells have been generated through in vitro transdifferentiation of stem cells and other types of cells and demonstrated to be capable of glycemic control. Moreover, several biomarkers including cell-surface receptors, soluble factors, and transcriptional factors have been identified or rediscovered in mediating the process of beta cell proliferation in rodents. This review summarizes the current progress and hurdles in the preclinical efforts in resurrecting beta cells. It may provide some useful insights into the future drug discovery for antidiabetic purposes.

Systematically labeling developmental stage-specific genes for the study of pancreatic β-cell differentiation from human embryonic stem cells

The applications of human pluripotent stem cell (hPSC)-derived cells in regenerative medicine has encountered a long-standing challenge: how can we efficiently obtain mature cell types from hPSCs? Attempts to address this problem are hindered by the complexity of controlling cell fate commitment and the lack of sufficient developmental knowledge for guiding hPSC differentiation. Here, we developed a systematic strategy to study hPSC differentiation by labeling sequential developmental genes to encompass the major developmental stages, using the directed differentiation of pancreatic β cells from hPSCs as a model. We therefore generated a large panel of pancreas-specific mono- and dual-reporter cell lines. With this unique platform, we visualized the kinetics of the entire differentiation process in real time for the first time by monitoring the expression dynamics of the reporter genes, identified desired cell populations at each differentiation stage and demonstrated the ability to isolate these cell populations for further characterization. We further revealed the expression profiles of isolated NGN3-eGFP(+) cells by RNA sequencing and identified sushi domain-containing 2 (SUSD2) as a novel surface protein that enriches for pancreatic endocrine progenitors and early endocrine cells both in human embryonic stem cells (hESC)-derived pancreatic cells and in the developing human pancreas. Moreover, we captured a series of cell fate transition events in real time, identified multiple cell subpopulations and unveiled their distinct gene expression profiles, among heterogeneous progenitors for the first time using our dual reporter hESC lines. The exploration of this platform and our new findings will pave the way to obtain mature β cells in vitro.

Islet and stem cell encapsulation for clinical transplantation

Over the last decade, improvements in islet isolation techniques have made islet transplantation an option for a certain subset of patients with long-standing diabetes. Although islet transplants have shown improved graft function, adequate function beyond the second year has not yet been demonstrated, and patients still require immunosuppression to prevent rejection. Since allogeneic islet transplants have experienced some success, the next step is to improve graft function while eliminating the need for systemic immunosuppressive therapy. Biomaterial encapsulation offers a strategy to avoid the need for toxic immunosuppression while increasing the chances of graft function and survival. Encapsulation entails coating cells or tissue in a semipermeable biocompatible material that allows for the passage of nutrients, oxygen, and hormones while blocking immune cells and regulatory substances from recognizing and destroying the cell, thus avoiding the need for systemic immunosuppressive therapy. Despite advances in encapsulation technology, these developments have not yet been meaningfully translated into clinical islet transplantation, for which several factors are to blame, including graft hypoxia, host inflammatory response, fibrosis, improper choice of biomaterial type, lack of standard guidelines, and post-transplantation device failure. Several new approaches, such as the use of porcine islets, stem cells, development of prevascularized implants, islet nanocoating, and multilayer encapsulation, continue to generate intense scientific interest in this rapidly expanding field. This review provides a comprehensive update on islet and stem cell encapsulation as a treatment modality in type 1 diabetes, including a historical outlook as well as current and future research avenues.

Tissue engineering approaches to cell-based type 1 diabetes therapy

Type 1 diabetes mellitus is an autoimmune disease resulting from the destruction of insulin-producing pancreatic β-cells. Cell-based therapies, involving the transplantation of functional β-cells into diabetic patients, have been explored as a potential long-term treatment for this condition; however, success is limited. A tissue engineering approach of culturing insulin-producing cells with extracellular matrix (ECM) molecules in three-dimensional (3D) constructs has the potential to enhance the efficacy of cell-based therapies for diabetes. When cultured in 3D environments, insulin-producing cells are often more viable and secrete more insulin than those in two dimensions. The addition of ECM molecules to the culture environments, depending on the specific type of molecule, can further enhance the viability and insulin secretion. This review addresses the different cell sources that can be utilized as β-cell replacements, the essential ECM molecules for the survival of these cells, and the 3D culture techniques that have been used to benefit cell function.

Preclinical studies for induced pluripotent stem cell-based therapeutics

Induced pluripotent stem cells (iPSCs) and their differentiated derivatives can potentially be applied to cell-based therapy for human diseases. The properties of iPSCs are being studied intensively both to understand the basic biology of pluripotency and cellular differentiation and to solve problems associated with therapeutic applications. Examples of specific preclinical applications summarized briefly in this minireview include the use of iPSCs to treat diseases of the liver, nervous system, eye, and heart and metabolic conditions such as diabetes. Early stage studies illustrate the potential of iPSC-derived cells and have identified several challenges that must be addressed before moving to clinical trials. These include rigorous quality control and efficient production of required cell populations, improvement of cell survival and engraftment, and development of technologies to monitor transplanted cell behavior for extended periods of time. Problems related to immune rejection, genetic instability, and tumorigenicity must be solved. Testing the efficacy of iPSC-based therapies requires further improvement of animal models precisely recapitulating human disease conditions.

Insulin producing cells established using non-integrated lentiviral vector harboring PDX1 gene

AIM: To investigate reprogramming of human adipose tissue derived stem cells into insulin producing cells using non-integrated lentivirus harboring PDX1 gene.

METHODS: In this study, human adipose tissue derived stem cells (hADSCs) were obtained from abdominal adipose tissues by liposuction, selected by plastic adhesion, and characterized by flow cytometric analysis. Human ADSCs were differentiated into adipocytes and osteocytes using differentiating medium to confirm their multipotency. Non-integrated lentiviruses harboring PDX1 (Non-integrated LV-PDX1) were constructed using specific plasmids (pLV-HELP, pMD2G, LV-105-PDX1-1). Then, hADSCs were transduced with non-integrated LV-PDX1. After transduction, ADSCs^PDX1+ were cultured in high glucose DMEM medium supplement by B27, nicotinamide and βFGF for 21 d. Expressions of PDX1 and insulin were detected at protein level by immunofluorescence analysis. Expressions of PDX1, neurogenin3 (Ngn3), glucagon, glucose transporter2 (Glut2) and somatostatin as specific marker genes were investigated at mRNA level by quantitative RT-PCR. Insulin secretion of hADSCs^PDX1+ in the high-glucose medium was detected by electrochemiluminescence test. Human ADSCs^PDX1+ were implanted into hyperglycemic rats.

RESULTS: Human ADSCs exhibited their fibroblast-like morphology and made colonies after 7-10 d of culture. Determination of hADSCs identified by FACS analysis showed that hADSCs were positive for mesenchymal cell markers and negative for hematopoietic cell markers that guaranteed the lack of hematopoietic contamination. In vitro differentiation of hADSCs into osteocytes and adipocytes were detected by Alizarin red and Oil red O staining and confirmed their multilineage differentiation ability. Transduced hADSCs^+PDX1 became round and clusters in the differentiation medium. The appropriate expression of PDX1 and insulin proteins was confirmed using immunocytochemistry analysis. Significant expressions of PDX1, Ngn3, glucagon, Glut2 and somatostatin were detected by quantitative RT-PCR. hADSCs^PDX1+ revealed the glucose sensing ability by expressing Glut2 when they were cultured in the medium containing high glucose concentration. The insulin secretion of hADSCs^PDX1+ in the high glucose medium was 2.32 μU/mL. hADSCs^PDX1+ implantation into hyperglycemic rats cured it two days after injection by reducing blood glucose levels from 485 mg/dL to the normal level.

CONCLUSION: Human ADSCs can differentiate into IPCs by non-integrated LV-PDX1 transduction and have the potential to be used as a resource in type 1 diabetes cell therapy.

Veterinary applications of induced pluripotent stem cells: regenerative medicine and models for disease?

Induced pluripotent stem cells (iPSCs) can now be derived from a tissue biopsy and represent a promising new platform for disease modelling, drug and toxicity testing, biomarker development and cell-based therapies for regenerative medicine. In regenerative medicine, large animals may represent the best models for man, and thereby provide invaluable systems in which to test the safety and the potential of iPSCs. Hence, testing iPSCs in veterinary species may serve a double function, namely, developing therapeutic products for regenerative medicine in veterinary patients while providing valuable background information for human clinical trials. The production of iPSCs from livestock or wild species is attractive because it could improve efficiency and reduce costs in various fields, such as transgenic animal generation and drug development, preservation of biological diversity, and because it also offers an alternative to xenotransplantation for in vivo generation of organs. Although the technology of cellular reprogramming using the so-called 'Yamanaka factors' is in its peak expectation phase and many concerns still need to be addressed, the rapid technical progress suggests that iPSCs could contribute significantly to novel therapies in veterinary and biomedical practice in the near future. This review provides an overview of the potential applications of iPSCs in veterinary medicine.

MicroRNA target sites as genetic tools to enhance promoter-reporter specificity for the purification of pancreatic progenitor cells from differentiated embryonic stem cells

Pluripotent cells hold great promise for cell replacement therapies in regenerative medicine. All known protocols for directed in vitro differentiation of pluripotent cells did not yield pure populations complicating the characterization of the derived cells. In addition, the risk of tumor formation due to residual undifferentiated cells is a serious unresolved problem. In the present study the tissue-specific mouse Pdx1 promoter was used to control the expression of the reporter gene GFP2 in mouse ES cells in order to purify them via FACS during in vitro differentiation. The background fluorescence of transduced ES cells hampered the purification of Pdx1-positive cells due to a contaminating population of partially undifferentiated cells. MicroRNAs (mir) are important regulators of gene expression and were used to enhance promoter specificity during differentiation towards pancreatic progenitor cells. The mouse mmu-mir-294 was found to be mainly expressed during pluripotency, whereas the expression of the mir-302 cluster was increased during early differentiation. Integration of a microRNA target site for the mmu-mir-294 into the lentiviral vector reduced the background fluorescence specifically during pluripotency and permitted re-occurrence of GFP2 expression upon differentiation. A combination of the microRNA target site with the Pdx1 promoter fragment allowed the purification of pancreatic progenitors from differentiated ES cells. This population reflected an early pancreatic progenitor population without other contaminating cell lineages. In conclusion, microRNA target sites are efficient regulatory elements to control transgene expression and to enhance tissue specificity as presented in this study facilitating the sorting and purification of Pdx1-positive pancreatic progenitor cells.

Induction of pluripotent stem cells from a cynomolgus monkey using a polycistronic simian immunodeficiency virus-based vector, differentiation toward functional cardiomyocytes, and generation of stably expressing reporter lines

Induced pluripotent stem cells (iPSCs) represent a novel cell source for regenerative therapies. Many emerging iPSC-based therapeutic concepts will require preclinical evaluation in suitable large animal models. Among the large animal species frequently used in preclinical efficacy and safety studies, macaques show the highest similarities to humans at physiological, cellular, and molecular levels. We have generated iPSCs from cynomolgus monkeys (Macaca fascicularis) as a segue to regenerative therapy model development in this species. Because typical human immunodeficiency virus type 1 (HIV-1)-based lentiviral vectors show poor transduction of simian cells, a simian immunodeficiency virus (SIV)-based vector was chosen for efficient transduction of cynomolgus skin fibroblasts. A corresponding polycistronic vector with codon-optimized reprogramming factors was constructed for reprogramming. Growth characteristics as well as cell and colony morphology of the resulting cynomolgus iPSCs (cyiPSCs) were demonstrated to be almost identical to cynomolgus embryonic stem cells (cyESCs), and cyiPSCs expressed typical pluripotency markers including OCT4, SOX2, and NANOG. Furthermore, differentiation in vivo and in vitro into derivatives of all three germ layers, as well as generation of functional cardiomyocytes, could be demonstrated. Finally, a highly efficient technique for generation of transgenic cyiPSC clones with stable reporter expression in undifferentiated cells as well as differentiated transgenic cyiPSC progeny was developed to enable cell tracking in recipient animals. In conclusion, our data indicate that cyiPSCs represent a valuable cell source for establishment of macaque-based allogeneic and autologous preclinical cell transplantation models for various fields of regenerative medicine.

Embryonic stem cells of the non-human primate Callithrix jacchus can be differentiated into definitive endoderm by Activin-A but not IDE-1/2

Pluripotent stem cells hold great promise for regenerative medicine, due to their unlimited self-renewal potential and the ability to differentiate into all somatic cell types. Differences between the rodent disease models and the situation in humans can be narrowed down with non-human primate models. The common marmoset monkey (Callithrix jacchus) is an interesting model for biomedical research because these animals are easy to breed, get relatively old (≤ 13 years), are small in size, are relatively cost-effective and have a high genetic proximity to the human. In particular, diseases of the liver and pancreas are interesting for cell replacement therapies but the in vitro differentiation of ESCs into the definitive endoderm germ layer is still a demanding task. Membrane-permeable, chemically defined small molecules can possibly replace recombinant growth factors used in most directed differentiation protocols. However, the potent small molecules IDE-1 and IDE-2 were not able to induce definitive endoderm-like cells when ESCs from the common marmoset were treated with these compounds, whereas the recombinant growth factor Activin A could force the differentiation into this lineage. Our results indicate that ESCs from the common marmoset are less sensitive or even insensitive to these small molecules. Thus, differences between the species of human ESCs and ESCs of this non-human primate might be a useful model to further evaluate the exact mode of action of these compounds.

Restoring insulin production for type 1 diabetes

Current therapies for the treatment of type 1 diabetes include daily administration of exogenous insulin and, less frequently, whole-pancreas or islet transplantation. Insulin injections often result in inaccurate insulin doses, exposing the patient to hypo- and/or hyperglycemic episodes that lead to long-term complications. Islet transplantation is also limited by lack of high-quality islet donors, early graft failure, and chronic post-transplant immunosuppressive treatment. These barriers could be circumvented by designing a safe and efficient strategy to restore insulin production within the patient's body. Porcine islets have been considered as a possible alternative source of transplantable insulin-producing cells to replace human cadaveric islets. More recently, embryonic or induced pluripotent stem cells have also been examined for their ability to differentiate in vitro into pancreatic endocrine cells. Alternatively, it may be feasible to generate new β-cells by ectopic expression of key transcription factors in endogenous non-β-cells. Finally, engineering surrogate β-cells by in vivo delivery of the insulin gene to specific tissues is also being studied as a possible therapy for type 1 diabetes. In the present review, we discuss these different approaches to restore insulin production.

Large animal induced pluripotent stem cells as pre-clinical models for studying human disease

The derivation of human embryonic stem cells and subsequently human induced pluripotent stem cells (iPSCs) has energized regenerative medicine research and enabled seemingly limitless applications. Although small animal models, such as mouse models, have played an important role in the progression of the field, typically, they are poor representations of the human disease phenotype. As an alternative, large animal models should be explored as a potentially better approach for clinical translation of cellular therapies. However, only fragmented information regarding the derivation, characterization and clinical usefulness of pluripotent large animal cells is currently available. Here, we briefly review the latest advances regarding the derivation and use of large animal iPSCs.

Potential of pluripotent stem cells for diabetes therapy

Diabetes mellitus type 1 (T1DM) and type 2 (T2DM) are common diseases. To date, it is widely accepted that all forms of DM lead to the loss of beta cells. Therefore, to avoid the debilitating comorbidities when glycemic control cannot be fully achieved, some would argue that beta cell replacement is the only way to cure the disease. Due to organ donor shortage, other cell sources for beta cell replacement strategies have to be employed. Pluripotent stem cells, including embryonic stem (ES) and induced pluripotent stem (iPS) cells offer a valuable alternative to provide the necessary cells to substitute organ transplants but also to serve as a model to study the onset and progression of the disease, resulting in better treatment regimens. This review will summarize recent progress in the establishment of pluripotent stem cells, their differentiation into the pancreatic lineage with a focus on two-dimensional (2D) and three-dimensional (3D) differentiation settings, the special role of iPS cells in the analysis of genetic predispositions to diabetes, and techniques that help to move current approaches to clinical applications. Particular attention, however, is also given to the long-term challenges that have to be addressed before ES or iPS cell-based therapies will become a broadly accepted treatment option.

Pluripotent stem cell-derived pancreatic β-cells: potential for regenerative medicine in diabetes

Diabetes mellitus, which affects 346 million people, is one of the leading causes of death worldwide. Pancreatic β-cells, existing in the islets of Langerhans, play central roles in the progression of diabetes. An efficient strategy to produce functional pancreatic β-cells is important for both transplantation therapy and disease modeling of diabetes. Human pluripotent stem cells, including human embryonic stem cells and induced pluripotent stem cells, provide unlimited starting materials to generate differentiated cells for regenerative studies. Significant progress has been made in human embryonic/induced pluripotent stem cell differentiation in the last several years. However, efficient generation of mature pancreatic β-cells with complete functional capabilities has not yet been accomplished. Here, we review recent successes as well as the technical and theoretical challenges in the use of pluripotent stem cell-derived pancreatic β-cells for disease modeling and replacement therapy of diabetes.

Diabetes-related alterations in the enteric nervous system and its microenvironment

Gastric intestinal symptoms common among diabetic patients are often caused by intestinal motility abnormalities related to enteric neuropathy. It has recently been demonstrated that the nitrergic subpopulation of myenteric neurons are especially susceptible to the development of diabetic neuropathy. Additionally, different susceptibility of nitrergic neurons located in different intestinal segments to diabetic damage and their different levels of responsiveness to insulin treatment have been revealed. These findings indicate the importance of the neuronal microenvironment in the pathogenesis of diabetic nitrergic neuropathy. The main focus of this review therefore was to summarize recent advances related to the diabetes-related selective nitrergic neuropathy and associated motility disturbances. Special attention was given to the findings on capillary endothelium and enteric glial cells. Growing evidence indicates that capillary endothelium adjacent to the myenteric ganglia and enteric glial cells surrounding them are determinative in establishing the ganglionic microenvironment. Additionally, recent advances in the development of new strategies to improve glycemic control in type 1 and type 2 diabetes mellitus are also considered in this review. Finally, looking to the future, the recent and promising results of metagenomics for the characterization of the gut microbiome in health and disease such as diabetes are highlighted.

Preparation of pancreatic β-cells from human iPS cells with small molecules

Human induced pluripotent stem (iPS) cells obtained from patients are expected to be a useful source for cell transplantation therapy, because many patients (including those with type 1 diabetes and severe type 2 diabetes) are on waiting lists for transplantation for a long time due to the shortage of donors. At present, many concerns related to clinical application of human iPS cells have been raised, but rapid development of methods for the establishment, culture, and standardization of iPS cells will lead autologous cell therapy to be realistic sooner or later. However, establishment of a method for preparing some of desired cell types is still challenging. Regarding pancreatic β-cells, there have been many reports about differentiation of these cells from human embryonic stem (ES)/iPS cells, but a protocol for clinical application has still not been established. Since there is clear proof that cell transplantation therapy is effective for diabetes based on the results of clinical islet transplantation, pancreatic β-cells prepared from human iPS cells are considered likely to be effective for reducing the burden on patients. In this article, the current status of procedures for preparing pancreatic β-cells from human ES/iPS cells, including effective use of small molecules, is summarized, and some of the problems that still need to be overcome are discussed.

Nonhuman primate induced pluripotent stem cells in regenerative medicine

Among the various species from which induced pluripotent stem cells have been derived, nonhuman primates (NHPs) have a unique role as preclinical models. Their relatedness to humans and similar physiology, including central nervous system, make them ideal for translational studies. We review here the progress made in deriving and characterizing iPS cell lines from different NHP species. We focus on iPS cell lines from the marmoset, a small NHP in which several human disease states can be modeled. The marmoset can serve as a model for the implementation of patient-specific autologous cell therapy in regenerative medicine.

Concise review: pancreas regeneration: recent advances and perspectives

The replacement of functional pancreatic β-cells is seen as an attractive potential therapy for diabetes, because diabetes results from an inadequate β-cell mass. Inducing replication of the remaining β-cells and new islet formation from progenitors within the pancreas (neogenesis) are the most direct ways to increase the β-cell mass. Stimulation of both replication and neogenesis have been reported in rodents, but their clinical significance must still be shown. Because human islet transplantation is limited by the scarcity of donors and graft failure within a few years, efforts have recently concentrated on the use of stem cells to replace the deficient β-cells. Currently, embryonic stem cells and induced pluripotent stem cells achieve high levels of β-cell differentiation, but their clinical use is still hampered by ethical issues and/or the risk of developing tumors after transplantation. Pancreatic epithelial cells (duct, acinar, or α-cells) represent an appealing alternative to stem cells because they demonstrate β-cell differentiation capacities. Yet translation of such capacity to human cells after significant in vitro expansion has yet to be achieved. Besides providing new β-cells, cell therapy also has to address the question on how to protect the transplanted cells from destruction by the immune system via either allo- or autoimmunity. Encouraging developments have been made in encapsulation and immunomodulation techniques, but many challenges still remain. Herein, we discuss recent advances in the search for β-cell replacement therapies, current strategies for circumventing the immune system, and mandatory steps for new techniques to be translated from bench to clinics.