Human Transgene-Free Amniotic-Fluid-Derived Induced Pluripotent Stem Cells for Autologous Cell Therapy

Human induced pluripotent stem cell-derived lung organoids in an ex vivo model of the congenital diaphragmatic hernia fetal lung

Three‐dimensional lung organoids (LOs) derived from pluripotent stem cells have the potential to enhance our understanding of disease mechanisms and to enable novel therapeutic approaches in neonates with pulmonary disorders. We established a reproducible ex vivo model of lung development using transgene‐free human induced pluripotent stem cells generated from fetuses and infants with Bochdalek congenital diaphragmatic hernia (CDH), a polygenic disorder associated with fetal lung compression and pulmonary hypoplasia at birth. Molecular and cellular comparisons of CDH LOs revealed impaired generation of NKX2.1⁺ progenitors, type II alveolar epithelial cells, and PDGFRα⁺ myofibroblasts. We then subjected these LOs to disease relevant mechanical cues through ex vivo compression and observed significant changes in genes associated with pulmonary progenitors, alveolar epithelial cells, and mesenchymal fibroblasts. Collectively, these data suggest both primary cell‐intrinsic and secondary mechanical causes of CDH lung hypoplasia and support the use of this stem cell‐based approach for disease modeling in CDH.

Hydrogel and neural progenitor cell delivery supports organotypic fetal spinal cord development in an ex vivo model of prenatal spina bifida repair

Studying how the fetal spinal cord regenerates in an ex vivo model of spina bifida repair may provide insights into the development of new tissue engineering treatment strategies to better optimize neurologic function in affected patients. Here, we developed hydrogel surgical patches designed for prenatal repair of myelomeningocele defects and demonstrated viability of both human and rat neural progenitor donor cells within this three-dimensional scaffold microenvironment. We then established an organotypic slice culture model using transverse lumbar spinal cord slices harvested from retinoic acid–exposed fetal rats to study the effect of fibrin hydrogel patches ex vivo. Based on histology, immunohistochemistry, gene expression, and enzyme-linked immunoabsorbent assays, these experiments demonstrate the biocompatibility of fibrin hydrogel patches on the fetal spinal cord and suggest this organotypic slice culture system as a useful platform for evaluating mechanisms of damage and repair in children with neural tube defects.

An Insight into DNA-free Reprogramming Approaches to Generate Integration-free Induced Pluripotent Stem Cells for Prospective Biomedical Applications

More than a decade ago, a pioneering study reported generation of induced Pluripotent Stem Cells (iPSCs) by ectopic expression of a cocktail of reprogramming factors in fibroblasts. This study has revolutionized stem cell research and has garnered immense interest from the scientific community globally. iPSCs hold tremendous potential for understanding human developmental biology, disease modeling, drug screening and discovery, and personalized cell-based therapeutic applications. The seminal study identified Oct4, Sox2, Klf4 and c-Myc as a potent combination of genes to induce reprogramming. Subsequently, various reprogramming factors were identified by numerous groups. Most of these studies have used integrating viral vectors to overexpress reprogramming factors in somatic cells to derive iPSCs. However, these techniques restrict the clinical applicability of these cells as they may alter the genome due to random viral integration resulting in insertional mutagenesis and tumorigenicity. To circumvent this issue, alternative integration-free reprogramming approaches are continuously developed that eliminate the risk of genomic modifications and improve the prospects of iPSCs from lab to clinic. These methods establish that integration of transgenes into the genome is not essential to induce pluripotency in somatic cells. This review provides a comprehensive overview of the most promising DNA-free reprogramming techniques that have the potential to derive integration-free iPSCs without genomic manipulation, such as sendai virus, recombinant proteins, microRNAs, synthetic messenger RNA and small molecules. The understanding of these approaches shall pave a way for the generation of clinical-grade iPSCs. Subsequently, these iPSCs can be differentiated into desired cell type(s) for various biomedical applications.

An insight into non-integrative gene delivery approaches to generate transgene-free induced pluripotent stem cells

Over a decade ago, a landmark study that reported derivation of induced Pluripotent Stem Cells (iPSCs) by reprogramming fibroblasts has transformed stem cell research attracting the interest of the scientific community worldwide. These cells circumvent the ethical and immunological concerns associated with embryonic stem cells, and the limited self-renewal ability and restricted differentiation potential linked to adult stem cells. iPSCs hold great potential for understanding basic human biology, in vitro disease modeling, high-throughput drug testing and discovery, and personalized regenerative medicine. The conventional reprogramming methods involving retro- and lenti-viral vectors to deliver reprogramming factors in somatic cells to generate iPSCs nullify the clinical applicability of these cells. Although these gene delivery systems are efficient and robust, they carry an enormous risk of permanent genetic modifications and are potentially tumorigenic. To evade these safety concerns and derive iPSCs for human therapy, tremendous technological advancements have resulted in the development of non-integrating viral- and non-viral approaches. These gene delivery techniques curtail or eliminate the risk of any genomic alteration and enhance the prospects of iPSCs from bench-to-bedside. The present review provides a comprehensive overview of non-integrating viral (adenoviral vectors, adeno-associated viral vectors, and Sendai virus vectors) and DNA-based, non-viral (plasmid transfection, minicircle vectors, transposon vectors, episomal vectors, and liposomal magnetofection) approaches that have the potential to generate transgene-free iPSCs. The understanding of these techniques could pave the way for the use of iPSCs for various biomedical applications.

Amniotic Fluid Stem Cells for the Treatment of Surgical Disorders in the Fetus and Neonate

Over the past decade, amniotic fluid‐derived stem cells have emerged as a novel experimental approach aimed at improving outcomes in children with congenital anomalies, including spina bifida, heart defects, and diaphragmatic hernia. Interest in these cells for the treatment of prenatally diagnosed diseases has arisen based on numerous studies demonstrating the relative ease of harvesting an abundant quantity of amniocytes from a small aliquot of fluid, the unique properties of amniocytes themselves, and the beneficial effects of amniotic fluid‐derived stem cells in experimental animal models. This report gives a brief overview of the rationale and current status of amniotic fluid stem cell‐based therapies, focusing on its relevance to birth defects affecting the fetus and neonate. The author proposes a roadmap for further study that would be required prior to clinical application of amniotic fluid stem cell technologies. stem cells translational medicine2018;7:767–773

Reprogramming Primary Amniotic Fluid and Membrane Cells to Pluripotency in Xeno-free Conditions

Autologous cell-based therapies got a step closer to reality with the introduction of induced pluripotent stem cells. Fetal stem cells, such as amniotic fluid and membrane mesenchymal stem cells, represent a unique type of undifferentiated cells with promise in tissue engineering and for reprogramming into iPSC for future pediatric interventions and stem cell banking. The protocol presented here describes an optimized procedure for extracting and culturing primary amniotic fluid and membrane mesenchymal stem cells and generating episomal induced pluripotent stem cells from these cells in fully chemically defined culture conditions utilizing human recombinant vitronectin and the E8 medium. Characterization of the new lines by applying stringent methods - flow cytometry, confocal imaging, teratoma formation and transcriptional profiling - is also described. The newly generated lines express markers of embryonic stem cells - Oct3/4A, Nanog, Sox2, TRA-1-60, TRA-1-81, SSEA-4 - while being negative for the SSEA-1 marker. The stem cell lines form teratomas in scid-beige mice in 6-8 weeks and the teratomas contain tissues representative of all three germ layers. Transcriptional profiling of the lines by submitting global expression microarray data to a bioinformatic pluripotency assessment algorithm deemed all lines pluripotent and therefore, this approach is an attractive alternative to animal testing. The new iPSC lines can readily be used in downstream experiments involving the optimization of differentiation and tissue engineering.

Methotrexate and Valproic Acid Affect Early Neurogenesis of Human Amniotic Fluid Stem Cells from Myelomeningocele

Myelomeningocele (MMC) is a severe type of neural tube defect (NTD), in which the backbone and spinal canal do not close completely during early embryonic development. This condition results in serious morbidity and increased mortality after birth. Folic acid significantly reduces, and conversely, folate antagonist methotrexate (MTX) and valproic acid (VPA) increase the occurrence of NTDs, including MMC. How these pharmacological agents exactly influence the early neurulation process is still largely unclear. Here, we characterized human amniotic fluid-derived stem cells (AFSCs) from prenatally diagnosed MMC and observed an effect of MTX and VPA administration on the early neural differentiation process. We found that MMC-derived AFSCs highly expressed early neural and radial glial genes that were negatively affected by MTX and VPA exposure. In conclusion, we setup a human cell model of MMC to study early neurogenesis and for drug screening purposes. We also proposed the detection of early neural gene expression in AFSCs as an additional MMC diagnostic tool.

Amniotic fluid stem cell models: A tool for filling the gaps in knowledge for human genetic diseases

Induced pluripotent stem (iPS) cells have attracted attention in recent years as a model of human genetic diseases. Starting from the diseased somatic cells isolated from an affected patient, iPS cells can be created and subsequently differentiated into various cell types that can be used to gain a better understanding of the disease at a cellular and molecular level. There are limitations of iPS cell generation, however, due to low efficiency, high costs, and lengthy protocols. The use of amniotic fluid stem cells (AFS) presents a worthy alternative as a stem cell source for modeling of human genetic diseases. Prenatal identification of chromosomal or Mendelian diseases may require the collection of amniotic fluid which is not only useful for the sake of diagnosis but also from this, AFS cells can be isolated and cultured. Since AFS cells show some characteristics of pluripotency, having the capacity to differentiate into various cell types derived from all three germ layers in vitro, they are a well-suited model for investigations regarding alterations in the molecular biology of a cell due to a specific genetic disease. This readily accessible source of stem cells can replace the necessity for generating iPS cells. Here, we expand on the applicability and importance of AFS cells as a model for discovery in the field of human genetic disease research. This paper is a review article. Referred literature in this paper has been listed in the references section. The data sets supporting the conclusions of this article are available online by searching various databases, including PubMed. Some original points in this article come from the laboratory practice in our research center and the authors’ experiences.

Differentiation of spontaneously contracting cardiomyocytes from non-virally reprogrammed human amniotic fluid stem cells

Congenital heart defects are the most common birth defect. The limiting factor in tissue engineering repair strategies is an autologous source of functional cardiomyocytes. Amniotic fluid contains an ideal cell source for prenatal harvest and use in correction of congenital heart defects. This study aims to investigate the potential of amniotic fluid-derived stem cells (AFSC) to undergo non-viral reprogramming into induced pluripotent stem cells (iPSC) followed by growth-factor-free differentiation into functional cardiomyocytes. AFSC from human second trimester amniotic fluid were transfected by non-viral vesicle fusion with modified mRNA of OCT4, KLF4, SOX2, LIN28, cMYC and nuclear GFP over 18 days, then differentiated using inhibitors of GSK3 followed 48 hours later by inhibition of WNT. AFSC-derived iPSC had high expression of OCT4, NANOG, TRA-1-60, and TRA-1-81 after 18 days of mRNA transfection and formed teratomas containing mesodermal, ectodermal, and endodermal germ layers in immunodeficient mice. By Day 30 of cardiomyocyte differentiation, cells contracted spontaneously, expressed connexin 43 and β-myosin heavy chain organized in sarcomeric banding patterns, expressed cardiac troponin T and β-myosin heavy chain, showed upregulation of NKX2.5, ISL-1 and cardiac troponin T with downregulation of POU5F1, and displayed calcium and voltage transients similar to those in developing cardiomyocytes. These results demonstrate that cells from human amniotic fluid can be differentiated through a pluripotent state into functional cardiomyocytes.

The Production of Pluripotent Stem Cells from Mouse Amniotic Fluid Cells Using a Transposon System

Induced pluripotent stem (iPS) cells are generated from mouse and human somatic cells by forced expression of defined transcription factors using different methods. Here, we produced iPS cells from mouse amniotic fluid cells, using a non-viral-based transposon system. All obtained iPS cell lines exhibited characteristics of pluripotent cells, including the ability to differentiate toward derivatives of all three germ layers in vitro and in vivo. This strategy opens up the possibility of using cells from diseased fetuses to develop new therapies for birth defects.

Non-integrating episomal plasmid-based reprogramming of human amniotic fluid stem cells into induced pluripotent stem cells in chemically defined conditions

Amniotic fluid stem cells (AFSC) represent an attractive potential cell source for fetal and pediatric cell-based therapies. However, upgrading them to pluripotency confers refractoriness toward senescence, higher proliferation rate and unlimited differentiation potential. AFSC were observed to rapidly and efficiently reacquire pluripotency which together with their easy recovery makes them an attractive cell source for reprogramming. The reprogramming process as well as the resulting iPSC epigenome could potentially benefit from the unspecialized nature of AFSC. iPSC derived from AFSC also have potential in disease modeling, such as Down syndrome or β-thalassemia. Previous experiments involving AFSC reprogramming have largely relied on integrative vector transgene delivery and undefined serum-containing, feeder-dependent culture. Here, we describe non-integrative oriP/EBNA-1 episomal plasmid-based reprogramming of AFSC into iPSC and culture in fully chemically defined xeno-free conditions represented by vitronectin coating and E8 medium, a system that we found uniquely suited for this purpose. The derived AF-iPSC lines uniformly expressed a set of pluripotency markers Oct3/4, Nanog, Sox2, SSEA-1, SSEA-4, TRA-1-60, TRA-1-81 in a pattern typical for human primed PSC. Additionally, the cells formed teratomas, and were deemed pluripotent by PluriTest, a global expression microarray-based in-silico pluripotency assay. However, we found that the PluriTest scores were borderline, indicating a unique pluripotent signature in the defined condition. In the light of potential future clinical translation of iPSC technology, non-integrating reprogramming and chemically defined culture are more acceptable.

Human Cardiomyocytes Prior to Birth by Integration-Free Reprogramming of Amniotic Fluid Cells

: The establishment of an abundant source of autologous cardiac progenitor cells would represent a major advance toward eventual clinical translation of regenerative medicine strategies in children with prenatally diagnosed congenital heart disease. In support of this concept, we sought to examine whether functional, transgene-free human cardiomyocytes (CMs) with potential for patient-specific and autologous applications could be reliably generated following routine amniocentesis. Under institutional review board approval, amniotic fluid specimens (8-10 ml) at 20 weeks gestation were expanded and reprogrammed toward pluripotency using nonintegrating Sendai virus (SeV) expressing OCT4, SOX2, cMYC, and KLF4. Following exposure of these induced pluripotent stem cells to cardiogenic differentiation conditions, spontaneously beating amniotic fluid-derived cardiomyocytes (AF-CMs) were successfully generated with high efficiency. After 6 weeks, quantitative gene expression revealed a mixed population of differentiated atrial, ventricular, and nodal AF-CMs, as demonstrated by upregulation of multiple cardiac markers, including MYH6, MYL7, TNNT2, TTN, and HCN4, which were comparable to levels expressed by neonatal dermal fibroblast-derived CM controls. AF-CMs had a normal karyotype and demonstrated loss of NANOG, OCT4, and the SeV transgene. Functional characterization of SIRPA⁺ AF-CMs showed a higher spontaneous beat frequency in comparison with dermal fibroblast controls but revealed normal calcium transients and appropriate chronotropic responses after β-adrenergic agonist stimulation. Taken together, these data suggest that somatic cells present within human amniotic fluid can be used to generate a highly scalable source of functional, transgene-free, autologous CMs before a child is born. This approach may be ideally suited for patients with prenatally diagnosed cardiac anomalies.

SIGNIFICANCE

This study presents transgene-free human amniotic fluid-derived cardiomyocytes (AF-CMs) for potential therapy in tissue engineering and regenerative medicine applications. Using 8-10 ml of amniotic fluid harvested at 20 weeks gestation from normal pregnancies, a mixed population of atrial, ventricular, and nodal AF-CMs were reliably generated after Sendai virus reprogramming toward pluripotency. Functional characterization of purified populations of beating AF-CMs revealed normal calcium transients and appropriate chronotropic responses after β-adrenergic agonist stimulation in comparison with dermal fibroblast controls. Because AF-CMs can be generated in fewer than 16 weeks, this approach may be ideally suited for eventual clinical translation at birth in children with prenatally diagnosed cardiac anomalies.

Amniotic Fluid Stem Cells: A Novel Source for Modeling of Human Genetic Diseases

In recent years, great interest has been devoted to the use of Induced Pluripotent Stem cells (iPS) for modeling of human genetic diseases, due to the possibility of reprogramming somatic cells of affected patients into pluripotent cells, enabling differentiation into several cell types, and allowing investigations into the molecular mechanisms of the disease. However, the protocol of iPS generation still suffers from technical limitations, showing low efficiency, being expensive and time consuming. Amniotic Fluid Stem cells (AFS) represent a potential alternative novel source of stem cells for modeling of human genetic diseases. In fact, by means of prenatal diagnosis, a number of fetuses affected by chromosomal or Mendelian diseases can be identified, and the amniotic fluid collected for genetic testing can be used, after diagnosis, for the isolation, culture and differentiation of AFS cells. This can provide a useful stem cell model for the investigation of the molecular basis of the diagnosed disease without the necessity of producing iPS, since AFS cells show some features of pluripotency and are able to differentiate in cells derived from all three germ layers “in vitro”. In this article, we describe the potential benefits provided by using AFS cells in the modeling of human genetic diseases.

Human amniotic fluid: a source of stem cells for possible therapeutic use

Stem cells are undifferentiated cells with the capacity for differentiation. Amniotic fluid cells have emerged only recently as a possible source of stem cells for clinical purposes. There are no ethical or sampling constraints for the use of amniocentesis as a standard clinical procedure for obtaining an abundant supply of amniotic fluid cells. Amniotic fluid cells of human origin proliferate rapidly and are multipotent with the potential for expansion in vitro to multiple cell lines. Tissue engineering technologies that use amniotic fluid cells are being explored. Amniotic fluid cells may be of clinical benefit for fetal therapies, degenerative disease, and regenerative medicine applications. We present a comprehensive review of the evolution of human amniotic fluid cells as a possible modality for therapeutic use.

Tissue-engineered rhesus monkey nerve grafts for the repair of long ulnar nerve defects: similar outcomes to autologous nerve grafts

Acellular nerve allografts can help preserve normal nerve structure and extracellular matrix composition. These allografts have low immunogenicity and are more readily available than autologous nerves for the repair of long-segment peripheral nerve defects. In this study, we repaired a 40-mm ulnar nerve defect in rhesus monkeys with tissue-engineered peripheral nerve, and compared the outcome with that of autograft. The graft was prepared using a chemical extract from adult rhesus monkeys and seeded with allogeneic Schwann cells. Pathomorphology, electromyogram and immunohistochemistry findings revealed the absence of palmar erosion or ulcers, and that the morphology and elasticity of the hypothenar eminence were normal 5 months postoperatively. There were no significant differences in the mean peak compound muscle action potential, the mean nerve conduction velocity, or the number of neurofilaments between the experimental and control groups. However, outcome was significantly better in the experimental group than in the blank group. These findings suggest that chemically extracted allogeneic nerve seeded with autologous Schwann cells can repair 40-mm ulnar nerve defects in the rhesus monkey. The outcomes are similar to those obtained with autologous nerve graft.

Upregulation of Nanog and Sox-2 genes following ectopic expression of Oct-4 in amniotic fluid mesenchymal stem cells

Octamer-binding transcription factor 4 (Oct-4), an important gene regulating stem cell pluripotency, is well-known for its ability to reprogram somatic cells in vitro, either alone or in concert with other factors. The aim of this study was to assess the effect of ectopic expression of Oct human amniotic fluid stem cells. We developed a novel method for isolation of putative human amniotic fluid-derived multipotent stem cells. These cells showing mesenchymal stem cell phenotypes (human amniotic fluid-derived mesenchymal stem cells, hAFMSCs) were transfected with a plasmid carrying genes for Oct-4 and the green fluorescent protein (GFP). The stably transfected cells, hAFMSCs-Oct4/GFP, were selected by using G418 and found to express the GFP reporter gene under the control of Oct-4 promoter. We found that hAFMSCs developed by our method possess very high self-renewal ability (about 78 cumulative population doublings) and multilineage differentiation potency. Significantly, the hAFMSCs-Oct4/GFP cells showed enhanced expression of the three major pluripotency genes Oct-4, Nanog, and Sox-2, and increased colony-forming ability and growth rate compared with the parental hAFMSCs. We demonstrated that the ectopic expression of Oct-4 gene in hAFMSCs with high self-renewal ability could upregulate Nanog and Sox-2 gene expression and enhance cell growth rate and colony-forming efficiency. Therefore, the ectopic expression of Oct-4 could be a strategy to develop pluripotency in hAFMSCs for clinical applications.

Genetic reprogramming of human amniotic cells with episomal vectors: neural rosettes as sentinels in candidate selection for validation assays

The promise of genetic reprogramming has prompted initiatives to develop banks of induced pluripotent stem cells (iPSCs) from diverse sources. Sentinel assays for pluripotency could maximize available resources for generating iPSCs. Neural rosettes represent a primitive neural tissue that is unique to differentiating PSCs and commonly used to identify derivative neural/stem progenitors. Here, neural rosettes were used as a sentinel assay for pluripotency in selection of candidates to advance to validation assays. Candidate iPSCs were generated from independent populations of amniotic cells with episomal vectors. Phase imaging of living back up cultures showed neural rosettes in 2 of the 5 candidate populations. Rosettes were immunopositive for the Sox1, Sox2, Pax6 and Pax7 transcription factors that govern neural development in the earliest stage of development and for the Isl1/2 and Otx2 transcription factors that are expressed in the dorsal and ventral domains, respectively, of the neural tube in vivo. Dissociation of rosettes produced cultures of differentiation competent neural/stem progenitors that generated immature neurons that were immunopositive for βIII-tubulin and glia that were immunopositive for GFAP. Subsequent validation assays of selected candidates showed induced expression of endogenous pluripotency genes, epigenetic modification of chromatin and formation of teratomas in immunodeficient mice that contained derivatives of the 3 embryonic germ layers. Validated lines were vector-free and maintained a normal karyotype for more than 60 passages. The credibility of rosette assembly as a sentinel assay for PSCs is supported by coordinate loss of nuclear-localized pluripotency factors Oct4 and Nanog in neural rosettes that emerge spontaneously in cultures of self-renewing validated lines. Taken together, these findings demonstrate value in neural rosettes as sentinels for pluripotency and selection of promising candidates for advance to validation assays.