Stem cell bioengineering: building from stem cell biology

Single-Cell RNA Sequencing: Technological Progress and Biomedical Application in Cancer Research

Single-cell RNA-seq (scRNA-seq) is a revolutionary technology that allows for the genomic investigation of individual cells in a population, allowing for the discovery of unusual cells associated with cancer and metastasis. ScRNA-seq has been used to discover different types of cancers with poor prognosis and medication resistance such as lung cancer, breast cancer, ovarian cancer, and gastric cancer. Besides, scRNA-seq is a promising method that helps us comprehend the biological features and dynamics of cell development, as well as other disorders. This review gives a concise summary of current scRNA-seq technology. We also explain the main technological steps involved in implementing the technology. We highlight the present applications of scRNA-seq in cancer research, including tumor heterogeneity analysis in lung cancer, breast cancer, and ovarian cancer. In addition, this review elucidates potential applications of scRNA-seq in lineage tracing, personalized medicine, illness prediction, and disease diagnosis, which reveals that scRNA-seq facilitates these events by producing genetic variations on the single-cell level.

A PLURIPOTENT STEM CELL PLATFORM FOR IN VITRO SYSTEMS GENETICS STUDIES OF MOUSE DEVELOPMENT

The directed differentiation of pluripotent stem cells (PSCs) from panels of genetically diverse individuals is emerging as a powerful experimental system for characterizing the impact of natural genetic variation on developing cell types and tissues. Here, we establish new PSC lines and experimental approaches for modeling embryonic development in a genetically diverse, outbred mouse stock (Diversity Outbred mice). We show that a range of inbred and outbred PSC lines can be stably maintained in the primed pluripotent state (epiblast stem cells -- EpiSCs) and establish the contribution of genetic variation to phenotypic differences in gene regulation and directed differentiation. Using pooled in vitro fertilization, we generate and characterize a genetic reference panel of Diversity Outbred PSCs (n = 230). Finally, we demonstrate the feasibility of pooled culture of Diversity Outbred EpiSCs as "cell villages", which can facilitate the differentiation of large numbers of EpiSC lines for forward genetic screens. These data can complement and inform similar efforts within the stem cell biology and human genetics communities to model the impact of natural genetic variation on phenotypic variation and disease-risk.

Mechanotransduction in stem cells

Nowadays, it is an established concept that the capability to reach a specialised cell identity via differentiation, as in the case of multi- and pluripotent stem cells, is not only determined by biochemical factors, but that also physical aspects of the microenvironment play a key role; interpreted by the cell through a force-based signalling pathway called mechanotransduction. However, the intricate ties between the elements involved in mechanotransduction, such as the extracellular matrix, the glycocalyx, the cell membrane, Integrin adhesion complexes, Cadherin-mediated cell/cell adhesion, the cytoskeleton, and the nucleus, are still far from being understood in detail. Here we report what is currently known about these elements in general and their specific interplay in the context of multi- and pluripotent stem cells. We furthermore merge this overview to a more comprehensive picture, that aims to cover the whole mechanotransductive pathway from the cell/microenvironment interface to the regulation of the chromatin structure in the nucleus. Ultimately, with this review we outline the current picture of the interplay between mechanotransductive cues and epigenetic regulation and how these processes might contribute to stem cell dynamics and fate.

Engineering pluripotent stem cells with synthetic biology for regenerative medicine

Pluripotent stem cells (PSCs), characterized by self-renewal and capacity of differentiating into three germ layers, are the programmable building blocks of life. PSC-derived cells and multicellular systems, particularly organoids, exhibit great potential for regenerative medicine. However, this field is still in its infancy, partly due to limited strategies to robustly and precisely control stem cell behaviors, which are tightly regulated by inner gene regulatory networks in response to stimuli from the extracellular environment. Synthetic receptors and genetic circuits are powerful tools to customize the cellular sense-and-response process, suggesting their underlying roles in precise control of cell fate decision and function reconstruction. Herein, we review the progress and challenges needed to be overcome in the fields of PSC-based cell therapy and multicellular system generation, respectively. Furthermore, we summarize several well-established synthetic biology tools and their applications in PSC engineering. Finally, we highlight the challenges and perspectives of harnessing synthetic biology to PSC engineering for regenerative medicine.

Stem cell-based ischemic stroke therapy: Novel modifications and clinical challenges

Ischemic stroke (IS) causes severe disability and high mortality worldwide. Stem cell (SC) therapy exhibits unique therapeutic potential for IS that differs from current treatments. SC's cell homing, differentiation and paracrine abilities give hope for neuroprotection. Recent studies on SC modification have enhanced therapeutic effects for IS, including gene transfection, nanoparticle modification, biomaterial modification and pretreatment. These methods improve survival rate, homing, neural differentiation, and paracrine abilities in ischemic areas. However, many problems must be resolved before SC therapy can be clinically applied. These issues include production quality and quantity, stability during transportation and storage, as well as usage regulations. Herein, we reviewed the brief pathogenesis of IS, the "multi-mechanism" advantages of SCs for treating IS, various SC modification methods, and SC therapy challenges. We aim to uncover the potential and overcome the challenges of using SCs for treating IS and convey innovative ideas for modifying SCs.

Programmable synthetic receptors: the next-generation of cell and gene therapies

Cell and gene therapies hold tremendous promise for treating a range of difficult-to-treat diseases. However, concerns over the safety and efficacy require to be further addressed in order to realize their full potential. Synthetic receptors, a synthetic biology tool that can precisely control the function of therapeutic cells and genetic modules, have been rapidly developed and applied as a powerful solution. Delicately designed and engineered, they can be applied to finetune the therapeutic activities, i.e., to regulate production of dosed, bioactive payloads by sensing and processing user-defined signals or biomarkers. This review provides an overview of diverse synthetic receptor systems being used to reprogram therapeutic cells and their wide applications in biomedical research. With a special focus on four synthetic receptor systems at the forefront, including chimeric antigen receptors (CARs) and synthetic Notch (synNotch) receptors, we address the generalized strategies to design, construct and improve synthetic receptors. Meanwhile, we also highlight the expanding landscape of therapeutic applications of the synthetic receptor systems as well as current challenges in their clinical translation.

Inferring Gene Regulatory Networks and Predicting the Effect of Gene Perturbations via IQCELL

IQCELL is a platform that infers Boolean gene regulatory networks from single-cell RNA sequencing data. Boolean networks can be simulated under normal and perturbed conditions. In this chapter, we provide a detailed guideline for implementing IQCELL from a raw dataset. The steps include processing data, inferring informative genes, inferring gene regulatory network, and simulating the resulted network under normal and perturbed conditions.

Transcriptome profiling of differentiating adipose-derived stem cells across species reveals new genes regulating adipogenesis

Adipose-derived stem cells (ADSCs) that are enriched in adipose tissue with multilineage differentiation potential have become an important tool in therapeutic research and tissue engineering. Certain breeds of sheep exhibit a unique fat tail trait such that tail tissue accounts for approximately 10 % of body weight and can provide an excellent source of ADSCs. Here, we describe isolation of primary ADSCs from ovine embryonic fat tail tissues that displayed high self-renewal capacity, multilineage differentiation and excellent adipogenic ability. Through transcriptome analysis covering ADSCs differentiating into adipocytes, 37 transcription factors were involved in early transcriptional events that initiate a regulatory cascade of adipogenesis; the entire adipogenic activity consists of a reduction in proliferation ability and upregulation of genes related to lipid generation and energy metabolism, as well as several genes associated with myogenesis. Furthermore, Comparative transcriptome analysis across species (sheep, human, and mouse) revealed enhanced basal metabolic ability in differentiating ovine ADSCs, which may relate to the excellent adipogenic capability of these cells. We also identified a small evolutionarily conserved gene set, consisting of 21 and 22 genes exhibiting increased and decreased expression, respectively. Almost half (20) of these genes have not previously been reported to regulate adipogenesis in mammals. In this study, we identified important regulators that trigger ovine adipocyte differentiation, main biological pathways involved in adipogenesis as well as the evolutionarily conserved genes governing adipogenic process across species. Our study provides a novel excellent biomaterial and novel genes regulating adipogenesis for cellular transplantation therapy and investigations of fat metabolism.

Unlocking the potential of stem cells: Their crucial role in the production of cultivated meat

Cellular agriculture is an emerging research field of agribiotechnology that aims to produce agricultural products using stem cells, without sacrificing animals or cultivating crops. Cultivated meat, as a representative cellular product of cellular agriculture, is being actively researched due to global food insecurity, environmental, and ethical concerns. This review focuses on the application of stem cells, which are the seeds of cellular agriculture, for the production of cultivated meat, with emphasis on deriving and culturing muscle and adipose stem cells for imitating fresh meat. Establishing standards and safety regulations for culturing stem cells is crucial for the market entry of cultured muscle tissue-based biomaterials. Understanding stem cells is a prerequisite for creating reliable cultivated meat and other cellular agricultural biomaterials. The techniques and regulations from the cultivated meat industry could pave the way for new cellular agriculture industries in the future.

Bone tissue engineering for treating osteonecrosis of the femoral head

Osteonecrosis of the femoral head (ONFH) is a devastating and complicated disease with an unclear etiology. Femoral head-preserving surgeries have been devoted to delaying and hindering the collapse of the femoral head since their introduction in the last century. However, the isolated femoral head-preserving surgeries cannot prevent the natural progression of ONFH, and the combination of autogenous or allogeneic bone grafting often leads to many undesired complications. To tackle this dilemma, bone tissue engineering has been widely developed to compensate for the deficiencies of these surgeries. During the last decades, great progress has been made in ingenious bone tissue engineering for ONFH treatment. Herein, we comprehensively summarize the state-of-the-art progress made in bone tissue engineering for ONFH treatment. The definition, classification, etiology, diagnosis, and current treatments of ONFH are first described. Then, the recent progress in the development of various bone-repairing biomaterials, including bioceramics, natural polymers, synthetic polymers, and metals, for treating ONFH is presented. Thereafter, regenerative therapies for ONFH treatment are also discussed. Finally, we give some personal insights on the current challenges of these therapeutic strategies in the clinic and the future development of bone tissue engineering for ONFH treatment.

Vascularized organ bioprinting: From strategy to paradigm

Over the past two decades, bioprinting has become a popular research topic worldwide, as it is the most promising approach for manufacturing vascularized organ in vitro. However, transitioning bioprinting from simple tissue models to real biomedical applications is still a challenge due to the lack of interdisciplinary theoretical knowledge and perfect multitechnology integration. This review examines the goals of vasculature manufacturing and proposes the objectives in three stages. We then outline a bidirectional manufacturing strategy consisting of top-down reproduction (bioprinting) and bottom-up regeneration (cellular behaviour). We also provide an in-depth analysis of the views from the four aspects of design, ink, printing, and culture. Furthermore, we present the 'constructing-comprehension cycle' research paradigm in Strategic Priority Research Program and the 'math-model-based batch insights generator' research paradigm for the future, which have the potential to revolutionize the biomedical field.

Biomaterials based on hyaluronic acid, collagen and peptides for three-dimensional cell culture and their application in stem cell differentiation

In recent decades, three-dimensional (3D) cell culture technologies have been developed rapidly in the field of tissue engineering and regeneration, and have shown unique advantages and great prospects in the differentiation of stem cells. Herein, the article reviews the progress and advantages of 3D cell culture technologies in the field of stem cell differentiation. Firstly, 3D cell culture technologies are divided into two main categories: scaffoldless and scaffolds. Secondly, the effects of hydrogels scaffolds and porous scaffolds on stem cell differentiation in the scaffold category were mainly reviewed. Among them, hydrogels scaffolds are divided into natural hydrogels and synthetic hydrogels. Natural materials include polysaccharides, proteins, and their derivatives, focusing on hyaluronic acid, collagen and polypeptides. Synthetic materials mainly include polyethylene glycol (PEG), polyacrylic acid (PAA), polyvinyl alcohol (PVA), etc. In addition, since the preparation techniques have a large impact on the properties of porous scaffolds, several techniques for preparing porous scaffolds based on different macromolecular materials are reviewed. Finally, the future prospects and challenges of 3D cell culture in the field of stem cell differentiation are reviewed. This review will provide a useful guideline for the selection of materials and techniques for 3D cell culture in stem cell differentiation.

hCINAP regulates the differentiation of embryonic stem cells by regulating NEDD4 liquid-liquid phase-separation-mediated YAP1 activation

YAP1 functions in lineage differentiation of pluripotent embryonic stem cells (ESCs); however, the detailed mechanisms underlying the regulation of YAP1 activity during ESC differentiation remain elusive. Here, we report that hCINAP serves as a negative regulator of YAP1 during ESC fate decisions. The expression of mCINAP, the murine homolog of hCINAP, is downregulated during the differentiation process of murine ESC (mESC) ectoderm lineage, leading to liquid-liquid phase separation (LLPS) of NEDD4 and activation of YAP1. Mechanistically, hCINAP interacts with and prevents NEDD4 from forming cytoplasmic condensates that compartmentalize YAP1 and its kinase NLK, facilitating YAP1 phosphorylation at Ser128 and promoting YAP1 activation. mCINAP depletion leads to the formation of NEDD4 condensates and YAP1 activation, which impedes endoderm differentiation of mESCs. Our study shows that hCINAP is a vital regulator of YAP1 activity and is essential for stem cell fate decisions, which provides mechanistic insight into early embryogenesis.

Therapeutic Potential of Mesenchymal Stem Cells in the Treatment of Epilepsy and Their Interaction with Antiseizure Medications

Epilepsy is a life-threatening neurological disease that affects approximately 70 million people worldwide. Although the vast majority of patients may be successfully managed with currently used antiseizure medication (ASM), the search for alternative therapies is still necessary due to pharmacoresistance in about 30% of patients with epilepsy. Here, we review the effects of ASMs on stem cell treatment when they could be, as expected, co-administered. Indeed, it has been reported that ASMs produce significant effects on the differentiation and determination of stem cell fate. In addition, we discuss more recent findings on mesenchymal stem cells (MSCs) in pre-clinical and clinical investigations. In this regard, their ability to differentiate into various cell types, reach damaged tissues and produce and release biologically active molecules with immunomodulatory/anti-inflammatory and regenerative properties make them a high-potential therapeutic tool to address neuroinflammation in different neurological disorders, including epilepsy. Overall, the characteristics of MSCs to be genetically engineered, in order to replace dysfunctional elements with the aim of restoring normal tissue functioning, suggested that these cells could be good candidates for the treatment of epilepsy refractory to ASMs. Further research is required to understand the potential of stem cell treatment in epileptic patients and its interaction with ASMs.

Synthetic gene circuits for cell state detection and protein tuning in human pluripotent stem cells

During development, cell state transitions are coordinated through changes in the identity of molecular regulators in a cell type‐ and dose‐specific manner. The ability to rationally engineer such transitions in human pluripotent stem cells (hPSC) will enable numerous applications in regenerative medicine. Herein, we report the generation of synthetic gene circuits that can detect a desired cell state using AND‐like logic integration of endogenous miRNAs (classifiers) and, upon detection, produce fine‐tuned levels of output proteins using an miRNA‐mediated output fine‐tuning technology (miSFITs). Specifically, we created an “hPSC ON” circuit using a model‐guided miRNA selection and circuit optimization approach. The circuit demonstrates robust PSC‐specific detection and graded output protein production. Next, we used an empirical approach to create an “hPSC‐Off” circuit. This circuit was applied to regulate the secretion of endogenous BMP4 in a state‐specific and fine‐tuned manner to control the composition of differentiating hPSCs. Our work provides a platform for customized cell state‐specific control of desired physiological factors in hPSC, laying the foundation for programming cell compositions in hPSC‐derived tissues and beyond.

A reductionist approach to determine the effect of cell-cell contact on human epidermal stem cell differentiation

The balance between stem cell renewal and differentiation is determined by the interplay between intrinsic cellular controls and extrinsic factors presented by the microenvironment, or 'niche'. Previous studies on cultured human epidermis have utilised suspension culture and restricted cell spreading to investigate regulation of differentiation in single keratinocytes. However, keratinocytes are typically adherent to neighbouring cells in vivo. We therefore developed experimental models to investigate the combined effects of cell-ECM adhesion and cell-cell contact. We utilized lipid-modified oligonucleotides to form clusters of keratinocytes which were subsequently placed in suspension to induce terminal differentiation. In this experimental model cell-cell contact had no effect on suspension-induced differentiation of keratinocytes. We next developed a high-throughput platform for robust geometrical confinement of keratinocytes to hexagonal ECM-coated islands permitting direct cell-cell contact between single cells. As in the case of circular islands, differentiation was stimulated on the smallest single hexagonal islands. However, the percentage of involucrin-positive cells on small bowtie islands was significantly lower than on single islands, demonstrating that cell-cell contact reduced differentiation in response to decreased substrate adhesion. None of the small bowtie islands contained two involucrin-positive cells. Rather, if one cell was involucrin-positive the other was involucrin-negative. This suggests that there is intrinsic asymmetry in the effect of cell-cell contact in decreasing differentiation. Thus, our reductionist approaches provide new insights into the effect of the niche on keratinocyte differentiation. STATEMENT OF SIGNIFICANCE: Stem cell behaviour is regulated by a combination of external signals, including the nature of the adhesive substrate and cell-cell interactions. An understanding of how different signals are integrated creates the possibility of developing new biomaterials to promote tissue regeneration and broaden our understanding of skin diseases such as eczema and psoriasis, in which stem cell proliferation and differentiation are perturbed. In this study we have applied two methods to engineer intercellular adhesion of human epidermal stem cells, one involving lipid-modified DNA and the other involving hexagonal micropatterns. We show that the effect of cell-cell adhesion depends on cell-substrate adhesion and uncover evidence that two cells in equivalent environments can nevertheless behave differently.

Temporal perturbation of histone deacetylase activity reveals a requirement for HDAC1-3 in mesendoderm cell differentiation

Histone deacetylases (HDACs) are a class of enzymes that control chromatin state and influence cell fate. We evaluated the chromatin accessibility and transcriptome dynamics of zinc-containing HDACs during cell differentiation in vitro coupled with chemical perturbation to identify the role of HDACs in mesendoderm cell fate specification. Single-cell RNA sequencing analyses of HDAC expression during human pluripotent stem cell (hPSC) differentiation in vitro and mouse gastrulation in vivo reveal a unique association of HDAC1 and -3 with mesendoderm gene programs during exit from pluripotency. Functional perturbation with small molecules reveals that inhibition of HDAC1 and -3, but not HDAC2, induces mesoderm while impeding endoderm and early cardiac progenitor specification. These data identify unique biological functions of the structurally homologous enzymes HDAC1-3 in influencing hPSC differentiation from pluripotency toward mesendodermal and cardiac progenitor populations.

Robust and tunable signal processing in mammalian cells via engineered covalent modification cycles

Engineered signaling networks can impart cells with new functionalities useful for directing differentiation and actuating cellular therapies. For such applications, the engineered networks must be tunable, precisely regulate target gene expression, and be robust to perturbations within the complex context of mammalian cells. Here, we use bacterial two-component signaling proteins to develop synthetic phosphoregulation devices that exhibit these properties in mammalian cells. First, we engineer a synthetic covalent modification cycle based on kinase and phosphatase proteins derived from the bifunctional histidine kinase EnvZ, enabling analog tuning of gene expression via its response regulator OmpR. By regulating phosphatase expression with endogenous miRNAs, we demonstrate cell-type specific signaling responses and a new strategy for accurate cell type classification. Finally, we implement a tunable negative feedback controller via a small molecule-stabilized phosphatase, reducing output expression variance and mitigating the context-dependent effects of off-target regulation and resource competition. Our work lays the foundation for establishing tunable, precise, and robust control over cell behavior with synthetic signaling networks.

Human umbilical cord mesenchymal stem cell promotes angiogenesis via integrin β1/ERK1/2/HIF-1α/VEGF-A signaling pathway for off-the-shelf breast tissue engineering

Background

Mesenchymal stem cells (MSC)-based tissue engineered breast represent the visible future for breast reconstruction after mastectomy. However, autologous MSCs might not be appropriate for the large graft construction due to cell senescence during excessive cell expansion, thus hindering its further off-the-shelf application. The human umbilical cord mesenchymal stem cells (hUCMSCs) have been found to induce low immune response and can be easily stored, making them ideal for off-the-shelf tissue engineering application. Here, we explored the feasibility of using umbilical cord mesenchymal stem cells as tissue-engineered breast seed cells.

Methods

The allogenic hUCMSCs were injected into transplanted fat tissue with or without breast scaffolds as an alternative for breast tissue engineering in vivo, and its potential mechanism of angiogenesis in vitro was explored.

Results

Transplantation of hUCMSCs promoted proliferation, migration, and angiogenesis of human umbilical vein endothelial cells (HUVECs) through paracrine mechanism by activating the integrin β1/ERK1/2/HIF-1α/VEGF-A signaling pathway. Histological examination of grafted fat revealed that the group which received hUCMSCs transplantation had more fat tissue [(93.60 ± 2.40) %] and fewer MAC2⁺CD206⁻ M1 macrophages [(0.50 ± 0.47) cells/field] compared to the control group [fat tissue (45.42 ± 5.96) and macrophage cells/field (5.00 ± 2.23)]. Moreover, the hUCMSCs- labeled with a tracing dye differentiated into adipocytes and vascular endothelial cells in the adipose tissue. When applied to the tissue-engineered breast with a scaffold, the group treated with hUCMSCs had more adipose tissues and CD31⁺ cells than the control group.

Conclusions

These results demonstrate that allogeneic hUCMSCs promote the regeneration of adipose tissue and can be used to construct a tissue engineered breast.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02770-x.

Extracellular Matrix in Human Craniofacial Development

The extracellular matrix (ECM) is a highly dynamic amalgamation of structural and signaling molecules whose quantitative and qualitative modifications drive the distinct programmed morphologic changes required for tissues to mature into their functional forms. The craniofacial complex houses a diverse array of tissues, including sensory organs, glands, and components of the musculoskeletal, neural, and vascular systems, alongside several other highly specialized tissues to form the most complex part of the vertebrate body. Through cell-ECM interactions, the ECM coordinates the cell movements, shape changes, differentiation, gene expression changes, and other behaviors that sculpt developing organs. In this review, we focus on several common key roles of the ECM to shape developing craniofacial organs and tissues. We summarize recent advances in our understanding of the ability of the ECM to biochemically and biomechanically orchestrate major events of craniofacial development, and we discuss how dysregulated ECM dynamics contributes to disease and disorders. As we expand our understanding of organ-specific matrix functionality and composition, we will improve our ability to rationally modify matrices to promote regeneration and/or prevent degenerative outcomes in vitro and in vivo.

The importance of cell culture parameter standardization: an assessment of the robustness of the 2102Ep reference cell line

Work undertaken using the embryonic carcinoma 2102Ep line, highlighted the requirement for robust, well-characterized and standardized protocols. A systematic approach utilizing 'quick hit' experiments demonstrated variability introduced into culture systems resulting from slight changes to culture conditions (route A). This formed the basis for longitudinal experiments investigating long-term effects of culture parameters including seeding density and feeding regime (route B).Results demonstrated that specific growth rates (SGR) of passage 59 (P59) cells seeded at 20,000 cells/cm2 and subjected to medium exchange after 48h prior to reseeding at 72h (route B2) on average was marginally higher than, P55 cells cultured under equivalent conditions (route A1); whereby SGR values were (0.021±0.004) and (0.019±0.004). Viability was higher in route B2 over 10 passages with average viability reported as (86.3%±8.1) compared to route A1 (83.3±8.8). The metabolite data demonstrated both culture route B1 (P57 cells seeded at 66,667 cells/cm2) and B2 had consistent-specific metabolite rates (SMR) for glucose, but SMR values of route B1 was consistently lower than route B2 (0.00001 mmol, cell-1.d-1 and 0.000025).Results revealed interactions between phenotype, SMR and feeding regime that may not be accurately reflected by growth rate or observed morphology. This implies that current schemes of protocol control do not adequately account for variability, since key cell characteristics, including phenotype and SMR, change regardless of standardized seeding densities. This highlights the need to control culture parameters through defined protocols, for processes that involve culture for therapeutic use, biologics production, and reference lines.

Chemically defined stem cell microniche engineering by microfluidics compatible with iPSCs' growth in 3D culture

The development of induced pluripotent stem cell (iPSCs) has opened unprecedented opportunities for biomedical applications, but poorly defined animal-derived matrices yield cells with limited therapeutic value. Considerable challenges remain in improving cell-culturing approaches to create the conditions for iPSCs' reliable expansion. Herein we report the development of a chemically defined, artificial three-dimensional (3D) microniche for iPSCs' growth and reliable expansion, constructed with degradable polyethyleneglycol-co-polycaprolactone and RGDfk-functionalized dendritic polyglycerol precursors according to bioorthogonal strain-promoted azide-alkyne cycloaddition by droplet-based microfluidics. This compatible microniche can allow for the robust production of iPSCs that maintain high pluripotency expression and excellent viability without pathogen or immunogen transfer risks. This microniche technology shows great promise in enabling iPSCs to achieve their full therapeutic potential.

Injectable silk nanofiber hydrogels as stem cell carriers to accelerate wound healing

Stem cells have potential utility in wound therapy, however the benefits are often limited due to cell injury from shear stress during injection and poor retention at the wound site. Here, shear-thinning silk nanofiber hydrogels were used to load bone marrow derived mesenchymal stem cells (BMSCs) and inject into wound sites to optimize cell retention and accelerate wound healing. The BMSCs in the silk nanofiber hydrogels maintained stemness better than the cells cultured on plates, and the expression of wound healing-related genes was significantly higher in the hydrogels with higher silk concentrations (2 wt%). The silk nanofibers physically prevented migration of BMSCs from the deposition site in the wound bed. In addition to faster wound healing, these BMSC-loaded hydrogels mediated angiogenesis and inflammation and improved collagen deposition and hair follicle regeneration in vivo in rats. Considering that these silk nanofiber hydrogels were successfully used here as carriers for stem cells to accelerate wound healing, further study for skin regeneration may be warranted.

miRNA induced co-differentiation and cross-talk of adipose tissue-derived progenitor cells for 3D heterotypic pre-vascularized bone formation

Engineered bone grafts require a vascular network to supply cells with oxygen, nutrients and remove waste. Using heterotypic mature cells to create these graftsin vivohas resulted in limited cell density, ectopic tissue formation and disorganized tissue. Despite evidence that progenitor cell aggregates, such as progenitor spheroids, are a potential candidate for fabrication of native-like pre-vascularized bone tissue, the factors dictating progenitor co-differentiation to create heterotypic pre-vascularized bone tissue remains poorly understood. In this study, we examined a three-dimensional heterotypic pre-vascularized bone tissue model, using osteogenic and endotheliogenic progenitor spheroids induced by miR-148b and miR-210 mimic transfection, respectively. Spheroids made of transfected cells were assembled into heterotypic structures to determine the impact on co-differentiation as a function of micro-RNA (miRNA) mimic treatment group and induction time. Our results demonstrated that miRNAs supported the differentiation in heterotypic structures, and that developing heterotypic structures is determined in part by progenitor maturity, as confirmed by gene and protein markers of osteogenic and endotheliogenic differentiation and the mineralization assay. As a proof of concept, miRNA-transfected spheroids were also bioprinted using aspiration-assisted bioprinting and organized into hollow structures to mimic the Haversian canal. Overall, the presented approach could be useful in fabrication of vascularized bone tissue using spheroids as building blocks.

Mechanobiological conceptual framework for assessing stem cell bioprocess effectiveness

Fully realizing the enormous potential of stem cells requires developing efficient bioprocesses and optimizations founded in mechanobiological considerations. Here, we emphasize the importance of mechanotransduction as one of the governing principles of stem cell bioprocesses, underscoring the need to further explore the behavioral mechanisms involved in sensing mechanical cues and coordinating transcriptional responses. We identify the sources of intrinsic, extrinsic, and external noise in bioprocesses requiring further study, and discuss the criteria and indicators that may be used to assess and predict cell-to-cell variability resulting from environmental fluctuations. Specifically, we propose a conceptual framework to explain the impact of mechanical forces within the cellular environment, identify key cell state determinants in bioprocesses, and discuss downstream implementation challenges.

Evening the playing field: microenvironmental control over stem cell competition during fate programming

Recent advancements in cellular engineering, including reprogramming of somatic cells into pluripotent stem cells, have opened the door to a new era of regenerative medicine. Given that cellular decisions are guided by microenvironmental cues, such as secreted factors and interactions with neighbouring cells, reproducible cell manufacturing requires robust control over cell-cell interactions. Cell competition has recently emerged as a previously unknown interaction that plays a significant role in shaping the growth and death dynamics of multicellular stem cell populations, both in vivo and in vitro. Although recent studies have largely focused on exploring how the differential expression of key genes mediate the competitive elimination of some cells, little is known about the impact of the microenvironment on cell competition, despite its critical role in shaping cell fate outcomes. Here, we explore recent findings that have brought cell competition into the spotlight, while dissecting the role of microenvironmental factors for controlling competition in cell fate programming applications.

Context-aware synthetic biology by controller design: Engineering the mammalian cell

The rise of systems biology has ushered a new paradigm: the view of the cell as a system that processes environmental inputs to drive phenotypic outputs. Synthetic biology provides a complementary approach, allowing us to program cell behavior through the addition of synthetic genetic devices into the cellular processor. These devices, and the complex genetic circuits they compose, are engineered using a design-prototype-test cycle, allowing for predictable device performance to be achieved in a context-dependent manner. Within mammalian cells, context effects impact device performance at multiple scales, including the genetic, cellular, and extracellular levels. In order for synthetic genetic devices to achieve predictable behaviors, approaches to overcome context dependence are necessary. Here, we describe control systems approaches for achieving context-aware devices that are robust to context effects. We then consider cell fate programing as a case study to explore the potential impact of context-aware devices for regenerative medicine applications.

Biomedical and societal impacts of in vitro embryo models of mammalian development

In recent years, a diverse array of in vitro cell-derived models of mammalian development have been described that hold immense potential for exploring fundamental questions in developmental biology, particularly in the case of the human embryo where ethical and technical limitations restrict research. These models open up new avenues toward biomedical advances in in vitro fertilization, clinical research, and drug screening with potential to impact wider society across many diverse fields. These technologies raise challenging questions with profound ethical, regulatory, and social implications that deserve due consideration. Here, we discuss the potential impacts of embryo-like models, and their biomedical potential and current limitations.

Intracellular label-free detection of mesenchymal stem cell metabolism within a perivascular niche-on-a-chip

The stem cell niche at the perivascular space in human tissue plays a pivotal role in dictating the overall fate of stem cells within it. Mesenchymal stem cells (MSCs) in particular, experience influential microenvironmental conditions, which induce specific metabolic profiles that affect processes of cell differentiation and dysregulation of the immunomodulatory function. Reports focusing specifically on the metabolic status of MSCs under the effect of pathophysiological stimuli - in terms of flow velocities, shear stresses or oxygen tension - do not model heterogeneous gradients, highlighting the need for more advanced models reproducing the metabolic niche. Organ-on-a-chip technology offers the most advanced tools for stem cell niche modelling thus allowing for controlled dynamic culture conditions while profiling tuneable oxygen tension gradients. However, current systems for live cell detection of metabolic activity inside microfluidic devices require the integration of microsensors. The presence of such microsensors poses the potential to alter microfluidics and their resolution does not enable intracellular measurements but rather a global representation concerning cellular metabolism. Here, we present a metabolic toolbox coupling a miniaturised in vitro system for human-MSCs dynamic culture, which mimics microenvironmental conditions of the perivascular niche, with high-resolution imaging of cell metabolism. Using fluorescence lifetime imaging microscopy (FLIM) we monitor the spatial metabolic machinery and correlate it with experimentally validated intracellular oxygen concentration after designing the oxygen tension decay along the fluidic chamber by in silico models prediction. Our platform allows the metabolic regulation of MSCs, mimicking the physiological niche in space and time, and its real-time monitoring representing a functional tool for modelling perivascular niches, relevant diseases and metabolic-related uptake of pharmaceuticals.

Endogenous suppression of WNT signalling in human embryonic stem cells leads to low differentiation propensity towards definitive endoderm

Low differentiation propensity towards a targeted lineage can significantly hamper the utility of individual human pluripotent stem cell (hPSC) lines in biomedical applications. Here, we use monolayer and micropatterned cell cultures, as well as transcriptomic profiling, to investigate how variability in signalling pathway activity between human embryonic stem cell lines affects their differentiation efficiency towards definitive endoderm (DE). We show that endogenous suppression of WNT signalling in hPSCs at the onset of differentiation prevents the switch from self-renewal to DE specification. Gene expression profiling reveals that this inefficient switch is reflected in NANOG expression dynamics. Importantly, we demonstrate that higher WNT stimulation or inhibition of the PI3K/AKT signalling can overcome the DE commitment blockage. Our findings highlight that redirection of the activity of Activin/NODAL pathway by WNT signalling towards mediating DE fate specification is a vulnerable spot, as disruption of this process can result in poor hPSC specification towards DE.

ZIF-8 Modified Polypropylene Membrane: A Biomimetic Cell Culture Platform with a View to the Improvement of Guided Bone Regeneration

PURPOSE

Despite the significant advances in modeling of biomechanical aspects of cell microenvironment, it remains a major challenge to precisely mimic the physiological condition of the particular cell niche. Here, the metal-organic frameworks (MOFs) have been introduced as a feasible platform for multifactorial control of cell-substrate interaction, given the wide range of physical and mechanical properties of MOF materials and their structural flexibility.

RESULTS

In situ crystallization of zeolitic imidazolate framework-8 (ZIF-8) on the polydopamine (PDA)-modified membrane significantly raised surface energy, wettability, roughness, and stiffness of the substrate. This modulation led to an almost twofold increment in the primary attachment of dental pulp stem cells (DPSCs) compare to conventional plastic culture dishes. The findings indicate that polypropylene (PP) membrane modified by PDA/ZIF-8 coating effectively supports the growth and proliferation of DPSCs at a substantial rate. Further analysis also displayed the exaggerated multilineage differentiation of DPSCs with amplified level of autocrine cell fate determination signals, like BSP1, BMP2, PPARG, FABP4, ACAN, and COL2A. Notably, osteogenic markers were dramatically overexpressed (more than 100-folds rather than tissue culture plate) in response to biomechanical characteristics of the ZIF-8 layer.

CONCLUSION

Hence, surface modification of cell culture platforms with MOF nanostructures proposed as a powerful nanomedical approach for selectively guiding stem cells for tissue regeneration. In particular, PP/PDA/ZIF-8 membrane presented ideal characteristics for using as a barrier membrane for guided bone regeneration (GBR) in periodontal tissue engineering.

Microtechnology-based methods for organoid models

Innovations in biomaterials and stem cell technology have allowed for the emergence of novel three-dimensional (3D) tissue-like structures known as organoids and spheroids. As a result, compared to conventional 2D cell culture and animal models, these complex 3D structures have improved the accuracy and facilitated in vitro investigations of human diseases, human development, and personalized medical treatment. Due to the rapid progress of this field, numerous spheroid and organoid production methodologies have been published. However, many of the current spheroid and organoid production techniques are limited by complexity, throughput, and reproducibility. Microfabricated and microscale platforms (e.g., microfluidics and microprinting) have shown promise to address some of the current limitations in both organoid and spheroid generation. Microfabricated and microfluidic devices have been shown to improve nutrient delivery and exchange and have allowed for the arrayed production of size-controlled culture areas that yield more uniform organoids and spheroids for a higher throughput at a lower cost. In this review, we discuss the most recent production methods, challenges currently faced in organoid and spheroid production, and microfabricated and microfluidic applications for improving spheroid and organoid generation. Specifically, we focus on how microfabrication methods and devices such as lithography, microcontact printing, and microfluidic delivery systems can advance organoid and spheroid applications in medicine.

Predicting pattern formation in embryonic stem cells using a minimalist, agent-based probabilistic model

The mechanisms of pattern formation during embryonic development remain poorly understood. Embryonic stem cells in culture self-organise to form spatial patterns of gene expression upon geometrical confinement indicating that patterning is an emergent phenomenon that results from the many interactions between the cells. Here, we applied an agent-based modelling approach in order to identify plausible biological rules acting at the meso-scale within stem cell collectives that may explain spontaneous patterning. We tested different models involving differential motile behaviours with or without biases due to neighbour interactions. We introduced a new metric, termed stem cell aggregate pattern distance (SCAPD) to probabilistically assess the fitness of our models with empirical data. The best of our models improves fitness by 70% and 77% over the random models for a discoidal or an ellipsoidal stem cell confinement respectively. Collectively, our findings show that a parsimonious mechanism that involves differential motility is sufficient to explain the spontaneous patterning of the cells upon confinement. Our work also defines a region of the parameter space that is compatible with patterning. We hope that our approach will be applicable to many biological systems and will contribute towards facilitating progress by reducing the need for extensive and costly experiments.

Modulating endothelial adhesion and migration impacts stem cell therapies efficacy

BACKGROUND

Limited knowledge of stem cell therapies` mechanisms of action hampers their sustainable implementation into the clinic. Specifically, the interactions of transplanted stem cells with the host vasculature and its implications for their therapeutic efficacy are not elucidated. We tested whether adhesion receptors and chemokine receptors on stem cells can be functionally modulated, and consequently if such modulation may substantially affect therapeutically relevant stem cell interactions with the host endothelium.

METHODS

We investigated the effects of cationic molecule polyethylenimine (PEI) treatment with or without nanoparticles on the functions of adhesion receptors and chemokine receptors of human bone marrow-derived Mesenchymal Stem Cells (MSC). Analyses included MSC functions in vitro, as well as homing and therapeutic efficacy in rodent models of central nervous system´s pathologies in vivo.

FINDINGS

PEI treatment did not affect viability, immunomodulation or differentiation potential of MSC, but increased the CCR4 expression and functionally blocked their adhesion receptors, thus decreasing their adhesion capacity in vitro. Intravenously applied in a rat model of brain injury, the homing rate of PEI-MSC in the brain was highly increased with decreased numbers of adherent PEI-MSC in the lung vasculature. Moreover, in comparison to untreated MSC, PEI-MSC featured increased tumour directed migration in a mouse glioblastoma model, and superior therapeutic efficacy in a murine model of stroke.

INTERPRETATION

Balanced stem cell adhesion and migration in different parts of the vasculature and tissues together with the local microenvironment impacts their therapeutic efficacy.

FUNDING

Robert Bosch Stiftung, IZEPHA grant, EU grant 7 FP Health.

Direct Readout of Neural Stem Cell Transgenesis with an Integration-Coupled Gene Expression Switch

Stable genomic integration of exogenous transgenes is essential in neurodevelopmental and stem cell studies. Despite tools driving increasingly efficient genomic insertion with DNA vectors, transgenesis remains fundamentally hindered by the impossibility of distinguishing integrated from episomal transgenes. Here, we introduce an integration-coupled On genetic switch, iOn, which triggers gene expression upon incorporation into the host genome through transposition, thus enabling rapid and accurate identification of integration events following transfection with naked plasmids. In vitro, iOn permits rapid drug-free stable transgenesis of mouse and human pluripotent stem cells with multiple vectors. In vivo, we demonstrate faithful cell lineage tracing, assessment of regulatory elements, and mosaic analysis of gene function in somatic transgenesis experiments that reveal neural progenitor potentialities and interaction. These results establish iOn as a universally applicable strategy to accelerate and simplify genetic engineering in cultured systems and model organisms by conditioning transgene activation to genomic integration.

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A gene expression switch powered by genomic integration

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Accelerated readout of additive transgenesis with one or multiple vectors

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Faithful lineage tracing and mosaic analysis by somatic transfection

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Near-universal applicability in cultured cells and animal models

High-throughput intracellular biopsy of microRNAs for dissecting the temporal dynamics of cellular heterogeneity

The capability to analyze small RNAs responsible for post-transcriptional regulation of genes expression is essential for characterizing cellular phenotypes. Here, we describe an intracellular biopsy technique (inCell-Biopsy) for fast, multiplexed, and highly sensitive profiling of microRNAs (miRNAs). The technique uses an array of diamond nanoneedles that are functionalized with size-dependent RNA binding proteins, working as "fishing rods" to directly pull miRNAs out of cytoplasm while keeping the cells alive, thus enabling quasi-single-cell miRNA analysis. Each nanoneedle works as a reaction chamber for parallel in situ amplification, visualization, and quantification of miRNAs as low as femtomolar, which is sufficient to detect miRNAs of a single-copy intracellular abundance with specificity to single-nucleotide variation. Using inCell-Biopsy, we analyze the temporal miRNA transcriptome over the differentiation of embryonic stem cells (ESCs). The combinatorial miRNA expression patterns derived by inCell-Biopsy identify emerging cell subpopulations differentiated from ESCs and reveal the dynamic evolution of cellular heterogeneity.

Biomimetic aorta-gonad-Mesonephros-on-a-Chip to study human developmental hematopoiesis

A fundamental limitation in the derivation of hematopoietic stem and progenitor cells is the imprecise understanding of human developmental hematopoiesis. Herein we established a multilayer microfluidic Aorta-Gonad-Mesonephros (AGM)-on-a-chip to emulate developmental hematopoiesis from pluripotent stem cells. The device consists of two layers of microchannels separated by a semipermeable membrane, which allows the co-culture of human hemogenic endothelial (HE) cells and stromal cells in a physiological relevant spatial arrangement to replicate the structure of the AGM. HE cells derived from human induced pluripotent stem cells (hiPSCs) were cultured on a layer of mesenchymal stromal cells in the top channel while vascular endothelial cells were co-cultured on the bottom side of the membrane within the microfluidic device. We show that this AGM-on-a-chip efficiently derives endothelial-to-hematopoietic transition (EHT) from hiPSCs compared with regular suspension culture. The presence of mesenchymal stroma and endothelial cells renders functional HPCs in vitro. We propose that the AGM-on-a-chip could serve as a platform to dissect the cellular and molecular mechanisms of human developmental hematopoiesis.

Ultrasensitive and rapid quantification of rare tumorigenic stem cells in hPSC-derived cardiomyocyte populations

The ability to detect rare human pluripotent stem cells (hPSCs) in differentiated populations is critical for safeguarding the clinical translation of cell therapy, as these undifferentiated cells have the capacity to form teratomas in vivo. The detection of hPSCs must be performed using an approach compatible with traceable manufacturing of therapeutic cell products. Here, we report a novel microfluidic approach, stem cell quantitative cytometry (SCQC), for the quantification of rare hPSCs in hPSC-derived cardiomyocyte (CM) populations. This approach enables the ultrasensitive capture, profiling, and enumeration of trace levels of hPSCs labeled with magnetic nanoparticles in a low-cost, manufacturable microfluidic chip. We deploy SCQC to assess the tumorigenic risk of hPSC-derived CM populations in vivo. In addition, we isolate rare hPSCs from the differentiated populations using SCQC and characterize their pluripotency.

Muscle tissue engineering in fibrous gelatin: implications for meat analogs

Bioprocessing applications that derive meat products from animal cell cultures require food-safe culture substrates that support volumetric expansion and maturation of adherent muscle cells. Here we demonstrate scalable production of microfibrous gelatin that supports cultured adherent muscle cells derived from cow and rabbit. As gelatin is a natural component of meat, resulting from collagen denaturation during processing and cooking, our extruded gelatin microfibers recapitulated structural and biochemical features of natural muscle tissues. Using immersion rotary jet spinning, a dry-jet wet-spinning process, we produced gelatin fibers at high rates (~ 100 g/h, dry weight) and, depending on process conditions, we tuned fiber diameters between ~ 1.3 ± 0.1 μm (mean ± SEM) and 8.7 ± 1.4 μm (mean ± SEM), which are comparable to natural collagen fibers. To inhibit fiber degradation during cell culture, we crosslinked them either chemically or by co-spinning gelatin with a microbial crosslinking enzyme. To produce meat analogs, we cultured bovine aortic smooth muscle cells and rabbit skeletal muscle myoblasts in gelatin fiber scaffolds, then used immunohistochemical staining to verify that both cell types attached to gelatin fibers and proliferated in scaffold volumes. Short-length gelatin fibers promoted cell aggregation, whereas long fibers promoted aligned muscle tissue formation. Histology, scanning electron microscopy, and mechanical testing demonstrated that cultured muscle lacked the mature contractile architecture observed in natural muscle but recapitulated some of the structural and mechanical features measured in meat products.

Characterization and Analysis of Collective Cellular Behaviors in 3D Dextran Hydrogels with Homogenous and Clustered RGD Compositions

The interactions between substrate materials and cells usually play an important role in the hydrogel-based 3D cell cultures. However, the hydrogels that are usually used could not be parametrically regulated, especially for quantitatively regulating the spatial distribution of the adhesion sites for cells in 3D. Here, we employed the semisynthetic hydrogel consisting of maleimide-dextran, Arg-Gly-Asp (RGD) peptides, and cell degradable crosslinkers to biochemically characterize the evolutionary behaviors of NIH-3T3 fibroblasts and C2C12 cells in 3D. Moreover, by comparing the cell-adhesive efficacy of 3D dextran hydrogels with four different RGD clustering rates, we explored the underlying regulation law of C2C12 connections and 3T3 aggregations. The results showed that mal-dextran hydrogel could promise cells stable viability and continuous proliferation, and induce more self-organized multicellular structures relative to 2D culture. More importantly, we found that RGD-clustered mal-dextran hydrogel has the advantage of enhancing C2C12 cell elongation and the breadthwise-aggregated connection, and promoting the 3T3 cell aggregating degree compared to that with homogenous RGD. Further, the advantages of RGD clustering hydrogel could be amplified by appropriately reducing RGD concentration. Such RGD-composition controllable mal-dextran hydrogel can function as a regulator of the collective cellular behaviors, which provides useful information for quantitatively designing the tailored hydrogel system and exploiting advanced biomaterials.

High-throughput micropatterning platform reveals Nodal-dependent bisection of peri-gastrulation-associated versus preneurulation-associated fate patterning

In vitro models of postimplantation human development are valuable to the fields of regenerative medicine and developmental biology. Here, we report characterization of a robust in vitro platform that enabled high-content screening of multiple human pluripotent stem cell (hPSC) lines for their ability to undergo peri-gastrulation-like fate patterning upon bone morphogenetic protein 4 (BMP4) treatment of geometrically confined colonies and observed significant heterogeneity in their differentiation propensities along a gastrulation associable and neuralization associable axis. This cell line-associated heterogeneity was found to be attributable to endogenous Nodal expression, with up-regulation of Nodal correlated with expression of a gastrulation-associated gene profile, and Nodal down-regulation correlated with a preneurulation-associated gene profile expression. We harness this knowledge to establish a platform of preneurulation-like fate patterning in geometrically confined hPSC colonies in which fates arise because of a BMPs signalling gradient conveying positional information. Our work identifies a Nodal signalling-dependent switch in peri-gastrulation versus preneurulation-associated fate patterning in hPSC cells, provides a technology to robustly assay hPSC differentiation outcomes, and suggests conserved mechanisms of organized fate specification in differentiating epiblast and ectodermal tissues.

DNA Methylation-Based Regulation of Human Bone Marrow-Derived Mesenchymal Stem/Progenitor Cell Chondrogenic Differentiation

Stem cells have essential applications in in vitro tissue engineering or regenerative medicine. However, there is still a need to understand more deeply the mechanisms of stem cell differentiation and to optimize the methods to control stem cell function. In this study, we first investigated the activity of DNA methyltransferases (DNMTs) during chondrogenic differentiation of human bone marrow-derived mesenchymal stem/progenitor cells (hBMSCs) and found that DNMT3A and DNMT3B were markedly upregulated during hBMSC chondrogenic differentiation. In an attempt to understand the effect of DNMT3A and DNMT3B on the chondrogenic differentiation of hBMSCs, we transiently transfected the cells with expression vectors for the two enzymes. Interestingly, DNMT3A overexpression strongly enhanced the chondrogenesis of hBMSCs, by increasing the gene expression of the mature chondrocyte marker, collagen type II, more than 200-fold. Analysis of the methylation condition in the cells revealed that DNMT3A and DNMT3B methylated the promoter sequence of early stem cell markers, NANOG and POU5F1(OCT-4). Conversely, the suppression of chondrogenic differentiation and the increase in stem cell markers of hBMSCs were obtained by chemical stimulation with the demethylating agent, 5-azacitidine. Loss-of-function assays with siRNAs targeting DNMT3A also significantly suppressed the chondrogenic differentiation of hBMSCs. Together, these results not only show the critical roles of DNMTs in regulating the chondrogenic differentiation of hBMSCs, but also suggest that manipulation of DNMT activity can be important tools to enhance the differentiation of hBMSCs towards chondrogenesis for potential application in cartilage tissue engineering or cartilage regeneration.

Biliary Obstruction Promotes Multilineage Differentiation of Hepatic Stem Cells

Because of their high regenerative potential, stem cells are an ideal resource for development of therapies that replace injured tissue mass and restore function in patients with end-stage liver diseases. Using a rat model of bile duct ligation (BDL) and biliary fibrosis, we investigated cell engraftment, liver repopulation, and ectopic tissue formation after intrasplenic transplantation of epithelial stem/progenitor cells. Fetal liver cells were infused into the spleens of Fisher 344 rats with progressing biliary fibrosis induced by common BDL or rats without BDL. Cell delivery was well tolerated. After migration to the liver, donor-derived stem/progenitor cells engrafted, differentiated into hepatocytes and cholangiocytes, and formed large cell clusters at 2 months in BDL rats but not controls. Substantial numbers of donor cells were also detected at the splenic injection site where they generated hepatic and nonhepatic tissue. Transplanted cells differentiated into phenotypes other than hepato/cholangiocytic cells only in rats that underwent BDL. Quantitative reverse-transcription polymerase chain reaction analyses demonstrated marked up-regulation of tissue-specific genes of nonhepatic endodermal lineages (e.g., caudal type homeobox 2 [Cdx2], pancreatic and duodenal homeobox 1 [Pdx1], keratin 13 [CK-13]), confirmed by immunohistochemistry. Conclusion: BDL and its induced fibrosis promote liver repopulation by ectopically transplanted fetal liver-derived cells. These cell fractions contain multipotent stem cells that colonize the spleen of BDL rats and differentiate into multiple gastrointestinal tissues, including liver, pancreas, intestine, and esophagus. The splenic microenvironment, therefore, represents an ideal niche to assess the differentiation of these stem cells, while BDL provides a stimulus that induces their differentiation.