Human pluripotent stem cell-derived acinar/ductal organoids generate human pancreas upon orthotopic transplantation and allow disease modelling

Modeling neoplastic disease with spheroids and organoids

Cancer is a complex disease in which both genetic defects and microenvironmental components contribute to the development, progression, and metastasization of disease, representing major hurdles in the identification of more effective and safer treatment regimens for patients. Three-dimensional (3D) models are changing the paradigm of preclinical cancer research as they more closely resemble the complex tissue environment and architecture found in clinical tumors than in bidimensional (2D) cell cultures. Among 3D models, spheroids and organoids represent the most versatile and promising models in that they are capable of recapitulating the heterogeneity and pathophysiology of human cancers and of filling the gap between conventional 2D in vitro testing and animal models. Such 3D systems represent a powerful tool for studying cancer biology, enabling us to model the dynamic evolution of neoplastic disease from the early stages to metastatic dissemination and the interactions with the microenvironment. Spheroids and organoids have recently been used in the field of drug discovery and personalized medicine. The combined use of 3D models could potentially improve the robustness and reliability of preclinical research data, reducing the need for animal testing and favoring their transition to clinical practice. In this review, we summarize the recent advances in the use of these 3D systems for cancer modeling, focusing on their innovative translational applications, looking at future challenges, and comparing them with most widely used animal models.

Biomaterials and Culture Systems for Development of Organoid and Organ-on-a-Chip Models

The development of novel 3D tissue culture systems has enabled the in vitro study of in vivo processes, thereby overcoming many of the limitations of previous 2D tissue culture systems. Advances in biomaterials, including the discovery of novel synthetic polymers has allowed for the generation of physiologically relevant in vitro 3D culture models. A large number of 3D culture systems, aided by novel organ-on-a-chip and bioreactor technologies have been developed to improve reproducibility and scalability of in vitro organ models. The discovery of induced pluripotent stem cells (iPSCs) and the increasing number of protocols to generate iPSC-derived cell types has allowed for the generation of novel 3D models with minimal ethical limitations. The production of iPSC-derived 3D cultures has revolutionized the field of developmental biology and in particular, the study of fetal brain development. Furthermore, physiologically relevant 3D cultures generated from PSCs or adult stem cells (ASCs) have greatly advanced in vitro disease modelling and drug discovery. This review focuses on advances in 3D culture systems over the past years to model fetal development, disease pathology and support drug discovery in vitro, with a specific focus on the enabling role of biomaterials.

Whole Organ Engineering: Approaches, Challenges, and Future Directions

End-stage organ failure remains a leading cause of morbidity and mortality across the globe. The only curative treatment option currently available for patients diagnosed with end-stage organ failure is organ transplantation. However, due to a critical shortage of organs, only a fraction of these patients are able to receive a viable organ transplantation. Those patients fortunate enough to receive a transplant must then be subjected to a lifelong regimen of immunosuppressant drugs. The concept of whole organ engineering offers a promising alternative to organ transplantation that overcomes these limitations. Organ engineering is a discipline that merges developmental biology, anatomy, physiology, and cellular interactions with enabling technologies such as advanced biomaterials and biofabrication to create bioartificial organs that recapitulate native organs in vivo. There have been numerous developments in bioengineering of whole organs over the past two decades. Key technological advancements include (1) methods of whole organ decellularization and recellularization, (2) three-dimensional bioprinting, (3) advanced stem cell technologies, and (4) the ability to genetically modify tissues and cells. These advancements give hope that organ engineering will become a commercial reality in the next decade. In this review article, we describe the foundational principles of whole organ engineering, discuss key technological advances, and provide an overview of current limitations and future directions.

Diabetes through a 3D lens: organoid models

Diabetes is one of the most challenging health concerns facing society. Available drugs treat the symptoms but there is no cure. This presents an urgent need to better understand human diabetes in order to develop improved treatments or target remission. New disease models need to be developed that more accurately describe the pathology of diabetes. Organoid technology provides an opportunity to fill this knowledge gap. Organoids are 3D structures, established from pluripotent stem cells or adult stem/progenitor cells, that recapitulate key aspects of the in vivo tissues they mimic. In this review we briefly introduce organoids and their benefits; we focus on organoids generated from tissues important for glucose homeostasis and tissues associated with diabetic complications. We hope this review serves as a touchstone to demonstrate how organoid technology extends the research toolbox and can deliver a step change of discovery in the field of diabetes.

"Tissues in a Dish": A Review of Organoids in Plastic Surgery

Organoids are in vitro miniaturized organ models—or, colloquially, “organs in a dish.” These 3-dimensional, multicellular structures are classically derived from pluripotent or multipotent stem cells. When guided by tissue-specific molecular factors, these cells exhibit self-organizing abilities that allow them to accurately recapitulate the architecture and function of the organ of interest. Organoid technology is a rapidly expanding field that endows researchers with an unprecedented ability to recreate, study, and manipulate complex biologic processes in vitro. When compared with standard 2- and 3-dimensional culture systems, which rely on co-culturing pre-established cell types, organoids provide a more biomimetic model with which to study the intercellular interactions necessary for in vivo organ function and architecture. Organoids have the potential to impact all avenues of medicine, including those fields most relevant to plastic and reconstructive surgery such as wound healing, oncology, craniofacial reconstruction, and burn care. In addition to their ability to serve as a novel tool for studying human-specific disease, organoids may be used for tissue engineering with the goal of developing biomimetic soft-tissue substitutes, which would be especially valuable to the plastic surgeon. Although organoids hold great promise for the field of plastic surgery, technical challenges in creating vascularized, multilineage organoids must be overcome to allow for the integration of this technology in clinical practice. This review provides a brief history of the organoid, highlights its potential clinical applications, discusses certain limitations, and examines the impact that this technology may have on the field of plastic and reconstructive surgery.

The preclinical discovery and development of the combination of ivacaftor + tezacaftor used to treat cystic fibrosis

INTRODUCTION

Cystic Fibrosis (CF) is caused by mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. The most common mutation, F508del, induces protein misprocessing and loss of CFTR function. The discovery through in vitro studies of the CFTR correctors (i.e. lumacaftor, tezacaftor) that partially rescue the misprocessing of F508del-CFTR with the potentiator ivacaftor is promising in giving an unprecedented clinical benefit in affected patients.

AREAS COVERED

Online databases were searched using key phrases for CF and CFTR modulators. Tezacaftor-ivacaftor treatment has proved to be safer than lumacaftor-ivacaftor, although clinical efficacy is similar. Further clinical efficacy has ensued with the introduction of triple therapy, i.e. applying second-generation correctors, such as VX-569 and VX-445 (elexacaftor) to tezacaftor-ivacaftor. The triple combinations will herald the availability of etiologic therapies for patients for whom no CFTR modulators are currently applied (i.e. F508del/minimal function mutations) and enhance CFTR modulator therapy for patients homozygous for F508del.

EXPERT OPINION

CF patient-derived tissue models are being explored to determine donor-specific response to current approved and future novel CFTR modulators for F508del and other rare mutations. The discovery and validation of biomarkers of CFTR modulation will complement these studies in the long term and in real-life world.

Targeting the cytoskeleton to direct pancreatic differentiation of human pluripotent stem cells

Generation of pancreatic β cells from human pluripotent stem cells (hPSCs) holds promise as a cell replacement therapy for diabetes. In this study, we establish a link between the state of the actin cytoskeleton and the expression of pancreatic transcription factors that drive pancreatic lineage specification. Bulk and single-cell RNA sequencing demonstrated that different degrees of actin polymerization biased cells toward various endodermal lineages and that conditions favoring a polymerized cytoskeleton strongly inhibited neurogenin 3-induced endocrine differentiation. Using latrunculin A to depolymerize the cytoskeleton during endocrine induction, we developed a two-dimensional differentiation protocol for generating human pluripotent stem-cell-derived β (SC-β) cells with improved in vitro and in vivo function. SC-β cells differentiated from four hPSC lines exhibited first- and second-phase dynamic glucose-stimulated insulin secretion. Transplantation of islet-sized aggregates of these cells rapidly reversed severe preexisting diabetes in mice at a rate close to that of human islets and maintained normoglycemia for at least 9 months.

Multi-lineage Human iPSC-Derived Platforms for Disease Modeling and Drug Discovery

Human induced pluripotent stem cells (hiPSCs) provide a powerful platform for disease modeling and have unlocked new possibilities for understanding the mechanisms governing human biology, physiology, and genetics. However, hiPSC-derivatives have traditionally been utilized in two-dimensional monocultures, in contrast to the multi-systemic interactions that influence cells in the body. We will discuss recent advances in generating more complex hiPSC-based systems using three-dimensional organoids, tissue-engineering, microfluidic organ-chips, and humanized animal systems. While hiPSC differentiation still requires optimization, these next-generation multi-lineage technologies can augment the biomedical researcher's toolkit and enable more realistic models of human tissue function.

Standardized GMP-compliant scalable production of human pancreas organoids

Background

Organoids are three-dimensional in vitro-grown cell clusters that recapitulate key features of native organs. In regenerative medicine, organoid technology represents a promising approach for the replacement of severely damaged organs, such as the pancreas in patients with type 1 diabetes. Isolation human pancreas organoids (hPOs) in chemically defined serum-free culture media would be a major milestone for this approach.

Methods

Starting from discarded pancreatic tissues, we developed a large-scale process for obtaining clinically relevant quantities of undifferentiated organoids, obviating enzymatic digestion and operator-dependent pancreatic ducts picking steps. hPO identity was characterized by molecular and flow cytometry analysis.

Results

This work demonstrates that it is possible to obtain a large-scale production of organoids. We introduced some innovations in the isolation, expansion, and freezing of hPOs from five donors. First of all, the choice of the starting material (islet-depleted pancreas) that allows obtaining a high quantity of hPOs at low passages. On the other hand, we introduced mechanical dissociation and we eliminated the picking step to exclude the operator-depending steps, without affecting the success of the culture (100% success rate). Another important improvement was to replace R-spondin-1 (Rspo1) conditioned medium with Rspo1 recombinant molecule to obtain a well-defined composition of the expansion medium. Finally, we implemented a GMP-compliant freezing protocol. hPOs showed exponential growth with diameter and area that increased three- and eight-fold in 7 days, respectively. Immunophenotypic profile and gene expression analysis revealed that hPOs were composed of ductal (82.33 ± 8.37%), acinar (2.80 ± 1.25%) cells, and pancreatic progenitors (5.81 ± 2.65%).

Conclusion

This work represents a milestone for a GMP-compliance hPO production and, ultimately, their clinical application as a type 1 diabetes therapy.

Generation of homogeneous midbrain organoids with in vivo-like cellular composition facilitates neurotoxin-based Parkinson's disease modeling

Recent studies have demonstrated the generation of midbrain-like organoids (MOs) from human pluripotent stem cells. However, the low efficiency of MO generation and the relatively immature and heterogeneous structures of the MOs hinder the translation of these organoids from the bench to the clinic. Here we describe the robust generation of MOs with homogeneous distribution of midbrain dopaminergic (mDA) neurons. Our MOs contain not only mDA neurons but also other neuronal subtypes as well as functional glial cells, including astrocytes and oligodendrocytes. Furthermore, our MOs exhibit mDA neuron-specific cell death upon treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, indicating that MOs could be a proper human model system for studying the in vivo pathology of Parkinson's disease (PD). Our optimized conditions for producing homogeneous and mature MOs might provide an advanced patient-specific platform for in vitro disease modeling as well as for drug screening for PD.

Long-term expansion, genomic stability and in vivo safety of adult human pancreas organoids

BACKGROUND

Pancreatic organoid systems have recently been described for the in vitro culture of pancreatic ductal cells from mouse and human. Mouse pancreatic organoids exhibit unlimited expansion potential, while previously reported human pancreas organoid (hPO) cultures do not expand efficiently long-term in a chemically defined, serum-free medium. We sought to generate a 3D culture system for long-term expansion of human pancreas ductal cells as hPOs to serve as the basis for studies of human pancreas ductal epithelium, exocrine pancreatic diseases and the development of a genomically stable replacement cell therapy for diabetes mellitus.

RESULTS

Our chemically defined, serum-free, human pancreas organoid culture medium supports the generation and expansion of hPOs with high efficiency from both fresh and cryopreserved primary tissue. hPOs can be expanded from a single cell, enabling their genetic manipulation and generation of clonal cultures. hPOs expanded for months in vitro maintain their ductal morphology, biomarker expression and chromosomal integrity. Xenografts of hPOs survive long-term in vivo when transplanted into the pancreas of immunodeficient mice. Notably, mouse orthotopic transplants show no signs of tumorigenicity. Crucially, our medium also supports the establishment and expansion of hPOs in a chemically defined, modifiable and scalable, biomimetic hydrogel.

CONCLUSIONS

hPOs can be expanded long-term, from both fresh and cryopreserved human pancreas tissue in a chemically defined, serum-free medium with no detectable tumorigenicity. hPOs can be clonally expanded, genetically manipulated and are amenable to culture in a chemically defined hydrogel. hPOs therefore represent an abundant source of pancreas ductal cells that retain the characteristics of the tissue-of-origin, which opens up avenues for modelling diseases of the ductal epithelium and increasing understanding of human pancreas exocrine biology as well as for potentially producing insulin-secreting cells for the treatment of diabetes.

Organoids: An invaluable tool in pharmacology

Advances in stem cell cultures and human-induced pluripotent stem cells have inculcated interests in a rapidly evolving concept – ”organoids.” These are three-dimensional (3D) structures mimicking some of the phenomena of the real organs at anatomical, multicellular, and functional levels in vitro. Organoids have been proven to be better than two-dimensional cell culture in replicating the functionality, architectural, and geometrical features of tissues in vivo. Recent advancements have led to the generation of models for organ development and disease, finding applications in the drug discovery, screening of novel compounds, and personalized medicine. Since organoids follow the same natural pathway as the normal tissue or pathology, they can be used to study the expression of various genotypes and phenotypic variations across different species. In the light of these advancements, organoids are now being merged with bioengineering to come up with even better and reliable models to predict the disease progression and effectiveness of precision medicines, few of its important applications. This article discusses the various aspects of this emerging concept along with its uses, both in the present times and near future, with a special focus on pharmacological applications.

Mouse pancreatic ductal organoid culture as a relevant model to study exocrine pancreatic ion secretion

Pancreatic exocrine secretory processes are challenging to investigate on primary epithelial cells. Pancreatic organoid cultures may help to overcome shortcomings of the current models, however the ion secretory processes in pancreatic organoids-and therefore their physiological relevance or their utility in disease modeling-are not known. To answer these questions, we provide side-by-side comparison of gene expression, morphology, and function of epithelial cells in primary isolated pancreatic ducts and organoids. We used mouse pancreatic ductal fragments for experiments or were grown in Matrigel to obtain organoid cultures. Using PCR analysis we showed that gene expression of ion channels and transporters remarkably overlap in primary ductal cells and organoids. Morphological analysis with scanning electron microscopy revealed that pancreatic organoids form polarized monolayers with brush border on the apical membrane. Whereas the expression and localization of key proteins involved in ductal secretion (cystic fibrosis transmembrane conductance regulator, Na+/H+ exchanger 1 and electrogenic Na+/HCO3- cotransporter 1) are equivalent to the primary ductal fragments. Measurements of intracellular pH and Cl- levels revealed no significant difference in the activities of the apical Cl-/HCO3- exchange, or in the basolateral Na+ dependent HCO3- uptake. In summary we found that ion transport activities in the mouse pancreatic organoids are remarkably similar to those observed in freshly isolated primary ductal fragments. These results suggest that organoids can be suitable and robust model to study pancreatic ductal epithelial ion transport in health and diseases and facilitate drug development for secretory pancreatic disorders like cystic fibrosis, or chronic pancreatitis.

Induced pluripotent stem cells for therapy personalization in pediatric patients: Focus on drug-induced adverse events

Adverse drug reactions (ADRs) are major clinical problems, particularly in special populations such as pediatric patients. Indeed, ADRs may be caused by a plethora of different drugs leading, in some cases, to hospitalization, disability or even death. In addition, pediatric patients may respond differently to drugs with respect to adults and may be prone to developing different kinds of ADRs, leading, in some cases, to more severe consequences. To improve the comprehension, and thus the prevention, of ADRs, the set-up of sensitive and personalized assays is urgently needed. Important progress is represented by the possibility of setting up groundbreaking patient-specific assays. This goal has been powerfully achieved using induced pluripotent stem cells (iPSCs). Due to their genetic and physiological species-specific differences and their ability to be differentiated ideally into all tissues of the human body, this model may be accurate in predicting drug toxicity, especially when this toxicity is related to individual genetic differences. This review is an up-to-date summary of the employment of iPSCs as a model to study ADRs, with particular attention to drugs used in the pediatric field. We especially focused on the intestinal, hepatic, pancreatic, renal, cardiac, and neuronal levels, also discussing progress in organoids creation. The latter are three-dimensional in vitro culture systems derived from pluripotent or adult stem cells simulating the architecture and functionality of native organs such as the intestine, liver, pancreas, kidney, heart, and brain. Based on the existing knowledge, these models are powerful and promising tools in multiple clinical applications including toxicity screening, disease modeling, personalized and regenerative medicine.

Establishment of a high-resolution 3D modeling system for studying pancreatic epithelial cell biology in vitro

OBJECTIVE

Translation of basic research from bench-to-bedside relies on a better understanding of similarities and differences between mouse and human cell biology, tissue formation, and organogenesis. Thus, establishing ex vivo modeling systems of mouse and human pancreas development will help not only to understand evolutionary conserved mechanisms of differentiation and morphogenesis but also to understand pathomechanisms of disease and design strategies for tissue engineering.

METHODS

Here, we established a simple and reproducible Matrigel-based three-dimensional (3D) cyst culture model system of mouse and human pancreatic progenitors (PPs) to study pancreatic epithelialization and endocrinogenesis ex vivo. In addition, we reanalyzed previously reported single-cell RNA sequencing (scRNA-seq) of mouse and human pancreatic lineages to obtain a comprehensive picture of differential expression of key transcription factors (TFs), cell-cell adhesion molecules and cell polarity components in PPs during endocrinogenesis.

RESULTS

We generated mouse and human polarized pancreatic epithelial cysts derived from PPs. This system allowed to monitor establishment of pancreatic epithelial polarity and lumen formation in cellular and sub-cellular resolution in a dynamic time-resolved fashion. Furthermore, both mouse and human pancreatic cysts were able to differentiate towards the endocrine fate. This differentiation system together with scRNA-seq analysis revealed how apical-basal polarity and tight and adherens junctions change during endocrine differentiation.

CONCLUSIONS

We have established a simple 3D pancreatic cyst culture system that allows to tempo-spatial resolve cellular and subcellular processes on the mechanistical level, which is otherwise not possible in vivo.

Intestinal organoids for Cystic Fibrosis research

Significant progress has been made in the development of CFTR modulator therapy; however, current CFTR modulator therapies are only available for a minority of the CF-patient population. Additionally, heterogeneity in in vivo modulator response has been reported among individuals carrying homozygous F508del-CFTR, adding to the desire for an optimal prediction of response-to-therapy on an individual level. In the last decade, a lot of progress has been made in the development of primary cell cultures into 3D patient-derived disease models. The advantage of these models is that the endogenous CFTR function is affected by the patient's mutation as well as other genetic or environmental factors. In this review we focus on intestinal organoids as in vitro model for CF, enabling for CF disease classification, drug development and treatment optimization in a personalized manner, taking into account rare CFTR mutations and clinical heterogeneity among individuals with CF.

Human stem cell models: lessons for pancreatic development and disease

A comprehensive understanding of mechanisms that underlie the development and function of human cells requires human cell models. For the pancreatic lineage, protocols have been developed to differentiate human pluripotent stem cells (hPSCs) into pancreatic endocrine and exocrine cells through intermediates resembling in vivo development. In recent years, this differentiation system has been employed to decipher mechanisms of pancreatic development, congenital defects of the pancreas, as well as genetic forms of diabetes and exocrine diseases. In this review, we summarize recent insights gained from studies of pancreatic hPSC models. We discuss how genome-scale analyses of the differentiation system have helped elucidate roles of chromatin state, transcription factors, and noncoding RNAs in pancreatic development and how the analysis of cells with disease-relevant mutations has provided insight into the molecular underpinnings of genetically determined diseases of the pancreas.

Towards manufacturing of human organoids

Organoids are 3D miniature versions of organs produced from stem cells derived from either patient or healthy individuals in vitro that recapitulate the actual organ. Organoid technology has ensured an alternative to pre-clinical drug testing as well as being currently used for "personalized medicine" to modulate the treatment as they are uniquely identical to each patient's genetic makeup. Researchers have succeeded in producing different types of organoids and have demonstrated their efficient application in various fields such as disease modeling, pathogenesis, drug screening and regenerative medicine. There are several protocols for fabricating organoids in vitro. In this comprehensive review, we focus on key methods of producing organoids and manufacturing considerations for each of them while providing insights on the advantages, applications and challenges of these methods. We also discuss pertinent challenges faced during organoid manufacturing and various bioengineering approaches that can improve the organoid manufacturing process. Organoids size, number and the reproducibility of the fabrication processes are touched upon. The major factors which are involved in organoids manufacturing such as spatio-temporal controls, scaffold designs/types, cell culture parameters and vascularization have been highlighted.

Human Serum Albumin Is an Essential Component of the Host Defense Mechanism Against Clostridium difficile Intoxication

Background

The pathogenic effects of Clostridium difficile are primarily attributable to the production of the large protein toxins (C difficile toxins [Tcd]) A (TcdA) and B (TcdB). These toxins monoglucosylate Rho GTPases in the cytosol of host cells, causing destruction of the actin cytoskeleton with cytotoxic effects. Low human serum albumin (HSA) levels indicate a higher risk of acquiring and developing a severe C difficile infection (CDI) and are associated with recurrent and fatal disease.

Methods

We used a combined approach based on docking simulation and biochemical analyses that were performed in vitro on purified proteins and in human epithelial colorectal adenocarcinoma cells (Caco-2), and in vivo on stem cell-derived human intestinal organoids and zebrafish embryos.

Results

Our results show that HSA specifically binds via its domain II to TcdA and TcdB and thereby induces their autoproteolytic cleavage at physiological concentrations. This process impairs toxin internalization into the host cells and reduces the toxin-dependent glucosylation of Rho proteins.

Conclusions

Our data provide evidence for a specific HSA-dependent self-defense mechanism against C difficile toxins and provide an explanation for the clinical correlation between CDI severity and hypoalbuminemia.

Gut organoids: mini-tissues in culture to study intestinal physiology and disease

In vitro, cell cultures are essential tools in the study of intestinal function and disease. For the past few decades, monolayer cellular cultures, such as cancer cell lines or immortalized cell lines, have been widely applied in gastrointestinal research. Recently, the development of three-dimensional cultures known as organoids has permitted the growth of normal crypt-villus units that recapitulate many aspects of intestinal physiology. Organoid culturing has also been applied to study gastrointestinal diseases, intestinal-microbe interactions, and colorectal cancer. These models are amenable to CRISPR gene editing and drug treatments, including high-throughput small-molecule testing. Three-dimensional intestinal cultures have been transplanted into mice to develop versatile in vivo models of intestinal disease, particularly cancer. Limitations of currently available organoid models include cost and challenges in modeling nonepithelial intestinal cells, such as immune cells and the microbiota. Here, we describe the development of organoid models of intestinal biology and the applications of organoids for study of the pathophysiology of intestinal diseases and cancer.

Management of pancreatic exocrine insufficiency

PURPOSE OF REVIEW

Pancreatic exocrine insufficiency (PEI) is one of the well known causes of malabsorption syndrome. An insufficient secretion of pancreatic enzymes and bicarbonate secondary to different pancreatic diseases and upper gastrointestinal and pancreatic surgery leads to maldigestion and malabsorption of nutrients. Patients with PEI may present with symptoms of malabsorption and different nutritional deficiencies. Recent data support the high clinical relevance of PEI and its treatment.

RECENT FINDINGS

Deficiencies of fat-soluble vitamins, proteins, micronutrients and antioxidants in patients with PEI are associated not only with an increased risk of osteoporosis and sarcopenia but also of cardiovascular events and mortality. Pancreatic enzyme replacement therapy (PERT) allows improving fat and protein digestion, relieving maldigestion-related symptoms, normalizing the nutritional status, and improving quality of life of patients with PEI. Recent data support the efficacy of PERT on survival in patients with pancreatic cancer. Dose of oral pancreatic enzymes should be adequate to normalize the nutritional status of PEI patients.

SUMMARY

Increasing evidence supports the relevance of PEI management by dietary advice and appropriate PERT. Well designed and powered randomized, placebo-controlled clinical trials are needed to further evaluate the clinical impact of PEI and its treatment in clinical practice.

Engineering tissue-specific blood vessels

Vascular diversity among organs has recently become widely recognized. Several studies using mouse and human fetal tissues revealed distinct characteristics of organ-specific vasculature in molecular and functional levels. Thorough understanding of vascular heterogeneities in human adult tissues is significant for developing novel strategies for targeted drug delivery and tissue regeneration. Recent advancements in microfabrication techniques, biomaterials, and differentiation protocols allowed for incorporation of microvasculature into engineered organs. Such vascularized organ models represent physiologically relevant platforms that may offer innovative tools for dissecting the effects of the organ microenvironment on vascular development and expand our present knowledge on organ-specific human vasculature. In this article, we provide an overview of the current structural and molecular evidence on microvascular diversity, bioengineering methods used to recapitulate the microenvironmental cues, and recent vascularized three-dimensional organ models from the perspective of tissue-specific vasculature.

The Antibiotic Bacitracin Protects Human Intestinal Epithelial Cells and Stem Cell-Derived Intestinal Organoids from Clostridium difficile Toxin TcdB

Bacitracin is an established antibiotic for local application and inhibits the cell wall synthesis of Gram-positive bacteria. Recently, we discovered a completely different mode of action of bacitracin and reported that this drug protects human cells from intoxication by a variety of medically relevant bacterial protein toxins including CDT, the binary actin ADP-ribosylating toxin of Clostridium (C.) difficile. Bacitracin prevents the transport of CDT into the cytosol of target cells, most likely by inhibiting the transport function of the binding subunit of this toxin. Here, we tested the effect of bacitracin towards TcdB, a major virulence factor of C. difficile contributing to severe C. difficile-associated diseases (CDAD) including pseudomembranous colitis. Bacitracin protected stem cell-derived human intestinal organoids as well as human gut epithelial cells from intoxication with TcdB. Moreover, it prevented the TcdB-induced disruption of epithelia formed by gut epithelium cells in vitro and maintained the barrier function as detected by measuring transepithelial electrical resistance (TEER). In the presence of bacitracin, TcdB was not able reach its substrate Rac1 in the cytosol of human epithelial cells, most likely because its pH-dependent transport across cell membranes into the cytosol is decreased by bacitracin. In conclusion, in addition to its direct antibiotic activity against C. difficile and its inhibitory effect towards the toxin CDT, bacitracin neutralizes the exotoxin TcdB of this important pathogenic bacterium.

Recent advances in the applications of iPSC technology

Pluripotent stems cells (PSCs) can be expanded indefinitely and differentiated into almost any organ-specific cell type. This has enabled the generation of disease relevant tissues from patients in scalable quantities. iPSC-derived organs and organoids are currently being evaluated both in regenerative therapy which are proceeding towards clinical trials, and for disease modeling, which are facilitating drug screening efforts for discovery of novel therapeutics. Here we will review the current efforts and advances in iPSC technology and its subsequent applications and provide a brief commentary on future outlook of this promising technology.

TGF-β signaling promotes tube-structure-forming growth in pancreatic duct adenocarcinoma

Tube-forming growth is an essential histological feature of pancreatic duct adenocarcinoma (PDAC) and of the pancreatic duct epithelium; nevertheless, the nature of the signals that start to form the tubular structures remains unknown. Here, we showed the clonal growth of PDAC cell lines in a three-dimensional (3D) culture experiment that modeled the clonal growth of PDAC. At the beginning of this study, we isolated the sphere- and tube-forming clones from established mouse pancreatic cancer cell lines via limiting dilution culture using collagen gel. Compared with cells in spherical structures, the cells in the formed tubes exhibited a lower CK19 expression in 3D culture and in the tumor that grew in the abdominal cavity of nude mice. Conversely, the expression of the transforming growth factor β (TGF-β)-signaling target mRNAs was higher in the formed tube vs the spherical structures, suggesting that TGF-β signaling is more active in the tube-forming process than the sphere-forming process. Treatment of sphere-forming clones with TGF-β1 induced tube-forming growth, upregulated the TGF-β-signaling target mRNAs, and yielded electron microscopic findings of a fading epithelial phenotype. In contrast, the elimination of TGF-β-signaling activation by treatment with inhibitors diminished the tube-forming growth and suppressed the expression of the TGF-β-signaling target mRNAs. Moreover, upregulation of the Fn1, Mmp2, and Snai1 mRNAs, which are hallmarks of tube-forming growth in PDAC, was demonstrated in a mouse model of carcinogenesis showing rapid progression because of the aggressive invasion of tube-forming cancer. Our study suggests that the tube-forming growth of PDAC relies on the activation of TGF-β signaling and highlights the importance of the formation of tube structures.

Drug screening for human genetic diseases using iPSC models

Induced pluripotent stem cells (iPSCs) enable the generation of previously unattainable, scalable quantities of disease-relevant tissues from patients suffering from essentially any genetic disorder. This cellular material has proven instrumental for drug screening efforts on these disorders, and has facilitated the identification of novel therapeutics for patients. Here we will review the foundational technologies that have enabled iPSCs, the power and limitations of iPSC-based compound screens along with screening guidelines, and recent examples of screening efforts. Additionally we will provide a brief commentary on the future scientific roadmap using pluripotent- and 3D organoid-based, combinatorial approaches.

Delivery of pancreatic digestive enzymes into the gastrointestinal tract by pancreatic exocrine tissue transplant

Exocrine pancreatic insufficiency, caused by disease-induced loss of pancreatic exocrine cells, may be treated through regenerative stem cell technologies that facilitate the production of pancreatic exocrine cells from induced pluripotent stem cells (iPSCs). However, delivering the digestive enzymes produced in the transplanted cells to the gastrointestinal tract remains a challenge. To generate an allogenic transplantation rat model, minced pancreas was transplanted into the gastric submucosal space with ablation of muscularis mucosa. In the allogenic transplantation, transplanted pancreatic cells were engrafted. Elevated amylase was detected in gastric juice, while transplanted cells disappeared through auto-digestion when the muscularis mucosa was not eliminated. Human iPSCs were differentiated into pancreatic exocrine cells by stage-specific treatment with growth factors and chemical compounds, and the differentiated pancreatic cells were implanted into the gastric submucosal space of nude rats. The transplanted cells were engrafted, and amylase was detected in the gastric juice in some cases. These findings suggest that transplantation of pancreatic exocrine cells into the gastric submucosal space with muscularis mucosa elimination will contribute to a regenerative approach for pancreatic exocrine insufficiency.

Kidney organoids in translational medicine: Disease modeling and regenerative medicine

The kidney is one of the most complex organs composed of multiple cell types, functioning to maintain homeostasis by means of the filtering of metabolic wastes, balancing of blood electrolytes, and adjustment of blood pressure. Recent advances in 3D culture technologies in vitro enabled the generation of "organoids" which mimic the structure and function of in vivo organs. Organoid technology has allowed for new insights into human organ development and human pathophysiology, with great potential for translational research. Increasing evidence shows that kidney organoids are a useful platform for disease modeling of genetic kidney diseases when derived from genetic patient iPSCs and/or CRISPR-mutated stem cells. Although single cell RNA-seq studies highlight the technical difficulties underlying kidney organoid generation reproducibility and variation in differentiation protocols, kidney organoids still hold great potential to understand kidney pathophysiology as applied to kidney injury and fibrosis. In this review, we summarize various studies of kidney organoids, disease modeling, genome-editing, and bioengineering, and additionally discuss the potential of and current challenges to kidney organoid research.

Accelerating the Drug Delivery Pipeline for Acute and Chronic Pancreatitis: Summary of the Working Group on Drug Development and Trials in Recurrent Acute Pancreatitis at the National Institute of Diabetes and Digestive and Kidney Diseases Workshop

Recurrent acute pancreatitis (RAP) is a complex clinical syndrome with significant morbidity, unpredictable outcomes, and limited treatment options. The National Institute of Diabetes and Digestive and Kidney Disease sponsored a workshop on July 25, 2018, in Pittsburgh, Pennsylvania, to address research gaps impeding development of effective therapies for pancreatitis. The RAP working group identified challenges to clinical progress using existing definitions, risk assessment, diagnostic and severity criteria, disease trajectories, outcomes, and research methods. Recurrent acute pancreatitis includes all the risk of acute pancreatitis and often progresses to chronic pancreatitis with variable complications of chronic pain, exocrine insufficiency, diabetes, and pancreatic cancer. However, the great variability among individuals with RAP requires better precision in defining the risks, individual episodes, as well as their frequency, pathogenic pathways, and specific outcome measures for each of the systems affected by pancreatic inflammation. Because of disease complexity, few patients are similar enough for traditional studies and methods to conduct clinical trials with small sample sizes are required. The need for genetic testing, biomarker development, and better imaging methods was highlighted. Adaptive and N-of-one study designs, better endpoints, and outcome measures including patient-reported outcomes should considered early in developing future therapeutic trial design and include all stakeholders.

Three-Dimensional Organoids in Cancer Research: The Search for the Holy Grail of Preclinical Cancer Modeling

Most solid tumors become therapy resistant and will relapse, with no durable treatment option available. One major impediment to our understanding of cancer biology and finding innovative approaches to cancer treatment stems from the lack of better preclinical tumor models that address and explain tumor heterogeneity and person-to-person differences in therapeutic and toxic responses. Past cancer research has been driven by inadequate in vitro assays utilizing two-dimensional monolayers of cancer cells and animal models. Additionally, animal models do not truly mimic the original human tumor, are time consuming, and usually costly. New preclinical models are needed for innovation in cancer translational research. Hence, it is time to welcome the three-dimensional (3D) organoids: self-organizing cells grown in 3D culture systems mimicking the parent tissues from which the primary cells originate. The 3D organoids offer deeper insights into the crucial cellular processes in tissue and organ formation and pathological processes. Generation of near-perfect physiological microenvironments allow 3D organoids to couple with gene editing tools, such as the clustered regularly interspersed short palindromic repeat (CRISPR)/CRISPR-associated 9 and the transcription activator-like effector nucleases to model human diseases, offering distinct advantages over current models. We explain in this expert review that through recapitulating patients' normal and tumor tissues, organoid technology can markedly advance personalized medicine and help reveal once hidden aspects of cancers. The use of defined tissue- or organ-specific matrices, among other factors, will likely allow organoid technology to realize its potential in innovating many fields of life sciences.

Modelling the endocrine pancreas in health and disease

Diabetes mellitus is a multifactorial disease affecting increasing numbers of patients worldwide. Progression to insulin-dependent diabetes mellitus is characterized by the loss or dysfunction of pancreatic β-cells, but the pathomechanisms underlying β-cell failure in type 1 diabetes mellitus and type 2 diabetes mellitus are still poorly defined. Regeneration of β-cell mass from residual islet cells or replacement by β-like cells derived from stem cells holds great promise to stop or reverse disease progression. However, the development of new treatment options is hampered by our limited understanding of human pancreas organogenesis due to the restricted access to primary tissues. Therefore, the challenge is to translate results obtained from preclinical model systems to humans, which requires comparative modelling of β-cell biology in health and disease. Here, we discuss diverse modelling systems across different species that provide spatial and temporal resolution of cellular and molecular mechanisms to understand the evolutionary conserved genotype-phenotype relationship and translate them to humans. In addition, we summarize the latest knowledge on organoids, stem cell differentiation platforms, primary micro-islets and pseudo-islets, bioengineering and microfluidic systems for studying human pancreas development and homeostasis ex vivo. These new modelling systems and platforms have opened novel avenues for exploring the developmental trajectory, physiology, biology and pathology of the human pancreas.

Pancreatic Progenitors and Organoids as a Prerequisite to Model Pancreatic Diseases and Cancer

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) are characterized by their unique capacity to stepwise differentiate towards any particular cell type in an adult organism. Pluripotent stem cells provide a beneficial platform to model hereditary diseases and even cancer development. While the incidence of pancreatic diseases such as diabetes and pancreatitis is increasing, the understanding of the underlying pathogenesis of particular diseases remains limited. Only a few recent publications have contributed to the characterization of human pancreatic development in the fetal stage. Hence, most knowledge of pancreatic specification is based on murine embryology. Optimizing and understanding current in vitro protocols for pancreatic differentiation of ESCs and iPSCs constitutes a prerequisite to generate functional pancreatic cells for better disease modeling and drug discovery. Moreover, human pancreatic organoids derived from pluripotent stem cells, organ-restricted stem cells, and tumor samples provide a powerful technology to model carcinogenesis and hereditary diseases independent of genetically engineered mouse models. Herein, we summarize recent advances in directed differentiation of pancreatic organoids comprising endocrine cell types. Beyond that, we illustrate up-and-coming applications for organoid-based platforms.

Stem cell-based retina models

From the early days of cell biological research, the eye-especially the retina-has evoked broad interest among scientists. The retina has since been thoroughly investigated and numerous models have been exploited to shed light on its development, morphology, and function. Apart from various animal models and human clinical and anatomical research, stem cell-based models of animal and human cells of origin have entered the field, especially during the last decade. Despite the observation that the retina of different species comprises endogenous stem cells, most stem cell-related research in the human retina is now based on pluripotent stem cell models. Herein, systems of two-dimensional (2D) cultures and co-cultures of distinctly differentiated retinal subtypes revealed a variety of cellular aspects but have in many aspects been replaced by three-dimensional (3D) structures-the so-called retinal organoids. These organoids not only contain all major retinal cell subtypes compared to the physiological situation, but also show a distinct layering in close proximity to the in vivo morphology. Nevertheless, all these models have inherent advantages and disadvantages, which are expounded and summarized in this review. Finally, we discuss current application aspects of stem cell-based retina models and the specific promises they hold for the future.

Updates in Pediatric Pancreatology: Proceedings of the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition Frontiers in Pediatric Pancreatology Symposium

The Pancreas Committee of the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition aims to promote awareness of pediatric pancreatic diseases, support clinical and basic science research in the field, educate pediatric gastroenterologists, and advocate on behalf of pediatric patients with pancreatic disorders. At the 2017 Annual North American Society for Pediatric Gastroenterology, Hepatology and Nutrition meeting, the Pancreas Committee held a full day symposium on pediatric pancreatic diseases, entitled, "Frontiers in Pediatric Pancreatology." The symposium served as a timely and novel academic meeting that brought together individuals with a vested interest in the care of children with pancreatic disorders. The objective of this day-long course was to update practicing gastroenterologists on the latest advances in research, management algorithms, endoscopic therapies, radiographic resources, surgical approaches, and novel drug therapies targeted to pediatric pancreatitis. Presentations were divided into 4 modules: diagnosis, risk factors, and natural history of pancreatitis; pancreatic imaging and exocrine function; management of pancreatitis; and new frontiers in pediatric pancreatitis research. The course fostered a unique ecosystem for interdisciplinary collaboration, in addition to promoting discussion and stimulating new research hypotheses regarding pediatric pancreatic disorders. Oral presentations by experts in various fields of pancreatology led to thought-provoking discussion; in addition, a meet-the-professor luncheon stimulated critical evaluation of current research in pediatric pancreatic diseases, highlighting knowledge gaps and future research endeavors. The current report summarizes the major learning points from this novel symposium focusing on the growing demographic of pediatric pancreatic diseases.

Generation of Pancreatic Ductal Organoids and Whole-Mount Immunostaining of Intact Organoids

Traditionally, studies of cells and tissues have been performed on isolated primary cells or immortalized cell lines by culturing them in 2D culture dishes or flasks. However, a caveat regarding 2D culture is that the cells poorly recapitulate their in vivo counterparts, mainly due to a lack of 3D cell-cell and cell-extracellular matrix interactions. In recent years, the development of in vitro organoids as 3D culture has gained substantial attention as a model to study different tissues. In adults, pancreatic ductal cells are considered as a source of stem or progenitor cells, so developing new methods to study ductal cells would be useful. Here, we provide a protocol to isolate mouse pancreatic ductal cells and a cost-effective protocol to generate 3D organoid structures from such ductal cells. Additionally, we have devised a protocol for immunostaining of intact whole organoids without sectioning. © 2018 by John Wiley & Sons, Inc.

Organoid technology in disease modelling, drug development, personalized treatment and regeneration medicine

Organoid technology bridges the gap between conventional two-dimensional cell line culture and in vivo models. The near-physiological technology can virtually recapitulates organ development and human diseases, such as infectious diseases, genetic abnormality and even cancers. In addition, organoids can more accurately predict drug responses, and serve as an excellent platform for drug development, including efficacy evaluation, toxicity testing and pharmacokinetics analysis. Furthermore, organoids can also be exploited to explore the possible optimized treatment strategies for each individual patient. Besides, organoid technology is a promising strategy for regeneration medicine and transplantation use, which can overcome the deficiency in the supply of healthy donor tissues and inherent immunological rejection through establishing isogenic organoids from minuscule amounts of patient biopsies. Collectively, organoids hold enormous potential for clinical applications and bring basic research closer to clinical practice. In this review, we described common organoid lines, summarized the potential clinical applications, and outlined the current limitations.

Perspective: The promise of multi-cellular engineered living systems

Recent technological breakthroughs in our ability to derive and differentiate induced pluripotent stem cells, organoid biology, organ-on-chip assays, and 3-D bioprinting have all contributed to a heightened interest in the design, assembly, and manufacture of living systems with a broad range of potential uses. This white paper summarizes the state of the emerging field of "multi-cellular engineered living systems," which are composed of interacting cell populations. Recent accomplishments are described, focusing on current and potential applications, as well as barriers to future advances, and the outlook for longer term benefits and potential ethical issues that need to be considered.

Maximizing the Translational Yield of mRNA Therapeutics by Minimizing 5'-UTRs

The 5'-untranslated region (5'-UTR) of mRNA contains structural elements, which are recognized by cell-specific RNA-binding proteins, thereby affecting the translation of the molecule. The activation of an innate immune response upon transfection of mRNA into cells is reduced when the mRNA comprises chemically modified nucleotides, putatively by altering the secondary structure of the molecule. Such alteration in the 5'-UTR in turn may affect the functionality of mRNA. In this study, we report on the impact of seven synthetic minimalistic 5'-UTR sequences on the translation of luciferase-encoding unmodified and different chemically modified mRNAs upon transfection in cell culture and in vivo. One minimalistic 5'-UTR, consisting of 14 nucleotides combining the T7 promoter with a Kozak consensus sequence, yielded similar or even higher expression than a 37 nucleotides human alpha-globin 5'-UTR containing mRNA in HepG2 and A549 cells. Furthermore, also the kind of modified nucleotides used in in vitro transcription, affected mRNA translation when using different translation regulators (Kozak vs. translation initiator of short UTRs). The in vitro data were confirmed by bioluminescence imaging of expression in mouse livers, 6 h postintravenous injection of a lipidoid nanoparticle-formulated RNA in female Balb/c mice. Luciferase measurements from liver and spleen showed that minimal 5'-UTRs (3 and 7) were either equally effective or better than human alpha-globin 5'-UTR. These findings were confirmed with a human erythropoietin (hEPO)-encoding mRNA. Significantly, higher levels of hEPO could be quantified in supernatants from A549 cells transfected with minimal 5'-UTR7 containing RNA when compared to commonly used benchmarks 5'-UTRs. Our results demonstrate the superior potential of synthetic minimalistic 5'-UTRs for use in transcript therapies.

Importance of organoids for personalized medicine

The establishment of organoid culture systems represents a milestone on the route toward successful personalized medicine. This mini review provides an update on the current status of organoid technology and summarizes their applications in personalized medicine. Organoids can be defined as 3D structures derived either from pluripotent or organ restricted stem cells harboring the ability to mimic in vivo architecture and multi lineage differentiation of terminally differentiated tissues. Due to their unique ability of virtually unlimited self-renewal, organoid cultures should be distinguished from previous 'sphere'-culture assays, for example, 'tumor spheres' that have already been described and applied over the last decades.

Pluripotent Stem Cells in Developmental Toxicity Testing: A Review of Methodological Advances

Millions of children are born each year with a birth defect. Many of these defects are caused by environmental factors, although the underlying etiology is often unknown. In vivo mammalian models are frequently used to determine if a chemical poses a risk to the developing fetus. However, there are over 80 000 chemicals registered for use in the United States, many of which have undergone little safety testing, necessitating the need for higher-throughput methods to assess developmental toxicity. Pluripotent stem cells (PSCs) are an ideal in vitro model to investigate developmental toxicity as they possess the capacity to differentiate into nearly any cell type in the human body. Indeed, a burst of research has occurred in the field of stem cell toxicology over the past decade, which has resulted in numerous methodological advances that utilize both mouse and human PSCs, as well as cutting-edge technology in the fields of metabolomics, transcriptomics, transgenics, and high-throughput imaging. Here, we review the wide array of approaches used to detect developmental toxicants, suggest areas for further research, and highlight critical aspects of stem cell biology that should be considered when utilizing PSCs in developmental toxicity testing.

Ductal Mucus Obstruction and Reduced Fluid Secretion Are Early Defects in Chronic Pancreatitis

Objective: Defective mucus production in the pancreas may be an important factor in the initiation and progression of chronic pancreatitis (CP), therefore we aimed to (i) investigate the qualitative and quantitative changes of mucus both in human CP and in an experimental pancreatitis model and (ii) to correlate the mucus phenotype with epithelial ion transport function. Design: Utilizing human tissue samples and a murine model of cerulein induced CP we measured pancreatic ductal mucus content by morphometric analysis and the relative expression of different mucins in health and disease. Pancreatic fluid secretion in CP model was measured in vivo by magnetic resonance cholangiopancreatography (MRCP) and in vitro on cultured pancreatic ducts. Time-changes of ductal secretory function were correlated to those of the mucin production. Results: We demonstrate increased mucus content in the small pancreatic ducts in CP. Secretory mucins MUC6 and MUC5B were upregulated in human, Muc6 in mouse CP. In vivo and in vitro fluid secretion was decreased in cerulein-induced CP. Analysis of time-course changes showed that impaired ductal ion transport is paralleled by increased Muc6 expression. Conclusion: Mucus accumulation in the small ducts is a combined effect of mucus hypersecretion and epithelial fluid secretion defect, which may lead to ductal obstruction. These results suggest that imbalance of mucus homeostasis may have an important role in the early-phase development of CP, which may have novel diagnostic and therapeutic implications.

Disease Modeling Using 3D Organoids Derived from Human Induced Pluripotent Stem Cells

The rising interest in human induced pluripotent stem cell (hiPSC)-derived organoid culture has stemmed from the manipulation of various combinations of directed multi-lineage differentiation and morphogenetic processes that mimic organogenesis. Organoids are three-dimensional (3D) structures that are comprised of multiple cell types, self-organized to recapitulate embryonic and tissue development in vitro. This model has been shown to be superior to conventional two-dimensional (2D) cell culture methods in mirroring functionality, architecture, and geometric features of tissues seen in vivo. This review serves to highlight recent advances in the 3D organoid technology for use in modeling complex hereditary diseases, cancer, host–microbe interactions, and possible use in translational and personalized medicine where organoid cultures were used to uncover diagnostic biomarkers for early disease detection via high throughput pharmaceutical screening. In addition, this review also aims to discuss the advantages and shortcomings of utilizing organoids in disease modeling. In summary, studying human diseases using hiPSC-derived organoids may better illustrate the processes involved due to similarities in the architecture and microenvironment present in an organoid, which also allows drug responses to be properly recapitulated in vitro.

Modeling human diseases with induced pluripotent stem cells: from 2D to 3D and beyond

The advent of human induced pluripotent stem cells (iPSCs) presents unprecedented opportunities to model human diseases. Differentiated cells derived from iPSCs in two-dimensional (2D) monolayers have proven to be a relatively simple tool for exploring disease pathogenesis and underlying mechanisms. In this Spotlight article, we discuss the progress and limitations of the current 2D iPSC disease-modeling platform, as well as recent advancements in the development of human iPSC models that mimic in vivo tissues and organs at the three-dimensional (3D) level. Recent bioengineering approaches have begun to combine different 3D organoid types into a single '4D multi-organ system'. We summarize the advantages of this approach and speculate on the future role of 4D multi-organ systems in human disease modeling.