iPSC-Derived Liver Organoids: A Journey from Drug Screening, to Disease Modeling, Arriving to Regenerative Medicine

Artificial Gametes and Human Reproduction in the 21st Century: An Ethical Analysis

Artificial gametes, derived from stem cells, have the potential to enable in vitro fertilization of embryos. Currently, artificial gametes are only being generated in laboratory animals; however, considerable efforts are underway to develop artificial gametes using human cell sources. These artificial gametes are being proposed as a means to address infertility through assisted reproductive technologies. Nonetheless, the availability of artificial gametes obtained from adult organisms can potentially expand the possibilities of reproduction. Various groups, such as same-sex couples, post-menopausal women, and deceased donors, could potentially utilize artificial gametes to conceive genetically related offspring. The advent of artificial gametes raises significant bioethical questions. Should all these reproductive scenarios be accepted? How can we delineate the range of future reproductive choices? A normative bioethical framework may be necessary to establish a consensus regarding the use of human artificial gametes. This review aims to present the current state of research on the biological roadmap for generating artificial gametes, while also summarizing proposed approaches to establish a normative framework that delineates ethically acceptable paths for reproduction.

Replacing Animal Testing with Stem Cell-Organoids : Advantages and Limitations

Various groups including animal protection organizations, medical organizations, research centers, and even federal agencies such as the U.S. Food and Drug Administration, are working to minimize animal use in scientific experiments. This movement primarily stems from animal welfare and ethical concerns. However, recent advances in technology and new studies in medicine have contributed to an increase in animal experiments throughout the years. With the rapid increase in animal testing, concerns arise including ethical issues, high cost, complex procedures, and potential inaccuracies.Alternative solutions have recently been investigated to address the problems of animal testing. Some of these technologies are related to stem cell technologies, such as organ-on-a-chip, organoids, and induced pluripotent stem cell models. The aim of the review is to focus on stem cell related methodologies, such as organoids, that can serve as an alternative to animal testing and discuss its advantages and limitations, alongside regulatory considerations.Although stem cell related methodologies has shortcomings, it has potential to replace animal testing. Achieving this requires further research on stem cells, with potential societal and technological benefits.

Human liver organoids: From generation to applications

In the last decade, research into human hepatology has been revolutionized by the development of mini human livers in a dish. These liver organoids are formed by self-organizing stem cells and resemble their native counterparts in cellular content, multicellular architecture, and functional features. Liver organoids can be derived from the liver tissue or pluripotent stem cells generated from a skin biopsy, blood cells, or renal epithelial cells present in urine. With the development of liver organoids, a large part of previous hurdles in modeling the human liver is likely to be solved, enabling possibilities to better model liver disease, improve (personalized) drug testing, and advance bioengineering options. In this review, we address strategies to generate and use organoids in human liver disease modeling, followed by a discussion of their potential application in drug development and therapeutics, as well as their strengths and limitations.

Landscape of human organoids: Ideal model in clinics and research

In the last decade, organoid research has entered a golden era, signifying a pivotal shift in the biomedical landscape. The year 2023 marked a milestone with the publication of thousands of papers in this arena, reflecting exponential growth. However, amid this burgeoning expansion, a comprehensive and accurate overview of the field has been conspicuously absent. Our review is intended to bridge this gap, providing a panoramic view of the rapidly evolving organoid landscape. We meticulously analyze the organoid field from eight distinctive vantage points, harnessing our rich experience in academic research, industrial application, and clinical practice. We present a deep exploration of the advances in organoid technology, underpinned by our long-standing involvement in this arena. Our narrative traverses the historical genesis of organoids and their transformative impact across various biomedical sectors, including oncology, toxicology, and drug development. We delve into the synergy between organoids and avant-garde technologies such as synthetic biology and single-cell omics and discuss their pivotal role in tailoring personalized medicine, enhancing high-throughput drug screening, and constructing physiologically pertinent disease models. Our comprehensive analysis and reflective discourse provide a deep dive into the existing landscape and emerging trends in organoid technology. We spotlight technological innovations, methodological evolution, and the broadening spectrum of applications, emphasizing the revolutionary influence of organoids in personalized medicine, oncology, drug discovery, and other fields. Looking ahead, we cautiously anticipate future developments in the field of organoid research, especially its potential implications for personalized patient care, new avenues of drug discovery, and clinical research. We trust that our comprehensive review will be an asset for researchers, clinicians, and patients with keen interest in personalized medical strategies. We offer a broad view of the present and prospective capabilities of organoid technology, encompassing a wide range of current and future applications. In summary, in this review we attempt a comprehensive exploration of the organoid field. We offer reflections, summaries, and projections that might be useful for current researchers and clinicians, and we hope to contribute to shaping the evolving trajectory of this dynamic and rapidly advancing field.

Hepatic spheroid-on-a-chip: Fabrication and characterization of a spheroid-based in vitro model of the human liver for drug screening applications

The integration of microfabrication and microfluidics techniques into cell culture technology has significantly transformed cell culture conditions, scaffold architecture, and tissue biofabrication. These tools offer precise control over cell positioning and enable high-resolution analysis and testing. Culturing cells in 3D systems, such as spheroids and organoids, enables recapitulating the interaction between cells and the extracellular matrix, thereby allowing the creation of human-based biomimetic tissue models that are well-suited for pre-clinical drug screening. Here, we demonstrate an innovative microfluidic device for the formation, culture, and testing of hepatocyte spheroids, which comprises a large array of patterned microwells for hosting hepatic spheroid culture in a reproducible and organized format in a dynamic fluidic environment. The device allows maintaining and characterizing different spheroid sizes as well as exposing to various drugs in parallel enabling high-throughput experimentation. These liver spheroids exhibit physiologically relevant hepatic functionality, as evidenced by their ability to produce albumin and urea at levels comparable to in vivo conditions and the capability to distinguish the toxic effects of selected drugs. This highlights the effectiveness of the microenvironment provided by the chip in maintaining the functionality of hepatocyte spheroids. These data support the notion that the liver-spheroid chip provides a favorable microenvironment for the maintenance of hepatocyte spheroid functionality.

Advancing Organoid Engineering for Tissue Regeneration and Biofunctional Reconstruction

Tissue damage and functional abnormalities in organs have become a considerable clinical challenge. Organoids are often applied as disease models and in drug discovery and screening. Indeed, several studies have shown that organoids are an important strategy for achieving tissue repair and biofunction reconstruction. In contrast to established stem cell therapies, organoids have high clinical relevance. However, conventional approaches have limited the application of organoids in clinical regenerative medicine. Engineered organoids might have the capacity to overcome these challenges. Bioengineering-a multidisciplinary field that applies engineering principles to biomedicine-has bridged the gap between engineering and medicine to promote human health. More specifically, bioengineering principles have been applied to organoids to accelerate their clinical translation. In this review, beginning with the basic concepts of organoids, we describe strategies for cultivating engineered organoids and discuss the multiple engineering modes to create conditions for breakthroughs in organoid research. Subsequently, studies on the application of engineered organoids in biofunction reconstruction and tissue repair are presented. Finally, we highlight the limitations and challenges hindering the utilization of engineered organoids in clinical applications. Future research will focus on cultivating engineered organoids using advanced bioengineering tools for personalized tissue repair and biofunction reconstruction.

A highly efficient cell culture method using oxygen-permeable PDMS-based honeycomb microwells produces functional liver organoids from human induced pluripotent stem cell-derived carboxypeptidase M liver progenitor cells

Recent advancements in bioengineering have introduced potential alternatives to liver transplantation via the development of self-assembled liver organoids, derived from human-induced pluripotent stem cells (hiPSCs). However, the limited maturity of the tissue makes it challenging to implement this technology on a large scale in clinical settings. In this study, we developed a highly efficient method for generating functional liver organoids from hiPSC-derived carboxypeptidase M liver progenitor cells (CPM+ LPCs), using a microwell structure, and enhanced maturation through direct oxygenation in oxygen-permeable culture plates. We compared the morphology, gene expression profile, and function of the liver organoid with those of cells cultured under conventional conditions using either monolayer or spheroid culture systems. Our results revealed that liver organoids generated using polydimethylsiloxane-based honeycomb microwells significantly exhibited enhanced albumin secretion, hepatic marker expression, and cytochrome P450-mediated metabolism. Additionally, the oxygenated organoids consisted of both hepatocytes and cholangiocytes, which showed increased expression of bile transporter-related genes as well as enhanced bile transport function. Oxygen-permeable polydimethylsiloxane membranes may offer an efficient approach to generating highly mature liver organoids consisting of diverse cell populations.

Stem Cell-Based Strategies: The Future Direction of Bioartificial Liver Development

Acute liver failure (ALF) results from severe liver damage or end-stage liver disease. It is extremely fatal and causes serious health and economic burdens worldwide. Once ALF occurs, liver transplantation (LT) is the only definitive and recommended treatment; however, LT is limited by the scarcity of liver grafts. Consequently, the clinical use of bioartificial liver (BAL) has been proposed as a treatment strategy for ALF. Human primary hepatocytes are an ideal cell source for these methods. However, their high demand and superior viability prevent their widespread use. Hence, finding alternatives that meet the seed cell quality and quantity requirements is imperative. Stem cells with self-renewing, immunogenic, and differentiative capacities are potential cell sources. MSCs and its secretomes encompass a spectrum of beneficial properties, such as anti-inflammatory, immunomodulatory, anti-ROS (reactive oxygen species), anti-apoptotic, pro-metabolomic, anti-fibrogenesis, and pro-regenerative attributes. This review focused on the recent status and future directions of stem cell-based strategies in BAL for ALF. Additionally, we discussed the opportunities and challenges associated with promoting such strategies for clinical applications.

Revolutionizing biomedical research: The imperative need for heart-kidney-connected organoids

Organoids significantly advanced our comprehension of organ development, function, and disease modeling. This Perspective underscores the potential of heart-kidney-connected organoids in understanding the intricate relationship between these vital organs, notably the cardiorenal syndrome, where dysfunction in one organ can negatively impact the other. Conventional models fall short in replicating this complexity, necessitating an integrated approach. By co-culturing heart and kidney organoids, combined with microfluidic and 3D bioprinting technologies, a more accurate representation of in vivo conditions can be achieved. Such interconnected systems could revolutionize our grasp of multi-organ diseases, drive drug discovery by evaluating therapeutic agents on both organs simultaneously, and reduce the need for animal models. In essence, heart-kidney-connected organoids present a promising avenue to delve deeper into the pathophysiology underlying cardiorenal disorders, bridging existing knowledge gaps, and advancing biomedical research.

Application Prospect of Induced Pluripotent Stem Cells in Organoids and Cell Therapy

Since its inception, induced pluripotent stem cell (iPSC) technology has been hailed as a powerful tool for comprehending disease etiology and advancing drug screening across various domains. While earlier iPSC-based disease modeling and drug assessment primarily operated at the cellular level, recent years have witnessed a significant shift towards organoid-based investigations. Organoids derived from iPSCs offer distinct advantages, particularly in enabling the observation of disease progression and drug metabolism in an in vivo-like environment, surpassing the capabilities of iPSC-derived cells. Furthermore, iPSC-based cell therapy has emerged as a focal point of clinical interest. In this review, we provide an extensive overview of non-integrative reprogramming methods that have evolved since the inception of iPSC technology. We also deliver a comprehensive examination of iPSC-derived organoids, spanning the realms of the nervous system, cardiovascular system, and oncology, as well as systematically elucidate recent advancements in iPSC-related cell therapies.

Insights on Three Dimensional Organoid Studies for Stem Cell Therapy in Regenerative Medicine

Regenerative medicine has developed as a promising discipline that utilizes stem cells to address limitations in traditional therapies, using innovative techniques to restore and repair damaged organs and tissues. One such technique is the generation of three-dimensional (3D) organoids in stem cell therapy. Organoids are 3D constructs that resemble specific organs' structural and functional characteristics and are generated from stem cells or tissue-specific progenitor cells. The use of 3D organoids is advantageous in comparison to traditional two-dimensional (2D) cell culture by bridging the gap between in vivo and in vitro research. This review aims to provide an overview of the advancements made towards regenerative medicine using stem cells to generate organoids, explore the techniques used in generating 3D organoids and their applications and finally elucidate the challenges and future directions in regenerative medicine using 3D organoids.

AI-enabled organoids: Construction, analysis, and application

Organoids, miniature and simplified in vitro model systems that mimic the structure and function of organs, have attracted considerable interest due to their promising applications in disease modeling, drug screening, personalized medicine, and tissue engineering. Despite the substantial success in cultivating physiologically relevant organoids, challenges remain concerning the complexities of their assembly and the difficulties associated with data analysis. The advent of AI-Enabled Organoids, which interfaces with artificial intelligence (AI), holds the potential to revolutionize the field by offering novel insights and methodologies that can expedite the development and clinical application of organoids. This review succinctly delineates the fundamental concepts and mechanisms underlying AI-Enabled Organoids, summarizing the prospective applications on rapid screening of construction strategies, cost-effective extraction of multiscale image features, streamlined analysis of multi-omics data, and precise preclinical evaluation and application. We also explore the challenges and limitations of interfacing organoids with AI, and discuss the future direction of the field. Taken together, the AI-Enabled Organoids hold significant promise for advancing our understanding of organ development and disease progression, ultimately laying the groundwork for clinical application.

The Material World of 3D-Bioprinted and Microfluidic-Chip Models of Human Liver Fibrosis

Biomaterials are extensively used to mimic cell-matrix interactions, which are essential for cell growth, function, and differentiation. This is particularly relevant when developing in vitro disease models of organs rich in extracellular matrix, like the liver. Liver disease involves a chronic wound-healing response with formation of scar tissue known as fibrosis. At early stages, liver disease can be reverted, but as disease progresses, reversion is no longer possible, and there is no cure. Research for new therapies is hampered by the lack of adequate models that replicate the mechanical properties and biochemical stimuli present in the fibrotic liver. Fibrosis is associated with changes in the composition of the extracellular matrix that directly influence cell behavior. Biomaterials could play an essential role in better emulating the disease microenvironment. In this paper, the recent and cutting-edge biomaterials used for creating in vitro models of human liver fibrosis are revised, in combination with cells, bioprinting, and/or microfluidics. These technologies have been instrumental to replicate the intricate structure of the unhealthy tissue and promote medium perfusion that improves cell growth and function, respectively. A comprehensive analysis of the impact of material hints and cell-material interactions in a tridimensional context is provided.

Localized T3 production modifies the transcriptome and promotes the hepatocyte-like lineage in iPSC-derived hepatic organoids

Thyroid hormone (TH) levels are low during development, and the deiodinases control TH signaling through tissue-specific activation or inactivation of TH. Here, we studied human induced pluripotent stem cell-derived (iPSC-derived) hepatic organoids and identified a robust induction of DIO2 expression (the deiodinase that activates T4 to T3) that occurs in hepatoblasts. The surge in DIO2-T3 (the deiodinase that activates thyroxine [T4] to triiodothyronine [T3]) persists until the hepatoblasts differentiate into hepatocyte- or cholangiocyte-like cells, neither of which expresses DIO2. Preventing the induction of the DIO2-T3 signaling modified the expression of key transcription factors, decreased the number of hepatocyte-like cells by ~60%, and increased the number of cholangiocyte-like cells by ~55% without affecting the growth or the size of the mature liver organoid. Physiological levels of T3 could not fully restore the transition from hepatoblasts to mature cells. This indicates that the timed surge in DIO2-T3 signaling critically determines the fate of developing human hepatoblasts and the transcriptome of the maturing hepatocytes, with physiological and clinical implications for how the liver handles energy substrates.

Lactate promotes survival and hepatocyte differentiation of human induced pluripotent stem cells in a medium without glucose and supplemented with galactose

Human induced pluripotent stem (iPS) cells initiate hepatocyte differentiation in a medium without glucose and supplemented with galactose, oncostatin M and small molecules [hepatocyte differentiation inducer (HDI)]. To clarify the metabolic differences between iPS cells in HDI and ReproFF (undifferentiated state), a metabolome analysis was performed. iPS cells were cultured in a medium without glucose and supplemented with galactose, as well as 1 mM of calcium lactate, sodium lactate or lactic acid. After 7 days of culture, the cells were subjected to reverse transcription-quantitative PCR analysis. The galactose-1-phosphate concentration was significantly higher in cells cultured in HDI than in those cultured with ReproFF. The lactate concentration in the HDI group was significantly lower than that in the ReproFF group. The expression levels of α-feto protein and albumin were significantly higher in the groups cultured with calcium lactate, sodium lactate and lactic acid as compared with ReproFF. It was suggested that lactate promoted the survival of iPS cells cultured in a medium without glucose and supplemented with galactose. Under these conditions, iPS cells begin to differentiate into a hepatocyte lineage. Lactate may be applied to produce hepatocytes from iPS cells more efficiently.

Exploring the promising potential of induced pluripotent stem cells in cancer research and therapy

The advent of iPSCs has brought about a significant transformation in stem cell research, opening up promising avenues for advancing cancer treatment. The formation of cancer is a multifaceted process influenced by genetic, epigenetic, and environmental factors. iPSCs offer a distinctive platform for investigating the origin of cancer, paving the way for novel approaches to cancer treatment, drug testing, and tailored medical interventions. This review article will provide an overview of the science behind iPSCs, the current limitations and challenges in iPSC-based cancer therapy, the ethical and social implications, and the comparative analysis with other stem cell types for cancer treatment. The article will also discuss the applications of iPSCs in tumorigenesis, the future of iPSCs in tumorigenesis research, and highlight successful case studies utilizing iPSCs in tumorigenesis research. The conclusion will summarize the advancements made in iPSC-based tumorigenesis research and the importance of continued investment in iPSC research to unlock the full potential of these cells.

Three-dimensional human bile duct formation from chemically induced human liver progenitor cells

Background: The intrahepatic bile ducts (BDs) play an important role in the modification and transport of bile, and the integration between the BD and hepatocytes is the basis of the liver function. However, the lack of a source of cholangiocytes limits in vitro research. The aim of the present study was to establish three-dimensional BDs combined with human mature hepatocytes (hMHs) in vitro using chemically induced human liver progenitor cells (hCLiPs) derived from hMHs. Methods: In this study, we formed functional BDs from hCLiPs using hepatocyte growth factor and extracellular matrix. BDs expressed the typical biliary markers CK-7, GGT1, CFTR and EpCAM and were able to transport the bile-like substance rhodamine 123 into the lumen. The established three-dimensional BDs were cocultured with hMHs. These cells were able to bind to the BDs, and the bile acid analog CLF was transported from the culture medium through the hMHs and accumulated in the lumen of the BDs. The BDs generated from the hCLiPs showed a BD function and a physiological system (e.g., the transport of bile within the liver) when they were connected to the hMHs. Conclusion: We present a novel in vitro three-dimensional BD combined with hMHs for study, drug screening and the therapeutic modulation of the cholangiocyte function.

Human iPSC-Derived 3D Hepatic Organoids in a Miniaturized Dynamic Culture System

The process of identifying and approving a new drug is a time-consuming and expensive procedure. One of the biggest issues to overcome is the risk of hepatotoxicity, which is one of the main reasons for drug withdrawal from the market. While animal models are the gold standard in preclinical drug testing, the translation of results into therapeutic intervention is often ambiguous due to interspecies differences in hepatic metabolism. The discovery of human induced pluripotent stem cells (hiPSCs) and their derivatives has opened new possibilities for drug testing. We used mesenchymal stem cells and hepatocytes both derived from hiPSCs, together with endothelial cells, to miniaturize the process of generating hepatic organoids. These organoids were then cultivated in vitro using both static and dynamic cultures. Additionally, we tested spheroids solely composed by induced hepatocytes. By miniaturizing the system, we demonstrated the possibility of maintaining the organoids, but not the spheroids, in culture for up to 1 week. This timeframe may be sufficient to carry out a hypothetical pharmacological test or screening. In conclusion, we propose that the hiPSC-derived liver organoid model could complement or, in the near future, replace the pharmacological and toxicological tests conducted on animals.

Fabrication of functional ameloblasts from hiPSCs for dental application

Tooth formation relies on two types of dental cell populations, namely, the dental epithelium and dental mesenchyme, and the interactions between these cell populations are important during tooth development. Although human-induced pluripotent stem cells (hiPSCs) can differentiate into dental epithelial and mesenchymal cells, organoid research on tooth development has not been established yet. This study focused on the hiPSC-derived human ameloblast organoid (hAO) using a three-dimensional (3D) culture system. hAOs had similar properties to ameloblasts, forming enamel in response to calcium and mineralization by interaction with the dental mesenchyme. hAOs simultaneously had osteogenic and odontogenic differentiation potential. Furthermore, hAOs demonstrated tooth regenerative potential upon interaction with the mouse dental mesenchyme. Our findings provide new insights into a suitable hiPSC-derived dental source and demonstrate that hAOs can be beneficial not only for tooth regeneration but also for the study of various dental diseases for which treatment has not been developed yet.

Cell therapy in end-stage liver disease: replace and remodel

Liver disease is prevalent worldwide. When it reaches the end stage, mortality rises to 50% or more. Although liver transplantation has emerged as the most efficient treatment for end-stage liver disease, its application has been limited by the scarcity of donor livers. The lack of acceptable donor organs implies that patients are at high risk while waiting for suitable livers. In this scenario, cell therapy has emerged as a promising treatment approach. Most of the time, transplanted cells can replace host hepatocytes and remodel the hepatic microenvironment. For instance, hepatocytes derived from donor livers or stem cells colonize and proliferate in the liver, can replace host hepatocytes, and restore liver function. Other cellular therapy candidates, such as macrophages and mesenchymal stem cells, can remodel the hepatic microenvironment, thereby repairing the damaged liver. In recent years, cell therapy has transitioned from animal research to early human studies. In this review, we will discuss cell therapy in end-stage liver disease treatment, especially focusing on various cell types utilized for cell transplantation, and elucidate the processes involved. Furthermore, we will also summarize the practical obstacles of cell therapy and offer potential solutions.

Therapeutic restoration of female reproductive and endocrine dysfunction using stem cells

Millions of women worldwide suffer from infertility associated with gynecologic disorders such as premature ovarian insufficiency, polycystic ovary syndrome, Asherman syndrome, endometriosis, preeclampsia, and fallopian tube obstruction. These disorders can lead to infertility and thereby affect the quality of life of the infertile couple because of their psychological impact and significant costs. In recent years, stem cell therapy has emerged as a therapeutic approach to repair or replace damaged tissues or organs. This review describes the recent development as well as the underlying mechanisms of stem cell therapy for a variety of female reproductive diseases, offering us new therapeutic options for the treatment of female reproductive and endocrine dysfunction.

Liver organoids: established tools for disease modeling and drug development

In the past decade, liver organoids have evolved rapidly as valuable research tools, providing novel insights into almost all types of liver diseases, including monogenic liver diseases, alcohol-associated liver disease, metabolic-associated fatty liver disease, various types of (viral) hepatitis, and liver cancers. Liver organoids in part mimic the microphysiology of the human liver and fill a gap in high-fidelity liver disease models to a certain extent. They hold great promise to elucidate the pathogenic mechanism of a diversity of liver diseases and play a crucial role in drug development. Moreover, it is challenging but opportunistic to apply liver organoids for tailored therapies of various liver diseases. The establishment, applications, and challenges of different types of liver organoids, for example, derived from embryonic, adult, or induced pluripotent stem cells, to model different liver diseases, are presented in this review.

Liver three-dimensional cellular models for high-throughput chemical testing

Drug-induced hepatotoxicity is a leading cause of drug withdrawal from the market. High-throughput screening utilizing in vitro liver models is critical for early-stage liver toxicity testing. Traditionally, monolayer human hepatocytes or immortalized liver cell lines (e.g., HepG2, HepaRG) have been used to test compound liver toxicity. However, monolayer-cultured liver cells sometimes lack the metabolic competence to mimic the in vivo condition and are therefore largely appropriate for short-term toxicological testing. They may not, however, be adequate for identifying chronic and recurring liver damage caused by drugs. Recently, several three-dimensional (3D) liver models have been developed. These 3D liver models better recapitulate normal liver function and metabolic capacity. This review describes the current development of 3D liver models that can be used to test drugs/chemicals for their pharmacologic and toxicologic effects, as well as the advantages and limitations of using these 3D liver models for high-throughput screening.

Human liver cancer organoids: Biological applications, current challenges, and prospects in hepatoma therapy

Liver cancer and disease are among the most socially challenging global health concerns. Although organ transplantation, surgical resection and anticancer drugs are the main methods for the treatment of liver cancer, there are still no proven cures owing to the lack of donor livers and tumor heterogeneity. Recently, advances in tumor organoid technology have attracted considerable attention as they can simulate the spatial constructs and pathophysiological characteristics of tumorigenesis and metastasis in a more realistic manner. Organoids may further contribute to the development of tailored therapies. Combining organoids with other emerging techniques, such as CRISPR-HOT, organ-on-a-chip, and 3D bioprinting, may further develop organoids and address their bottlenecks to create more practical models that generalize different tissue or organ interactions in tumor progression. In this review, we summarize the various methods in which liver organoids may be generated and describe their biological and clinical applications, present challenges, and prospects for their integration with emerging technologies. These rapidly developing liver organoids may become the focus of in vitro clinical model development and therapeutic research for liver diseases in the near future.

The native liver as inspiration to create superior in vitro hepatic models

Drug induced liver injury (DILI) is one of the major reasons of drug withdrawal during the different phases of drug development. The later in the drug development a drug is discovered to be toxic, the higher the economical as well as the ethical impact will be. In vitro models for early detection of drug liver toxicity are under constant development, however to date a superior model of the liver is still lacking. Ideally, a highly reliable model should be established to maintain the different hepatic cell functionalities to the greatest extent possible, during a period of time long enough to allow for tracking of the toxicity of compounds. In the case of DILI, toxicity can appear even after months of exposure. To reach this goal, an in vitro model should be developed that mimics the in vivo liver environment, function and response to external stimuli. The different approaches for the development of liver models currently used in the field of tissue engineering will be described in this review. Combining different technologies, leading to optimal materials, cells and 3D-constructs will ultimately lead to an ideal superior model that fully recapitulates the liver.

Induced Pluripotent Stem Cell-Derived Organoids: Their Implication in COVID-19 Modeling

The outbreak of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a significant global health issue. This novel virus's high morbidity and mortality rates have prompted the scientific community to quickly find the best COVID-19 model to investigate all pathological processes underlining its activity and, more importantly, search for optimal drug therapy with minimal toxicity risk. The gold standard in disease modeling involves animal and monolayer culture models; however, these models do not fully reflect the response to human tissues affected by the virus. However, more physiological 3D in vitro culture models, such as spheroids and organoids derived from induced pluripotent stem cells (iPSCs), could serve as promising alternatives. Different iPSC-derived organoids, such as lung, cardiac, brain, intestinal, kidney, liver, nasal, retinal, skin, and pancreatic organoids, have already shown immense potential in COVID-19 modeling. In the present comprehensive review article, we summarize the current knowledge on COVID-19 modeling and drug screening using selected iPSC-derived 3D culture models, including lung, brain, intestinal, cardiac, blood vessels, liver, kidney, and inner ear organoids. Undoubtedly, according to reviewed studies, organoids are the state-of-the-art approach to COVID-19 modeling.

"iPSC-derived liver organoids and inherited bleeding disorders: Potential and future perspectives"

The bleeding phenotype of hereditary coagulation disorders is caused by the low or undetectable activity of the proteins involved in hemostasis, due to a broad spectrum of genetic alterations. Most of the affected coagulation factors are produced in the liver. Therefore, two-dimensional (2D) cultures of primary human hepatocytes and recombinant overexpression of the factors in non-human cell lines have been primarily used to mimic disease pathogenesis and as a model for innovative therapeutic strategies. However, neither human nor animal cells fully represent the hepatocellular biology and do not harbor the exact genetic background of the patient. As a result, the inability of the current in vitro models in recapitulating the in vivo situation has limited the studies of these inherited coagulation disorders. Induced Pluripotent Stem Cell (iPSC) technology offers a possible solution to overcome these limitations by reprogramming patient somatic cells into an embryonic-like pluripotent state, thus giving the possibility of generating an unlimited number of liver cells needed for modeling or therapeutic purposes. By combining this potential and the recent advances in the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 technology, it allows for the generation of autologous and gene corrected liver cells in the form of three-dimensional (3D) liver organoids. The organoids recapitulate cellular composition and organization of the liver, providing a more physiological model to study the biology of coagulation proteins and modeling hereditary coagulation disorders. This advanced methodology can pave the way for the development of cell-based therapeutic approaches to treat inherited coagulation disorders. In this review we will explore the use of liver organoids as a state-of-the-art methodology for modeling coagulation factors disorders and the possibilities of using organoid technology to treat the disease.

Generation of Organoids and Analysis of Ferroptosis in Organoids

Ferroptosis is a unique form of iron-dependent cell death induced by lipid peroxidation and subsequent plasma membrane rupture, which sets it apart from other types of regulated cell death. Ferroptosis has been linked to a diverse range of biological processes, such as aging, immunity, and cancer. Organoids, on the other hand, are three-dimensional (3D) miniaturized model systems of different organs in vitro cultures, which have gained widespread interest for modeling tissue development and disease, drug screening, and cell therapy. Organoids offer tremendous potential for improving our understanding of human diseases, particularly in the search for the field of ferroptosis in pathological processes of organs. Furthermore, cancer organoids are utilized to investigate molecular mechanisms and drug screening in vitro due to the anti-tumor effect of ferroptosis. Currently, the development of liver organoids has reached a relatively mature stage. Here, we present the protocols for the generation of liver organoids and liver cancer organoids, along with the methods for detecting ferroptosis in organoids.

Therapeutic strategies of three-dimensional stem cell spheroids and organoids for tissue repair and regeneration

Three-dimensional (3D) stem cell culture systems have attracted considerable attention as a way to better mimic the complex interactions between individual cells and the extracellular matrix (ECM) that occur in vivo. Moreover, 3D cell culture systems have unique properties that help guide specific functions, growth, and processes of stem cells (e.g., embryogenesis, morphogenesis, and organogenesis). Thus, 3D stem cell culture systems that mimic in vivo environments enable basic research about various tissues and organs. In this review, we focus on the advanced therapeutic applications of stem cell-based 3D culture systems generated using different engineering techniques. Specifically, we summarize the historical advancements of 3D cell culture systems and discuss the therapeutic applications of stem cell-based spheroids and organoids, including engineering techniques for tissue repair and regeneration.

Advancement of Organoid Technology in Regenerative Medicine

Purpose

Organoids are three-dimensional cultures of stem cells in an environment similar to the body's extracellular matrix. This is also a novel development in the realm of regenerative medicine. Stem cells can begin to develop into 3D structures by modifying signaling pathways. To form organoids, stem cells are transplanted into the extracellular matrix. Organoids have provided the required technologies to reproduce human tissues. As a result, it might be used in place of animal models in scientific study. The key goals of these investigations are research into viral and genetic illnesses, malignancies, and extracellular vesicles, pharmaceutical discovery, and organ transplantation. Organoids can help pave the road for precision medicine through genetic editing, pharmaceutical development, and cell therapy.

Methods

PubMed, Google Scholar, and Scopus were used to search for all relevant papers written in English (1907-2021). The study abstracts were scrutinized. Studies on the use of stem-cell-derived organoids in regenerative medicine, organoids as 3D culture models for EVs analysis, and organoids for precision medicine were included. Articles with other irrelevant aims, meetings, letters, commentaries, congress and conference abstracts, and articles with no available full texts were excluded.

Results

According to the included studies, organoids have various origins, types, and applications in regenerative and precision medicine, as well as an important role in studying extracellular vesicles.

Conclusion

Organoids are considered a bridge that connects preclinical studies to clinical ones. However, the lack of a standardized protocol and other barriers addressed in this review, hinder the vast use of this technology.

Lay Summary

Organoids are 3D stem cell propagations in biological or synthetic scaffolds that mimic ECM to allow intercellular or matrix-cellular crosstalk. Because these structures are similar to organs in the body, they can be used as research models. Organoids are medicine's future hope for organ transplantation, tumor biobank formation, and the development of precision medicine. Organoid models can be used to study cell-to-cell interactions as well as effective factors like inflammation and aging. Bioengineering technologies are also used to define the size, shape, and composition of organoids before transforming them into precise structures. Finally, the importance of organoid applications in regenerative medicine has opened a new window for a better understanding of biological research, as discussed in this study.

Current Research Trends in the Application of In Vitro Three-Dimensional Models of Liver Cells

The liver produces and stores various nutrients that are necessary for the body and serves as a chemical plant, metabolizing carbohydrates, fats, hormones, vitamins, and minerals. It is also a vital organ for detoxifying drugs and exogenous harmful substances. Culturing liver cells in vitro under three-dimensional (3D) conditions is considered a primary mechanism for liver tissue engineering. The 3D cell culture system is designed to allow cells to interact in an artificially created environment and has the advantage of mimicking the physiological characteristics of cells in vivo. This system facilitates contact between the cells and the extracellular matrix. Several technically different approaches have been proposed, including bioreactors, chips, and plate-based systems in fluid or static media composed of chemically diverse materials. Compared to conventional two-dimensional monolayer culture in vitro models, the ability to predict the function of the tissues, including the drug metabolism and chemical toxicity, has been enhanced by developing three-dimensional liver culture models. This review discussed the methodology of 3D cell cultures and summarized the advantages of an in vitro liver platform using 3D culture technology.

Generation of Hepatocytes and Nonparenchymal Cell Codifferentiation System from Human-Induced Pluripotent Stem Cells

To date, hepatocytes derived from human-induced pluripotent stem cells (hiPSC) provide a potentially unlimited resource for clinical application and drug development. However, most hiPSC-derived hepatocyte-like cells initiated differentiation from highly purified definitive endoderm, which are insufficient to accurately replicate the complex regulation of signals among multiple cells and tissues during liver organogenesis, thereby displaying an immature phenotypic and short survival time in vitro. Here, we described a protocol to achieve codifferentiation of endoderm-derived hepatocytes and mesoderm-derived nonparenchymal cells by the inclusion of BMP4 into hepatic differentiation medium, which has a beneficial effect on the hepatocyte maturation and lifespan in vitro. Our codifferentiation system suggests the important role of nonparenchymal cells in liver organogenesis. Hopefully, these hepatocytes described here provide a promising approach in the therapy of liver diseases.

Merits of hiPSC-Derived Cardiomyocytes for In Vitro Research and Testing Drug Toxicity

The progress of medical technology and scientific advances in the field of anticancer treatment have increased the survival probabilities and duration of life of patients. However, cancer-therapy-induced cardiac dysfunction remains a clinically salient problem. Effective anticancer therapies may eventually induce cardiomyopathy. To date, several studies have focused on the mechanisms underlying cancer-treatment-related cardiotoxicity. Cardiomyocyte cell lines with no contractile physiological characteristics cannot adequately model “true” human cardiomyocytes. However, applying “true” human cardiomyocytes for research is fraught with many obstacles (e.g., invasiveness of the procedure), and there is a proliferative limitation for rodent primary cultures. Human-induced pluripotent stem-cell-differentiated cardiomyocytes (hiPSC-CMs), which can be produced efficiently, are viable candidates for mimicking human cardiomyocytes in vitro. We successfully performed cardiac differentiation of human iPSCs to obtain hiPSC-CMs. These hiPSC-CMs can be used to investigate the pathophysiological basis and molecular mechanism of cancer-treatment-related cardiotoxicity and to develop novel strategies to prevent and rescue such cardiotoxicity. We propose that hiPSC-CMs can be used as an in vitro drug screening platform to study targeted cancer-therapy-related cardiotoxicity.

Vascularization in Bioartificial Parenchymal Tissue: Bioink and Bioprinting Strategies

Among advanced therapy medicinal products, tissue-engineered products have the potential to address the current critical shortage of donor organs and provide future alternative options in organ replacement therapy. The clinically available tissue-engineered products comprise bradytrophic tissue such as skin, cornea, and cartilage. A sufficient macro- and microvascular network to support the viability and function of effector cells has been identified as one of the main challenges in developing bioartificial parenchymal tissue. Three-dimensional bioprinting is an emerging technology that might overcome this challenge by precise spatial bioink deposition for the generation of a predefined architecture. Bioinks are printing substrates that may contain cells, matrix compounds, and signaling molecules within support materials such as hydrogels. Bioinks can provide cues to promote vascularization, including proangiogenic signaling molecules and cocultured cells. Both of these strategies are reported to enhance vascularization. We review pre-, intra-, and postprinting strategies such as bioink composition, bioprinting platforms, and material deposition strategies for building vascularized tissue. In addition, bioconvergence approaches such as computer simulation and artificial intelligence can support current experimental designs. Imaging-derived vascular trees can serve as blueprints. While acknowledging that a lack of structured evidence inhibits further meta-analysis, this review discusses an end-to-end process for the fabrication of vascularized, parenchymal tissue.

Microfluidics for 3D Cell and Tissue Cultures: Microfabricative and Ethical Aspects Updates

The necessity to improve in vitro cell screening assays is becoming ever more important. Pharmaceutical companies, research laboratories and hospitals require technologies that help to speed up conventional screening and therapeutic procedures to produce more data in a short time in a realistic and reliable manner. The design of new solutions for test biomaterials and active molecules is one of the urgent problems of preclinical screening and the limited correlation between in vitro and in vivo data remains one of the major issues. The establishment of the most suitable in vitro model provides reduction in times, costs and, last but not least, in the number of animal experiments as recommended by the 3Rs (replace, reduce, refine) ethical guiding principles for testing involving animals. Although two-dimensional (2D) traditional cell screening assays are generally cheap and practical to manage, they have strong limitations, as cells, within the transition from the three-dimensional (3D) in vivo to the 2D in vitro growth conditions, do not properly mimic the real morphologies and physiology of their native tissues. In the study of human pathologies, especially, animal experiments provide data closer to what happens in the target organ or apparatus, but they imply slow and costly procedures and they generally do not fully accomplish the 3Rs recommendations, i.e., the amount of laboratory animals and the stress that they undergo must be minimized. Microfluidic devices seem to offer different advantages in relation to the mentioned issues. This review aims to describe the critical issues connected with the conventional cells culture and screening procedures, showing what happens in the in vivo physiological micro and nano environment also from a physical point of view. During the discussion, some microfluidic tools and their components are described to explain how these devices can circumvent the actual limitations described in the introduction.

Identification of MAEL as a promoter for the drug resistance model of iPSCs derived from T-ALL

Significant progress has been made in the diagnosis and treatment of the drug‐resistant and highly recurrent refractory T cell acute lymphoblastic leukemia (T‐ALL). Primary tumor cell‐derived induced pluripotent stem cells (iPSCs) have become very useful tumor models for cancer research including drug sensitivity tests. In the present study, we investigated the mechanism underlying drug resistance in T‐ALL using the T‐ALL‐derived iPSCs (T‐iPSCs) model. T‐ALL cells were transformed using iPSC reprogramming factors (Sox‐2, Klf4, Oct4, and Myc) via nonintegrating Sendai virus. T‐iPSCs with the Notch1 mutation were then identified through genomic sequencing. Furthermore, T‐iPSCs resistant to 80 μM LY411575, a γ‐secretase and Notch signal inhibitor, were also established. We found a significant difference in the expression of drug resistance‐related genes between the drug‐resistant T‐iPSCs and drug‐sensitive groups. Among the 27 genes, six most differently expressed genes (DEGs) based on Log₂FC >5 were identified. Knockdown analyses using RNA interference (RNAi) revealed that MAEL is the most important gene associated with drug resistance in T‐ALL cells. Also, MAEL knockdown downregulated expression of MRP and LRP in drug‐resistant T‐iPSCs. Interestingly, this phenomenon partially restored the sensitivity of the cells to LY411575. Furthermore, overexpression of the MAEL gene enhanced drug resistance against LY411575. Conclusively, MAEL promotes LY411575 resistance in T‐ALL cells increasing the expression of MRP and LRP genes.

Elimination of Reprogramming Transgenes Facilitates the Differentiation of Induced Pluripotent Stem Cells into Hepatocyte-like Cells and Hepatic Organoids

Hepatocytes and hepatic organoids (HOs) derived from human induced pluripotent stem cells (hiPSCs) are promising cell-based therapies for liver diseases. The removal of reprogramming transgenes can affect hiPSC differentiation potential into the three germ layers but not into hepatocytes and hepatic organoids in the late developmental stage. Herein, we generated hiPSCs from normal human fibroblasts using an excisable polycistronic lentiviral vector based on the Cre recombinase-mediated removal of the loxP-flanked reprogramming cassette. Comparing the properties of transgene-carrying and transgene-free hiPSCs with the same genetic background, the pluripotent states of all hiPSCs were quite similar, as indicated by the expression of pluripotent markers, embryonic body formation, and tri-lineage differentiation in vitro. However, after in vitro differentiation into hepatocytes, transgene-free hiPSCs were superior to the transgene-residual hiPSCs. Interestingly, the generation and hepatic differentiation of human hepatic organoids (hHOs) were significantly enhanced by transgene elimination from hiPSCs, as observed by the upregulated fetal liver (CK19, SOX9, and ITGA6) and functional hepatocyte (albumin, ASGR1, HNF4α, CYP1A2, CYP3A4, and AAT) markers upon culture in differentiation media. Thus, the elimination of reprogramming transgenes facilitates hiPSC differentiation into hepatocyte-like cells and hepatic organoids with properties of liver progenitor cells. Our findings thus provide significant insights into the characteristics of iPSC-derived hepatic organoids.

Induced pluripotent stem cell-based organ-on-a-chip as personalized drug screening tools: A focus on neurodegenerative disorders

The Organ-on-a-Chip (OoC) technology shows great potential to revolutionize the drugs development pipeline by mimicking the physiological environment and functions of human organs. The translational value of OoC is further enhanced when combined with patient-specific induced pluripotent stem cells (iPSCs) to develop more realistic disease models, paving the way for the development of a new generation of patient-on-a-chip devices. iPSCs differentiation capacity leads to invaluable improvements in personalized medicine. Moreover, the connection of single-OoC into multi-OoC or body-on-a-chip allows to investigate drug pharmacodynamic and pharmacokinetics through the study of multi-organs cross-talks. The need of a breakthrough thanks to this technology is particularly relevant within the field of neurodegenerative diseases, where the number of patients is increasing and the successful rate in drug discovery is worryingly low. In this review we discuss current iPSC-based OoC as drug screening models and their implication in development of new therapies for neurodegenerative disorders.

Liver regeneration biology: Implications for liver tumour therapies

The liver has remarkable regenerative potential, with the capacity to regenerate after 75% hepatectomy in humans and up to 90% hepatectomy in some rodent models, enabling it to meet the challenge of diverse injury types, including physical trauma, infection, inflammatory processes, direct toxicity, and immunological insults. Current understanding of liver regeneration is based largely on animal research, historically in large animals, and more recently in rodents and zebrafish, which provide powerful genetic manipulation experimental tools. Whilst immensely valuable, these models have limitations in extrapolation to the human situation. In vitro models have evolved from 2-dimensional culture to complex 3 dimensional organoids, but also have shortcomings in replicating the complex hepatic micro-anatomical and physiological milieu. The process of liver regeneration is only partially understood and characterized by layers of complexity. Liver regeneration is triggered and controlled by a multitude of mitogens acting in autocrine, paracrine, and endocrine ways, with much redundancy and cross-talk between biochemical pathways. The regenerative response is variable, involving both hypertrophy and true proliferative hyperplasia, which is itself variable, including both cellular phenotypic fidelity and cellular trans-differentiation, according to the type of injury. Complex interactions occur between parenchymal and non-parenchymal cells, and regeneration is affected by the status of the liver parenchyma, with differences between healthy and diseased liver. Finally, the process of termination of liver regeneration is even less well understood than its triggers. The complexity of liver regeneration biology combined with limited understanding has restricted specific clinical interventions to enhance liver regeneration. Moreover, manipulating the fundamental biochemical pathways involved would require cautious assessment, for fear of unintended consequences. Nevertheless, current knowledge provides guiding principles for strategies to optimise liver regeneration potential.

Recent Advances in Three-Dimensional Stem Cell Culture Systems and Applications

Cell culture is one of the most core and fundamental techniques employed in the fields of biology and medicine. At present, although the two-dimensional cell culture method is commonly used in vitro, it is quite different from the cell growth microenvironment in vivo. In recent years, the limitations of two-dimensional culture and the advantages of three-dimensional culture have increasingly attracted more and more attentions. Compared to two-dimensional culture, three-dimensional culture system is better to realistically simulate the local microenvironment of cells, promote the exchange of information among cells and the extracellular matrix (ECM), and retain the original biological characteristics of stem cells. In this review, we first present three-dimensional cell culture methods from two aspects: a scaffold-free culture system and a scaffold-based culture system. The culture method and cell characterizations will be summarized. Then the application of three-dimensional cell culture system is further explored, such as in the fields of drug screening, organoids and assembloids. Finally, the directions for future research of three-dimensional cell culture are stated briefly.

Cardiotoxicity of Antineoplastic Therapies and Applications of Induced Pluripotent Stem Cell-Derived Cardiomyocytes

The therapeutic landscape for the treatment of cancer has evolved significantly in recent decades, aided by the development of effective oncology drugs. However, many cancer drugs are often poorly tolerated by the body and in particular the cardiovascular system, causing adverse and sometimes fatal side effects that negate the chemotherapeutic benefits. The prevalence and severity of chemotherapy-induced cardiotoxicity warrants a deeper investigation of the mechanisms and implicating factors in this phenomenon, and a consolidation of scientific efforts to develop mitigating strategies. Aiding these efforts is the emergence of induced pluripotent stem cells (iPSCs) in recent years, which has allowed for the generation of iPSC-derived cardiomyocytes (iPSC-CMs): a human-based, patient-derived, and genetically variable platform that can be applied to the study of chemotherapy-induced cardiotoxicity and beyond. After surveying chemotherapy-induced cardiotoxicity and the associated chemotherapeutic agents, we discuss the use of iPSC-CMs in cardiotoxicity modeling, drug screening, and other potential applications. Improvements to the iPSC-CM platform, such as the development of more adult-like cardiomyocytes and ongoing advances in biotechnology, will only enhance the utility of iPSC-CMs in both basic science and clinical applications.

Induced Pluripotent Stem Cells (iPSCs)-Roles in Regenerative Therapies, Disease Modelling and Drug Screening

The discovery of induced pluripotent stem cells (iPSCs) has made an invaluable contribution to the field of regenerative medicine, paving way for identifying the true potential of human embryonic stem cells (ESCs). Since the controversy around ethicality of ESCs continue to be debated, iPSCs have been used to circumvent the process around destruction of the human embryo. The use of iPSCs have transformed biological research, wherein increasing number of studies are documenting nuclear reprogramming strategies to make them beneficial models for drug screening as well as disease modelling. The flexibility around the use of iPSCs include compatibility to non-invasive harvesting, and ability to source from patients with rare diseases. iPSCs have been widely used in cardiac disease modelling, studying inherited arrhythmias, neural disorders including Alzheimer’s disease, liver disease, and spinal cord injury. Extensive research around identifying factors that are involved in maintaining the identity of ESCs during induction of pluripotency in somatic cells is undertaken. The focus of the current review is to detail all the clinical translation research around iPSCs and the strength of its ever-growing potential in the clinical space.

Stem Cells for Next Level Toxicity Testing in the 21st Century

The call for a paradigm change in toxicology from the United States National Research Council in 2007 initiates awareness for the invention and use of human-relevant alternative methods for toxicological hazard assessment. Simple 2D in vitro systems may serve as first screening tools, however, recent developments infer the need for more complex, multicellular organotypic models, which are superior in mimicking the complexity of human organs. In this review article most critical organs for toxicity assessment, i.e., skin, brain, thyroid system, lung, heart, liver, kidney, and intestine are discussed with regards to their functions in health and disease. Embracing the manifold modes-of-action how xenobiotic compounds can interfere with physiological organ functions and cause toxicity, the need for translation of such multifaceted organ features into the dish seems obvious. Currently used in vitro methods for toxicological applications and ongoing developments not yet arrived in toxicity testing are discussed, especially highlighting the potential of models based on embryonic stem cells and induced pluripotent stem cells of human origin. Finally, the application of innovative technologies like organs-on-a-chip and genome editing point toward a toxicological paradigm change moves into action.

Developing liver organoids from induced pluripotent stem cells (iPSCs): An alternative source of organoid generation for liver cancer research

Primary liver cancer (PLC) represents a significant proportion of all human cancers and constitutes a substantial health and economic burden to society. Traditional therapeutic approaches such as surgical resection and chemotherapy often fail due to tumour relapse or innate tumour chemoresistance. There is a dearth of efficient treatments for PLC in part due to the poor capacity of current laboratory models to reflect critical features of the native tumour in vivo. The increasing incorporation of organoid systems has led to a resurgence of interest in liver cancer research. Organoid systems show promise as the gold standard for recapitulating tumours in vitro. Further, developments in culturing techniques will improve the various shortcomings of the current systems. Induced pluripotent stem cell (iPSC)-derived liver organoids are a promising alternative to the conventional liver organoid model as it circumvents the need to rely on primary resections which are often scarce. In this concise review, we will discuss novel techniques for organoid culture with a focus on organoid co-cultures and their advantages over traditional organoid systems. A detailed technical protocol for the generation of iPSC-derived liver organoids is provided as an appendix.

Human Induced Pluripotent Stem Cell-Derived Exosomes as a New Therapeutic Strategy for Various Diseases

Recently, an increasing number of studies have demonstrated that induced pluripotent stem cells (iPSCs) and iPSC-derived cells display therapeutic effects, mainly via the paracrine mechanism in addition to their transdifferentiation ability. Exosomes have emerged as an important paracrine factor for iPSCs to repair injured cells through the delivery of bioactive components. Animal reports of iPSC-derived exosomes on various disease models are increasing, such as in heart, limb, liver, skin, bone, eye and neurological disease and so forth. This review aims to summarize the therapeutic effects of iPSC-derived exosomes on various disease models and their properties, such as angiogenesis, cell proliferation and anti-apoptosis, with the hopes of improving their potential role in clinical applications and functional restoration.