Human retinal model systems: Strengths, weaknesses, and future directions.

The retina is a complex neuronal structure that converts light energy into visual perception. Many specialized aspects of the primate retina, including a cone rich macula for high acuity vision, ocular size, and cell type diversity are not found in other animal models. In addition, the unique morphologies and distinct laminar positions of cell types found in the retina make this model system ideal for the study of neuronal cell fate specification. Many key early events of human retinal development are inaccessible to investigation as they occur during gestation. For these reasons, it has been necessary to develop retinal model systems to gain insight into human-specific retinal development and disease. Recent advances in culturing retinal tissue have generated new systems for retinal research and have moved us closer to generating effective regenerative therapies for vision loss. Here, we describe the strengths, weaknesses, and future directions for different human retinal model systems including dissociated primary tissue, explanted primary tissue, retinospheres, and stem cell-derived retinal organoids.

Evolution of organoid technology: Lessons learnt in Co-Culture systems from developmental biology.

In recent years, the development of 3D organoids has opened new avenues of investigation into development, physiology, and regenerative medicine. Organoid formation and the process of organogenesis share common developmental pathways; thus, our knowledge of developmental biology can help model the complexity of different organs to refine organoids into a more sophisticated platform. The developmental process is strongly dependent on complex networks and communication of cell-cell and cell-matrix interactions among different cell populations and their microenvironment, during embryogenesis. These interactions affect cell behaviors such as proliferation, survival, migration, and differentiation. Co-culture systems within the organoid technology were recently developed and provided the highly physiologically relevant systems. Supportive cells including various types of endothelial and stromal cells provide the proper microenvironment, facilitate organoid assembly, and improve vascularization and maturation of organoids. This review discusses the role of the co-culture systems in organoid generation, with a focus on how knowledge of developmental biology has directed and continues to shape the development of more evolved 3D co-culture system-derived organoids.

Adoptive T cell transfer for cancer immunotherapy in the era of synthetic biology.

Adoptive T cell transfer for cancer and chronic infection is an emerging field that shows promise in recent trials. Synthetic-biology-based engineering of T lymphocytes to express high-affinity antigen receptors can overcome immune tolerance, which has been a major limitation of immunotherapy-based strategies. Advances in cell engineering and culture approaches to enable efficient gene transfer and ex vivo cell expansion have facilitated broader evaluation of this technology, moving adoptive transfer from a "boutique" application to the cusp of a mainstream technology. The major challenge currently facing the field is to increase the specificity of engineered T cells for tumors, because targeting shared antigens has the potential to lead to on-target off-tumor toxicities, as observed in recent trials. As the field of adoptive transfer technology matures, the major engineering challenge is the development of automated cell culture systems, so that the approach can extend beyond specialized academic centers and become widely available.

A systematic review on thyroid organoid models: time-trend and its achievements.

Current in vitro models have played important roles in improving knowledge and understanding of cellular and molecular biology, but cannot exactly recapitulate the physiology of human tissues such as thyroid. In this article, we conducted a systematic review to present scientific and methodological time-trends of the reconstruction and generation of 3 D functional thyroid follicles and organoids for thyroid research in health and disease. "Web of Science (ISI)", "Scopus", "Embase", "Cochrane Library", and "PubMed" were systematically searched for papers published since 1950 to May 2020 in English language, using the predefined keywords. 212 articles were reviewed and finally 28 papers that met the inclusion and exclusion criteria were selected. Among the evidence for the examination of 3 D cell culture methods in thyroid research, there were only a few studies related to the organoid technology and its potential applications in understanding morphological, histological, and physiological characteristics of the thyroid gland and reconstructing this tissue. Besides, there was no study using organoids to investigate the tumorigenesis process of thyroid. Based on the results of this study, despite all the limitations and controversies, the exciting and promising organoid technology offers researchers a wide range of potential applications for more accurate modeling of thyroid in health and diseases and provides an excellent preclinical in vitro platform. In future, organoid technology can provide a better understanding of the molecular mechanisms of pathogenesis and tumorigenesis of thyroid tissue and more effective treatment for related disorders due to more accurate simulation of the thyroid physiology.

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.

Advance in Human Epithelial-Derived Organoids Research.

Organoids have complex three-dimensional structures that exhibit functionalities and feature architectures similar to those of in vivo organs and are developed from adult stem cells, embryonic stem cells, and pluripotent stem cells through a self-organization process. Organoids derived from adult epithelial stem cells are the most mature and extensive. In recent years, using organoid culture techniques, researchers have established various adult human tissue-derived epithelial organoids, including intestinal, colon, lung, liver, stomach, breast, and oral mucosal organoids, all of which exhibit strong research and application prospects. Studies have shown that epithelial organoids are mainly applied in drug discovery, personalized drug response testing, disease mechanism research, and regenerative medicine. In this review, we mainly discuss current organoid culture systems and potential applications of this technique with human epithelial tissue.

The prospects for recombinant proteins from transgenic animals: A few successes along with the advent of new technologies increase the allure of transgenic animals for the production of therapeutic human proteins.

The use of GM animals to produce human recombinant therapeutic proteins has progressed only slowly. But recent successes and new technologies could speed up development.

Recent Advances in Maturation of Pluripotent Stem Cell-Derived Cardiomyocytes Promoted by Mechanical Stretch.

Stem cells have significant potential use in tissue regeneration, especially for treating cardiac diseases because of their multi-directional differentiation capability. By mimicking the in vivo physiological environment of native cardiomyocytes during their development and maturation, researchers have been able to induce pluripotent stem cell-derived cardiomyocytes (PSC-CMs) at high purity. However, the phenotype of these PSC-CMs is immature compared with that of adult cardiomyocytes. Various strategies have been explored to improve the maturity of PSC-CMs, such as long-term culturing, mechanical stimuli, chemical stimuli, and combinations of these strategies. Among these strategies, mechanical stretch as a key mechanical stimulus plays an important role in PSC-CM maturation. In this review, the optimal parameters of mechanical stretch, the effects of mechanical stretch on maturation of PSC-CMs, underlying molecular mechanisms as well as existing problems are discussed. Mechanical stretch is a powerful approach to promote the maturation of SC-CMs in terms of morphology, structure, and functionality. Nonetheless, further research efforts are needed to reach a satisfactory standard for clinical applications of PSC-CMs in treating cardiac diseases.

A brief history of organoids.

In vitro cell cultures are crucial research tools for modeling human development and diseases. Although the conventional monolayer cell cultures have been widely used in the past, the lack of tissue architecture and complexity of such model fails to inform the true biological processes in vivo. Recent advances in the organoid technology have revolutionized the in vitro culture tools for biomedical research by creating powerful three-dimensional (3D) models to recapitulate the cellular heterogeneity, structure, and functions of the primary tissues. Such organoid technology enables researchers to recreate human organs and diseases in a dish and thus holds great promises for many translational applications such as regenerative medicine, drug discovery, and precision medicine. In this review, we provide an overview of the organoid history and development. We discuss the strengths and limitations of organoids as well as their potential applications in the laboratory and the clinic.

Pluripotent stem cells in regenerative medicine: challenges and recent progress.

After years of incremental progress, several recent studies have succeeded in deriving disease-relevant cell types from human pluripotent stem cell (hPSC) sources. The prospect of an unlimited cell source, combined with promising preclinical data, indicates that hPSC technology may be on the verge of clinical translation. In this Review, we discuss recent progress in directed differentiation, some of the new technologies that have facilitated the success of hPSC therapies and the remaining hurdles on the road towards developing hPSC-based cell therapies.

Microphysiological Systems: A Pathologist's Perspective.

High-throughput in vitro models lack human-relevant complexity, which undermines their ability to accurately mimic in vivo biologic and pathologic responses. The emergence of microphysiological systems (MPS) presents an opportunity to revolutionize in vitro modeling for both basic biomedical research and applied drug discovery. The MPS platform has been an area of interdisciplinary collaboration to develop new, predictive, and reliable in vitro methods for regulatory acceptance. The current MPS models have been developed to recapitulate an organ or tissue on a smaller scale. However, the complexity of these models (ie, including all cell types present in the in vivo tissue) with appropriate structural, functional, and biochemical attributes are often not fully characterized. Here, we provide an overview of the capabilities and limitations of the microfluidic MPS model (aka organs-on-chips) within the scope of drug development. We recommend the engagement of pathologists early in the MPS design, characterization, and validation phases, because this will enable development of more robust and comprehensive MPS models that can accurately replicate normal biology and pathophysiology and hence be more predictive of human responses.

Recent advances in the use of microcarriers for cell cultures and their ex vivo and in vivo applications.

Microcarriers are 100- to 300-micron support matrices that permit the growth of adherent cells in bioreactor systems. They have a larger surface area to volume ratio in comparison to single cell monolayers, enabling cost-effective cell production and expansion. Microcarriers are composed of a solid matrix that must be separated from expanded cells during downstream processing stages. The detachment method is chosen on the basis of several factors like cell type, microcarrier surface chemistry, cell confluency and degree of aggregation. The development of microcarriers with a range of physiochemical properties permit controlled cell and protein associations that hold utility for novel therapeutics. In this review, we provide an overview of the recent advances in microcarrier cell culture technology. We also discuss its significance as an ex vivo research tool and the therapeutic potential of newly designed microcarrier systems in vivo.

The application of three-dimensional cell culture in clinical medicine.

Three-dimensional cell culture technology is a novel cell culture technology, which can simulate the growth state of cells in vivo by scaffolds or special devices. Cells can form tissues or organs in vitro. It combines some advantages of traditional cell experiments and animal model experiments. Because of its advantages, it is widely used in clinical medical research, including research on stem cell differentiation, research on cell behavior, migration and invasion, study on microenvironment, study on drug sensitivity and radio-sensitivity of tumor cells, etc. In this paper, the evolution and classification of three-dimensional cell culture are reviewed, also the advantages and shortages are compared. The application of three-dimensional cell culture in clinical medicine are summarized to provide an insight into translational medicine.

Livestock pluripotency is finally captured in vitro.

Pluripotent stem cells (PSCs) have demonstrated great utility in improving our understanding of mammalian development and continue to revolutionise regenerative medicine. Thanks to the improved understanding of pluripotency in mice and humans, it has recently become feasible to generate stable livestock PSCs. Although it is unlikely that livestock PSCs will be used for similar applications as their murine and human counterparts, new exciting applications that could greatly advance animal agriculture are being developed, including the use of PSCs for complex genome editing, cellular agriculture, gamete generation and invitro breeding schemes.

An arduous journey from human pluripotent stem cells to functional pancreatic ß cells.

Type 1 and type 2 diabetes are caused by a destruction and decrease in the number of functional insulin-producing ß cells, respectively; therefore, the generation of functional ß cells from human embryonic stem cells and human induced pluripotent stem cells, collectively known as human pluripotent stem cells (hPSCs), for potential cell replacement therapy and disease modelling is an intensely investigated area. Recent scientific breakthroughs enabled derivation of large quantities of human pancreatic ß-like cells in vitro, although with varied glucose-stimulated insulin secretion kinetics. In the present review, we comprehensively summarize, compare and critically analyze the intricacies of these developing technologies, including differentiation platforms, robustness of protocols, and methodologies used to characterize hPSC-derived ß-like cells. We also discuss experimental issues that need to be resolved before these ß-like cells can be used clinically.

Plant cell culture technology in the cosmetics and food industries: current state and future trends.

The production of drugs, cosmetics, and food which are derived from plant cell and tissue cultures has a long tradition. The emerging trend of manufacturing cosmetics and food products in a natural and sustainable manner has brought a new wave in plant cell culture technology over the past 10 years. More than 50 products based on extracts from plant cell cultures have made their way into the cosmetics industry during this time, whereby the majority is produced with plant cell suspension cultures. In addition, the first plant cell culture-based food supplement ingredients, such as Echigena Plus and Teoside 10, are now produced at production scale. In this mini review, we discuss the reasons for and the characteristics as well as the challenges of plant cell culture-based productions for the cosmetics and food industries. It focuses on the current state of the art in this field. In addition, two examples of the latest developments in plant cell culture-based food production are presented, that is, superfood which boosts health and food that can be produced in the lab or at home.

Impact of Three-Dimentional Culture Systems on Hepatic Differentiation of Puripotent Stem Cells and Beyond.

Generation of functional hepatocytes from human pluripotent stem cells (hPSCs) is a vital tool to produce large amounts of human hepatocytes, which hold a great promise for biomedical and regenerative medicine applications. Despite a tremendous progress in developing the differentiation protocols recapitulating the developmental signalling and stages, these resulting hepatocytes from hPSCs yet achieve maturation and functionality comparable to those primary hepatocytes. The absence of 3D milieu in the culture and differentiation of these hepatocytes may account for this, at least partly, thus developing an optimal 3D culture could be a step forward to achieve this aim. Hence, review focuses on current development of 3D culture systems for hepatic differentiation and maturation and the future perspectives of its application.

Recent advances in three-dimensional cell culturing to assess liver function and dysfunction: from a drug biotransformation and toxicity perspective.

The liver is a vital organ fulfilling a central role in over 500 major metabolic functions, including serving as the most essential site for drug biotransformation. Dysfunction of the drug biotransformation processes may result in the exposure of the liver (and other organs) to hepatotoxins, potentially interacting with cellular constituents and causing toxicity and various lesions. Hepatotoxicity can be investigated on a tissue, cellular and molecular level by employing various in vivo and in vitro techniques, including novel three-dimensional (3 D) cell culturing methods. This paper reflects on the liver and its myriad of functions and the influence of drug biotransformation on liver dysfunction. Current in vivo and in vitro models used to study liver function and dysfunction is outlined, emphasizing their advantages and disadvantages. The advantages of novel in vitro 3 D cell culture models are discussed and the possibility of novel models to bridge the gap between in vitro and in vivo models is explained. Progression made in the field of cell culturing methods such as 3 D cell culturing techniques over the last decade promises to reduce the use of in vivo animal models in biotransformation and toxicological studies of the liver.

3D culture for cardiac cells.

This review discusses historical milestones, recent developments and challenges in the area of 3D culture models with cardiovascular cell types. Expectations in this area have been raised in recent years, but more relevant in vitro research, more accurate drug testing results, reliable disease models and insights leading to bioartificial organs are expected from the transition to 3D cell culture. However, the construction of organ-like cardiac 3D models currently remains a difficult challenge. The heart consists of highly differentiated cells in an intricate arrangement.Furthermore, electrical "wiring", a vascular system and multiple cell types act in concert to respond to the rapidly changing demands of the body. Although cardiovascular 3D culture models have been predominantly developed for regenerative medicine in the past, their use in drug screening and for disease models has become more popular recently. Many sophisticated 3D culture models are currently being developed in this dynamic area of life science. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Integration of Developmental and Environmental Cues in the Heart edited by Marcus Schaub and Hughes Abriel.

Recent advances for spermatogonial stem cell transplantation in livestock.

At the foundation of spermatogenesis are the actions of spermatogonial stem cells (SSCs), and a remarkable feature of these cells is the capacity to regenerate spermatogenesis following transplantation into testes of a recipient male that lacks endogenous germline. This ability could be exploited in livestock production as a breeding tool to enhance genetic gain. A key element to success is derivation of culture conditions that support proliferation of SSCs to provide sufficient numbers of cells for transfer into multiple recipient males. Using methodology devised for rodent cells as a foundation, advances in culturing cattle SSCs have occurred over the past few years and efforts are underway to extend this capability to pig cells. Another critical component to SSC transplantation is generation of males with germline ablation but intact somatic support cell function that can serve as surrogate sires for donor-derived spermatogenesis in a natural mating scheme. Recent advances in pigs using gene editing technologies have demonstrated that knockout of a key male germ cell-specific gene, namely NANOS2, leads to male-specific germline ablation but otherwise normal physiology, including intact seminiferous tubules. Together with recent advances in culturing spermatogonia of higher-order mammals, the now efficient means of producing germline-ablated recipient males have brought the application of SSC transplantation in livestock as a production tool closer to reality than ever before.