The current COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has completely changed human life for more than two years. Upon the emergence of this new lethal virus, multiple approaches were utilized to gain basic knowledge about its biology. Moreover, modern technologies, such as the organoid model system and next-generation sequencing, enabled us to rapidly establish strategies to tackle the disease, including vaccines and therapeutics. The recently developed organoid technology reflects human physiology more closely than other model systems. Coupled with its rapidness, high efficiency, and outstanding reliability, it has provided an opportunity to develop new drugs and understand the impact of the viral pathogen on the host. Recent findings using organoids have successfully revealed the cellular tropism of the virus in different organs and identified potential drug candidates that impact the disease. This review will summarize current achievements made with organoids in the fight against COVID-19.

Glia have been known for its pivotal roles in physiological and pathological conditions in the nervous system. To study glial biology, multiple approaches have been applied to utilize glial cells for research, including stem cell-based technologies. Human glial cells differentiated from pluripotent stem cells are now available, allowing us to study the structural and functional roles of glia in the nervous system, although the efficiency is still low. Direct conversion is an advanced strategy governing fate conversion of diverse cell types directly into the desired lineage. This novel strategy stands as a promising approach for preliminary research and regenerative medicine. Direct conversion employs genetic and environmental cues to change cell fate to that with the required functional cell properties while retaining maturity-related molecular features. As an alternative method, it is now possible to obtain a variety of mature cell populations that could not be obtained using conventional differentiation methods. This review summarizes current achievements in obtaining glia, particularly oligodendrocytes and Schwann cells.

Region specific brain organoids are brain organoids derived by patterning protocols using extrinsic signals as opposed to cerebral organoids obtained by self-patterning. The main focus of this review is to discuss various region-specific brain organoids developed so far and their application in modeling neurodevelopmental disease. We first discuss the principles of neural axis formation by series of growth factors, such as SHH, WNT, BMP signalings, that are critical to generate various region-specific brain organoids. Then we discuss various neurodevelopmental disorders modeled so far with these region-specific brain organoids, and findings made on mechanism and treatment options for neurodevelopmental disorders (NDD).

The emergence of brain organoids as a model system has been a tremendously exciting development in the field of neuroscience. Brain organoids are a gateway to exploring the intricacies of human-specific neurogenesis that have so far eluded the neuroscience community. Regardless, current culture methods have a long way to go in terms of accuracy and reproducibility. To perfectly mimic the human brain, we need to recapitulate the complex in vivo context of the human fetal brain and achieve mature neural circuitry with an intact cytoarchitecture. In this review, we explore the major challenges facing the current brain organoid systems, potential technical breakthroughs to advance brain organoid techniques up to levels similar to an in vivo human developing brain, and the future prospects of this technology.

Organoids show great potential in clinical translational research owing to their intriguing properties to represent a near physiological model for native tissues. However, the dependency of organoid generation on the use of poorly defined matrices has hampered their clinical application. Current organoid culture systems mostly reply on biochemical signals provided by medium compositions and cell-cell interactions to control growth. Recent studies have highlighted the importance of the extracellular matrix (ECM) composition, cell-ECM interactions, and mechanical signals for organoid expansion and differentiation. Thus, several hydrogel systems prepared using natural or synthetic-based materials have been designed to recreate the stem cell niche in vitro, providing biochemical, biophysical, and mechanical signals. In this review, we discuss how recapitulating multiple aspects of the tissue-specific environment through designing and applying matrices could contribute to accelerating the translation of organoid technology from the laboratory to therapeutic and pharmaceutical applications.

The advent of human intestinal organoid systems has revolutionized the way we understand the interactions between the human gut and microorganisms given the host tropism of human microorganisms. The gut microorganisms have regionality (i.e., small versus large intestine) and the expression of various virulence factors in pathogens is influenced by the gut milieu. However, the culture conditions, optimized for human intestinal organoids, often do not fully support the proliferation and functionality of gut microorganisms. In addition, the regional identity of human intestinal organoids has not been considered to study specific microorganisms with regional preference. In this review we provide an overview of current efforts to understand the role of microorganisms in human intestinal organoids. Specifically, we will emphasize the importance of matching the regional preference of microorganisms in the gut and tailoring the appropriate luminal environmental conditions (i.e., oxygen, pH, and biochemical levels) for modeling real interactions between the gut and the microorganisms with human intestinal organoids.

Background and Objectives: Brain organoids have the potential to improve our understanding of brain development and neurological disease. Despite the importance of brain organoids, the effect of vascularization on brain organoids is largely unknown. The objective of this study is to develop vascularized organoids by assembling vascular spheroids with cerebral organoids. Methods and Results: In this study, vascularized spheroids were generated from non-adherent microwell culture system of human umbilical vein endothelial cells, human dermal fibroblasts and human umbilical cord blood derived mesenchymal stem cells. These vascular spheroids were used for fusion with iPSCs induced cerebral organoids. Immunostaining studies of vascularized organoids demonstrated well organized vascular structures and reduced apoptosis. We showed that the vascularization in cerebral organoids up-regulated the Wnt/β-catenin signaling. Conclusions: We developed vascularized cerebral organoids through assembly of brain organoids with vascular spheroids. This method could not only provide a model to study human cortical development but also represent an opportunity to explore neurological disease.

Background and Objectives: In recent years, brain organoid technologies have been the most innovative advance in neural differentiation research. In line with this, we optimized a method to establish cerebral organoids from feeder-free cultured human pluripotent stem cells. In this study, we focused on the consistent and robust production of cerebral organoids comprising neural progenitor cells and neurons. We propose an optimal protocol for cerebral organoid generation that is applicable to both human embryonic stem cells and human induced pluripotent stem cells. Methods and Results: We investigated formation of neuroepithelium, neural tube, and neural folding by observing the morphology of embryoid bodies at each stage during the cerebral organoid differentiation process. Furthermore, we characterized the cerebral organoids via immunocytochemical staining of sectioned organoid samples, which were prepared using a Cryostat and Vibratome. Finally, we established a routine method to generate early cerebral organoids comprising a cortical layer and a neural progenitor zone. Conclusions: We developed an optimized methodology for the generation of cerebral organoids using hESCs and hiPSCs. Using this protocol, consistent and efficient cerebral organoids could be obtained from hiPSCs as well as hESCs. Further, the morphology of brain organoids could be analyzed through 2D monitoring via immunostaining and tissue sectioning, or through 3D monitoring by whole tissue staining after clarification.

Many of early findings regarding intestinal stem cells (ISCs) and their niche in the human intestine have relied on colorectal cancer cell lines and labor-intensive and time-consuming mouse models. However, these models cannot accurately recapitulate the physiologically relevant aspects of human ISCs. In this study, we demonstrate a reliable and robust culture method for 3D expanding intestinal spheroids (InS^exp) mainly comprising ISCs and progenitors, which can be derived from 3D human intestinal organoids (HIOs). We did functional chararcterization of InS^exp derived from 3D HIOs, differentiated from human pluripotent stem cells, and optimization culture methods. Our results indicate that InS^exp can be rapidly expanded and easily passaged, and show enhanced growth rates via WNT pathway activation. InS^exp are capable of exponential cell expansion and cryopreservation. Furthermore, in vitro-matured HIO-derived InS^exp proliferate faster than immature HIO-derived InS^exp with preservation of the parental HIO characteristics. These findings may facilitate the development of scalable culture systems for the long-term maintenance of human ISCs and provide an alternative platform for studying ISC biology.