Apical-out airway organoids as a platform for studying viral infections and screening for antiviral drugs.

Airway organoids are polarized 3D epithelial structures that recapitulate the organization and many of the key functions of the in vivo tissue. They present an attractive model that can overcome some of the limitations of traditional 2D and Air-Liquid Interface (ALI) models, yet the limited accessibility of the organoids' apical side has hindered their applications in studies focusing on host-pathogen interactions. Here, we describe a scalable, fast and efficient way to generate airway organoids with the apical side externally exposed. These apical-out airway organoids are generated in an Extracellular Matrix (ECM)-free environment from 2D-expanded bronchial epithelial cells and differentiated in suspension to develop uniformly-sized organoid cultures with robust ciliogenesis. Differentiated apical-out airway organoids are susceptible to infection with common respiratory viruses and show varying responses upon treatment with antivirals. In addition to the ease of apical accessibility, these apical-out airway organoids offer an alternative in vitro model to study host-pathogen interactions in higher throughput than the traditional air-liquid interface model.

Culture Methods to Study Apical-Specific Interactions using Intestinal Organoid Models.

The lining of the gut epithelium is made up of a simple layer of specialized epithelial cells that expose their apical side to the lumen and respond to external cues. Recent optimization of in vitro culture conditions allows for the re-creation of the intestinal stem cell niche and the development of advanced 3-dimensional (3D) culture systems that recapitulate the cell composition and the organization of the epithelium. Intestinal organoids embedded in an extracellular matrix (ECM) can be maintained for long-term and self-organize to generate a well-defined, polarized epithelium that encompasses an internal lumen and an external exposed basal side. This restrictive nature of the intestinal organoids presents challenges in accessing the apical surface of the epithelium in vitro and limits the investigation of biological mechanisms such as nutrient uptake and host-microbiota/host-pathogen interactions. Here, we describe two methods that facilitate access to the apical side of the organoid epithelium and support the differentiation of specific intestinal cell types. First, we show how ECM removal induces an inversion of the epithelial cell polarity and allows for the generation of apical-out 3D organoids. Second, we describe how to generate 2-dimensional (2D) monolayers from single cell suspensions derived from intestinal organoids, comprised of mature and differentiated cell types. These techniques provide novel tools to study apical-specific interactions of the epithelium with external cues in vitro and promote the use of organoids as a platform to facilitate precision medicine.

Automation, Monitoring, and Standardization of Cell Product Manufacturing.

Although regenerative medicine products are at the forefront of scientific research, technological innovation, and clinical translation, their reproducibility and large-scale production are compromised by automation, monitoring, and standardization issues. To overcome these limitations, new technologies at software (e.g., algorithms and artificial intelligence models, combined with imaging software and machine learning techniques) and hardware (e.g., automated liquid handling, automated cell expansion bioreactor systems, automated colony-forming unit counting and characterization units, and scalable cell culture plates) level are under intense investigation. Automation, monitoring and standardization should be considered at the early stages of the developmental cycle of cell products to deliver more robust and effective therapies and treatment plans to the bedside, reducing healthcare expenditure and improving services and patient care.

Feeder-free and serum-free in vitro assay for measuring the effect of drugs on acute and chronic myeloid leukemia stem/progenitor cells.

Research on chronic and acute myeloid leukemia (CML/AML) is focused on the development of novel therapeutic strategies to eliminate leukemic stem/progenitor cells that are responsible for drug resistance and disease relapse. Methods to culture hematopoietic stem/progenitor cells (HSPCs) from blood or bone marrow samples are indispensable for investigating disease pathogenesis and delineating drug responses in individual patients. A key challenge in this area is that primary leukemic cells grow poorly in culture or rapidly differentiate and lose their hematopoietic potential. Access to patient samples can also be limiting or cell numbers too low to enable large-scale assays and/or to obtain reproducible quantitative data. Here we describe a feeder cell-free and serum-free liquid culture system for the expansion of CD34+ HSPCs from CML/AML samples and healthy control tissues. Following 7 or 14 days of culture, CD34+ cells are expanded 30- to 65-fold or 400- to 800-fold, yielding a purity of ∼80% and ∼60% CD34+ cells, respectively. This system was adapted to a 96-well format to measure the sensitivity of leukemic and normal HSPCs to cytotoxic drugs after only 7 days. The assay requires only 103 cells per well to determine drug IC50 values and can be performed with uncultured and culture-expanded cells. Importantly, resulting IC50 values strongly correlate with those obtained in the classic colony-forming unit (CFU) assay. Compared with the CFU assay, this novel 96-well liquid-based assay designed specifically for leukemic and normal HSPCs is faster and simpler, with more flexible readout methods for selecting candidates for further drug development.

Enumeration of neural stem and progenitor cells in the neural colony-forming cell assay.

Advancement in our understanding of the biology of adult stem cells and their therapeutic potential relies heavily on meaningful functional assays that can identify and measure stem cell activity in vivo and in vitro. In the mammalian nervous system, neural stem cells (NSCs) are often studied using a culture system referred to as the neurosphere assay. We previously challenged a central tenet of this assay, that all neurospheres are derived from a NSC, and provided evidence that it overestimates NSC frequency, rendering it inappropriate for quantitation of NSC frequency in relation to NSC regulation. Here we report the development and validation of the neural colony-forming cell assay (NCFCA), which discriminates stem from progenitor cells on the basis of their proliferative potential. We anticipate that the NCFCA will provide additional clarity in discerning the regulation of NSCs, thereby facilitating further advances in the promising application of NSCs for therapeutic use.

Generation and differentiation of neurospheres from murine embryonic day 14 central nervous system tissue.

Murine embryonic day 14 or E14 neural stem cells (NSCs), first isolated and characterized as a stem cell in culture, are a unique population of cells capable of self-renewal. In addition, they produce a large number of progeny capable of differentiating into the three primary phenotypes-neurons, astrocytes, and oligodendrocytes-found in the adult mammalian central nervous system (CNS). A defined serum-free medium supplemented with epidermal growth factor (EGF) is used to maintain the NSCs in an undifferentiated state in the form of clusters of cells, called neurospheres, for several culture passages. When EGF is removed and serum added to the medium, the intact or dissociated neurospheres differentiate into the three primary CNS phenotypes. This chapter outlines the simple NSC culture methodology and provides some of the more important details of the assay to achieve reproducible cultures.

Enumerating stem cell frequency: neural colony forming cell assay.

Recent reports have highlighted several parameters of the neurosphere culture or assay system which render it unreliable as a quantitative in vitro assay for measuring neural stem cell (NSC) frequency. The single-step semi-solid based assay, the Neural Colony Forming Cell (NCFC) assay is an assay which was developed to overcome some of the limitations of the neurospheres assay in terms of accurately measuring NSC numbers. The NCFC assay allows the discrimination between NSCs and progenitors by the size of colonies they produce (i.e. their proliferative potential). The NCFC assay and other improved tissue culture tools offer further advances in the promising application of NSCs for therapeutic use.

Methods to culture, differentiate, and characterize neural stem cells from the adult and embryonic mouse central nervous system.

Since the discovery of neural stem cells (NSC) in the embryonic and adult mammalian central nervous system (CNS), there have been a growing numbers of tissue culture media and protocols to study and functionally characterize NSCs and its progeny in vitro. One of these culture systems introduced in 1992 is referred to as the Neurosphere Assay, and it has been widely used to isolate, expand, differentiate and even quantify NSC populations. Several years later because its application as a quantitative in vitro assay for measuring NSC frequency was limited, a new single-step semisolid based assay, the Neural Colony Forming Cell (NCFC) assay was developed to accurately measure NSC numbers. The NCFC assay allows the discrimination between NSCs and progenitors by the size of colonies they produce (i.e., their proliferative potential). The evolution and continued improvements made to these tissue culture tools will facilitate further advances in the promising application of NSCs for therapeutic use.

Neural-colony forming cell assay: an assay to discriminate bona fide neural stem cells from neural progenitor cells.

The neurosphere assay (NSA) is one of the most frequently used methods to isolate, expand and also calculate the frequency of neural stem cells (NSCs). Furthermore, this serum-free culture system has also been employed to expand stem cells and determine their frequency from a variety of tumors and normal tissues. It has been shown recently that a one-to-one relationship does not exist between neurosphere formation and NSCs. This suggests that the NSA as currently applied, overestimates the frequency of NSCs in a mixed population of neural precursor cells isolated from both the embryonic and adult mammalian brain. This video practically demonstrates a novel collagen based semi- solid assay, the neural-colony forming cell assay (N-CFCA), which has the ability to discriminate stem from progenitor cells based on their long-term proliferative potential, and thus provides a method to enumerate NSC frequency. In the N-CFCA, colonies ≥2 mm in diameter are derived from cells that meet all the functional criteria of a NSC, while colonies < 2mm are derived from progenitors. The N-CFCA procedure can be used for cells prepared from different sources including primary and cultured adult or embryonic mouse CNS cells. Here we use cells prepared from passage one neurospheres generated from embryonic day 14 mice brain to perform N-CFCA. The cultures are replenished with proliferation medium every seven days for three weeks to allow the plated cells to exhibit their full proliferative potential and then the frequency of neural progenitor and bona fide neural stem cells is calculated respectively by counting the number of colonies that are < 2mm and the ones that are ≥2mm in reference to the number of cells that were initially plated.