Lubna Hussain Senior Global Product Manager Lonza
Revolutionize Respiratory Research with 3D In Vitro Models
Taking Cell Culture to the Next Dimension
The respiratory epithelial cells line the trachea and bronchial tubes, moistening and protecting the airways while providing a barrier to potential pathogens. As such, this cellular layer is pivotal for the prevention of infection and injury. The physical barrier is maintained by tight junctions between adjacent cells and is reinforced by the secretion of mucus. These cell types have been well studied via traditional monolayer methods. 2D culture methods, however, are unable to replicate the complexity of in vivo cells.
Current drug targets for asthma and COPD include specific enzymes and receptors know to regulate key cells that are involved in pathogenic immunity and the inflammatory response. But airway epithelial cells are a new and more direct target, with therapeutic developers now turning to them and looking for drugs with specific, targeted mechanisms of action through the development of new systems or the identification of new drug targets. Furthermore, advances in molecular testing that enable the identification of disease subtypes are facilitating the discovery of new biomarkers for disease. For example, bronchial thermoplasty, a new treatment for asthma, permanently alleviates symptoms of a constricted airway lumen, although there are concerns surrounding this model about other pathologies that could result, such as increased mucus production and airway remodeling. An optimal co-culture model is needed to truly understand the cellular interactions and mimic the features of remodeling in the diseased state. Tissue injury, such as that obtained from long-term COPD, is associated with airway remodelling, and certain airway epithelial-derived mediators can stimulate the proliferation of smooth muscle cells.
COPD however has no cure. For manufacturers to develop effective therapeutics, access to diseased primary cells is critical, providing a biologically relevant model to asses both genetic and phenotypic changes from healthy tissues. It is vital that the culture accurately represents the in vivo environment, a requirement that has proved limiting for success with the older monolayer culture methods, as they lack the complexity, depth, and interactions of human lung cells in the body.
3D Culture Systems
One of the cell culture methods being more widely adopted today is that of 3D model systems. Such systems allow cell growth in all directions, with the ability to mimic intricate cell-cell and cell-matrix interactions, making them more representative of the in vivo environment. Because they more directly resemble the human airways, 3D models should facilitate better experimental design and, therefore, yield better results. But even with 3D methods, it can be challenging to achieve the complexity of an airway model due to the layers of multiple cell types.
One of the major limitations of monolayer methods is that they are submerged in culture medium, when in vivo airway cells have an interface with air. Instead, researchers need a system that provides a functional reconstitution of the airway mucosa in a bicompartmental model, where the primary cells are grown on a suspended membrane and fed from both apical and basal chambers. Once a monolayer has grown, the cells are fed only from the basal chamber, allowing the apical chamber to be exposed to air. This air-liquid interface can accurately reproduce the in vivo distribution of the airway lining, where epithelial cells face the lumen and the basal pole of the cells attach to a filter membrane, forming a tight, polarized multilayer. Growing cells in this manner allows the culture of a heterogenous population of basal, secretory, and ciliated cells.
By enabling researchers to culture a system that accurately represents the in vivo environment, drug discovery and development laboratories can assess cellular structure and function—as well as cell-cell interactions in diseased lung tissue—and compare mutant cells to wild-type cells. In this way, scientists would be able to identify the key differentiators between normal and atypical cells in pulmonary disease, create hypotheses about the potential causes of lung disease, and make progress toward the development of effective therapeutics for various lung-related ailments.
The prevalence of respiratory disease is high, and is a therapeutic area of significance. COPD can have a dramatic impact on patient quality of life and has no known functional cure. Access to a full range of diseased primary cells will provide a biologically relevant model to assess genetic and phenotypic changes in cells, while avoiding the discrepancies and ethical issues surrounding animal models. Barriers to the development of primary cell models include the limitations associated with monolayer cultures and the inconsistencies between 2D-cultured cells and in vivo cells. The more recent introduction of 3D-culture methods, however, enables researchers to benefit from a more accurate and phenotypically relevant growth method. By mimicking the complex cellular interactions that occur in lung cells, and the lung structure through use of a bronchial-air-liquid interface, a more relevant experimental model can be developed. Systems that accurately mimic the human lung provide researchers with a unique way to investigate new areas of research, including gene therapy, host defense, gene expression analysis, and preclinical drug development.