Leveraging 3D Model Systems to Understand Viral Interactions with the Respiratory Mucosa

Abstract

Respiratory viruses remain a significant cause of morbidity and mortality in the human population, underscoring the importance of ongoing basic research into virus-host interactions. However, many critical aspects of infection are difficult, if not impossible, to probe using standard cell lines, 2D culture formats, or even animal models. In vitro systems such as airway epithelial cultures at air-liquid interface, organoids, or 'on-chip' technologies allow interrogation in human cells and recapitulate emergent properties of the airway epithelium-the primary target for respiratory virus infection. While some of these models have been used for over thirty years, ongoing advancements in both culture techniques and analytical tools continue to provide new opportunities to investigate airway epithelial biology and viral infection phenotypes in both normal and diseased host backgrounds. Here we review these models and their application to studying respiratory viruses. Furthermore, given the ability of these systems to recapitulate the extracellular microenvironment, we evaluate their potential to serve as a platform for studies specifically addressing viral interactions at the mucosal surface and detail techniques that can be employed to expand our understanding.

Keywords: 3D model; microscopy; mucosal barrier; mucus; periciliary layer; tissue engineering; viral infection.

Figure 1

In vitro model systems of the human respiratory tract with emergent properties. Air liquid interface (ALI) systems utilize porous membranes for cell attachment, giving rise to consistent open-air lumen development. Organoid systems self-organize within a matrix or scaffold, often leading to variable orientations of the lumen. Organ on-a-chip models utilize multiple tissue lineages on a mechanically manipulated scaffold, capturing dynamic tissue–tissue interactions. Created with BioRender.com.

Figure 2

Cross-section of the respiratory tract mucosal barrier. Epithelial cells of the proximal airways are protected by a dense PCL and overlying mucus gel layer. Pathogens can be slowed or trapped in this restrictive gel while the coordinated beating of underlying ciliated epithelial cells propels this gel away from the more vulnerable distal airways towards gastrointestinal clearance. Created with BioRender.com.

Figure 3

Probing the extracellular barrier: (A) Representative 2 s exposure image of fluorescent microspheres to illustrate mucociliary transport on normal and CF human tracheobronchial epithelial cell cultures. Reprinted with permission from Button, B.; Picher, M.; Boucher, R. “Differential effects of cyclic and constant stress on ATP release and mucociliary transport by human airway epithelia”. The Journal of Physiology 2007, 580(2), 577-592. Copyright 2007, The Physiological Society [285]. (B) Trajectories and mean squared displacement (MSD) of adeno-associated virus serotype 1 (AAV1) and adeno-associated virus serotype 6 (AAV6) in sputum samples from CF patients, * p < 0.05; Mann-Whitney test. Reprinted with permission from Duncan, G.; Kim, N.; Colon-Cortes, Y.; Rodriguez, J.; Mazur, M.; Birket, S.; Rowe, S.; West, N.; Livraghi-Butrico, A.; Boucher, R.; Hanes, J.; Aslanidi, G.; and Suk, J. “An adeno-associated viral vector capable of penetrating the mucus barrier to inhaled gene therapy” (https://doi.org/10.1016/j.omtm.2018.03.006). Molecular Therapy—Methods & Clinical Development 2018, 9:296-304. Copyright 2018, The American Society of Gene and Cell Therapy [286].