In Vitro Modelling of Respiratory Virus Infections in Human Airway Epithelial Cells - A Systematic Review

Abstract

Respiratory tract infections (RTI) are a major cause of morbidity and mortality in humans. A large number of RTIs is caused by viruses, often resulting in more severe disease in infants, elderly and the immunocompromised. Upon viral infection, most individuals experience common cold-like symptoms associated with an upper RTI. However, in some cases a severe and sometimes life-threatening lower RTI may develop. Reproducible and scalable in vitro culture models that accurately reflect the human respiratory tract are needed to study interactions between respiratory viruses and the host, and to test novel therapeutic interventions. Multiple in vitro respiratory cell culture systems have been described, but the majority of these are based on immortalized cell lines. Although useful for studying certain aspects of viral infections, such monomorphic, unicellular systems fall short in creating an understanding of the processes that occur at an integrated tissue level. Novel in vitro models involving primary human airway epithelial cells and, more recently, human airway organoids, are now in use. In this review, we describe the evolution of in vitro cell culture systems and their characteristics in the context of viral RTIs, starting from advances after immortalized cell cultures to more recently developed organoid systems. Furthermore, we describe how these models are used in studying virus-host interactions, e.g. tropism and receptor studies as well as interactions with the innate immune system. Finally, we provide an outlook for future developments in this field, including co-factors that mimic the microenvironment in the respiratory tract.

Keywords: airway modeling; co-culture; organoid culture; primary airway epithelium culture; respiratory viral diseases.

Figure 1

PRISMA flow diagram of the study selection process.

Figure 2

Composition of the respiratory tract. (A) Division between the upper and lower respiratory tract. (B) Schematic representation of epithelial layer in the different parts of the respiratory tract.

Figure 3

Considerations for using primary cells: differences in donor variability (1), anatomic source of the cells (2), culture methods (e.g. medium and growth factors) (3) and the use of undifferentiated versus differentiated cells (4).

Figure 4

Sources of stem cells and culture methods. Several sources for stem cells are shown: embryonic stem cells, induced pluripotent stem cells (iPSC) and organ-derived or nasal brushing-derived. (A) Shows a Transwell system on which primary cells or stem-cell based cells can be cultured, (B) shows an airway organoid sphere with cilia and mucus on the inside.