Multifactorial Analysis Identifies Conditions for Robust HCoV-OC43 Replication in Primary Human Bronchial Epithelial...

Air-liquid interface (ALI) cultures recapitulate key features of the airway epithelium by driving basal cell differentiation into ciliated, club, and goblet cells and by generating a functional mucus barrier, thereby representing a highly relevant model of the human respiratory tract. Using a reduced factorial Design of Experiments (DoE) methodology, we simultaneously investigated the effects of seven variables on human coronavirus OC43 (HCoV-OC43) replication in air-liquid interface (ALI)-cultured primary human bronchial epithelial cells (pHBECs) to identify robust conditions that support infection and viral replication. Epithelial differentiation was monitored by measuring transepithelial electrical resistance and determining expression levels of marker genes for basal, goblet, club, and ciliated cells using reverse transcription quantitative PCR (RT-qPCR). HCoV-OC43 replication was monitored by quantifying genomic and subgenomic RNA by RT-qPCR. Viral RNA peaked three days post-infection in cell lysates and four days post-infection in apical washes. Initiation of ALI conditions induced epithelial differentiation, which was complete after 21 days and emerged as the strongest determinant of viral replication. Differentiated pHBEC cultures showed significantly reduced viral RNA compared with undifferentiated cultures, particularly following apical infection. In contrast, basal infection resulted in lower viral RNA levels in undifferentiated cultures than apical infection but was less dependent on epithelial differentiation. However, productive infection following basal exposure was less consistent and more strongly dependent on viral inoculum size. We further demonstrate that repeated mucus washes prior to infection increased HCoV-OC43 replication in mature cultures. In summary, our findings show that epithelial differentiation negatively affects HCoV-OC43 replication and we identify conditions that maximize viral replication in fully differentiated pHBEC cultures.