Human airway cells prevent SARS-CoV-2 multibasic cleavage site cell culture adaptation

Lamers, Mart M; Mykytyn, Anna Z; Breugem, Tim I; Wang, Yiquan; Wu, Douglas C; Riesebosch, Samra; van den Doel, Petra B; Schipper, Debby; Bestebroer, Theo; Wu, Nicholas C; Haagmans, Bart L

Virus propagation methods generally use transformed cell lines to grow viruses from clinical specimens, which may force viruses to rapidly adapt to cell culture conditions, a process facilitated by high viral mutation rates. Upon propagation in VeroE6 cells, SARS-CoV-2 may mutate or delete the multibasic cleavage site (MBCS) in the spike protein. Previously, we showed that the MBCS facilitates serine protease-mediated entry into human airway cells (Mykytyn et al., 2021). Here, we report that propagating SARS-CoV-2 on the human airway cell line Calu-3 – that expresses serine proteases – prevents cell culture adaptations in the MBCS and directly adjacent to the MBCS (S686G). Similar results were obtained using a human airway organoid-based culture system for SARS-CoV-2 propagation. Thus, in-depth knowledge on the biology of a virus can be used to establish methods to prevent cell culture adaptation.