SARS-CoV-2 entry into human airway organoids is serine protease-mediated and facilitated by the multibasic cleavage site.

Coronavirus entry is mediated by the spike protein which binds the receptor and mediates fusion after cleavage by host proteases. The proteases that mediate entry differ between cell lines and it is currently unclear which proteases are relevant in vivo. A remarkable feature of the SARS-CoV-2 spike is the presence of a multibasic cleavage site (MBCS), which is absent in the SARS-CoV spike. Here, we report that the SARS-CoV-2 spike MBCS increases infectivity on human airway organoids (hAOs). Compared with SARS-CoV, SARS-CoV-2 entered faster into Calu-3 cells, and more frequently formed syncytia in hAOs. Moreover, the MBCS increased entry speed and plasma membrane serine protease usage relative to cathepsin-mediated endosomal entry. Blocking serine proteases, but not cathepsins, effectively inhibited SARS-CoV-2 entry and replication in hAOs. Our findings demonstrate that SARS-CoV-2 enters relevant airway cells using serine proteases, and suggest that the MBCS is an adaptation to this viral entry strategy.