King's College London

The appearance of new dominant variants of concern (VOCs) of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) threatens the global response to the COVID-19 pandemic. Of these, the alpha variant (also known as B.1.1.7) that appeared initially in the UK became the dominant variant in much of Europe and North America in the first half of 2021. The spike (S) glycoprotein of alpha acquired seven mutations and two deletions compared to the ancestral virus, including the P681H mutation adjacent to the polybasic cleavage site that has been suggested to enhance S cleavage. Here, we show that the alpha spike protein confers a level of resistance to interferon- (IFN in human lung epithelial cells. This correlates with resistance to an entry restriction mediated by interferon-induced transmembrane protein 2 (IFITM2) and a pronounced infection enhancement by IFITM3. Furthermore, the P681H mutation is essential for resistance to IFN and context-dependent resistance to IFITMs in the alpha S. P681H reduces dependence on endosomal cathepsins consistent with enhanced cell-surface entry. However, reversion of H681 does not reduce cleaved spike incorporation into particles, indicating it exerts its role on entry and IFNdownstream of furin cleavage. Overall, we suggest that, in addition to adaptive immune escape, mutations associated with VOCs may well also confer replication and/or transmission advantage through adaptation to resist innate immune mechanisms.