ACE2 and infection: For example, the lung adenocarcinoma cell line A549 was previously understood to be a cell which was not susceptible to SARS-CoV-2 (Chu et al., 2020; Wurtz et al., 2021), but the overexpression of human ACE2 in this cell line makes infection with SARS-CoV-2 possible (Figure 3) (Weston et al., 2020; Xie et al., 2020).