ACE2 and infection: We extended our observations to Calu-3 cells, a lung epithelial cell line that expresses both ACE2 and TMPRSS2 [47], and observed a dose-dependent inhibition of SARS-CoV-2pp infection with an IC50 of 1.77μM compared to 0.23μM for Vero-TMPRSS2 cells and no detectable effect on cell viability (Fig 1B).