Cells
African green monkey kidney epithelial Vero E6 (Vero 76, clone E6, Vero E6, ATCC® CRL-1586) authenticated by ATCC and tested negative for mycoplasma contamination prior to commencement were maintained in a humidified atmosphere at 37°C with 5% CO2, in Dulbecco’s modified Eagle’s medium (DMEM) containing 10% (v/v) fetal bovine serum (FBS, Invitrogen). ACE2-expressing A549 cells, a human lung epithelial cell line, were a kind gift from Brad Rosenberg. A549-ACE2 cells were cultured in DMEM supplemented with 10% FBS and maintained at 37°C with 5% CO2. Caco-2 (ATCC® HTB-37) human colon epithelial cells were maintained in a humidified atmosphere at 37°C with 5% CO2 in DMEM-containing 20% (v/v) FBS.