Viruses and cell lines

Monkey LLC-MK2 cells were cultured in minimal essential medium with Earle’s salt (MEM; Gibco, Grand Island, USA) containing 8% (vol/vol) heat-inactivated fetal calf serum (FCS, Sigma–Aldrich, St. Louis USA), 100× nonessential amino acid (Sciencell, San Diego, California, USA), 200 mM l-Glutamine (Lonza, Verviers, Belgium), 100 IU/mL Penicillin and 100 mg/mL Streptomycin (Gibco, Grand Island, USA). Human colon cancer cell line Caco-2 cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM; Lonza, Verviers, Belgium) containing 10% (vol/vol) heat-inactivated fetal calf serum (FCS, Sigma–Aldrich, St. Louis USA), 100 IU/mL Penicillin and 100 mg/mL Streptomycin (Gibco, Grand Island, USA). Human lung cancer cell line Calu-3 cells were cultured in advanced DMEM/F12 supplemented with 1% (vol/vol) GlutaMAXTM Supplement (Gibco, Grand island, USA), 10 mM HEPES. HCoV-NL63 stock was produced by consecutively inoculating the virus onto LLC-MK2 cells. A humidified incubator was used for cells culturing at 33 °C, with 5% CO₂. SARS-CoV-2 (isolate BetaCoV/Munich/BavPat1/2020; European Virus Archive Global #026V-03883, GenBank: {"type":"entrez-nucleotide","attrs":{"text":"MT270101","term_id":"1843472678","term_text":"MT270101"}}MT270101) was kindly provided by Dr. Bart Haagmans (Department of Viroscience, Erasmus MC). SARS-CoV-2 stock was produced by consecutively inoculating the virus onto Calu-3 cells. Cell lines were analyzed by genotyping and confirmed to be mycoplasma negative.