TMPRSS2 and infection: Spheroids_4MACE2-TMPRSS2 and Spheroids_15M63ACE2-TMPRSS2 were then exposed to parental SARS-CoV-2 (strain WK-521, PANGO lineage A; GISAID identifier [ID] EPI_ISL_408667) (SARS-CoV-2WK-521) at a multiplicity of infection (MOI) of 0.05 in Eppendorf microtubes and continuously incubated for 3 h.