TMPRSS2 and infection: To examine the capacity of SerpinB3 variants to inhibit SARS-CoV-2 replication, we employed an infection model using Vero-E6/TMPRSS2 cells and SARS-CoV-2 (WT, D614G) where the percentage of SARS-CoV-2-infected cells was determined at 18 h post-infection (pi) by flow cytometry analysis of nucleocapsid protein-positive cells (Figure 4B).