TMPRSS2 and infection: Subsequently, we used the BSL-2 test to assess the antiviral effectiveness of KC against SARS-CoV-2 in vitro by infecting ACE2/TMPRSS2-overexpressing HEK293T cells with pseudotyped SARS-CoV-2, which substitutes the lentiviral VSV-G envelope protein for the SARS-CoV-2 spike protein and contains a gene that can express the GFP protein after infection.