TMPRSS2 and COVID-19: Thus, we incubated ACE2 and transmembrane serine protease 2 (TMPRSS2)-expressing A549 (ACE2-TMPRSS2-A549) highly permissive cells with OxATP, BzATP or serum of convalescent COVID-19 patients during 4 hours before their infection with green fluorescent protein (GFP)-tagged HIV-1NL4-3ΔEnv variant (defective in viral envelope) pseudotyped with the SARS-CoV-2 spike (S) envelope (S-GFP-LV) (Figures 6A-E).