TMPRSS2 and infection: In order to determine whether the results obtained by SSPL also apply to replication competent SARS-CoV-2, transgenic A549-ACE2/TMPRSS2 cells as well as Calu-3 human lung cells representing the most extensively studied surrogate lung cell infection model expressing ACE2 and TMPRSS2 endogenously [53], were infected with the Wuhan type isolate SARS-CoV-2PR−1 and the respective VOCs (Figure 2).