A. Western blot analysis of MLVpp-SARS-CoV-2 S produced in ± dec-RVKR-CMK and treated with ± furin. S was detected using a rabbit antibody against the SARS-CoV-2 S2 subunit. MLV content was detected using a mouse antibody against MLV p30. B. Pseudoparticle infectivity assays in Vero E6 and Vero-TMPRSS2 cells. Cells were infected with MLVpps harboring the VSV-G, SARS-CoV-2 S (WT), SARS-CoV-2 S A.23.1 variant, SARS-CoV-2 S WT with P681R mutation. Data represents the average luciferase activity of cells of four independent experiments (Vero E6 and Vero-TMPRSS2). Error bars represent G standard deviation (n = 3). Asterisks indicate statistical significance compared to the untreated control. Statistical analysis was performed using an unpaired Student’s t test. * p < 0.1, **** p < 0.0001. C. Pseudoparticle infectivity assays in A549-ACE2-TMPRSS2 cells. Cells were infected with MLVpps harboring the VSV-G, SARS-CoV-2 S (WT), SARS-CoV-2 S A.23.1 variant, SARS-CoV-2 S WT with P681R mutation. Data represents the average luciferase activity of cells of three independent experiments. Error bars represent G standard deviation (n = 3). Asterisks indicate statistical significance compared to the untreated control. Statistical analysis was performed using an unpaired Student’s t test. **** p < 0.0001.