SERINC3 and infection: To ensure that the SERINC5-mediated reduction in SARS-CoV-2 S-mediated entry is not due to the HIV-1 proviral packaging plasmid we used, we produced SARS-CoV-2 S pseudoviruses in the presence of SERINC3 and 5 using an MLV packaging plasmid and a luciferase reporter followed by infection of 293T-hACE2 cells.