We prepared SARS-CoV-2, SARS-CoV, and MERS-CoV pseudoviruses capable of single-cycle infection by transfecting HEK293T/17 cells with an HIV-1 Env-deleted proviral backbone plasmid, pNL4-3∆Env-NanoLuc, together with the respective spike plasmid [36]. Here, ERVW-1 is linked to infection.