ERVW-1 and HIV-1 infection: For HIV-1 infection, CEM-SS were infected with NL4-3.HSA.R+E- (Vpr+, Env-), a VSV-G pseudotyped HIV strain with the murine heat stable antigen CD24 (HSA) gene inserted into the nef region to facilitate surface HSA staining of HIV-1-positive cells [43].