Clearly residue 192 is not the only position governing sensitivity/resistance to the late IFN-induced block in MT4 cells as both sensitive and resistant viruses encode arginine at this position, and additional resistance determinant(s) likely reside within env. However, given that the site identified during in vitro adaptation is apparently enriched during transmission or early infection, it appears that the factor(s) that mediate the late block described here may influence HIV-1 transmission and/or pathogenesis. Here, ERVW-1 is linked to infection.