Recent studies of viral env C2V3 sequences have shown that, although there appears to be little viral compartmentalization among cell subsets, switching coreceptor usage to X4 results in dramatically increased infection in naïve cells.[37] If this exceeded homeostatic mechanisms, then the switch from a R5- to a X4-tropic virus may indeed represent a pressure that may lead to a slow erosion of these cells. Here, ERVW-1 is linked to infection.