This is, on the one hand, the downregulation of ASCT2 in the M13SV1_Syn1 cells, which is probably due to an effect called superinfection resistance, which has already been observed with Syncytin-1 and other retroviral elements that downregulate their own receptor after infection of a cell in order to prevent infection by another, related virus [81,82,83,84]. The gene discussed is ERVW-1; the disease is infection.