Tang and collaborators described pseudotyping of HIV-1 with HTLV-1 envelope glycoprotein during HIV-1/HTLV-1 coinfection, facilitating direct HIV-1 infection of female genital epithelial cells and implicating it in the sexual transmission of HIV in nonpermissive genital cells (43). The gene discussed is ERVW-1; the disease is HIV-1 infection.