In addition to OX40L, HTLV-1+ cell lines may exert additional suppressing effect on R5 HIV-1 infection via Tax protein, since Tax proteins of HTLV-1 and HTLV-2 have been shown to play a role in generating antiviral responses against HIV-1 via induction of CCR5-binding chemokines in vitro[32]. Here, TNFSF4 is linked to HIV-1 infection.