Enhancement of anti-STLV-1/HTLV-1 immune responses through multimodal effects of anti-CCR4 antibody

Human T-cell leukemia virus type 1 (HTLV-1) causes adult T-cell leukemia and inflammatory diseases. Because anti-HTLV-1 immune responses are critical for suppressing infected cells, enhancing cellular immunity is beneficial for the treatment of HTLV-1-associated diseases. Using simian T-cell leukemia virus type 1 (STLV-1) infected Japanese macaques, we analyzed the immune responses to viral antigens and the dynamics of virus-infected cells. The chemokine receptor CCR4 is expressed on STLV-1 infected cells, and administration of humanized monoclonal antibody to CCR4, mogamulizumab, dramatically decreased the number of STLV-1-infected cells in vivo. Concurrently, mogamulizumab treatment enhanced STLV-1 specific CD4(+) and CD8(+) T cell responses by simultaneously targeting CCR4(+) effector regulatory T (Treg) cells and infected cells. Mogamulizumab promoted the phagocytosis of CCR4(+) infected cells by macrophages, which likely enhanced antigen presentation. Vaccination with recombinant vaccinia virus (rVV) expressing viral antigens suppressed the proviral load and the number of Tax-expressing cells. Enhanced T-cell responses were also observed in some ATL patients who were treated with mogamulizumab. This study shows that mogamulizumab works not only by killing CCR4(+) infected cells directly, but also by enhancing T cell responses by increasing the phagocytosis of infected cells by antigen-presenting cells and suppressing CCR4(+) effector Treg cells.