RecruitingPhase 2Drug trialA Study of Mogamulizumab to Prevent Adult T-cell Leukemia/Lymphoma in People With HTLV-1The purpose of this study is to find out whether the study drug mogamulizumab is effective in preventing the development of adult T-cell leukemia/lymphoma (ATL) in people who are at higher risk for this type of cancer because they are infected with the HTLV-1 virus and because of changes seen in some of their immune system cells called T-cells.