Simplified schematic model showing events from infection with HTLV1 to onset of ATL. Panel A illustrates the HTLV-1 genome organization, including the HBZ open reading frame. Panel B is a schematic presentation of the hypothetical flow of events occurring between the initial infection with HTLV-1 and the onset of ATL. Although the occurrence of ATL is limited in patients infected with HTLV-1, ATL remains an aggressive form of adult leukemia with no actual effective treatment. As the presence of the HBZ protein has been demonstrated in several clones derived from infected patients and because its function could be associated with HTLV-1–related pathogenesis, this viral protein thus becomes an interesting new target for ATL treatment.