HBZ (HTLV-1 basic leucine-zipper factor) is a viral protein encoded by human T-cell leukemia virus-1 (HTLV-1), not a human hemoglobin gene as the gene name suggests. HBZ functions as a critical oncogenic factor in HTLV-1 pathogenesis 1. Unlike the viral transactivator Tax-1, HBZ is constitutively expressed in all adult T-cell leukemia (ATL) cases and is essential for maintaining the neoplastic state 1. Mechanistically, HBZ promotes T-cell proliferation and lymphoma development in transgenic mice 2, while modulating host cell signaling pathways including NF-κB and microRNA networks 3. HBZ demonstrates distinct subcellular localization patterns during HTLV-1 infection: exclusive cytoplasmic localization in asymptomatic carriers and HAM/TSP patients, transitioning to nuclear localization in leukemic cells 4. HBZ expression levels correlate with proviral load and disease severity in HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients 5. Clinically, HBZ serves as a potential prognostic biomarker and therapeutic target 6, with elevated HBZ expression distinguishing ATL patients from asymptomatic carriers 6. These findings establish HBZ as a central viral factor in both ATL oncogenesis and inflammatory HTLV-1 disease pathogenesis 7.