The clinical use of an anti-chemokine receptor mAb, mogamulizumab, specific for the C–C chemokine receptor type 4 (CCR4) has been granted in Japan for the immunotherapy of patients with relapsed or refractory CCR4+ adult T-cell leukemia (ATL) (24). The gene discussed is CCR4; the disease is adult T-cell leukemia/lymphoma.