Mogamulizumab (Poteligeo®) is a defucosylated, humanized monoclonal antibody targeting CC chemokine receptor 4 (CCR4). Development is being carried out by its owner Kyowa Hakko Kirin for various haematological malignancies, and by licensee Amgen for asthma. Mogamulizumab was conceived through Kyowa Hakko Kirin's Potelligent® technology, which produces antibodies with enhanced antibody-dependent cellular cytotoxicity. This is achieved largely by reducing fucose content in the oligosaccharide structure of the Fc region. Mogamulizumab has been approved in Japan for the treatment of relapsed or refractory adult T-cell leukaemia-lymphoma (ATL) and is the first Potelligent® antibody to receive marketing approval anywhere in the world. Phase II development is underway for adult T-cell leukaemia-lymphoma (ATL) and cutaneous T-cell lymphoma in the US, and for peripheral T-cell lymphoma in the US and Europe. Amgen is conducting a phase I US-based study in patients with asthma. This article summarizes the milestones in the development of intravenous mogamulizumab leading to this first approval.