Emergence of Photosensitivity with Decreased Treg Cells in a Patient with Mycosis Fungoides Treated with Anti-CC Chemokine Receptor 4 Antibody Mogamulizumab

Mogamulizumab is a therapeutic monoclonal antibody that targets the CC chemokine receptor 4 (CCR4). The treatment exhibits strong cytotoxicity for adult T-cell leukaemia/lymphoma (ATLL) cells via antibody-dependent cellular cytotoxicity (ADCC), although it carries the risk of serious adverse reactions to the skin, such as StevensJohnson syndrome (1, 2). We report here a patient with mycosis fungoides (MF) at tumour stage treated with mogamulizumab, who developed a photosensitivity reaction during the course of treatment. At the onset of photosensitivity, a reduction in both circulating and skin infiltrating regulatory T cells (Tregs) was observed.