A novel mouse model of cutaneous T‐cell lymphoma revealed the combined effect of mogamulizumab with psoralen and ultraviolet a therapy

Mycosis fungoides (MF) is a subtype of cutaneous T‐cell lymphoma (CTCL). Topical or systemic treatment with psoralen, such as 8‐methoxypsoralen (8‐MOP), followed by ultraviolet A (UVA) irradiation (PUVA therapy) is an effective phototherapy for early‐stage MF. However, the efficacy of PUVA therapy for advanced‐stage MF is not satisfactory, and the ideal combination partner for PUVA therapy has not yet been found. In this study, we developed a new mouse model of CTCL in which efficacy of PUVA was detected and further evaluated the efficacy of combination treatment of PUVA and mogamulizumab, an anti‐CCR4 monoclonal antibody. Cytotoxicity of PUVA therapy against HH cells, a CTCL cell line, was observed in vitro. The cytotoxicity was dependent on both 8‐MOP and UVA. Using HH cells, we developed a mouse model in which HH cells were subcutaneously inoculated in the ear. In this model, PUVA therapy suppressed tumour growth with statistical significance, while 8‐MOP or UVA alone did not. Combination therapy of PUVA and mogamulizumab showed greater antitumor activity than either monotherapy with statistical significance. In the histological analysis of the tumour tissue, PUVA accelerated tumour necrosis and then induced the infiltration inflammatory cells in the necrotic area, suggesting that these cells served as effector cells for mogamulizumab. This combination therapy is expected to be a beneficial option for CTCL therapy.