Patients with cutaneous T-cell lymphoma treated with mogamulizumab, an anti-CCR4 depleting antibody, and immune-mediated skin rashes had a completely modified immune microenvironment at the time of rash, better treatment responses, and longer overall survival, suggesting that modulation of the immune microenvironment is key in achieving long-term disease control. Here, CCR4 is linked to Skin rash.