C-C chemokine receptor type 4 is a receptor for the following CC chemokines: CCL2, CCL4, CCL5, CCL17, CCL22, belongs to the G protein-coupled receptor family. Chemokines are a group of small polypeptide, structurally related molecules that regulate cell trafficking of various types of leukocytes. The chemokines also play fundamental roles in the development, homeostasis, and function of the immune system, and they have effects on cells of the central nervous system as well as on endothelial cells involved in angiogenesis or angiostasis. CCR4 is often expressed on leukemic cells in cutaneous T-cell lymphoma (CTCL). Mogamulizumab is a humanized monoclonal antibody targeted at CCR4and is an investigational drug for CTCL.