CD4 and adult T-cell leukemia/lymphoma: C-C chemokine receptor type 4 (CCR4) is a seven-transmembrane G-protein-coupled receptor principally expressed on Th2 cells and CD4+ regulatory T cells,131,132 as well as in various types of PTCLs, including MF and ATLL.133,134 Furthermore, CCR4 expression was found to be an independent and significant unfavorable prognostic factor in these diseases,133,134 which makes it a promising target in the treatment of PTCL and ATLL.