CCR4 and nasopharyngeal carcinoma: Accumulating evidence has suggested that the enrichment of Tregs in the NPC microenvironment is also caused by tumor-mediated recruitment, where CCR4+ and CCR6+ resting Treg are migrated from peripheral blood and activated into a suppressive phenotype via tumor-secreted CXCL10, CXCL16, CCL20, and CD70 binding (50, 71, 72).