CCL22 and neoplasm: The accumulation of Treg in tumors is explained by several mechanisms, such as the conversion of CD4+ T cells to Treg in response to membrane-bound TGF-β, the recruitment of Tregs by chemokines as CCL17, CCL22 and CCL28 and tumor secretion of VEGF-A in response to hypoxia, which inhibits DC maturation.