CCL17 and neoplasm: Treg recruitment into the TME is accomplished via CCR4/CCL22 or CCR4/CCL17 pathways after interactions between CCR4+ Tregs and CCL22/CCL17 secreted by TAMs and tumor cells [151]; as such, CCR4+ Tregs abundantly infiltrate the TME and are considered the most immunosuppressive subset of Tregs.