CCL22 and neoplasm: There are three possible reasons for its enrichment in the tumour microenvironment: firstly, proliferation: TGF-β secreted by tumour cells can prompt Tregs proliferation in the TME (60); secondly, recruitment: Tregs can be recruited from the peripheral blood to the tumour by interacting with chemokines such as CCL22, which are secreted by tumour cells and macrophages in the TME (59, 61).