CXCL12 and neoplasm: Additionally, CCR4/CCL17 or 22 and CXCR4/CXCL12 are vital chemokine signalling pathways for the recruitment of immune cells (regulatory T cells (Tregs) [46–48], neutrophils [49, 50] and dendritic cells (DCs) [48]) and participate in the metastatic colonization of tumour cells as well [16, 47, 48, 51–53].