CXCL12 and neoplasm: Tregs are known to accumulate in tumor tissues and this is mainly promoted by CC chemokine receptor 4 (CCR4)-CC motif ligand 17/22 (CCL17/22), CCR10-CCL28, and CXC chemokine receptor 4 (CXCR4)-CXC motif ligand 12 (CXCL12).