CXCL12 and neoplasm: As CXCL12 promoter contains two HIF-1α binding sites, several studies have pointed out that hypoxia in tumors could upregulate the expression of CXCL12 and induce its secretion60,61, which in turn inhibited the function of the immune system by preventing cytotoxic T cells from infiltrating the tumor and killing cancer cells62,63.