Conversely, the upregulation of HIF-1α increases the production of CXCL12, VEGF and FOXP3, activates Treg cells, myeloid-derived suppressor cells, and tumor-associated fibroblasts,178 as well as promotes the polarization of macrophages and monocytes from an antitumor phenotype (M1) to a pro-tumor phenotype (M2), leading to radioresistance. The gene discussed is CXCL12; the disease is neoplasm.