CD4 and neoplasm: Indeed, the absence of NK at the fetal-maternal interface increases hypoxia.359 Therefore, NK cells maintain an oxygen and nutrient-rich environment, influence trophoblasts, and promote the development of the invasive trophoblast lineage necessary for optimal blood supply between mother and fetus through the mother KIRs and fetal HLA interactions.360,361 Going back to tumor physiology, strikingly, the deletion of HIF-1α in NK cells reduced their recruitment into tumors, while it did not affect that of CD4 or CD8 T-cells.