For example, it has been shown that hypoxia increases the expression of the immune checkpoint programmed death-ligand 1 (PD-L1) on melanoma cells and tumor infiltrating immune cells, via the transcriptional activity of hypoxia-inducible factor-1α (HIF-1α), leading to lower levels of CTL activation and tumor elimination [8]. The gene discussed is HIF1A; the disease is melanoma.