CD274 and cancer: Barsoum et al. reported that the up-regulation in expression of PD-L1 in tumor cells upon exposure to hypoxia, in vitro, increased the rate of apoptosis of cytotoxic T lymphocytes, which suggests that HIF-1α plays a crucial role in driving immune escape from cytotoxic T lymphocytes, and that the inhibition of PD-L1 expression in hypoxic tumor cells could be promising for cancer immunotherapy [21].