HLA-E and central nervous system cancer: Significant differences in HLA-E expression could be observed between low-grade and high-grade glioma (HGG, Grade III and IV) tissues (p = 0.001 and p <  0.001, t-test, LGGs versus AGs and LGGs versus GBMs, respectively, Fig. 1), while no significant difference in HLA-E expression was identified between AGs and GBMs (p = 0.477, t-test, Fig. 1).