HLA-E and neoplasm: In this study, we found that cluster 2 had much greater levels of HLA-E and HLA-F expression over cluster 1, and that the high expressions of non-classical HLA-I antigens in tumor tissues could not only mediate resistance to cytotoxic T lymphocytes (CTL), but also lead to tolerance to NK cell-mediated cytotoxicity (Ferris 2015; Gornalusse et al. 2017).