PCNA and neoplasm: They analyzed GSC derived from primary tumor samples by mass cytometry, and the GSC expressed normal levels of NK cell activation receptor ligands (ULBP2, ULBP3, VIM) and upregulated levels of NK cell inhibitory receptor ligands (HLA-A, HLA-B, HLA-C, HLA-E, HLA-G, PCNA) compared with non-GSC.