Because the human tumor cell lines that we analyzed weakly expressed surface HLA‐E, we transfected the squamous cell carcinoma CAL‐27 cell line, whose expression of HLA‐E was at baseline around 20%, with a plasmid encoding the HLA‐E plus the HLA‐G signal peptide to achieve HLA‐E surface expression (Fig 7B). Here, HLA-E is linked to squamous cell carcinoma.