For example, an in vivo CRISPR screen found that loss of Qa-1b (murine homolog of HLA-E) function was associated with increased efficacy of PD-1 immunotherapy [66] whilst a high frequency of PD-1+NKG2A+ CD8+ T lymphocytes were observed in head and neck squamous cell carcinoma (HNSCC), colorectal cancer (CRC) and lung cancer patients [62]. This evidence concerns the gene HLA-E and colorectal cancer.