In melanoma patients, tumor-infiltrating NK cells were present at low frequencies in metastatic melanoma, had downregulated expression of both TIGIT and CD226, and in vitro experiments had shown their dysfunctional phenotype with higher lytic potential but lower lytic activity compared with TIGIT− NK cells against CD155+ MHC class I–deficient melanoma cells (145). The gene discussed is PVR; the disease is melanoma.