CD226 and ovarian carcinoma: Studies have shown that human ovarian cancer cells express a high level of NK cell-activated receptor ligands (e.g., NKG2D, NCRs, and DNAM-1) and a low level of NK cell-inhibited receptor ligands (e.g., NKG2A/CD94, PD-1, and TIGIT), which suggest that NK cells may show high sensitivity to ovarian cancer cells [14,15].