In the present study, we demonstrated that HLA-C knockdown by siRNA treatment induced a significant increase in pNK cytotoxicity against A2780 ovarian cancer cells, with a high expression level of HLA-C1 and HLA-C2 and low pNK cytotoxicity, implying that the alloreactivity of pNK cells is related to inhibitory KIR-KIRL mismatch. Here, HLA-C is linked to ovarian cancer.