We then cocultured these cells with HER2-positive breast cancer cells and found that the blockade of KIR2DL4, but not that of ILT2, improved trastuzumab-mediated killing by NK cells to a level comparable to treatment with HLA-G antibody, suggesting that HLA-G exerts an inhibitory effect by binding to KIR2DL4 on NK cells (Fig. 2b and Supplementary Fig. S6a). Here, KIR2DL4 is linked to breast carcinoma.