KIR3DL1 and breast cancer: To further investigate the functional relevance of HLA class I as an inhibitor for NK cell anti-breast cancer responses under hypoxic conditions and in combination with trastuzumab, we investigated the degranulation level of NK cells that encounter their HLA class I ligand (KIR-ligand-matched) versus NK cells that do not encounter their ligand (KIR-ligand-mismatched).