NCR and NKG2D are the main activating receptors involved in NK recognition of bone marrow-derived myeloma cells. KMS12BM (A) and KMS21BM (B) killing by resting purified NK cells. Target cells were treated with control antibody (○), anti-NCR (▪), anti-NKG2D (▴), and anti-NCR + NKG2D (•). One representative experiment of 4 performed is reported. E/T ratio indicated on abscissa are 12:1 (1) and 6:1 (2). (C-D) Average NK lysis and SEM are calculated from 4 experiments with KMS12BM and KMS21BM, respectively. The target treatment with different antibodies is reported on the abscissa: untreated target cell percentage of killing is indicated as cnt. Separately, anti-NCR and anti-NKG2D treatment of NK cells inhibited BM myeloma cells recognition; when used together, a clear synergistic inhibitory effect emerged.