Respective sensitivity of BC cells to NK cells was determined using the CytoTox 96 cytotoxicity assay kit (Promega, 017317) according to the manufacturer's instructions. In brief, 1 × 104 BCap37 or MDA-MB-231 target cells were seeded in triplicate at NK cell-to-target cell (E:T) ratios of 10:1, 5:1 and 2.5:1. An anti-NKG2D Ab (50 mg/ml, Novus, Littleton, USA, clone 149810) or control mAb (50 mg/ml, Novus) was added to experiments 1 h before co-culture. After 4 h of incubation, the supernatant was removed for analysis. The following formulas were used to calculate spontaneous and specific cytotoxicity: % specific release=(experimental release−effector spontaneous release−target spontaneous release)/(target maximum release−target spontaneous release) × 100%.