Ex-vivo expanded NK cells recognize autologous gastric tumor cells through different activating receptor-ligand interactions. PBMC from two gastric cancer patients were ex-vivo expanded for 14 days and then tested for cytolytic activity against autologous gastric tumor cells in 4 hour 51Cr release assays. (A) Ex-vivo expanded cells from both patients (patient 1 and patient 2), but not freshly purified non-expanded NK cells from patient 2, efficiently lysed autologous gastric tumor cells (Effector to Target Ratio 20:1). To evaluate the impact of activating receptor-ligand interactions on autologous tumor cell lysis indicated blocking antibodies (10 μg/ml) were added during 4 hours of incubation. (B) Cytotoxicity was reduced in the presence of DNAM-1 (P = 0.0309) and NKp30 (P = 0.0056) for patient 1 and in the presence of NKp46 (P = 0.0003) for patient 2. In both patients autologous cytolytic activity was abrogated in the presence of all four blocking antibodies with P = 0.0111 and P = 0.0001, respectively. Statistical analysis is based on triplicate wells of four (patient 1) and two (patient 2) experiments performed, respectively. Error bars represent the SD. * P < 0.05. MoIgG1 indicates mouse IgG1.