Figure 1: ADCC model system and the derivation of ADCC resistance.

A, An in vitro NK cell-mediated ADCC model system consisting of an NK-like cell line (NK92-CD16V), an EGFR monoclonal antibody (cetuximab; red-filled circles), and EGFR-expressing A431 cells. The combination of target, effector, and antibody create optimal conditions for ADCC. B, Schematic of the work flow of the four conditions of continuous exposure. Untreated control, cetuximab (1 μg/ml)-treated contro,l and NK cell-mediated ADCC in absence and presence of cetuximab (1 μg/ml). C, Time course of A431 cell survival in response to ADCC exposure conditions. A431 cells were seeded and exposed to ADCC conditions for the indicated times, as described in Materials and Methods. ***, p < 0.001 by two-tailed t-test across all time points as indicated on graph. Error bars represent SEM. D, Specific lysis of 20,000 ADCCR1 cells and 20,000 ADCCS1 cells by NK92-CD16V cells in the presence of cetuximab (1 µg/mL) for 4 hours at a 1:1 E:T ratio. **, p < 0.01 by two-tailed t-test. Error bars represent SEM. E, In vitro proliferation of ADCCS1 cells and ADCCR1 cells in absence of ADCC conditions. ***, p < 0.001 and **, p < 0.01 by two-tailed t-test for day 2-6 and day 7, respectively. Error bars represent SEM. F, Growth of subcutaneous tumors derived from ADCCS1 and ADCCR1 cells in Balb/c nude mice. N = 10 in each group. p-value calculated by two-tailed t-test as indicated on graph. *, p < 0.05; **, p < 0.01; ***, p < 0.001. Error bars represent SEM. G, Influence of secreted factors by ADCCR1 cells on ADCC sensitivity of ADCCS1 cells. Bar graph shows ADCCR1 (R1) cells compared to mixed ADCCR1/ADCCS1 (S) cells at indicated percentages. Error bars represent SEM.