Purpose: Epidermal growth factor receptor (EGFR) is commonly overexpressed in lung cancer. Cetuximab is a chimeric mouse-human antibody targeted against EGFR. Compared with its inhibitory properties, its immunologic mechanisms have not been well studied. In this study, we investigated the antibody-dependent cellular cytotoxicity (ADCC) activity of cetuximab against lung cancer cell lines.

Experimental Design: We studied the correlation between EGFR expression in lung cancer cell lines and the ADCC activity of cetuximab as well as the influence of interleukin-2 and chemotherapy on the ADCC activity. EGFR expression was measured by a quantitative flow cytometric analysis and immunohistochemistry. The ADCC activity was assessed by a 4-h ⁵¹Cr release assay. Peripheral blood mononuclear cells, purified T cells, natural killer (NK) cells, and monocytes from healthy donors or lung cancer patients were used as effector cells.

Results: Fresh peripheral blood mononuclear cells exhibited cetuximab-mediated ADCC activity against lung cancer cell lines at a low concentration of cetuximab (0.25 μg/mL). A logarithmic correlation was observed between the number of EGFRs and ADCC activity. Even low EGFR expression, which was weakly detectable by immunohistochemistry, was sufficient for maximum ADCC activity, and further increases in EGFR expression on the target cells had no further effect on the ADCC activity. In addition, ADCC activity was enhanced by interleukin-2 mainly through activation of NK cells and was less susceptible to immunosuppression by chemotherapy than NK activity in lung cancer patients.

Conclusions: These observations suggest the importance of ADCC activity as an immunologic mechanism of cetuximab in biological therapy for lung cancer patients.