Squamous cell carcinoma of the head and neck (SCCHN) is the sixth most common cancer worldwide and epidermal growth factor receptor (EGFR) is overexpressed in greater than 90% of patient tumors. Cetuximab is a monoclonal antibody that binds to EGFR and can activate immune cells, such as natural killer (NK) cells, that express receptors for the Fc (constant region) of immunoglobulin G. IL-15 (interleukin-15) is a critical factor for the development, proliferation and activation of effector NK cells. A novel IL-15 compound known as ALT-803 that consists of genetically modified IL-15 plus the IL-15 receptor alpha protein (IL15Rα) fused to the Fc portion of IgG1 has recently been developed. We hypothesized that treatment with ALT-803 would increase NK cell-mediated cytotoxicity of cetuximab-coated head and neck squamous cells. CD56+ NK cells from normal healthy donors were treated overnight with ALT-803 and tested for their ability to lyse cetuximab-coated tumor cells. Cytotoxicity was greater following NK cell ALT-803 activation, as compared to controls. ALT-803-treated NK cells secreted significantly higher levels of IFN-γ than control conditions. Additionally, NK cells showed increased levels of phospho-ERK and phospho-STAT5 when co-cultured with cetuximab-coated tumors and ALT-803. Administration of both cetuximab and ALT-803 to mice harboring Cal27 SCCHN tumors resulted in significantly decreased tumor volume when compared to controls and compared to single-agent treatment alone. Overall, the present data suggest that cetuximab treatment in combination with ALT-803 in patients with EGFR-positive SCCHN may result in significant NK cell activation and have important anti-tumor activity.
Keywords: ALT-803; Antibody-dependent cellular cytotoxicity; Cetuximab; IL-15; Natural killer cells; Squamous cell carcinoma of the head and neck.