Abstract A41: Patterns and kinetics of interferon-γ secretion by natural killer cell subsets co-cultured with cetuximab-coated head and neck cancer cells and dendritic cells.

Despite over-expression of epidermal growth factor receptor (EGFR) in 80-90% of head and neck cancers (HNC), only ~20% of HNC patients are clinically responsive the EGFR-specific therapeutic monoclonal antibody (mAb) cetuximab. In addition to blocking EGFR signaling that leads to tumor cell survival and proliferation, increasing evidence suggests that innate and adaptive immunity likely plays a significant role in patient response to cetuximab. Natural killer (NK) cells recognize the Fc-region of EGFR-bound cetuximab via their activating Fcγ receptor IIIa (FcγRIIIa, also known as CD16) and mediate tumor cell lysis by antibody dependent cellular cytotoxicity (ADCC). NK cells are increasingly recognized as key mediators of crosstalk bridging the innate and adaptive arms of the immune response to human malignancies. We have previously shown that in addition to being direct effectors of ADCC against cetuximab-coated HNC cells, NK cells are instrumental in indirectly promoting an anti-tumor adaptive immune response via secretion of immunomodulatory cytokines such as IFNγ, which is known to enhance dendritic cell (DC) antigen processing and presentation to CD8+ T cells. Multiple studies have consistently demonstrated a relative decrease in the CD56dimCD16bright NK cell subset, traditionally considered to be primarily cytotoxic effectors, and an increase in the immunoregulatory CD56brightCD16dim NK cell subset in the peripheral blood of patients with various malignancies. However, given that the immunoregulatory CD56brightCD16dim NK cells are generally considered to be the more prolific cytokine producing subset, it was unclear how this redistribution of NK cell subsets might affect the dynamics of cytokine-mediated NK:DC crosstalk in the presence of mAb-coated tumor cells. Using primary NK cells and monocyte-derived DC isolated from PBMC of healthy donors, we therefore sought to better elucidate the patterns and kinetics of IFNγ secretion by the two NK cell subsets in response to cetuximab-coated HNC cells in the presence of DC. In this context, we found that while CD56brightCD16dim NK cells express more of the activating NKG2D receptor, rapid (by 4hrs) IFNγ secretion by CD56dimCD16bright NK cells is a CD16-dependent process. CD56brightCD16dim NK cells only produced IFNγ following stimulation for at least 12 hours with a combination of IL-12 and IL-15. IL-12/IL-15 stimulation also induced IFNγ secretion by CD56dimCD16bright NK cells, though to a lesser extent as compared to the CD56brightCD16dim subset. Taken together, these data contribute significantly to a mechanistic understanding of how NK cells function to bridge innate and adaptive anti-tumor responses in the context of mAb cancer therapies. Understanding this link is of broad relevance to the optimization of current therapeutic mAbs and will help devise novel ways to improve clinical responses. Citation Format: Christopher A. Lord, Raghvendra M. Srivastava, Robert L. Ferris. Patterns and kinetics of interferon-γ secretion by natural killer cell subsets co-cultured with cetuximab-coated head and neck cancer cells and dendritic cells. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr A41.