Background: Cetuximab is an anti-epidermal growth factor receptor (EGFR) monoclonal antibody (mAb) that prolongs survival in the treatment of head and neck cancer (HNC), but only in 10-20%. An immunological mechanism of action including natural killer (NK) cell-mediated antibody-dependent cellular cytotoxicity (ADCC) has been suggested. We investigated the effects of activating toll-like receptor (TLR)-8 to enhance activity of cetuximab-stimulated, FcγR bearing cells.

Objective: To determine the capability of TLR8-stimulation to enhance the activation and function of NK cells and dendritic cells (DC) in the presence of cetuximab-coated HNC cells.

Methods: Peripheral blood mononuclear cells (PBMC), NK, DC and CD8+ T cells were isolated and analyzed using 51Cr release ADCC, flow cytometry analysis, cytokine ELISA, and EGFR853-861 tetramer staining.

Results: TLR8 stimulation of unfractionated PBMC led to enhanced cetuximab-mediated ADCC in healthy donors (p=0.01) and HNC patients (p<0.05), which was dependent on NK cells. Secretion of Th1 cytokines TNFα(p<0.0001), IFNγ(p<0.0001), and IL-12p40(p<0.005) was increased. NK cells in TLR8 stimulated PBMC showed higher degranulation marker CD107a expression after incubation with cetuximab-treated HNC cells (p<0.001). TLR8 stimulation enhanced DC maturation markers CD80, CD83, and CD86 in co-culture with NK cells and cetuximab-treated HNC cells. Stimulation of DC using TLR8 agonist plus cetuximab-activated NK cells significantly increased EGFR-specific CD8+ T cell induction, compared to either condition alone (p<0.01).

Discussion: VTX-2337 and cetuximab combination therapy can activate innate and adaptive anti-cancer immune responses. Further investigation in human trials will be important for determining the clinical benefit from this combination, and for determining biomarkers of response.

Citation Format: Ryan M. Stephenson, Chwee Ming Lim, Maura Matthews, Gregory Dietsch, Robert Hershberg, Robert L. Ferris. TLR8 stimulation enhances cetuximab-mediated natural killer cell lysis of head and neck cancer cells and dendritic cell cross priming of EGFR-specific CD8+ T cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4738. doi:10.1158/1538-7445.AM2013-4738