Cetuximab-mediated Immune-enhancing Effects in Vitro and in Metastatic Colorectal Cancer (mCRC) Patients

6140 POSTER Cetuximab-mediated Immune-enhancing Effects in Vitro and in Metastatic Colorectal Cancer (mCRC) Patients P. Correale1, C. Botta1, M.G. Cusi2, E. Bestoso1, S. Apollinari1, M. Caraglia3, M.T. Del Vecchio4, A. Abbruzzese3, A. Aquino5, P. Tagliaferri6. 1“S. Maria alle Scotte” Siena University Hospital, Department of Oncology, Siena, Italy; 2“S. Maria alle Scotte” Siena University Hospital, Department of Molecular Biology Microbiology Section, Siena, Italy; 3II University of Naples, Department of Biochemistry and Biophysics, Naples, Italy; 4“S. Maria alle Scotte” University Hospital of Siena, Section of Pathological Anatomy Department of Human Pathology and Oncology, Siena, Italy; 5“Tor Vergata” University, Department of Neurosciences Pharmacology Section, Rome, Italy; 6Magna Græcia University and Tommaso Campanella Cancer Center Catanzaro, Medical Oncology, Catanzaro, Italy Introduction: Cetuximab is a chimeric human-murine monoclonal IgG1 to the Epidermal-growth-factor-Receptor, approved for colorectal cancer treatment with chemotherapy. Its human constant fragment (Fc), throughout receptor binding, trigger additional immune-mediated effects, which may offer significant contribute to the final therapeutic effect. We investigated cetuximab ability in vitro to promote colon cancer cell phagocytosis and antigen-cross-priming by dendritic cells (DCs) to tumour-specific cytotoxic- T-cell (CTL) precursors. We also carried-out an immunological study in 26 mCRC patients enrolled in an on-going phase 2 trial, receiving an experimental biochemotherapy (GILFICet) regimen combining gemcitabine, irinotecan, fluoruracil, levofolinate, cetuximab, and metronomic sc. aldesleukine. Material and Methods: Transmission-electron-microscopy (TEM) and Flow cytometry were used to evaluate the susceptibility of multiple colon cancer cell lines to DC-mediated phagocytosis. Human DCs loaded with cetuximab-coated colon cancer cells, exposed or not to a combination of anti-cancer drugs, were used to in vitro sensitize human PBMCs from normal donors and cancer patients collected at baseline and after 3 GILFICet courses. T-cell cultures were characterized for immunephenotype and tumour-antigen specific CTL activity by Flow cytometry, LDH release and IFNg-ELISPOT. Results: ILF (irinotecan+ folinate+5-flurouracil) and GILF (gemcitabine+ ILF) poly-chemotherapies confirmed their ability to induce antigen remodelling and danger signals in colon cancer cells. After exposure to poly-chemotherapy and cetuximab these cells became highly susceptible to Fc-receptor-mediated phagocytosis/trogocytosis by human DCs, promoted their activation, and increased their ability to elicit a highly efficient CTL response on human PBMCs in vitro. Our study on the PBMCs of colon cancer patients enrolled in the GILFICet trial, revealed a significant treatment-related increase in na¨ıve and central-memory-Tcells, activated-CTLs, NK/NKTs, mature-activated DCs and IFNg-releasing cells. Substantial differences were observed in T-cell lines generated from patients’ PBMCs taken before and after biochemotherapy. In the latter group there was in fact, a remarkable increase in proliferating CD8+Ki67+CTLs and tumour-antigen specific CTLs’ precursors. Discussion: These results suggest that cetuximab may exert immuneenhancing effects with potential antitumour activit