Abstract 780: Immune escape in colorectal carcinoma: role of the IFN-γ pathway

Abstract

Abstract The presence of a Th1 adaptive immune response in colorectal carcinoma (CRC) has been associated with improved clinical outcome and survival of patients. The Th1 adaptive immune response is mediated by IFN-γ, a known anti-proliferative, pro-apoptotic and pro-immunogenic cytokine. We have previously identified the guanylate-binding protein 1 (GBP-1), one of the proteins the most highly induced by IFN-γ, as a sensitive marker for the detection of this immune response in CRC in vivo. In a tissue microarray study with 388 CRC tumors, 30% showed GBP-1 expression. Interestingly, in these tumors the expression of GBP-1 was only induced in the cells of the desmoplastic stroma and not observed in adjacent tumor cells. This suggested that CRC tumor cells might undergo an immune escape from the Th1 adaptive immune response, characterized by the loss of IFN-γ responsiveness. Therefore, we investigated the responsiveness to IFN-γ in sixth different CRC cell lines and in normal colon epithelial cells. After treatment with IFN-γ, three of the sixth CRC cell lines (DLD-1, SW480 and HCT116) failed to express GBP-1 as well as other IFN-induced proteins such as caspase-1 and MxA. On the contrary, a robust GBP-1 induction was present in normal colon epithelial cells, in T84, WiDr and HT29 cells. We then investigated whether the loss of expression of IFN-γ target genes was associated with phenotypic changes in CRC cells. In fact, we found that DLD-1, HCT116 and SW480 were resistant to IFN-γ-induced apoptosis. Furthermore, the loss of IFN-γ responsiveness correlated in SW480 and HCT116 with the absence of expression of the IFN-γ receptor alpha chain (IFNγRα). Tumor xenotransplant experiments using DLD-1 cells with reconstituted GBP-1 expression resulted in significantly reduced tumor growth as compared to xentotransplants with control vector transfected DLD-1 cells. This indicated that GBP-1 expression may mediate the anti-tumorigenic effects of the Th1 response. Overall, these data suggested that loss of IFN-γ responsiveness may be a common event in CRC and may protect tumor cells against the anti-tumorigenic (e.g. pro-apoptotic) effects of IFN-γ. The presence of an immune escape from the Th1 adaptive immune response may have important repercussions for prognosis and patients recruitment for immune-based therapy in CRC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 780. doi:10.1158/1538-7445.AM2011-780