A mouse model for cancer immunoediting with renal cell carcinoma to explore mechanisms of immune escape.

Abstract

11074 Background: Cancer immunosurveillance is the immune system's ability to recognize and destroy newly arising malignant cells. Recent data suggests that the immune system functions also to apply a selective pressure, leading to growth of less immunogenic tumors, a process termed cancer immunoediting. However, direct experimental evidence to support this hypothesis has been lacking. Methods: We examined the interaction between tumor and tumor-specific CD8 T cells in vivo with a model tumor antigen, influenza hemagglutinin (HA), in a renal cell carcinoma cell line (Renca-HA) and studied the HA-specific CD8 T cell response to Renca-HA in vivo. Naïve HA-specific CD8 T cells (Thy1.1+) purified from HA-TCR transgenic mice that recognize a Kd-restricted HA epitope were transferred into congenic Thy1.2+recipients inoculated the day prior with Renca-HA or wild type Renca (Renca-WT). At subsequent time points, recipient lymphocytes and pulmonary tumors were harvested and analyzed. Results: Four days after transfer, vigorous proliferation of HA-specific CD8 T cells was detected in Renca-HA inoculated mice, but not Renca-WT inoculated mice, leading to activation and effector differentiation of HA-specific T cells. HA-specific CD8 T cell activation resulted in destruction of Renca-HA in vivo, causing a significant (p <0.001) reduction of tumor burden and prolongation of survival. However, a small fraction of Renca-HA tumor cells survived immune-mediated killing and evaded immune surveillance. Microarray technology identified upregulation of transforming growth factor β-3 (TGF-β3) expression in edited Renca-HA, but not in unedited Renca-HA, compared with Renca-WT, confirmed by real-time quantitative PCR. Functional abrogation of TGF-β3 signaling on tumor-specific CD8 T cells delayed Renca HA tumor growth in vivo. Conclusions: These data provide direct evidence for the cancer immunosurveillance and immunoediting processes, and suggest that tumor induction of TGFβ-3 during the immunoediting process suppresses tumor-specific CD8 T cell function in vivo, allowing tumor immune escape. Our results provide mechanistic insights as well as potential strategies to block cancer immune evasion.