Abstract P072: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) foster myeloid-derived suppressor cell-mediated tumor immune evasion in cholangiocarcinoma
Authors: Loeuillard Emilien , Wang Juan , Yang Jingchun , Dong Haidong , Gores Gregory , Ilyas Sumera 
Published: January 2022

Abstract
Background and Aims: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is predominantly expressed on immune cells. Although TRAIL biology has garnered considerable interest as a potential anti-cancer strategy, TRAIL agonists have had very limited anti-cancer activity in humans. TRAIL signaling in T cells may also potentially provide an immune checkpoint function as it can inhibit T cell activation and proliferation by interfering with T cell receptor signaling. However, this potential immune checkpoint function of TRAIL has not been examined in cancer biology. Cholangiocarcinoma (CCA), a highly lethal biliary tract cancer, provides a model to examine the potential immune checkpoint function of TRAIL. Methods: Using a syngeneic, orthotopic murine model of CCA (PMID: 29464042), murine CCA cells (SB cells) that express both TRAIL and TRAIL receptor (TR) were implanted into livers of WT and Tr−/− mice. Hence, in this model the host immune cells express TRAIL but not the receptor; therefore, they would be capable of inducing TRAIL-mediated apoptosis in CCA cells but would be resistant to TRAIL-mediated immunosuppression. After 4 weeks of tumor growth, mice were sacrificed, and tumors were characterized using flow cytometry. Results: We observed that Tr−/− mice had a significant reduction in tumor burden compared to WT mice. Moreover, tumor bearing Tr−/− mice had a significant increase in cytotoxic T lymphocytes (CTLs) and enhanced CTL effector function. However, coculture of T cells with SB cells or SB cells deficient in Tr (SB-Tr−/−) did not result in a significant difference in T cell apoptosis or function, implying that TRAIL-TR is not a direct T cell checkpoint. Myeloid derived suppressor cells (MDSCs) were significantly decreased in Tr−/− tumors compared to WT tumors. Furthermore, implantation of SB cells devoid of Trail (SB-Trail−/−) into WT mice resulted in a significant reduction in tumor burden and MDSC infiltration. Coculture of SB cells with MDSCs from Tr−/− mice attenuated MDSC proliferation and immunosuppression compared to WT MDSCs. Moreover, treatment of MDSCs from Tr−/− mice with TRAIL recombinant protein resulted in a reduction in their proliferation and immunosuppressive function compare to MDSCs from WT mice implying that TRAIL-TR fosters MDSC growth and immunosuppressive function. In conclusion, we have demonstrated that Tr−/− mice have a significant reduction in CCA tumor burden and MDSC infiltration. Consequently, Tr−/− mice bearing tumors have enhanced CTL infiltration and function. These data suggest that the TRAIL-TR system mediates tumor immune evasion via MDSCs. Herein, we suggest that TRAIL-TR appears to function as an indirect T cell checkpoint by augmenting the immunosuppressive effects of MDSCs.
Citation Format: Emilien Loeuillard, Juan Wang, Jingchun Yang, Haidong Dong, Gregory Gores, Sumera Ilyas. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) foster myeloid-derived suppressor cell-mediated tumor immune evasion in cholangiocarcinoma [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2021 Oct 5-6. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(1 Suppl):Abstract nr P072.