Abstract 2555: Engineering adoptive T cell therapy to co-opt Fas ligand-mediated death signaling in solid tumors

Over 20,000 women are diagnosed with ovarian cancer annually, and over half will die within 5 years. This rate has changed little in the last 20 years, highlighting the need for therapy innovation. A promising new strategy with the potential to control tumor growth without toxicity to healthy tissues employs immune T cells engineered to target proteins uniquely overexpressed in tumors. Mesothelin (MSLN) contributes to the malignant and invasive phenotype in ovarian cancer, and has limited expression in healthy cells, making it a candidate immunotherapy target in these tumors. Using patient-derived cell lines and the ID8 mouse cell line, we found that T cells engineered to express a human or mouse MSLN-specific high-affinity T cell receptor (TCR MSLN ) can kill respectively human or murine ovarian tumor cells in vitro. In a disseminated ID8 tumor model, adoptively transferred TCR MSLN T cells preferentially accumulated within established tumors, delayed ovarian tumor growth, and significantly prolonged mouse survival. However, our data also revealed that elements in the tumor microenvironment (TME) limit engineered T cell persistence and ability to kill cancer cells. To identify immunosuppressive features active in the ovarian TME in both human and murine disease, we performed gene expression analyses on whole tumor tissue (Thermo Fisher) or sorted cell populations (Nanostring). Deep transcriptome profiling confirmed the expression of similar gene signatures in human cancers and the preclinical ID8 model, including immunosuppressive pathways. RNA sequencing revealed consistently high expression of Fas ligand (FasL), notable because FasL signaling can play a significant role in the generation and persistence of tumors. Fas/FasL signaling can mediate T cell death, including activation-induced cell death, an apoptotic mechanism responsible for regulating T cell expansion, suggesting tumor cells may upregulate FasL for protection from tumor-infiltrating lymphocytes. By flow cytometry and immunohistochemistry, we and others previously detected FasL in the tumor vasculature and TME of human ovarian cancer. To overcome this potential T cell evasion mechanism, we generated a panel of immunomodulatory fusion proteins (IFP) containing the Fas receptor (Fas) extracellular binding domain fused to a CD28 or 4-1BB co-stimulatory domain rather than the natural death domain. Relative to T cells modified with only TCR MSLN , T cells engineered to express both TCR MSLN and a Fas IFP better infiltrate tumors, preferentially expand/persist, and retain function in the TME when transferred into tumor-bearing mice. Moreover, adoptive immunotherapy with IFP + T cells significantly prolonged survival in tumor-bearing mice, relative to TCR MSLN T cells lacking an IFP. As many solid tumors overexpress FasL, the use of IFPs may provide an opportunity to enhance engineered adoptive T cell therapy in many other malignancies. Citation Format: Kristin Anderson, Shannon Oda, Breanna Bates, Edison Chiu, Christopher Morse, Nicolas Garcia, Philip Greenberg. Engineering adoptive T cell therapy to co-opt Fas ligand-mediated death signaling in solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2555.