Abstract 1542: A FasL-targeted immunomodulatory fusion protein replaces a pro-death with a costimulatory signal, enhancing T cell function, adoptive cell therapy, and altering the tumor microenvironment

Abstract

Abstract Improved therapies are urgently needed for several cancers, including acute myeloid leukemia (AML) and pancreatic cancers. Adoptive cell therapy (ACT) with genetically-modified T cells has shown impressive results against B cell malignancies, but limited efficacy in other hematologic and solid tumors. To address this need, we have developed immunomodulatory fusion proteins (IFPs) that combine the ectodomain of an inhibitory receptor with a costimulatory endodomain, providing positive signals exclusively delivered to the T cells concurrently engineered to target tumor-expressed antigens, avoiding the systemic T cell activation seen with immune checkpoint-blocking therapies. We developed an IFP to target Fas ligand (FasL), which is commonly over-expressed in TMEs and induces apoptosis in tumor-infiltrating T cells. We replaced the Fas intracellular tail with the costimulatory, pro-survival 4-1BB signaling domain since both Fas and 4-1BB signal as trimers. After exposure to a murine AML cell line, IFP-transduced murine T cells effectively generated 4-1BB signaling, with metabolic reprogramming, and showed enhanced in vitro proliferation, accumulation and function. IFP T cells resisted exhaustion and effectively eradicated AML, improving survival to 71% in the FBL disseminated AML murine model (vs.11% survival with control T cells). We next engineered T cells with a single-vector that combined the IFP with a tumor-targeted mesothelin-targeted T cell receptor (TCR), for studies with the KPC mouse model of PDA that recapitulates the immunosuppressive characteristics of human disease. TCR/Fas-4-1BB T cells showed increased intratumoral concentration over control TCR-only T cells and increased median survival (65 vs. 37 days, P=0.0042). Human TCR/Fas-4-1BB T cells induced significantly more PDA tumor cell lysis than a dominant negative Fas receptor, supporting the increased benefit of the costimulatory signal. Single-cell RNA sequencing results suggest that IFP-ACT can also improve endogenous antitumor immunity, and Fas-4-1BB primary human T cells showed increased in vitro expansion and cytokine production, relative to TCR-only human T cells. We have now developed a toolbox of IFPs with distinct costimulatory domains and we show that IFPs can substantially improve therapeutic efficacy against liquid and solid tumors, supporting clinical translation. Citation Format: Margot McMurray, Shannon Oda. A FasL-targeted immunomodulatory fusion protein replaces a pro-death with a costimulatory signal, enhancing T cell function, adoptive cell therapy, and altering the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1542.