Abstract 2156: IL-18 pathway agonism expands intratumoral PD1+ Tcf1+ stem-like CD8+ cells and their polyfunctional effector progeny to promote anti-tumor immunity

Abstract

Abstract Recombinant cytokines were the first modern immunotherapies to produce durable cures in metastatic cancer, but their application has been hampered by only modest efficacy and limited tolerability. A major limitation to cytokine therapies is their lack of selectivity for the small fraction of lymphocytes that specifically recognize tumors. To identify cytokine pathways with greater selectively for anti-tumor lymphocytes, we analyzed single-cell RNA-seq expression data and flow cytometric profiles of tumor-infiltrating lymphocytes (TILs). Among detectable cytokine pathways, Interleukin-18 (IL-18) and its receptors IL-18R1 and IL-18RAP were markedly upregulated in activated and dysfunctional TILs, suggesting the potential of IL-18R agonism to promote anti-tumor immunity. However, recombinant IL-18 therapy has consistently failed to demonstrate anti-tumor efficacy in clinical trials. We hypothesized this may be due to the upregulation of an ultra-high affinity inhibitory decoy receptor of IL-18, IL-18BP. Indeed, IL-18BP is highly expressed in the tumor microenvironment, which we found by immunohistochemical staining and qPCR analysis of IL-18BP levels in several human cancers and syngeneic murine tumor models. Using directed evolution with yeast-surface display, we engineered “decoy-resistant” IL-18 (DR-18), a variant of IL-18 that maintains signaling potential but is impervious to binding and inhibition by IL-18BP. In multiple syngeneic tumor models including YUMMER1.7, MC38, and CT26, we found that recombinant WT IL-18 was ineffective by itself or in combination with anti-PD-1 treatment, similar to the clinical experience of rIL-18 in patients. However, in the same models, DR-18 showed robust monoagent activity that was commensurate or superior to anti-PD-1 antibodies, and it produced added therapeutic synergism when combined with anti-PD-1. Single-cell RNA-seq profiling and flow cytometry analysis of DR-18 treated tumors indicated that DR-18 treatment drives the development of poly-functional effector CD8+ T cells and NK cells. Importantly, DR-18 expands the pool of intratumoral Tcf1+ memory precursor PD1+ CD8+ T cells and decreases the prevalence of exhausted CD8+ T cells that express TOX. Mechanistically, we demonstrate that tumor antigen specific CD8+ T cells were sufficient to mediate tumor regression using LCMV epitope GP33 specific P14 CD8+ T cells in a B16-GP33 model. Together, these results highlight DR-18 is able to remodel the tumor-immune landscape to bias immune cells towards potent anti-tumor effector cells and away from the T exhausted lineage. Therefore, we conclude that the IL-18 pathway is a powerful target for immunotherapeutic intervention and implicate the secreted checkpoint IL-18BP as an obstacle to effective IL-18 immunotherapy. Citation Format: Ting Zhou, Orr-El Weizman, William Damsky, Meaghan McGeary, Marcus W. Bosenberg, Aaron M. Ring. IL-18 pathway agonism expands intratumoral PD1+ Tcf1+ stem-like CD8+ cells and their polyfunctional effector progeny to promote anti-tumor immunity [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2156.