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

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.