Supplemental Figure S5. IL-18BP blockade alters the immune infiltrate composition of E0771 tumors.

Supplemental Figure S4. Anti-IL-18BP Ab induced immunogenic memory response in E0771 tumor model.

Supplemental Figure S3. Antitumor activity of anti-mouse-IL-18BP Ab in mice studies.

Supplemental Figure S1. IL-18BP is a potential soluble immune checkpoint in cancer.

Supplemental Figure S2. COM503 releases IL-18 activity in biochemical and functional assays.

Abstract Recombinant cytokines have limited anticancer efficacy mostly due to a narrow therapeutic window and systemic adverse effects. IL18 is an inflammasome-induced proinflammatory cytokine, which enhances T- and NK-cell activity and stimulates IFNγ production. The activity of IL18 is naturally blocked by a high-affinity endogenous binding protein (IL18BP). IL18BP is induced in the tumor microenvironment (TME) in response to IFNγ upregulation in a negative feedback mechanism. In this study, we found that IL18 is upregulated in the TME compared with the periphery across multiple human tumors and most of it is bound to IL18BP. Bound IL18 levels were largely above the amount required for T-cell activation in vitro, implying that releasing IL18 in the TME could lead to potent T-cell activation. To restore the activity of endogenous IL18, we generated COM503, a high-affinity anti-IL18BP that blocks the IL18BP:IL18 interaction and displaces precomplexed IL18, thereby enhancing T- and NK-cell activation. In vivo, administration of a surrogate anti-IL18BP, either alone or in combination with anti-PD-L1, resulted in significant tumor growth inhibition and increased survival across multiple mouse tumor models. Moreover, the anti-IL18BP induced pronounced TME-localized immune modulation including an increase in polyfunctional nonexhausted T- and NK-cell numbers and activation. In contrast, no increase in inflammatory cytokines and lymphocyte numbers or activation state was observed in serum and spleen. Taken together, blocking IL18BP using an Ab is a promising approach to harness cytokine biology for the treatment of cancer.

Abstract IL-18 is an inflammasome induced proinflammatory cytokine that augments T and NK cell activity and stimulates IFNγ production. The activity of IL-18 is naturally blocked by a high affinity endogenous binding protein (IL-18BP). IL-18BP is induced in the tumor microenvironment (TME) in response to IFNγ upregulation in a negative feedback mechanism. By evaluating 88 human tumor specimens and serum samples we were able to show that IL-18 is upregulated in the TME (median 11.2ng/gr) compared to serum samples (median 0.3ng/ml). Moreover, we showed that most of the IL-18 is bound by IL-18BP. IL-18BP-bound IL-18 levels were largely above the amount required for T cell activation in vitro (1.2ng/gr), implying that blocking IL-18BP has the potential to release IL-18 in tumors above the minimum range required for immune system stimulation. Next, to assess whether tumor endogenous IL-18 levels released by IL-18BP blockade are sufficient to provoke anti-tumor responses, COM503, a high affinity (<1pM) anti-IL-18BP Ab, was generated and examined in T and NK cell-based assays. In a co-culture assay of tumor cells with ex-vivo stimulated human tumor infiltrating CD8+ lymphocytes, COM503 was able to displace IL-18 from a pre-formed complex and enhance IFNγ (197%, p<0.01) and TNFα (84% p<0.01) secretion. Additionally, COM503 induced human NK cell activation as reflected by increased IFNγ secretion (26-fold, p<0.001). Finally, in human ex vivo dissociated tumor cells assay, COM503 mediated an increase in Granzyme B (25%), IFNγ (38%), TNFα (58%) and IL-12 (50%) production. In vivo, administration of an anti-mouse IL-18BP Ab resulted in potent anti-tumor responses and increased survival across multiple mouse tumor models. In orthotopic E0771 tumor model, anti-IL-18BP Ab induced significant tumor growth inhibition (91% TGI, p<0.0001), as well as pronounced TME-localized immune modulation. This modulation included an increase in CD8+ T cells expansion (108.5%, p=0.015) and activation, specifically in polyfunctional effector IFNγ+GrB+CD8+ T cells (259%, p=0.02) and IFNγ+TNFα+NK cells (77%, p=0.001). Similarly, anti-tumor effects were shown in MC38OVAdim model (58% TGI, p<0.001), accompanied by a robust TME-localized immune modulation including increased CD8+ T cells expansion (85%, p=0.009) and IFNγ secretion (76%, p=0.052). In contrast to immune modulation in the TME, no increase in inflammatory cytokines and lymphocyte numbers or activation state was observed in serum and spleen. Taken together, our data suggest that IL-18 is upregulated in the TME, mostly bound by IL-18BP, and could be exploited to induce pronounced TME-localized immune modulation. Anti-IL-18BP Ab approach has a leading edge in inhibiting tumor growth while avoiding peripheral toxicity associated with administration of a cytokine. COM503 is currently undergoing IND-enabling studies. Citation Format: Assaf Menachem, Zoya Alteber, Gady Cojocaru, Tal Fridman Kfir, Dan Blat, Olga Leiderman, Moran Galperin, Lital Sever, Nadav Cohen, Keren Cohen, Roy Zvi Granit, Sandra Vols, Masha Frenkel, Lior Faigenbloom, Liron Soffer, Karin Meyer, Keren Menachem, Hadas Galon Tilleman, Dina Morein, Itamar Borukhov, Amir Toporik, Michal Perpinial Shahor, Evgeny Tatirovsky, Pierre Ferre, Eran Ophir. Unleashing natural IL-18 activity using an anti-IL-18BP blocker antibody induces potent immune stimulation and anti-tumor effects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4072.