Unleashing natural IL-18 activity using an anti-IL-18BP blocker antibody induces potent immune stimulation and anti-tumor effects

Recombinant cytokines have limited anti-cancer efficacy mostly due to narrow therapeutic window and systemic adverse effects. IL-18 is an inflammasome induced proinflammatory cytokine that enhances T and NK cell activity and stimulates IFNg 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 IFNg upregulation in a negative feedback mechanism. In this study we found that IL-18 is upregulated in the TME compared to the periphery across multiple human tumors and most of it is bound to IL-18BP. Bound IL-18 levels were largely above the amount required for T cell activation in vitro, implying that releasing IL-18 in the TME could lead to potent T cell immune activation. To restore the activity of endogenous IL-18 we generated COM503, a high affinity anti-IL-18BP antibody (Ab), that blocks the IL-18BP:IL-18 interaction and displaces pre-complexed IL-18 to enhance T cell and NK cell activation. In vivo, administration of a surrogate anti-IL-18BP Ab, either alone or in combination with anti-PD-L1 Ab, resulted in significant tumor growth inhibition and increased survival across multiple mouse tumor models. Moreover, anti-IL-18BP Ab induced pronounced TME-localized immune modulation including an increase in polyfunctional non-exhausted 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 IL-18BP using an Ab is a promising novel approach to harness cytokine biology for the treatment of cancer. E0771 tumor cells were inoculated in C57Bl/6 mice. At tumor volume of 250mm^3, mice were randomized (n=6 per group) and either treated with anti-IL-18BP Ab or isotype control (15mg/kg) twice a week for total of 3 treatments. Tumors were harvested 24 hours after the 3rd treatment and enzymatically dissociated to generate cell suspension, following CD45 enrichment cells were profiled using 10x Chromium X.