Targeting highly attenuated IL-18 to PD-1 for enhanced anti-tumor activity.

Checkpoint inhibitors targeting the PD-1/PD-L1 axis have revolutionized cancer immunotherapy, yet response rates remain limited. To enhance efficacy, next-generation approaches target T cell-activating cytokines to PD-1 via antibodies. The goal is simultaneous checkpoint blockade and cytokine potentiation but fine-tuning cytokine activity such that checkpoint inhibition can be preserved with manageable toxicity has been a difficult challenge. We hypothesized that targeting a highly attenuated interleukin (IL)-18 to PD-1 can activate PD-1+ T cells and oppose exhaustion while antagonizing PD-1. We generated a highly attenuated IL-18 variant, which is resistant to IL-18BP binding and assessed its receptor binding ability. Tumor growth inhibition was evaluated across multiple models. Additionally, we examined post-remission tumor resistance and lymphocyte infiltration into the tumor ex vivo using flow cytometry. The IL-18 fusion resisted interleukin-18 binding protein (IL-18BP) inhibition and exhibited a 10,000-fold reduction in activity while preserving cis-signaling and demonstrated strong efficacy across tumor models. It increased CD8+ progenitor-exhausted tumor-infiltrating lymphocytes (TILs) while reducing myeloid TILs. Attaching a highly attenuated IL-18 to an anti-PD-1 antibody goes beyond simply targeting a cytokine to PD-1, representing a novel cytokine-enhanced checkpoint inhibitor that activates PD-1+ T cells via the cytokine receptor while simultaneously antagonizing PD-1.