Antibody-cytokine conjugates leverage orthogonal mechanisms of action (MoA) in one molecule to induce potent antitumor immune responses. PD-1-targeting conjugates are of particular interest since they preferentially target antigen-experienced PD-1+ CD8+ T cells enriched in the tumor microenvironment (TME) while simultaneously blocking the PD-(L)1 pathway and inducing potent cytokine receptor stimulation in the same CD8+ T cell in cis (cis-signaling). Interleukin 18 (IL-18) is a proinflammatory cytokine able to integrate both innate and adaptive immunity resulting in profound anti-tumor immune responses mediated by T effector and NK cells. BPT567 has been generated via chemical conjugation of the anti-PD-1 Ab LipustobartTM to an enhanced human IL-18 variant of increased potency and reduced sensitivity to IL-18 binding protein (IL-18BP). BPT567 is designed to specifically target and activate a subset of tumor-infiltrating PD-1+ IL18R+ CD8+ T effector cells recently described to exhibit superior cytotoxic and proliferative activity (Codarri Deak et al., Nature 2022). Due to its ability to signal in cis, BPT567 shows enhanced potency as well as increased resistance to IL-18BP when analyzing IFNγ release in vitro in PD-1+ cells. Subsequent PD-1 receptor occupancy analyses showed that it is fully sufficient for BPT567 to engage a low number of PD-1 receptors to induce maximum IFNγ release in NK92 cells expressing human PD-1. Strikingly, despite addressing overlapping epitopes in PD-1, even a 200-fold excess of pembrolizumab has no impact on the in vitro potency of BPT567. In vivo, BPT567 exhibits strong anti-tumor efficacy at significantly lower IL-18 doses compared to the combination of an untargeted antibody-IL-18 conjugate and an anti-PD1 Ab further corroborating the importance of cis-signaling as a unique MoA of this PD1-IL18 conjugate. Detailed analyses of tumor-infiltrating immune leukocytes (TIL) revealed that BPT567 triggers a preferential expansion of CD8+ T effector memory cells within the TME. In line with this finding, activity in the MC38 tumor model is dependent on the presence of CD8+ T cells while depletion of other immune cell subsets (e.g. NK cells, CD4+ T cells, macrophages) had no impact on efficacy. Although not required for anti-tumor efficacy, CD4+ T cells are essential for proficient formation of an immunological memory. In an effort to confirm findings generated in murine models in relevant human ex vivo systems, we analyzed the release of cytokines and chemokines in dissociated cells isolated from primary human tumor explants. Also in this human model, BPT567 is able to induce significantly stronger IFNγ release compared to either single agents or the combination of untargeted IL-18 and an anti-PD1 Ab, thus confirming the unique MoA of the PD1-IL18 conjugate triggering superior TIL activation in cis.

Citation Format: Kea Martin, Thuy Luu, Jean-Philippe Carralot, Lilian Gremlich, Petra Herzig, Caoimhe Herr, Roy Meoded, Philipp Moosmann, Arnaud Goepfert, Alfred Zippelius, Vijaya Pattabiraman, Bertolt Kreft. The first-in-class PD1-IL18 conjugate BPT567 induces potent anti-tumor immunity by preferentially activating PD1+IL18R+ intratumoral effector T cells in cis [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 4071.