Abstract 3463: A novel nanobody based IL-18 surrogate cytokine agonist, used alone or combined with immune checkpoint inhibitors, demonstrated synergistic tumor suppression

Abstract IL-18 is a cytokine belonging to IL-1 family regulating both innate and acquired immune responses, acting on innate lymphocytes and antigen-experienced T cells to produce interferon gamma (IFNγ). However, clinical efficacy of IL-18 monotherapy in cancer patients has been proved to be slight, which is mainly caused by the upregulation of IL-18 binding protein (IL-18BP), a decoy protein that binds IL-18 with extremely high affinity, produced in the tumor microenvironment. In this study, we have developed an innovative approach to activate IL-18 receptors without the need for the cytokine itself. We achieved this by employing human IL-18Ra and human IL-18Rb-targeting nanobodies, which mimic the natural IL-18 cytokine. This strategy leads to the formation of functional receptor dimers and initiates the subsequent signaling cascade. IL-18Ra and IL-18Rb nanobodies with high affinity were selected out from the immune libraries constructed from PBMCs isolated from camels immunized with IL-18Ra and IL-18Rb respectively. And then IL-18Ra/IL-18Rb bispecific nanobodies were constructed and evaluated for their induction of IFNγ release in primary peripheral blood mononuclear cells (PBMCs). Modality with best IFNγ stimulation was chosen for further development. And the humanized most potent IL-18Ra/IL-18Rb nanobody was named LQ058. Compared to wild type IL-18, LQ058 demonstrated superior IFNγ stimulation from PBMCs. And CD8+ T cells RNA-sequencing evaluation demonstrated that LQ058 is IL-18BP resistant. In human PK59 and H23 tumor xenograft models, LQ058 illustrated better tumor growth suppression compared with wild type IL-18. Meanwhile, LQ058 showed synergistic tumor inhibition when administrated together with anti-PD-1 or anti-CTLA4 therapies. Besides, LQ058 is designed to have extended half-life which would improve medication convenience. Overall, these positive characteristics of LQ058 make it a promising therapy possible to overcome the limitations of current IL-18 therapies for malignant tumor treatment. Citation Format: Yakun Wan, Min Zhu, Junwei Gai, Yanyang Nan, Yuping Huang, Xuyao Zhang. A novel nanobody based IL-18 surrogate cytokine agonist, used alone or combined with immune checkpoint inhibitors, demonstrated synergistic tumor suppression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3463.