Abstract 6709: P329G-Engager: A novel universal antibody-based adaptor platform for cancer immunotherapy

Abstract Bispecific immune cell engagers are showing promise in cancer immunotherapy. To achieve optimal efficacy, there is a growing need for patient personalization, tackling intra-tumor heterogeneity, and simplified combination therapies. Here, we present a novel modular anti-P329G adaptor platform aiming to address these issues, which is based on the recognition of the P329G mutation in the Fc portion of a targeting adaptor antibody. This P329G mutation can serve to recruit different anti-P329G effector cell engagers, including innate cell engagers, T cell engagers, costimulators or immunocytokines. Specifically, upon identifying patient-specific tumor surface targets, the primary antigen-binding IgG1 antibodies bearing Fc-silencing P329G LALA mutations are applied. Subsequently, based on the tumor’s immune profile, the best-suited anti-tumoral effector cell type is chosen for recruitment and activation. Based on this information, the secondary antibody recognizing the P329G mutation is chosen from an array of effector cell engagers with different modes of action: P329G-T cell bispecifics (P329G-TCB), ADCC-competent P329G innate cell engagers (P329G-ICE), P329G costimulatory molecules (P329G-CD28/4-1BBL) or P329G immunocytokines (P329G-IL2v). In vitro assays showed all P329G modalities inducing anti-tumoral and/or immunomodulatory cell activity. Anti-tumoral efficacy of secondary antibodies was observed only in presence of tumor-targeted P329G adaptors, while no effect was observed in their absence. The readouts consisted of tumor killing quantification, CD4+ and CD8+ T cell activation, cytokine release and cytokine receptor signaling. As a proof of concept study in vivo, an experiment in MKN-45 (CEACAM5+)-bearing humanized mice was performed, using an anti-CEACAM5 P329G-IgG adaptor and a P329G-TCB. Both tumor volume shrinkage and T cell infiltration into the tumor confirmed anti-tumoral efficacy of the platform, as compared to a conventional CEACAM5-targeted TCB. Neither the individual P329G IgG nor the individual P329G-TCB induced anti-tumoral efficacy, validating the requirement for primary and secondary antibody binding for T cell engaging activity. These results provide in vitro and in vivo evidence that the universal P329G engager platform can be used as an efficacious cancer treatment. Ultimately, this modular approach may enable off-the-shelf personalization via combination of patient-specific antibodies and universal effector cell engagers based on the patient’s tumor target and immune profile. Citation Format: Marlena Surowka, Idil Hutter-Karakoc, Diana Darowski, Christina Claus, Claudia Ferrara Koller, Anne Freimoser-Grundschober, Thomas Hofer, Andrzej Sobieniecki, Denis Assisi, Stephane Leclair, Ekkehard Moessner, Pablo Umaña, Maria Amann, Christian Klein. P329G-Engager: A novel universal antibody-based adaptor platform for cancer immunotherapy [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 6709.