Abstract 6017: L19-mTNF as a novel synergistic combination partner to enhance the efficacy of CD3-based bispecific antibodies in colorectal cancer

Abstract T-cell-engaging bispecific antibodies (TCBs) are an expanding modality in immunotherapy, designed to redirect T-cell cytotoxicity toward tumor cells by cross-linking them with tumor-associated antigens1. While TCBs have shown significant efficacy in hematological malignancies, their success in solid tumors remains limited2. This is likely due to multiple factors, including the low number of T cells in the tumor microenvironment and the presence of immunosuppressive conditions that hinder T-cell activity3, 4. In this study, we evaluated the potential of three clinical-stage antibody-cytokine fusion proteins as combination partners to enhance the efficacy of a CEA-targeting CD3-based TCB in a challenging solid tumor model. Using the murine colorectal cancer cell line MC38-CEA, we combined the TCB with L19-mTNF, L19-mIL12, and L19-mIL2. Among these, L19-mTNF demonstrated remarkable synergistic anti-tumor activity, achieving complete tumor regression in treated mice, a significant improvement compared to the limited activity of either agent alone.Our findings suggest that TNF enhances TCB activity by transforming "cold" tumors into "hot" ones. L19-mTNF appears to increase vascular permeability within the tumor microenvironment, improving T-cell and TCB infiltration and amplifying the immune response.These results highlight the novel potential of L19-mTNF as a powerful combination partner for CD3-based TCBs, offering a promising strategy to overcome the challenges of solid tumor immunotherapy. This preclinical work provides a strong rationale for future clinical translation, underscoring the importance of integrating cytokine-based therapies to maximize TCB efficacy in solid malignancies. 1. Labrijn, A. F., Janmaat, M. L., Reichert, J. M., & Parren, P. W. H. I. (2019). Bispecific antibodies: A mechanistic review of the pipeline. Nature Reviews Drug Discovery, 18(8), 585-608. https://doi.org/10.1038/s41573-019-0028-1 2. Kassner, J., et al. (2024). Current landscape of CD3 bispecific antibodies in hematologic malignancies. Trends in Cancer, 10(8), 708-732.3. Appleman, L. J., & Boussiotis, V. A. (2003). T cell anergy and costimulation. Immunological Reviews, 192, 161-180.4. Mueller, D. L., Jenkins, M. K., & Schwartz, R. H. (1989). Clonal expansion versus functional clonal inactivation: A costimulatory signalling pathway determines the outcome of T cell antigen receptor occupancy. Annual Review of Immunology, 7(1), 445-480. Citation Format: Gudrun Thorhallsdottir, Ramon Benz, Emanuele Puca, Mattia Matasci, Dario Neri, Abdullah Elsayed. L19-mTNF as a novel synergistic combination partner to enhance the efficacy of CD3-based bispecific antibodies in colorectal cancer [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 6017.