Abstract 2866: An innovative T cell engager platform with optimized CD3 affinity and formats for targeting hematologic and solid tumors

Abstract Background: T-cell engagers (TCEs) are a promising class of immunotherapies that bridge T cells to tumor cells, triggering T-cell activation and subsequent tumor cell cytotoxicity. While TCEs demonstrated substantial efficacy in hematologic malignancies, their clinical benefit in solid tumors remains less established. The development of effective TCEs is hindered by challenges related to the complex interplay between CD3 affinity, TCE format, tumor-associated antigen (TAA) density, and specificity. To address these challenges, we have developed an innovative TCE platform designed to optimize CD3 affinity and TCE format to better match TAA expression profile and improve therapeutic efficacy. Methods: Humanized CD3 and TAA-targeting antibodies were generated by Mabwell’s integrated novel antibody discovery system. CD3 activity was assessed through T-cell binding and activation assays, while TAA binding potency was measured using tumor cell binding assays. Various bispecific and trispecific TCE formats were evaluated and optimized for developability, stability, and functional activity. Tumor-directed cytotoxicity (TDCC) assays were used to assess the efficacy of TCEs in vitro, while cytokine release syndrome (CRS) potential was also evaluated. Results: CD3 parental antibodies with varying T-cell binding and activation potencies, including cross-reactivity with monkey CD3, were generated. TAAs were identified and prioritized using a bioinformatics analysis system, leading to the selection of tumor-specific targets such as LILRB4, CLL-1, CLDN6, MUC16, MSLN, CDH17, GUCY2C, SEZ6, DLL3, and ENPP3. Several optimized 1+1, 1+2, and 2+2 TCE formats were developed, demonstrating excellent developability and potent in vitro tumor cell killing. Importantly, these TCEs exhibited minimal cytokine release syndrome (CRS) potential. Our platform also integrates comprehensive indication analysis, target validation, and TCE format optimization, facilitating the identification of multiple TAAs across a broad range of cancer types. Conclusion: Our innovative TCE platform offers a flexible and powerful approach for designing TCEs with enhanced efficacy and minimal CRS. This platform holds significant promise for developing novel T-cell engagers with robust therapeutic activity and favorable safety profiles for both hematologic and solid tumor indications. Citation Format: Cuicui Guo, Yu Pang, Zhen Han, Fenglin Yun, Ao Li, Hai Wu, Xun Gui. An innovative T cell engager platform with optimized CD3 affinity and formats for targeting hematologic and solid tumors [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 2866.