Abstract 6343: AnTenGagerTM, a novel “2+1” T cell engager platform, enables conditional T cell activation with reduced risk of CRS

Abstract Background: CD3+ T cell engaging bispecific antibodies (TCE) redirect T cells to attack targeted tumor cells by simultaneously binding TAA on cancer cells and CD3 complex on a T cell to form a TCR-independent immune synapse. Multiple TCEs have demonstrated promising therapeutic efficacy in the treatment of hematological malignancies. In contrast, suboptimal efficacy in the treatment of solid tumors and the risk of inducing cytokine release syndrome (CRS) continue to be major challenges. Several factors, such as format, affinity, and valency of the antibody, TAA copy number, and antigen size and epitope, can impact the therapeutic efficacy and safety of a TCE. In this study, we developed a novel “2+1” TCE platform, AnTenGagerTM, which enables conditional T cell binding and activation upon TAA-crosslinking, potent anti-tumor activity, and reduced risk of CRS. Methods: Humanized CD3 antibodies were derived from mouse hybridoma, followed by affinity optimization utilizing Computer Aided Drug Design. The Fab-scFv-Fab format was used as the backbone structure of AnTenGagers. The anti-CD3 scFv sequences and the length of peptide linkers between VH/VL, scFv/CH1, and scFv/CH2 were screened and compared in different preclinical assays. LALA mutations (L234A, L235A) were introduced to abolish the Fc receptor binding capability. In a series of in vitro and/or in vivo models, the efficacy, safety and developability of AnTenGagers targeting multiple TAAs, such as Her2, GD2, CDH6, LILRB4, FLT3 and GPRC5D, were evaluated. Results: A library of humanized parental CD3 antibodies with a broad spectrum of affinities were generated, some of which cross react with monkey CD3. AnTenGagers exhibited limited binding to CD3-positive cells before TAA-crosslinking, suggesting a reduced risk of CRS that is caused by systemic CD3+T cell activation. Four CD3 sequences with varying affinities were utilized to construct AnTenGagers with identical TAA-targeting arm. Compared to clinical benchmarks targeting the same TAA, all AnTenGagers demonstrated substantially lower binding capacity to CD3+ cells in the absence of TAA-crosslinking, while inducing increased cytotoxicity against target-positive tumor cells. In addition, they induced significantly less ex-vivo cytokine release by human PBMC than benchmarks. Notably, all AnTenGagers demonstrated enhanced in vivo efficacy compared to the benchmark, exhibiting complete response (CR) in PBMC humanized MM1S mouse CDX model while the serum concentration of proinflammatory cytokines was substantially lower in groups treated with AnTenGagers. AnTenGagers also demonstrated good developability with high expression yield, good thermostability and high stability under different stress conditions. Conclusions: These results suggested that AnTenGagerTM is a promising platform for developing the next generation of TCEs with enhanced efficacy and safety. Citation Format: Bing Hou, Hui Yuwen, Tengteng Li, Yijing Ren, Ao Sun, Zaoshun Hu, Jay Mei, Bo Shan. AnTenGagerTM, a novel “2+1” T cell engager platform, enables conditional T cell activation with reduced risk of CRS [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 6343.