Abstract 6705: A novel tri-specific T cell engager targeting the intracellular oncoprotein WT1

Abstract Background: Wilms' tumor gene 1 (WT1) is considered an oncogenic factor, with high expression observed in several hematological malignancies and solid tumors. However, its expression is rarely found in normal adult tissue. WT1 can be degraded by the proteasome, processed and presented on the cell surface as major histocompatibility complex (MHC) I epitopes and recognized by T cell receptors (TCR). Here, we described the development of WT1-TOPAbody, a novel tri-specific T cell engager (TCE), that activated T cells by both CD3 and 4-1BB signaling upon recognition of WT1 in the context of HLA-A02, leading to superior anti-tumor efficacy. Materials and Methods: WT1-TOPAbody was evaluated for its antigen binding activity and target specificity by a series protein/peptide and cell-based assays. In vitro cytotoxicity and T cell activation mediated by WT1-TOPAbody was further assessed in a panel of WT1+ tumor cell lines in coculture with effector cells. Anti-tumor activity was investigated in a humanized syngeneic mice model bearing WT1/HLA-A02 expressing tumors. Safety assessment including cytokine release assay (CRA) and preliminary CMC developability was also performed. Results: WT1-TOPAbody exhibited superior binding affinity to the WT1/HLA-A02 complex while displaying lower binding to off-target peptides and CD34+ HSC from healthy donor than clinical benchmark WT1-CD3 bispecific antibody, RG-6007. WT1-TOPAbody effectively induced tumor lysis in multiple WT1+ tumors including leukemia, ovarian, breast, and colon cancer cells. Moreover, serial killing of tumor cells were observed in WT1-TOPAbody treated T cells, accompanied by lower exhaustion markers expressed, suggesting a prolonged anti-tumor inhibition effect of WT1-TOPAbody. In a humanized CD3e/4-1BB/HLA-A2.1 mouse model, WT1-TOPAbody significantly inhibited tumor growth in a dose-dependent manner and the efficacy was superior than that of the benchmark. Additionally, IL-6 release was minimal in PBMC upon treatment of the antibody, indicating a reduced risk of inducing cytokine release syndrome (CRS). Drug developability assessment indicated that the leading WT1-TOPAbody was a reasonably developable molecule to be taken forward. Conclusion: WT1-TOPAbody is a differentiated WT1/HLA-A02 targeted T cell engagers that displayed potent and durable anti-tumor activity. These results collectively support the potential of WT1-TOPAbody as a novel therapeutic agent against WT1/HLA-A02+ cancers and warrant its further development. Citation Format: Shan Gao, Liu Yang, Jun Du, Wenqing Jiang, Lei Fang. A novel tri-specific T cell engager targeting the intracellular oncoprotein WT1 [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 6705.