Abstract 3521: A novel T cell engager targeting HLA-A02:01 TP53-R175H for cancer immunotherapy

Background: The tumor suppressor protein p53 (TP53) plays a pivotal role in preventing tumor formation by inducing cell cycle arrest and apoptosis in response to DNA damage. However, TP53 mutations are prevalent across various cancer types, and these mutations not only result in loss of tumor suppressive functions but also confer gain-of-function properties that drive oncogenesis. Among these mutations, HLA-A0201 TP53-R175H represents the largest TP53 population with >34,000 cases per year in the US and EU across all solid tumor indications, with no therapies explicitly targeting this mutation in the clinic. Leveraging Affini-T’s TETHER™ platform, we present the development of a novel TCR-based T cell engager designed to redirect the cytotoxic potential of T cells against mutant TP53-expressing cancer cells. Methods: A bispecific T cell engager was engineered to simultaneously engage T cells via CD3 and target TP53-R175H-expressing cancer cells by an affinity-matured specific TCR. Affinity maturation of the TCR was performed to increase its specificity and binding affinity towards the mutant peptide. Tumor co-culture assays were conducted to evaluate T cell-mediated cytotoxicity. T cell activation was assessed by measuring cytokine production. The tolerability profile of the engagers was established by X-scan, evaluating T cell activation by normal tissue. Results: The data demonstrate successful affinity maturation of the TCR, resulting in enhanced recognition of the HLA-A0201 TP53-R175H peptide with high specificity. Tumor co-culture assays revealed potent T cell-mediated killing of mutant TP53-R175H-expressing cancer cells by the engager, accompanied by robust T cell activation characterized by cytokine production. Importantly, the engager exhibited favorable tolerability profiles, demonstrated by minimal off-target activation via X-scan and with minimal T cell activation towards normal tissue. Conclusions: These findings highlight the promising activity and tolerability profile of a novel T cell engager targeting HLA-A02 TP53-R175H for cancer immunotherapy. Harnessing the cytotoxic potential of T cells against mutant TP53-expressing tumors presents a promising approach for the development of innovative cancer treatments. Citation Format: Mark Ng, Emily Zygiel, Alexander McQuown, Jinsheng Liang, Luhua Shen, Joshua Francis, Xingyue He, Hubert Lam, Gary Shapiro, Loic Vincent. A novel T cell engager targeting HLA-A02:01 TP53-R175H for cancer immunotherapy [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 2521.