Abstract 2636: Tumor microenvironment-activated T-cell engager (TMEA-TCE) targeting claudin 6 demonstrates efficacy without inducing cytokine release syndrome.

Abstract The CD3 protein complex serves as a critical role of T cell activation and signal transduction. While CD3 T-cell engagers (TCEs) are highly potent, they can elicit severe adverse immune effects on various normal tissues due to pervasive T cell activation and excessive inflammatory cytokine release, leading to cytokine release syndrome (CRS) and limiting their therapeutic margin. CLDN6, a member of the claudin family of tight junction proteins, is highly expressed in multiple solid tumors such as ovarian, endometrial, testicular, and gastric cancers, but rarely in healthy adult tissues. The CLDN6-CD3 TCE demonstrates high affinity and specificity for CLDN6, without cross-reactivity to CLDN9 or CLDN4. To enhance tumor selectivity and address CD3-associated toxicity, CLDN6-CD3 TCE is further engineered via chemical conjugation of a legumain-cleavable linker that masks the variable region of the anti-CD3 domain, leading to the formation of a tumor microenvironment-activated (TMEA)-TCEs and the development of CLDN6-CD3 TMEA-TCE (IMD-1743). IMD-1743 can be activated by legumain, an active protease overexpressed extracellularly in the TME, triggering the release of TCE in the TME or in vitro. This activation strategy follows the same proof-of-concept demonstrated by the successful phase 3 studies of legubicin, an albumin-drug conjugate (ALDC). IMD-1743 exhibited dose-dependent anti-tumor activity in human ovarian PA-1 and OVCAR3 as well as human hepatocellular carcinoma HepG2-Luc mouse models at doses of 1, 3, and 10 mg/kg. Complete tumor elimination was observed in the ovarian PA-1 model at 3 and 10 mg/kg, with no associated mouse weight loss. Preclinical toxicology studies in cynomolgus monkeys showed that IMD-1743 was well tolerated after repeated dosing of 15 mg/kg, with no evidence of CRS based on serum cytokine assays. Pharmacokinetic studies in cynomolgus monkeys revealed high concentrations of IMD-1743 and minimal free TCE, indicating that the molecule is highly stable in circulation. In summary, these findings highlight a favorable therapeutic margin for IMD-1743 as a safe and effective TCE candidate targeting claudin 6. The strong preclinical efficacy combined with its tolerability profile supports further clinical development of IMD-1743 to address the significant unmet medical needs of patients with CLDN6-expressing tumors. Citation Format: Chengli Ding, Cheng Liu, Yuan Liu, . Tumor microenvironment-activated T-cell engager (TMEA-TCE) targeting claudin 6 demonstrates efficacy without inducing cytokine release syndrome abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 2636.