Abstract 1625: VHH nanobody-masked conditionally active CDH17 T cell engager for colorectal cancer

Abstract T cell engagers (TCEs) bind antigens on tumor cells on one arm and CD3-TCR complex on the other arm to induce cytotoxic immune synapses and redirect nonspecific T cells to kill in a specific manner. TCEs have demonstrated convincing efficacy in multiple blood cancers and have recently with Tarlatamab made breakthrough in solid tumors. However, major hurdles remain for the realization of the full potential of this exciting modality in solid tumors - most importantly the lack of clean and specific antigens. CDH17 is a type-1 transmembrane glycoprotein of the cadherin superfamily and its expression is normally restricted to the lateral area of epithelial tight junctions of the intestines and the pancreatic duct. CDH17 is highly expressed in over 95% of colorectal cancers, and its upregulation and tumor tissue disorganization results in disoriented CDH17 expression susceptible to T cell surveillance In order to accommodate CDH17 that is highly expressed on tumor cells but is indeed present on some normal tissues, we developed a next-generation conditionally active masked CD3 TCE platform. Instead of using traditional linear peptide masks that oscillate and are prone to digestion, we generated anti-idiotypic VHH nanobody specifically for our clinical stage CD3 binder (NCT05579132). The structured VHH masking moiety prevents premature unmasking and activation. In addition, we designed enzyme cleavable linker specifically to be resistant to enzymes that are highly expressed in normal tissues. These designs ensured good tolerability. Anti-idiotypic VHH mask binds CD3 binder with high affinity and fine-tuned kinetics. VHH-masked CD3 binder is no longer able to induce effective T cell killing. The newly designed cleavable linker can be effectively cut by certain MMPs and other enzymes enriched in the tumors. The resulting masked CDH17xCD3 TCE showed good serum stability and remained inactive after extensive incubation. Once activated with corresponding enzymes, the VHH mask is effectively released and the TCE is activated to induce potent tumor cell killing. In multiple CDX models of human tumors, masked CD3 TCE demonstrated convincing in vivo efficacy on par with the corresponding non-masked TCE. Moreover, exploratory toxicity study in NHP showed significantly higher MTD and improved safety profile. WuXi Biologics has developed a conditionally active CDH17 TCE with the proprietary VHH-masked CD3 TCE platform. The molecule has demonstrated great efficacy and better tolerability preclinically, and is to be further evaluated in the clinic. Citation Format: Lei Wu, Guoxin Ni, Xiaoyue Liu, Sha Cheng, Senfeng Xiang, Yi Liu, Xia Wang, Donghui Wu, Tengfei Yu, Jijie Gu, . VHH nanobody-masked conditionally active CDH17 T cell engager for colorectal cancer 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 1625.