Abstract 6087: A novel Ly6G6D/4-1BB bispecific antibody targeting DNA mismatch repair proficient colorectal cancers shows potent antitumor activities

Abstract HEC921 is a novel bispecific agonistic antibody targeting Lymphocyte Antigen 6 Family Member G6D (Ly6G6D) and the immune agonistic receptor 4-1BB for the treatment of colorectal cancers. Ly6G6D is a tumor associated antigen highly expressed in DNA mismatch repair proficient (pMMR) colorectal cancers frequently resistant to immune check-point therapies. Activating monoclonal antibodies against 4-1BB have shown clinical efficacy but was limited by systemic toxicity. The design of HEC921 enables Ly6G6D-dependent agonism of 4-1BB in the presence of Ly6G6D positive tumor cells, enabling tumor specific T cell activation while minimizing systemic immune toxicity. A high affinity antibody against Ly6G6D and a nanobody against 4-1BB were identified for the construction of HEC921 containing an ADCC-silenced Fc. HEC921 shows potent co-binding to both Ly6G6D and 4-1BB targets and is cross reactive to the cynomolgus orthologues. In an assay using 4-1BB high expression 293 cells with NFκB-luciferase reporter, HEC921 mediated 4-1BB activation in the presence of Ly6G6D positive cells but not Ly6G6D negative cells. HEC921 promoted the production of cytokines IFN-γ, IL-2, and IL-4 in co-cultures of human T cells and Ly6G6D positive tumor cell lines. HEC921 demonstrated effective tumor growth inhibition in xenograft models of Ly6G6D positive tumor lines. Initial drug feasibility and toxicity studies results of HEC921 were favorable. Overall result demonstrated that HEC921 is a promising candidate for Ly6G6D positive cancer immunotherapy. Citation Format: Zhiheng Ren, Xiang Li, Shushan Lin, Kuo Zhang, Zhaofeng Li, Xiao Lin, Kaifeng Li, Ju Peng, Mi Zheng, Wen Yang, LiJia Li, Xiaoping Li, Stewart Leung. A novel Ly6G6D/4-1BB bispecific antibody targeting DNA mismatch repair proficient colorectal cancers shows potent antitumor activities [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 6087.