Abstract 3415: Preclinical characterization of LG anti-LILRB1, a potent antagonist targeting LILRB1

Abstract LILRB1 is an inhibitory receptor found on various immune cells, including T cells, B cells, NK cells, and monocytes. It interacts with multiple ligands, including HLA class I molecules, with the highest affinity for HLA-G, and induces inhibitory signals that allow cancer cells to escape cancer immunosurveillance, impeding clearance from immune cells such as NK cells, T cells, and macrophages. This inhibitory effect in the tumor microenvironment may lead to disease progression, tumor metastasis, and poor clinical outcomes. For this reason, the blockade of LILRB1/HLA-G interaction could be a novel therapeutic target for the treatment of cancer. Additionally, recent studies indicate that LILRB1 may play an independent role in T cell functions beyond those regulated by PD1, suggesting that anti-LILRB1 therapy could potentially help in overcoming resistance mechanisms to anti-PD1 treatments. Therefore, LILRB1 is a promising target for cancer immunotherapy in human cancers due to its potential to mediate immune suppression across a wide range of tumor-associated immune cells. The protein-based and cell-based binding affinity of anti-LILRB1 antibody was measured using SPR and FACS analysis. A competitive ligand blocking assay was used to evaluate the ability of anti-LILRB1 antibody to block the interaction of LILRB1 with HLA-G. NK cell-mediated cellular cytotoxicity was evaluated by flow cytometry against HLA-G expressing tumors. The activities of NK cells and T cells were evaluated following the blockade of LILRB1. The in vivo anti-tumor efficacy of anti-LILRB1 antibody was evaluated in the human LILRB1 transgenic mouse and MC38-HLA-G syngeneic model. The binding affinity of the anti-LILRB1 antibody against LILRB1, quantified as 60 kD, was measured using a protein-based assay, and the EC50 was determined to be 20 nM using a cell-based assay. The binding of anti-LILRB1 antibody blocked interaction with HLA-G. In studies using human NK cell line and primary NK cells demonstrated that the anti-LILRB1 antibody enhanced their killing activity against HLA-G expressing tumors. In both systems, anti-LILRB1 antibody increased expression of CD69 and CD137, which are activation markers of NK cells, and IFN-Γ secretion. In LIR-overexpressing Jurkat cell line, anti-LILRB1 antibody enhanced IL-2 secretion. Importantly, the anti-LILRB1 antibody showed tumor growth inhibition in syngeneic model of human LILRB1 transgenic mice with MC38-HLA-G tumor. Based on these preclinical data, phase 1a study is currently ongoing (NCT06332755). Blockade of LILRB1/HLA-G interaction by antibody targeting LILRB1 enhances the immuno-modulatory effect of target immune cells. Furthermore, LILRB1 blockade enhanced anti-tumor efficacy in tumor bearing LILRB1-Tg mice model. These findings suggest that LILRB1 blockade antibodies have the potential to be developed as a therapeutic agent for the cancer immunotherapy for further investigation. Citation Format: Seok-Joo Kim, Younghoon Kim, Han Byoul Kim, Junhaeng Cho, Minsoon Kim, JungA Kim, Suji Hong, Heehang Kim, Shin-Young Kang, Hyungjin Cho, Jeeyeon Roh. Preclinical characterization of LG anti-LILRB1, a potent antagonist targeting LILRB1 [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 3415.