Abstract 5663: Discovery and characterization of anti-LILRB2 antibody SPX-104

Abstract T-cell based immunotherapies have produced durable remission in certain cancer patients, but owing at least partially to immunosuppression in the tumor microenvironment, response rates with current therapies remains challenging. Reversing the immunosuppression is a recognized pathway for enhancing the activity of existing IO therapies. LILRB2 (ILT4) is a key receptor for macrophage maturation and polarization and an emerging therapeutic target in immuno-oncology. This research aims to produce anti-LILRB2 antibodies to redirect the polarization of myeloid cells, specifically macrophages, in the tumor microenvironment. The LILRB2 antibodies were generated through the mouse hybridoma method. After humanization and maturation, potent and selective IgG4 anti-LILRB2 antibodies were obtained. Binding affinities were evaluated through ELISA and 293T-LILRB2 cell flow cytometry binding assays which demonstrated sub-nanomolar binding affinity as well as effective blocking of the interaction of LILRB2 with its ligands HLA-G and HLA-A2 for multiple antibodies. SPX-104 was shown to redirect macrophage polarization in primary cultured human PBMC and human monocyte derived macrophage (HMDM) models. SPX-104 treatment induced hTNFa expression and suppressed hIL10 expression in the LPS stimulated PBMC model. In the HMDM model, SPX-104 effectively induced pro-inflammatory cytokine hTNFα expression in M-CSF. Furthermore, an autologous mixed lymphocyte reaction (auto-MLR) assay to evaluate T cell response showed dose-dependent increases in hIFNγ and hGM-CSF expression following SPX-104 treatment. In a CD34-humanized hLILRB2 transgenic mouse efficacy model, SPX-104 in combination with an immune checkpoint inhibitor, effectively inhibited tumor growth. These results confirm enhanced T cell activity following macrophage redirected polarization. The in vitro and in vivo evaluation, of SPX-104 relative to other anti-LILRB2 antibodies will be presented. Citation Format: Anthony Haight, Qian Chen, Ernesto Rodriguez, Martin Siekierzycki, Victoria Hall, Brandon Williams, Jun Shi, Dinh-Duc Nguyen, Robert Cai, Jichun Ma, Michael White, Jingdong Qin, Jadon Shen, Chuanke Zhao, Zhuona Rong, Lin Meng, Chengchao Shou. Discovery and characterization of anti-LILRB2 antibody SPX-104. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5663.