Abstract 6008: Effective depletion of tumor-infiltrating Tregs by a novel anti-CCR8 antibody (LM-108): Addressing resistance associated with immune checkpoint inhibitors
Authors: Luo Jie , Huang Wentao , Yang Junwei , Li Jin , Li Yifan , Fei Da , Qin Xia , Li Runsheng 
Published: June 2022

Abstract
Immune checkpoint inhibitors (ICIs) have generated durable clinical responses in multiple tumor types, but their therapeutic efficacy is limited by development of primary or acquired resistance. The tumor microenvironment (TME) contains many factors influencing ICI responses. The ratio of effector T-cells (Teffs) and regulatory T-cells (Tregs) in tumors has been shown to be associated with the efficacy of ICIs in murine models, indicating that increasing Teffs or decreasing Tregs in tumor may prevent development of resistance to immunotherapy. There is a high and restricted expression of CC motif chemokine receptor 8 (CCR8) on tumor-infiltrating Tregs, whereas they are negligibly expressed on Teffs. Deletion of tumor-infiltrating Tregs via murine anti-CCR8 surrogates has shown effective anti-tumor activity in tumor models.LM-108 is a novel humanized anti-CCR8 monoclonal antibody with engineered IgG1 that enhances antibody-dependent cell-mediated cytotoxicity (ADCC). The expression of CCR8 and Foxp3 on tumor-infiltrating lymphocytes (TILs) was analyzed using published single-cell sequencing data. The binding affinity of LM-108 was assessed by flow cytometry using CCR8 high- and low-expressing cell lines. In vitro measurements of ADCC and antibody-dependent cellular phagocytosis (ADCP) mediated by LM-108 were conducted in CCR8 overexpressing HEK293, CHO-K1, and Jurkat cells. Furthermore, in vivo anti-tumor activity of LM-108 as monotherapy and in combination with anti-PD-1 therapy was evaluated in syngeneic models and PD-1-resistant tumor models with human CCR8 knock-in mice. Analysis of published single-cell sequencing data showed that in comparison with CCR4, CCR8 gene expression was specifically overlapped with Foxp3 in TILs of breast cancer. Fluorescence-activated cell sorting (FACS) assay revealed that LM-108 specifically binds with high affinity to human CCR8 in a dose-dependent manner. ADCC and ADCP effects induced by LM-108 were observed in HEK293 and CHO-K1 cells with different levels of CCR8 expression. In vivo data of CT26 syngeneic model showed that LM-108 murine surrogate antibody alone or in combination with anti-PD-1 antibody significantly inhibited tumor growth. Treatment with LM-108 effectively depleted tumor-infiltrating Tregs accompanied by increase in CD8/Treg ratio in tumors, leading to significant anti-tumor activity in MC38 model. Finally, LM-108 showed a synergistic therapeutic efficacy in PD-1 resistant models in combination with anti-PD-1 antibody. To conclude, LM-108 is a novel Fc-optimized CCR8 antibody that selectively depletes tumor infiltrating Tregs thereby improving anti-tumor immune response either as monotherapy or combination therapy. Thus, LM-108 can be a promising therapeutic approach to overcome ICI resistance in cancer patients.
Citation Format: Jie Luo, Wentao Huang, Junwei Yang, Jin Li, Yifan Li, Da Fei, Xia Qin, Runsheng Li. Effective depletion of tumor-infiltrating Tregs by a novel anti-CCR8 antibody (LM-108): Addressing resistance associated with immune checkpoint inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6008.