Abstract 177: Targeting murine or human KLRG1 exerts potent anti-tumor efficacy involving both CD8T cells and NK cells

Abstract Clinical response to anti-PD-1 immunotherapy is correlated with patients who have a T cell-inflamed tumor microenvironment. Some patients with immune cell infiltration fail to respond, and some patients experiencing an initial clinical response develop acquired resistance. It is likely that additional immune-regulatory pathways need to be targeted to expand the efficacy of immunotherapies. To identify a broader array of therapeutic relevant immunotherapy molecules in T cell-inflamed tumors, our lab utilized gene expression profiling to characterize tumor antigen-specific dysfunctional CD8+ T cells in the tumor microenvironment. One molecule that was found to be overexpressed on these CD8+ T cells was C-type lectin inhibitory receptor, KLRG1. KLRG1 is an ITIM domain-containing receptor mostly explored on NK cells, and the known ligands are N- and E- cadherins which are broadly expressed in solid cancers. Analysis of single cell RNA-Seq data from tumor biopsies of melanoma patients classified as responders or non-responders to anti-PD-1 therapy revealed significantly higher expression of KLRG1 expression on tumor-infiltrating T cell subsets in non-responders, suggesting a possible salvage immune suppressive role. To determine the potential functional relevance of KLRG1 on tumor control, we generated KLRG1 knockout (KO) mice, then implanted tumors and assessed tumor growth rate in vivo. KLRG1 KO mice showed markedly slowed B16 melanoma tumor growth compared to WT mice, arguing it is a critical negative regulator of anti-tumor immunity. Both antigen-specific CD8+ T cells and NK cells were expanded in these tumors, and depletion of CD8+ T cells or NK cells eliminated this tumor control. Genetic deletion of N-cadherin from B16 cells also resulted in slowed tumor growth, suggesting that tumor cells are providing the functionally relevant ligand. To assess the degree of inhibitory function of human KLRG1, we generated a humanized KLRG1 knock-in mouse model. We confirmed that human KLRG1 can biochemically interact with murine cadherins. Knock-in mice with the humanized KLRG1 protein had significantly increased tumor growth compared to both WT and KLRG1 KO mice, indicating a stronger immunosuppressive effect of human KLRG1 compared to murine KLRG1. An antagonistic antibody blocking interaction of human KLRG1 with its ligands was generated, which potentiated human T cell activation in vitro. Administration of anti-human KLRG1 Ab to tumor-bearing humanized KLRG1 mice led to markedly reduced tumor growth. In summary, our data support KLRG1 as a functionally critical negative regulator of the anti-tumor immune response and that blocking KLRG1-cadherin interactions has potential as a therapeutic candidate. Citation Format: Tyler A. Jones, Stephen Sinicrope, Kei Yasuda, Jan Pinkas, Thomas F. Gajewski. Targeting murine or human KLRG1 exerts potent anti-tumor efficacy involving both CD8T cells and NK cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 177.