IDDF2024-ABS-0157 Targeting tumor-intrinsic METTL5 reverses immune exclusion and enhances anti-PD-1 therapy efficacy in intrahepatic cholangiocarcinoma

<h3>Background</h3> Intrahepatic cholangiocarcinoma (ICC) is an aggressive and heterogeneous malignancy derived from the biliary tract in the liver, with poor prognosis and limited treatment options. In this study, we explore the role of METTL5 in promoting ICC progression by reshaping the tumor immune microenvironment and its therapeutic potential. <h3>Methods</h3> Liver-specific <i>Mettl5</i> knockout (cKO) mouse model and human ICC samples were employed to investigate the role of METTL5 in ICC progression. Functional and mechanistic studies were performed using single-cell transcriptomic (scRNA-seq) and T-cell receptor sequencing (scTCR-seq), flow cytometry and <i>in vitro</i> experiments. The efficacy of METTL5 knockdown using lipid nanoparticle-encapsulated siRNA and anti-PD-1 antibody was evaluated <i>in vivo</i>. <h3>Results</h3> By establishing ICC tumors in <i>Mettl5</i> wildtype and cKO mice, we show that <i>Mettl5,</i> as the 18S rRNA m⁶A methytransferase, promotes ICC progression via reshaping tumor immune microenvironment. scRNA-seq and scTCR-seq analysis unraveled intratumoral IFN-γ⁺CD8⁺ T cell infiltration and expansion as well as reduction of immunosuppressive Ms4a7⁺C1qa⁺ tumor-associated macrophages (TAMs) in <i>Mettl5</i> cKO mice. Mechanistically, METTL5-mediated 18S rRNA m⁶A modification downregulated the mRNA translation of <i>CXCL16</i> to exclude CD8⁺T cells, while upregulated <i>CX3CL1</i> to recruit TAMs for ICC tumorigenicity. Concordantly, low METTL5 expression correlated with increased CD8⁺T cells and decreased TAMs in human ICCs, which correlated with better prognosis and responsiveness to immunotherapy. Combined METTL5 targeting using lipid nanoparticle encapsulated siRNA and PD-1 blockade provoked anti-tumor immunity to eradicate ICC tumors, highlighting the strong immuno-evasive ability of METTL5 as a promising therapeutic target. <h3>Conclusions</h3> METTL5 regulates the translation of chemokine mRNA through ribosome 18S rRNA m⁶A modification, and targeting METTL5-mediated immunosuppression unleashes anti-tumor immunity and improves the efficacy of anti-PD-1 therapy.