Tumor-associated macrophages educated by IGSF9 exhibit a senescence-associated secretory phenotype to promote tumor immune escape.

backgroundIGSF9, immunoglobulin superfamily member 9, has been reported to inhibit T cell proliferation and activation, thereby promoting tumor immune escape. Tumor-associated macrophages (TAMs), the most abundant tumor-infiltrating immune cells, play a crucial role in forming the immunosuppressive tumor microenvironment. We find that IGSF9 strongly binds to TAMs, however, how it affects TAMs function remains unreported.

methodsThe spatial transcriptomics dataset (GSE189487) was analyzed to clarify the relationship among IGSF9, senescent TAMs, and T cells. RNA-seq revealed differentially expressed genes. Flow cytometry was employed to assess the binding of IGSF9-ECD proteins to macrophages. Macrophage-educated by IGSF9 were co-cultured with T cells, and the phagocytosis was observed. Membrane-system yeast two-hybrid screening, GST pull-down, and co-IP were used to identify the binding partner of IGSF9. Cellular senescence markers and the senescence-associated secretory phenotype (SASP) were assessed by flow cytometry and immunofluorescence. LL/2-control or LL/2-

resultsThe spatial transcriptomics dataset (GSE189487) revealed that the level of IGSF9 in tumor cells was positively correlated with the senescence of TAMs, and RNA-seq revealed the differentially expressed genes which were related to senescence. Macrophage educated by IGSF9 exhibited distinct senescence phenotypes and immunosuppressive features, and IGSF9 bound to TMUB1 to activate the IL-6/STAT3 signal pathway to trigger the above phenotype. In vivo data showed that IGSF9 could induce TAM senescence, leading to inhibition of T cell activity and formation of an immunosuppressive microenvironment, then promoting tumor immune escape. Treatment with anti-IGSF9, including the LALAPG-mutant variant that reduces antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis, mitigated TAM senescence and immunosuppression, activated T cells, and suppressed tumor growth.

conclusionsTMUB1 as a binding protein of IGSF9 is first discovered, and TAMs educated by IGSF9 exhibit senescent and suppressive phenotype to orchestrate an inhibitory tumor microenvironment, which can be reversed by anti-IGSF9 to suppress tumor progression.