SLFN11 Drives GM-CSF–mediated M1 Macrophage Polarization and Enhances Immunotherapy Response in Renal Cell Carcinoma

Background/Aim: Advanced renal cell carcinoma (RCC) is commonly treated with immune checkpoint inhibitor (ICI)-based therapies. However, patient responses vary, and predictive biomarkers remain limited. Here, we demonstrate that Schlafen 11 (SLFN11), which has emerged as an important gene in immunity and drug response, acts as a key enhancer of antitumor immunity in advanced RCC. Materials and Methods: We analyzed transcriptome data from in-house and public RCC patient cohorts to evaluate associations between SLFN11 expression, clinical outcomes, and immune contexture. Transcriptome profiling of RCC cell lines was performed to identify SLFN11-regulated cytokines. Functional assays included co-culture of wild-type or SLFN11-knockout RCC cells with M0 macrophages, immature macrophages, followed by cytokine quantification and phenotypic analyses. Multiplex immunofluorescence staining was applied to formalin-fixed paraffin-embedded samples from ICI-treated patients to validate immune cell infiltration in the tumor microenvironment. Results: Clinically, patients with SLFN11-high RCC treated with ICI-based regimen showed significantly prolonged progression-free survival in both our cohort and public datasets. SLFN11-high RCC tumors exhibited increased infiltration of anti-tumoral M1 macrophages and up-regulation of immune-related pathways compared to SLFN11-low tumors. Mechanistically, transcriptome as well as proteome analysis revealed that, in RCC cells, SLFN11 significantly up-regulated the expression of colony stimulating factor 2 (CSF2) encoding granulocyte-macrophage colony-stimulating factor (GM-CSF), which promotes polarization from M0 macrophages to M1 macrophages. Consequently, SLFN11-positive RCC cells co-cultured with M0 macrophages secreted significantly higher levels of GM-CSF than SLFN11-negative cells and promoted M1 macrophage differentiation. Consistently, multiplex immunofluorescence staining of RCC patient sample analysis confirmed that the number of M1 macrophages was significantly higher in the tumor microenvironment of SLFN11-high tumor than in SLFN11-low tumor. Conclusion: SLFN11 enhances antitumor immunity in RCC by increasing GM-CSF secretion and activating M1 macrophages, potentially improving ICI efficacy.