FN1+ macrophages fuel aggressive sarcomatoid differentiation and immunotherapy refractory outcome in clear cell renal cell carcinoma.

Immune checkpoint blockade (ICB) based therapy improved clinical outcomes in clear cell renal cell carcinoma (ccRCC), yet prognosis remains dismal in patients with advanced disease, especially those with sarcomatoid differentiation. Tumor-associated macrophages (TAMs), abundantly infiltrating in the tumor immune microenvironment (TIME), emerge as regulators of tumor evolution and immune evasion. This study aims to characterize the clinical relevance, functional phenotypes, and therapeutic vulnerability of FN1+ TAMs. We performed an integrated analysis across five cohorts to assess the clinical relevance of FN1+ TAMs infiltration in ccRCC. Single-cell and spatial transcriptomics analyses characterized the transcriptomic profiles and spatial distribution of FN1+ TAMs. Flow cytometry analysis further quantified the phenotype of FN1+ TAMs and associated CD8+ T cells features. Ex vivo functional assays using patient-derived tumors assessed the efficacy of FN1 blockade, as well as combination with PD-1 blockade. FN1+ TAMs preferentially enriched in tumors with sarcomatoid differentiation and correlated with epithelial-mesenchymal transition (EMT) signatures. High infiltration of FN1+ TAMs related to immunotherapy resistance and inferior survival outcomes in ccRCC. FN1+ TAMs exhibited an M2-polarized immunosuppressive phenotype and were associated with CD8+ T cells dysfunction. FN1 blockade reversed EMT-associated transcriptional programs, reduced immunosuppressive molecule expression in macrophages, and restored CD8+ T cells effector function. Combination therapy targeting FN1 and PD-1 synergistically enhanced T cell cytotoxicity and tumor cell apoptosis. FN1+ TAMs, enriched in sarcomatoid-differentiated ccRCC, mediate immune suppression and confer resistance to immunotherapy. FN1 blockade remodels the TIME, promotes tumor apoptosis, and represents a potential therapeutic strategy in ccRCC.