Spatially segregated APOE⁺ macrophages restrict immunotherapy efficacy in clear cell renal cell carcinoma

Background: Immunotherapy has revolutionized cancer treatment and holds great potential for them, including metastatic clear cell renal cell carcinoma (ccRCC). However, immune resistance remains a major obstacle, limiting its efficacy and durability. Understanding the mechanisms of immune tolerance in the tumor microenvironment (TME) is pivotal for overcoming these challenges and enhancing therapeutic outcomes. Methods: Over 2000 samples, including a real-world cohort of 230 advanced ccRCC patients treated with immune checkpoint blockade (ICB) were analyzed. Single-cell RNA sequencing data from 13 tumor regions were categorized into ICB-exposed, ICB-resistant, and ICB-responsive groups. Multiple robust algorithms and multiplex immunofluorescence were used to explore TME composition and macrophage heterogeneity. Spatial communication dynamics were further investigated. In vitro experiments were performed to evaluate the impact of SPP1 on 786-O and 769-P cells. Co-culture experiments with THP-1-derived macrophages, followed by Western blot, flow cytometry, and functional assays, were performed to investigate SPP1-mediated macrophage polarization and its impact on tumor progression. Results: The results revealed an elevated presence of Apolipoprotein E (APOE)⁺ macrophages in ICB-resistant ccRCC. Notably, higher APOE⁺ macrophage proportion indicated shorter prognosis and worse response to ICB (P < 0.001). Elevated expression of CCAAT Enhancer Binding Protein Delta (CEBPD) was markedly linked to several immunosuppressive pathways, hindering T cell recruitment, promoting exhaustion, ultimately diminishing poorer prognosis and worse ICB efficacy. Meanwhile, upregulated Secreted Phosphoprotein 1 (SPP1) significantly enhances the proliferation, clonal formation, and migration of ccRCC cells. Tumor-derived SPP1. Additionally, SPP1 signaling from malignant cells appeared to recruit APOE⁺ macrophages to tumor margins, and promotes macrophage polarization into APOE⁺ M2-like macrophages. In the vicinity of the tumor, these APOE⁺ macrophages shape immunosuppressive TME by releasing abundant TGF-β signals, limiting anti-tumor effector T cells activity in ICB-resistant tumors, and contributing to tumor progression. Conclusion: This study reveals the critical role of APOE⁺ macrophages in promoting immune suppression and resistance to ICB therapy in ccRCC. By promoting T cell exhaustion and immunosuppressive signaling, particularly via localized TGF-β, these spatially segregated macrophages undermine treatment efficacy. Targeting APOE⁺ macrophages, especially in conjunction with ICB, presents a promising strategy to overcome immune resistance and enhance outcomes for ccRCC patients.