CRISPR Screening Reveals SAA1-Driven Neutrophil Extracellular Traps Promote CD8⁺ T Cell Dysfunction in Renal Cell Carcinoma.

Immune checkpoint inhibitors are a frontline treatment for metastatic renal cell carcinoma (RCC), one of the most common malignancies of the urinary system. However, a large proportion of patients exhibit poor responses or develop resistance, which severely limits the therapeutic efficacy and patient survival. In this study, we constructed a custom CRISPR activation library based on the top 500 genes upregulated in anti-PD-1-resistant RCC cells. Functional screening identified serum amyloid A1 (SAA1) as a critical mediator of resistance; SAA1 activation promoted immune evasion, while deficiency sensitized RCC cells to anti-PD-1 treatment. SAA1 promoted anti-PD-1 resistance both in RCC patients and in mouse models. Mechanistically, SAA1 bound to toll-like receptor 2 (TLR2) and activated the NF-κB signaling pathway, thereby inducing the formation of neutrophil extracellular traps (NETs). These NETs not only acted as physical barriers that blocked direct contact between CD8⁺ T cells and tumor cells but also promoted CD8⁺ T cell exhaustion, facilitating tumor immune evasion and resistance to immunotherapy. Both in vitro and in vivo experiments demonstrated that suppression of SAA1 significantly reduced NET formation and enhanced the efficacy of immunotherapy. In conclusion, SAA1 promotes immunotherapy resistance in RCC by driving NET formation via the TLR2/NF-κB axis and inducing CD8⁺ T cell dysfunction. Targeting SAA1 may represent a promising strategy to overcome immune resistance in RCC.