Tumor-derived KLK5 activates TMEM158+ cancer-associated fibroblasts to induce CD8+ T cell exhaustion and confer immunotherapy resistance in lung cancer.

AIM: Immune checkpoint blockade (ICB) has improved the treatment landscape of lung squamous cell carcinoma (LUSC), but durable clinical benefit is limited by frequent therapeutic resistance. We aimed to define the microenvironmental mechanisms underlying ICB resistance in LUSC. METHODS: Surgical specimens from LUSC patients treated with neoadjuvant anti-PD-1 therapy plus chemotherapy were analyzed using integrated single-cell and spatial transcriptomics. Our findings were validated in independent bulk RNA-seq and multiplex immunofluorescence cohorts and functionally tested in fibroblast-specific conditional knockout and humanized mouse models. RESULTS: We identified a TMEM158⁺ cancer-associated fibroblast (CAF) subpopulation enriched in non-responders and associated with poor prognosis. Spatial and functional analyses showed that TMEM158⁺ CAFs promoted CD8⁺ T-cell exhaustion. Mechanistically, tumor-derived KLK5 engaged TMEM158, recruited SDCBP, activated the MEK/ERK-ELK1 signaling axis, and induced TNC and SPP1 expression, thereby establishing an immunosuppressive niche. Genetic ablation or functional inhibition of TMEM158⁺ CAFs enhanced sensitivity to anti-PD-1 therapy in LUSC. CONCLUSION: TMEM158⁺ CAFs are key stromal mediators of immune evasion and ICB resistance in LUSC and represent a promising biomarker and therapeutic target.