Patient-derived organoid-immune co-cultures integrated with multi-omics reveal immunotherapy resistance mechanisms in urothelial carcinoma.

Immunotherapy resistance presents a formidable challenge in tumor biology. While fibroblast growth factor receptor 3 (FGFR3) serves as a pivotal oncogenic driver in a multitude of cancers, the exploration of its role in immune checkpoint inhibitor (ICI) resistance remains scarce, thus impeding a deeper understanding of the tumor immune microenvironment (TIME) in the era of immunotherapy. Employing patient-derived urothelial carcinoma (UC) organoids and co-cultured systems, along with single-cell RNA sequencing (scRNA-seq), whole-exome sequencing (WES), bulk RNA-seq, and CUT& Tag epigenomics in UC cohorts, we identified and characterized the key downstream mediators of FGFR3. The TIME associated with FGFR3 mutations exhibited a depletion of NK and CD8+ T cells, while simultaneously harboring an accumulation of exhausted effectors, correlating with diminished ICI response. Erdafitinib reprogrammed this "cold" TME into an inflamed state through a novel FGFR3-STAT5-IRF2 signaling cascade. These findings, corroborated by a wealth of evidence, advocate for the combination of FGFR3-targeted therapy with immunotherapy for UC, bridging critical pre-clinical and clinical insights.