Tumor-stromal crosstalk and macrophage enrichment are associated with chemotherapy response in bladder cancer.

Gemcitabine/Cisplatin (Gem/Cis) chemotherapy is a standard treatment for muscle-invasive bladder cancer (MIBC) but yields suboptimal response rates. The contribution of tumor-stromal crosstalk and macrophage recruitment to chemoresistance remains poorly understood. This study investigated these mechanisms using a functional ex vivo bladder cancer tissue slice model combined with n = 64 spatial transcriptomics. Spatial analysis revealed transcriptomic changes involving the immunomodulating gene SPP1 that has been also recently presented as a putative predictive biomarker for neoadjuvant chemotherapy in bladder cancer. Moreover, Non-Responders exhibited upregulation of chemokines including CXCL1 and CXCL8 and enrichment of immunoregulatory M2 macrophages in tumor regions, suggesting active macrophage recruitment from the stroma. On the contrary, Responders showed upregulation of complement components, proinflammatory macrophage subsets and signals associated with cytotoxic lymphocyte recruitment. Tissue slices corresponding cell cultures confirmed overexpression of immunomodulating markers including checkpoints PD-L1 and PD-L2 in Non-Responder cancer cells upon Gem/Cis treatment. Using TCGA bladder cancer data, the transcriptomic gene set was further validated revealing a prognostic signature associated with patients' outcome. These findings uncover a novel mechanism of chemotherapy resistance in bladder cancer driven by tumor-stromal interactions and macrophage recruitment and suggest that targeting macrophage infiltration may improve chemotherapy response in bladder cancer.