Targeting CXCR4-expressing TAMs in muscle-invasive bladder cancer to enhance tumor control after immunotherapy

Bladder cancer (BC) is a prevalent malignancy with poor prognosis in advanced stages. While immune checkpoint blockade has revolutionized immunotherapy, its efficacy remains limited for most advanced BC patients. The detailed characterization of BC’s tumor microenvironment (TME) is a prerequisite to understand these mechanisms of resistance and to develop new therapeutic strategies. In this study, we used a genetically engineered BC mouse model resistant to anti-PD1 treatment, and BC patient samples, to investigate the evolution of tumor-associated macrophages (TAMs) during BC progression. We identified a subset of pro-tumor TAMs expressing CXCR4, predominantly found in advanced stages of BC-bearing mice and in half of muscle-invasive BC patients from the studied cohort. Interestingly, CXCR4 ⁺ TAM-rich regions were associated with CD8 T cell-excluded areas in both mice and patients. Administration of a small molecule CXCR4 inhibitor significantly reduced the number of pro-tumor TAMs within the tumor and markedly prolonged mouse survival. Incorporating this inhibitor into a tri-immunotherapy regimen further enhanced survival, highlighting the potential of targeting multiple pathways to strongly enhance anti-tumor effects and offering new hope for improving immunotherapy in advanced BC.