Bone metastases diminish extraosseous response to checkpoint blockade immunotherapy through osteopontin-producing osteoclasts.

Bone metastatic lesions typically associate with suboptimal responses to immune checkpoint blockade (ICB) therapies. In this study, we observed that across multiple clinical cohorts and a variety of mouse models, the presence of osseous metastases induces ICB resistance in extraosseous tumors. Mechanistically, this long-distance communication is mediated by osseous tumor-conditioned osteoclasts producing osteopontin (OPN). Through circulation, OPN reprograms the extraosseous tumor microenvironment and impairs T cell recruitment and differentiation of CD8+TCF1+ precursor cells, an essential population for ICB efficacy. In mice, ICB responsiveness is restored by αRANKL blockade of osteoclastogenesis, neutralization of OPN in circulation, or tissue-specific depletion of OPN in osteoclasts. Both the mode of action and therapeutic benefit were validated in clinical cohorts with the αRANKL-ICB combinatory regimen. These findings establish bone as a specific immunoregulatory organ exploited by tumor metastasis and suggest osteoclastogenesis as a promising target to improve ICB prognosis in patients with bone metastasis.