Denosumab Enhances Antitumor Immunity by Suppressing SPP1 and Boosting Cytotoxic T Cells

Denosumab, a RANK ligand inhibitor, is primarily used to prevent osteoclastogenesis in the treatment of conditions such as osteoporosis, bone metastasis, and giant cell tumor of bone (GCTB). RANK ligand also plays an important role in immunity by activating NF-κB and its target genes, including the osteopontin-coding gene SPP1 (also known as OPN), which is linked to CXCL9:SPP1 macrophage polarization and prognosis. In this study, we explored an additional role of denosumab in enhancing antitumor immunity in patients. Single-cell RNA sequencing was performed on nine human GCTB samples, including six untreated and three treated only with denosumab, to exclude confounding treatment factors linked with bone metastasis samples. We further analyzed paired samples collected before and after denosumab treatment from a cohort of nine patients with GCTB and conducted a pan-cancer analysis of 34 distinct types of cancers. Our single-cell analysis of GCTB resulted in a comprehensive cell atlas revealing an antitumor role of denosumab in inhibiting SPP1 expression and augmenting active cytotoxic T-cell abundance. Furthermore, we validated this immunomodulatory role of denosumab using the paired GCTB samples. Finally, the pan-cancer analysis supported a negative correlation between SPP1 and CD8A levels, with the CD8A:SPP1 ratio correlating with overall survival in 14 cancer types, which was superior to either CD8A or SPP1 alone. Our research provides clinical evidence that denosumab improves antitumor immunity by decreasing SPP1 expression and enhancing cytotoxic T-cell activity, serving as a milestone in the development of innovative use of denosumab and offering potential benefits to patients with elevated levels of SPP1.