Immune modulation with RANKL-blockade through denosumab treatment in cancer patients

Denosumab is a fully human monoclonal antibody that binds receptor activator of nuclear factor-κB ligand (RANKL) and is routinely administered to cancer patients to reduce the incidence of new bone metastasis. RANK-RANKL regulates bone turnover by controlling osteoclast recruitment, development, and activity. However, this interaction also can regulate a broad range of immune cells including dendritic cells and medullary thymic epithelial cells (mTECs). Inhibition of the latter results in reduced thymic negative selection of T cells and could enhance the generation of tumor-specific T cells. We examined whether administering denosumab could modify modulate circulating immune cells in cancer patients. Blood was collected from 23 prostate cancer patients and 3 renal cell carcinoma patients, who provided written informed consent, with advanced disease who were receiving denosumab, prior to and during denosumab treatment. Using high-dimensional mass cytometry, we found that denosumab treatment by itself induced modest effects on circulating immune cell frequency and activation. We also found minimal changes in the circulating T cell repertoire and the frequency of new thymic emigrants with denosumab treatment. However, when we stratified patients by whether they were receiving chemotherapy and/or steroids, patients receiving these concomitant treatments showed significantly greater immune modulation, including an increase in the frequency of NK cells early and classical monocytes later. We also saw broad induction of CTLA-4 and TIM3 expression in circulating lymphocytes and some monocyte populations. These findings suggest that denosumab treatment by itself has modest immunomodulatory effects, but when combined with conventional cancer treatment, can lead to the induction of immunologic checkpoints. Serial blood samples were collected from patients starting standard of care denosumab at UCSF. Patients had blood drawn for PBMC isolation and cryopreservation from the following timepoints: TP1 is pre-denosuman treatment, TP2 is prior to dose 2, TP3 is prior to dose 3, and TP4 is prior to dose 6.