A mechanism of action study of a combination of anti-CTLA-4 and anti-RANKL antibodies in subcutaneous and metastatic murine tumor models revealed improved tumor control, increased cytokine production, and increased T cell recruitment compared with either monotherapy. The synergistic effect gained by blocking the interaction between RANKL+ TILs and RANK+ myeloid cells was depended on cross-presenting Batf3+ DCs.

Purpose: Novel partners for established immune checkpoint inhibitors in the treatment of cancer are needed to address the problems of primary and acquired resistance. The efficacy of combination RANKL and CTLA4 blockade in anti-tumor immunity has been suggested by recent case reports in melanoma. Here we provide a rationale for this combination in mouse models of cancer.
Experimental Design: The efficacy and mechanism of a combination of RANKL and CTLA4 blockade was examined by tumor infiltrating lymphocyte analysis, tumor growth and metastasis using a variety of neutralizing antibodies and gene-targeted mice.
Results: RANKL blockade improved the efficacy of anti-CTLA4 mAbs against solid tumors and experimental metastases, with regulatory T cell (Treg) depleting anti-CTLA4 mAbs of the mouse IgG2a isotype showing greatest combinatorial activity. The optimal combination depended on the presence of activating Fc receptors and lymphocytes (NK cells for metastatic disease and predominantly CD8+ T cells for subcutaneous tumor control), while anti-RANKL alone did not require FcR. The significantly higher T-cell infiltration into solid tumors post anti-RANKL and anti-CTLA-4 was accompanied by increased T-cell effector function (cytokine polyfunctionality), and anti-RANKL activity occurred independently of Treg depletion. The majority of RANKL expression in tumors was on T cells whereas RANK-expressing cells were mostly tumor-associated macrophages (TAMs), with some expression also observed on dendritic cells (DC) and myeloid derived suppressor cells (MDSCs).
Conclusions: These results provide a rationale for the further investigation of RANKL-RANK interactions in tumor immunity and a basis for development of translational markers of interest in human clinical trials.

Author Info: (1) Immunology in Cancer and Infection Laboratory, QIMR Berghofer Medical Research Institute. (2) Cancer Immunoregulation and Immunotherapy Laboratory, QIMR Berghofer Medical Resea

Author Info: (1) Immunology in Cancer and Infection Laboratory, QIMR Berghofer Medical Research Institute. (2) Cancer Immunoregulation and Immunotherapy Laboratory, QIMR Berghofer Medical Research Institute. (3) Immunology in Cancer and Infection Laboratory, QIMR Berghofer Medical Research Institute. (4) Cancer Immunoregulation and Immunotherapy Laboratory, QIMR Berghofer Medical Research Institute. (5) Division of Cell Biology, Biomedical Research Center, Juntendo University, Graduate School of Medicine. (6) Department of Immunology, Juntendo University School of Medicine. (7) Medical Oncology, Royal Brisbane and Women's Hospital. (8) Immunology in Cancer and Infection, QIMR Berghofer. (9) Cancer Immunoregulation and Immunotherapy Laboratory, QIMR Berghofer Medical Research Institute. (10) Immunology in Cancer and Infection Laboratory, QIMR Berghofer Medical Research Institute mark.smyth@qimrberghofer.edu.au.