Bone remodeling associated with CTLA-4 inhibition: an unreported side effect

Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is an important component of the immune checkpoint pathway. CTLA-4 inhibition causes T-cell activation and proliferation, increases T-cell responsiveness, and enhances the anti-tumor immune response. CTLA-4 inhibition also results in immune-related adverse reactions such as colitis, hepatitis, and endocrinopathies. Preclinical investigations have recently shown that CTLA-4 inhibition can cause cytokine-mediated increase in bone remodeling.1,2(p4) Ipilimumab, a recombinant IgG1 kappa antibody against human CTLA-4, has been approved for use in unresectable or metastatic melanoma. We hypothesize that ipilumumab results in increase in bone remodeling manifesting as an autoimmune reaction.