Ipilimumab is a human cytotoxic T-lymphocyte antigen 4 (CTLA-4) blocking antibody used to treat metastatic or unresectable melanoma.Ipilimumab is a fully humanized IgG1 monoclonal antibody that blocks cytotoxic T lymphocyte antigen-4 (CTLA-4). Blocking CTLA-4 removes an inhibitory signal from reducing the activity of T lymphocytes.Cytotoxic T-lymphocyte antigen-4 (CTLA-4) is an inhibitory molecule that competes with the stimulatory CD28 for binding to B7 on antigen presenting cells. CTLA-4 and CD28 are both presented on the surface of T-cells. Ipilimumab is a human IgG1 that binds CTLA-4, preventing the inhibition of T-cell mediated immune responses to tumors.