A human immunoglobulin G1 (IgG1) monoclonal antibody directed against the human T-cell-expressed receptor cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4; CTLA4; CD152), with potential immunomodulatory and antineoplastic activities. Upon administration, anti-CTLA-4 monoclonal antibody GIGA-564 targets and binds to CTLA-4, and may induce Fc receptor (FcR) signaling. This may deplete regulatory T-cells (Tregs) in the tumor microenvironment (TME), decrease the proliferation of the remaining Tregs in the TME, and reactivate antitumor immune responses. CTLA-4, an inhibitory receptor and member of the immunoglobulin superfamily (IgSF), plays a key role in the downregulation of the immune system. GIGA-564 has limited checkpoint inhibitory activity as it only weakly blocks the interaction between CTLA-4 and its B7 ligands CD80 and CD86.