A recombinant human heavy chain only antibody (HCAb) directed against the human T-cell-expressed receptor cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4;CTLA4), with potential immune checkpoint inhibitory and antineoplastic activities. Upon administration, anti-CTLA-4 monoclonal antibody HBM4003 targets and binds to CTLA-4 expressed on T-cells, and inhibits the CTLA-4-mediated downregulation of T-cell activation. This leads to a cytotoxic T-lymphocyte (CTL)-mediated immune response against cancer cells. In addition, HBM4003 induces an antibody-dependent cell cytotoxicity (ADCC). CTLA-4, an inhibitory receptor and member of the immunoglobulin superfamily (IgSF), plays a key role in the downregulation of the immune system. HBM4003, being a HCAb, is smaller than conventional antibodies which may allow for increased tissue penetration.