An agonistic monoclonal antibody targeting the co-stimulatory receptor OX40 (CD134; tumor necrosis factor receptor superfamily member 4; TNFRSF4), with potential immunostimulatory and antineoplastic activities. Upon administration, anti-OX40 agonist monoclonal antibody BGB-A445 selectively binds to OX40, thereby activating OX40. This induces the proliferation of memory and effector T-lymphocytes and results in a T-cell-mediated immune response against tumor cells, which leads to tumor cell lysis. OX40, a cell surface glycoprotein and member of the tumor necrosis factor receptor superfamily (TNFRSF), is expressed on T-lymphocytes and provides a co-stimulatory signal that promotes both the proliferation and survival of activated T-cells.