An agonistic, humanized monoclonal antibody against receptor OX40 (CD134), with potential immunostimulatory activity. Upon administration, anti-OX40 monoclonal antibody MEDI0562 selectively binds to and activates the OX40 receptor. OX40 receptor activation induces proliferation of memory and effector T-lymphocytes. In the presence of tumor-associated antigens (TAAs), this agent may promote an immune response against TAAs-expressing tumor cells. OX40, a cell surface glycoprotein and member of the tumor necrosis factor (TNF) receptor family, is expressed on T-lymphocytes and provides a co-stimulatory signal for the proliferation and survival of activated T-cells.