An agonistic monoclonal antibody against receptor OX40 (CD134), with potential immunostimulatory activity. Mimicking the natural OX4 ligand (OX40L), anti-OX40 monoclonal antibody selectively binds to and activates the OX40 receptor. Receptor activation induces proliferation of memory and effector T lymphocytes. In the presence of tumor associated antigens (TAAs), this may promote an immune response against the TAA-expressing tumor cells. OX40, a cell surface glycoprotein and member of the tumor necrosis factor (TNF) receptor family, is expressed by CD4 T cells and provides a costimulatory signal for T cell activation.