OX40,also known as CD134 or TNFRSF4 ,is a member of the TNFR superfamily.OX40 is a co-stimulatory receptor,and it interacts with its ligand to provide a positive signal for T cell activation. OX 40 is not expressed on naive T cells, however its expression goes up after 24 to72 hours following activation.Disruption of the OX40 pathway leads to defective T cell responses, and overexpression of OX4O causes massive immune activation. Due to its importance in keeping immune homeostasis, strategies modulating the OX40 pathway hold great promise in efforts against cancer and autoimmune diseases.