This is a human IgG1 monoclonal antibody using the same sequences as the therapeutic antibody durvalumab. It functions as a programmed death-ligand 1 (PDL1) blocking antibody, facilitating the promotion of normal immune responses against tumor cells. The expression of PDL1 is an adaptive immune response by tumor cells, resulting in the over-expression of the molecule in some cancers. PDL1 interacts with PD1 and CD80, which leads to blocked cytotoxic T cell activation, T cell proliferation, and cytokine production. By binding to PDL1 and preventing its association with PD1 and CD80, durvalumab stimulates immune responses mediated by cytotoxic T cells that target tumor cells. It exhibits selective and high affinity toward PDL1 but not PDL2, which is expressed to a lesser extent in tumor cells and involved in regulating inflammation and T cell differentiation. Durvalumab is an FDA-approved immune checkpoint inhibitor drug specifically indicated for certain types of bladder, lung and biliary tract cancer.