CD274 and cancer: Consequently, several checkpoint inhibitors, such as anti-PD-L1 monoclonal antibody, have been developed to block this inhibitory pathway and reactivate T-cell activity against cancer cells.6,9 High levels of PD-1 expression are detected in circulating and tumor-infiltrating lymphocytes in different cancer tissues.10–13 These antibodies function by blocking tumor PD-L1-PD-1 interaction that preserves the PD-1 expressing anti-tumor T cell function, so that they can attack tumor cells expressing PD-L1.