CD274 and cancer: To further interrogate the influence of platelet-derived PD-L1 on PD-L1 negative cancer cell growth, we inoculated PD-L1−/− mice subcutaneously with PD-L1 knockout MC38 cells followed by platelet depletion via injection of a platelet-depleting antibody which targets mouse glycoprotein (GP) IBα (GPIBα) on platelets.