CD274 and neoplasm: Antitumor activity was evaluated in double knock-in (dKI) transgenic C57BL/6 mice engineered with human PD-L1 (hPD-L1) and a 4-1BB extracellular domain that were subcutaneously engrafted with MC38 tumor cells transfected with hPD-L1 (MC38-hPD-L1) to establish tumors (Fig. 2A).