ISG15 and lung cancer: Therefore, IRF1 and STAT1 were knockdown in lung cancer A549 cells (Fig. 2C), which decreased 20 ng/mL of IFNα/γ-mediated gene expression, including IRF1, STAT1 (Fig. 2C), PD-L1, CXCL10, and ISG15 (Fig. 2D).