PD-L1 is up-regulated on C1498.GFP after injection into wild-type mice. (A) C1498.GFP cells grown in vitro were analyzed for expression of PD-L1 by flow cytometry either at baseline or after in vitro exposure to IFN-γ for 48 hours. The shaded histogram represents staining with an isotype control antibody. The dashed line represents PD-L1 expression at baseline, and the solid line represents PD-L1 expression after exposure to IFN-γ. (B) C57BL/6 mice were challenged with 10⁶ C1498.GFP cells IV. Twelve days later, mice were killed and livers were surgically removed. After generation of single-cell suspensions, the specimens were analyzed by flow cytometry after staining with an anti–PD-L1 antibody and gating on GFP⁺ cells.