9p24.1 amplification and PD-1 ligand cell-surface expression in HL and MLBCL cell lines. Flow cytometric analysis of cell-surface PD-1 ligand (PD-L1 and PD-L2) expression in DLBCL, MLBCL, and HL cell lines (PD-L1 or PD-L2, open black lines; isotype controls, solid gray histograms). DLBCL and HL cell lines are arranged according to PD-1 ligand copy number (normal to high, left to right).