Inflammatory composition of EBV⁺and EBV⁻CHL. Representative images from (A) EBV⁺ and (B) EBV⁻ CHL (specimens CHL-23 and CHL-12, respectively; see Table 1) are shown. HRS tumor cells are identified by anti-CD30 IHC and EBER ISH. A predominance of CD8⁺ T cells and IDO⁺ histiocytes was observed in EBV⁺ cases, whereas increased GITR⁺ lymphocytes were seen in EBV⁻ cases. Robust CD3⁺ T-cell infiltrates and PD-L1 expression on HRS cells and infiltrating immune cells were observed regardless of EBV status. Slides were imaged on an Olympus BX46 microscope with an Olympus DP72 camera at ×200 magnification with an aperture of 0.5, and Olympus cellSens Standard 1.5 image acquisition software was used. Bar, 50 μm. H&E, hematoxylin and eosin.