Fig. 1

PD-L1 is expressed on melanoma cells located close to T cell-enriched tumor regions. H&E-stained human metastatic melanoma tissues (A, B) with necrotic tissue regions (black asterisk + encircled with white dashed lines). B-F Shows the magnification of the identical region of the tumor as indicated by the black rectangle (dashed lines) in (A). B-F In the viable melanoma tumor tissue (black asterisk), C SOX-10-expressing melanoma cells were discriminated from the (D) CD3 + T cell infiltrate. In addition, viable tumor regions were discriminated from necrotic tumor regions based on (E) Ki67 expression patterns. IHC showed that tumor regions with pronounced (F) PD-L1 expression (black rectangle) were located near the tumor immune cell infiltrate that was identified based on the cell morphology. G At higher magnification (white rectangle) it is visible that PD-L1 positive cells also express SOX-10. The immunofluorescence double staining of PD-L1 and SOX10 (H) of the serial section (F) shows the same region of the tumor (black rectangle) with PD-L1 positive cells surrounding an immune cell infiltrate. Scale bars: 500 μm (A), 100 μm (B-F), 50 μm (H), 20 μm (G)