Immunohistochemistry of tumor-associated immune cells

PD-L1 and PD-1 positive IC were tested for additional common immune marker proteins in 81 of the cases (IHC: CD8⁺, CD4⁺, FoxP3, CD68, CD163, CD79a). PD-L1-positive ICs were predominantly found positive for CD68 and CD163 (Figs. S1, 2). Cytomorphology was compatible with PD-L1-positive monocytes / macrophages. PD-1 positive ICs co-localized with cells positive for lymphocytic marker proteins (CD4⁺, FoxP3, CD8⁺, CD79a) but not with monocytic markers (CD68, CD163) (Fig. S3). Cytomorphology was compatible with PD-1 positive lymphocytes, however, stainings were performed on individual, subsequent paraffin sections, precluding detailed co-localization studies.