Formalin-fixed and paraffin-embedded specimens were sectioned at 5 μm thickness and mounted on glass slides. The PD-L1 (clone 5H1) antibody was obtained from Lieping Chen (12 (link)). In brief, antigen retrieval was achieved with citrate buffer. Anti-PD-L1/B7-H1 murine IgG (1:1000) was applied on tissue sections overnight at 4°C. After washing with TBS (0.05 M Tris base, 0.9% NaCl, pH 8.4), tissue sections were incubated with biotinylated anti-mouse IgG (1:100; BA-2001, Vector Laboratories) followed by incubation with Elite ABC kit for 30 min at room temperature. Antibody binding was detected with the TSA Biotin System (NEL700A001KT, PerkinElmer) and DAB (DAKO, K3468). Murine PD-L1 staining was performed using the polyclonal antibody against mouse B7-H1/PD-L1 antibody (1:100, R&D Systems). Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and KIT immunostaining (1:200, D13A2; Cell Signaling Technology) were performed as described (24 (link)). Slides were analyzed and imaged on the Axio Imager 2 wide-field microscope (Zeiss).