Fig. 1

Histology and immunohistochemistry (IHC) of endomyocardial biopsies from patients treated with immune checkpoint inhibitors. Representative areas of each respective biopsy sample that underwent staining from serial sequential sections are shown. The hematoxylin and eosin (H&E)-stained slides did not show definite evidence of myocarditis by Dallas criteria in either A Patient 5 or C Patient 20 but did demonstrate cardiomyocyte necrosis and loss with increased inflammatory infiltrates in B Patient 25. The CD68 stain showed an increased number of interstitial macrophages that overlap with the inflammatory cell infiltration and the cardiomyocyte necrosis perceived in H&E-stain in E Patient 25. CD68 macrophage stain also showed an increased number of interstitial macrophages in F Patient 20 but not in D Patient 5. Insets show magnified views with arrows highlighting representative CD68 stained macrophages. Scale bar = 100 µm. ID = identification