CD4 and myocarditis: Endomyocardial biopsy is the gold standard diagnostic procedure, and the immunohistochemical staining of irAE-myocarditis typically shows predominantly CD8+ T cells interspersed with CD4+ T cells and macrophages.3 In addition, several articles3,4 have described the up-regulation and positive staining of PD-L1 in myocardial tissue in irAE-myocarditis.