Histological analyses of patients and monkey models with ICI-associated myocarditis have revealed that the infiltration of predominant CD4+/CD8+ T lymphocytes and a few macrophages (CD68+ cells) are the main cause of ICI-associated myocarditis (Johnson et al., 2016a; Ganatra and Neilan, 2018; Ji et al., 2019) (Figure 1). The gene discussed is CD8A; the disease is myocarditis.