CD4 and immunoglobulin G4-related sclerosing disease: CD4+ CTLs have been previously identified in human with chronic viral infections (Appay et al., 2002), hepatocellular carcinoma (Zheng et al., 2017), and autoimmune fibrotic diseases, including IgG4-RD (Allard-Chamard et al., 2021; Maehara et al., 2017; Mattoo et al., 2016, 2017; Yabe et al., 2021).