CD4 and autoimmune disease: Tr1 cells and Foxp3+ regulatory T cells are highly immune‐suppressive subsets of CD4+ T cells, and they exert important suppressive and homeostasis effects on cancer, autoimmune disorders, and inflammatory responses (Jia et al., 2019; Josefowicz et al., 2012; Kleinewietfeld & Hafler, 2014; Roncarolo et al., 2014, 2018; Zeng et al., 2015).