CD4 and multiple sclerosis: Through whittling TGF-β signaling and Treg cell induction, let-7i, up-regulated in CD4+ T cells from patients with multiple sclerosis, modulates the pathogenesis of multiple sclerosis (157), while loss of Lin28b expression in fetal T cells leads to increased mature let-7, which reduces fetal T cells differentiate into Treg cells (158).