MiR-21 expression was significantly elevated in the serum of diffuse large B-cell lymphoma (DLBCL) patients, and it promoted inducible co-stimulator (ICOS) expression on Tregs, thereby assisting the COS ligand (ICOSL) on endothelial cells to crosstalk with Tregs (117). The gene discussed is ICOSLG; the disease is diffuse large B-cell lymphoma.