Bregs negatively regulate antitumor immunity through different mechanisms: 1) they produce immunosuppressive mediators such as cytokines (e.g. IL-10, TGF-β and IL-35) and IDO-1, which can suppress the proliferation and activation of T and NK cells 40; 2) Bregs inactivate these immunostimulatory cells by expressing immune checkpoints (e.g. PD-L1) 77; 3) when Bregs express the death-inducing molecule Fas ligand (FASL), they will induce the apoptosis of effector T cells 78; 4) Bregs promote tumor progression by secreting TGF-β for epithelial-mesenchymal transition (EMT) 79. The gene discussed is IDO1; the disease is neoplasm.