CD8+ regulatory T (Treg) cells and γδ Treg cells profoundly suppress host immune responses and thus protect against autoimmune disease while restricting desired immune responses such as antitumor immunity. Synthetic phosphorothioate-protected, guanosine-containing oligonucleotides can directly reverse the suppressive activity of Treg cells without involving dendritic cells. This effect appears to be transduced by signaling through Toll-like receptor (TLR) 8 and engagement of the MyD88 and IRAK4 molecules in Treg cells, in specific embodiments. Stimulation of Treg cells with natural ligands for human TLR8 recapitulated the effect of the synthetic guanosine-containing oligonucleotides.