RNA molecules such as single-stranded RNA (ssRNA) and small interfering RNA (siRNA) duplexes induce Toll-like receptor (TLR)–mediated immune stimulation after intracellular delivery. We have previously shown that selective incorporation of 2′-O-methyl (2′OMe) residues into siRNA abrogates cytokine production without reduction of gene silencing activity. Here we show that 2′OMe-modified RNA acts as a potent inhibitor of RNA-mediated cytokine induction in both human and murine systems. This activity does not require the direct incorporation of 2′OMe nucleotides into the immunostimulatory RNA or that the 2′OMe nucleotide–containing RNA be annealed as a complementary strand to form a duplex. Our results indicate that 2′OMe RNA acts as a potent antagonist of immunostimulatory RNA. We further show that 2′OMe RNA is able significantly to reduce both interferon-α (IFN-α) and interleukin-6 (IL-6) induction by the small-molecule TLR7 agonist loxoribine in human peripheral blood mononuclear cells (human PBMCs), in murine Flt3L dendritic cells (Flt3L DCs), and in vivo in mice. These results indicate that 2′OMe-modified RNA may have utility as an inhibitor of TLR7 with potential applications in the treatment of inflammatory and autoimmune diseases that involve TLR7-mediated immune stimulation.
