Profiling immunostimulatory small interfering (si)RNAs. (a) A panel of siRNAs including negative and positive controls were evaluated in an in vitro human peripheral blood mononuclear cell (PBMC) assay as described previously  with supernatants examined for tumor necrosis factor (TNF) (left panel) and interferon-α (right panel) levels. The right-hand side of each panel has a chemically unmodified siRNA, which is compared with the same sequence after incorporation of a combination of phosphorothioate and 2'-O-methyl chemical modifications. (b) The left-hand panels show a series of immunostimulatory (A-D) and non- immunostimulatory (X-Z) siRNAs evaluated in an in vitro PBMC assay. The right-hand panel shows plasma cytokine profiles in mice injected intravenously with the same siRNAs formulated in LNP01 . Common immunostimulatory siRNAs are identified by the in vitro and in vivo assays.