A minimal human immunostimulatory CpG motif that potently induces IFN-γ and IFN-α production

Abstract

Recent reports have shown that immunostimulatory sequences (ISS) containing CpG motifs have minimal length requirements (≥12 bases) for the exertion of immune-enhancing function upon mammalian cells. Herein we demonstrate that short ISS (5-7 bases), which exhibit no activity on their own, induce IFN-γ and IFN-α secretion from human peripheral blood mononuclear cells when adsorbed to the surface of cationic poly(D, L-lactide-co-glycolide) microparticles (cPLGA). Utilizing this technique, we discovered a minimal ISS sequence for induction of IFN-γ and IFN-α from human cells: 5′-TCGXX-3′. These short ISS/cPLGA formulations targeted PDC in similar fashion to longer ISS ODN, the activity of which does not require (but is enhanced by) cPLGA. PDC stimulated with short ISS/cPLGA responded with enhanced uptake of ISS and elevated production of cytokines, including IFN-α. However, ISS-responsive B cells did not respond to short ISS/cPLGA, underlining the plasmacytoid dendritic cell selectivity of this formulation. These results describe a novel technique for formulating active, but very short, ISS oligodeoxynucleotide that allows for the dissection and characterization of minimal immunostimulatory CpG motifs.