Self-stabilized CpG DNAs optimally activate human B cells and plasmacytoid dendritic cells

Abstract

We recently showed that 5 ′-terminal secondary structures in CpG DNA affect activity significantly more than those at the 3 ′-end [Biochem. Biophys. Res. Commun. 306 (2003) 948]. The need for an accessible 5 ′-end of CpG DNA for activity suggested that the receptor reads the DNA sequence from this end. In continuation of these studies, we have designed immunomodulatory oligonucleotides (IMOs), consisting of a nine-mer stimulatory domain, containing a CpG motif and a hairpin-loop structure at the 3 ′-end, referred to as self-stabilized CpG DNAs. We studied the ability of self-stabilized CpG DNAs to stimulate human B-cell proliferation and interferon-α (IFN-α) secretion in plasmacytoid dendritic cell (pDC) culture assays. Self-stabilized CpG DNAs activated human B cells and induced plasmacytoid dendritic cells to secrete high levels of IFN-α. While both stimulatory and secondary structures in CpG DNAs were required for pDC activation, CpG motifs were sufficient to activate B cells. Interestingly, CpG motifs were not required for activity in the hairpin duplex region. Further modifications of the hairpin duplex region with a mixture of oligodeoxynucleotides and oligo-2 ′- O-methylribonucleotides in a heteroduplex formation permitted activation of both human B cells and pDCs.