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

Area of Science:

• Immunology
• Molecular Biology
• Oligonucleotide Chemistry

Background:

• Previous research indicated 5'-terminal secondary structures in CpG DNA significantly influence activity more than 3'-terminal structures.
• The accessibility of the 5'-end of CpG DNA for activity suggests a directional reading mechanism by the receptor.

Purpose of the Study:

• To design and evaluate self-stabilized CpG DNAs, featuring a 3'-terminal hairpin-loop structure, for their immunomodulatory potential.
• To investigate the differential roles of CpG motifs and secondary structures in activating human B cells and plasmacytoid dendritic cells (pDCs).

Main Methods:

• Design of immunomodulatory oligonucleotides (IMOs) with a nine-mer stimulatory domain containing a CpG motif and a 3'-terminal hairpin-loop.
• Assays involving human B-cell proliferation and interferon-alpha (IFN-alpha) secretion in pDC cultures.
• Modification of the hairpin duplex region with oligodeoxynucleotides and oligo-2'-O-methylribonucleotides to form heteroduplexes.

Main Results:

• Self-stabilized CpG DNAs effectively stimulated human B-cell proliferation and induced high levels of IFN-alpha secretion from pDCs.
• CpG motifs were sufficient for B-cell activation, while both stimulatory sequences and secondary structures were necessary for pDC activation.
• CpG motifs were not essential for activity within the hairpin duplex region; heteroduplex formation enabled activation of both cell types.

Conclusions:

• Self-stabilized CpG DNAs are potent immunomodulators capable of activating key immune cells.
• The structural organization of CpG DNA, particularly the 5'-end and hairpin structures, plays a critical role in differential immune cell activation.
• Modified oligonucleotide structures offer versatile strategies for developing novel immunomodulatory therapeutics.