G-Quadruplex Structure Improves the Immunostimulatory Effects of CpG Oligonucleotides

Area of Science:

• Immunology
• Molecular Biology
• Oligonucleotide Chemistry

Background:

• Unmethylated cytosine-phosphate-guanine (CpG) oligodeoxynucleotides (ODNs) activate Toll-like receptor 9 (TLR9) and innate immunity.
• Current CpG ODN immunotherapeutics often use phosphorothioate backbones, which can cause adverse effects.
• There is a need for nuclease-resistant CpG ODNs with improved safety profiles.

Purpose of the Study:

• To design and evaluate novel, nuclease-resistant, non-modified CpG ODNs that form G-quadruplex structures.
• To assess the impact of G-quadruplex formation on CpG ODN stability, cellular uptake, and immunostimulatory activity.

Main Methods:

• Design of CpG ODNs incorporating G-quadruplex forming sequences.
• Assessment of nuclease resistance and cellular uptake of designed CpG ODNs.
• Evaluation of interleukin-6 production in human B lymphocyte cell lines and peripheral blood mononuclear cells.

Main Results:

• G-quadruplex formation significantly enhanced the nuclease resistance of non-modified CpG ODNs.
• Cellular uptake of G-quadruplex forming CpG ODNs was increased compared to controls.
• The designed G-quadruplex CpG ODNs effectively induced interleukin-6 production, indicating immunostimulatory activity.

Conclusions:

• G-quadruplex formation is a viable strategy to enhance the stability and immunostimulatory potential of CpG ODNs with natural phosphodiester backbones.
• This approach offers a promising avenue for developing safer and more effective CpG ODN-based immunotherapeutics.
• G-quadruplex CpG ODNs represent a novel class of immune-stimulating agents with potential therapeutic applications.