Phosphorothioate-modified oligodeoxynucleotides inhibit human cytomegalovirus replication by blocking virus entry

Area of Science:

• Immunology
• Virology
• Molecular Biology

Background:

• Toll-like receptor 9 (TLR9) agonists, like CpG oligodeoxynucleotides (ODNs), are known to offer indirect protection against viral infections via cytokine induction.
• The direct antiviral potential of CpG ODNs remains largely unexplored.

Purpose of the Study:

• To investigate the direct antiviral activity of CpG ODNs against human cytomegalovirus (HCMV).
• To elucidate the mechanism of action and identify key molecular components responsible for the observed antiviral effects.

Main Methods:

• Treatment of primary fibroblasts and endothelial cells with various CpG ODNs and viral pathogens (HCMV, murine CMV, HSV-1, adenovirus, VSV).
• Assessment of viral replication inhibition and viral entry inhibition using techniques like pp65 nuclear localization and input viral DNA detection.
• Comparative analysis of ODNs with and without CpG motifs, and variations in backbone structure (phosphorothioate vs. phosphodiester).

Main Results:

• Specific CpG ODNs demonstrated potent, near-complete suppression of HCMV replication in human cells and murine CMV replication.
• Antiviral activity was most effective when ODNs were added before or during virus adsorption, suggesting inhibition of early viral entry.
• Inhibitory activity was observed even with ODNs lacking CpG motifs, but was dependent on the phosphorothioate backbone, not the CpG sequence itself.

Conclusions:

• CpG ODNs possess a previously unrecognized direct antiviral activity against HCMV, primarily by inhibiting viral entry.
• The antiviral mechanism is linked to the ODN's phosphorothioate backbone, independent of TLR9 activation via CpG motifs.
• These findings suggest a novel therapeutic avenue for developing anti-HCMV agents based on ODN structure.