Aggregation and secondary loop structure of oligonucleotides do not determine their ability to inhibit TLR9

Imbalance in the ratio of CpG and polyG contributes to impaired interferon-α expression

The secretion of interferon-α (IFN-α) is impaired during hepatitis B virus (HBV) infection. DNA sequences purified from distinct viruses, for example, HBV versus members of Herpesviridae, have been shown to differ in their IFN-α signaling properties. The present study found that DNA from HBV inhibited, while DNA from members of Herpesviridae induced, the expression of IFN-α. Furthermore, stimulatory cytosine-phosphate-guanosine (CpG) sequences derived from these DNA viruses could induce the secretion of IFN-α, while inhibitory guanosine-rich oligodeoxynucleoti (polyG) oligonucleotide sequences derived from these DNA viruses could inhibit CpG-induced IFN-α secretion. Using a computational analysis of genomic DNA sequences, the discrimination between the genomes of HBV and those of other DNA viruses that can also cause inflammation of the liver is based on different frequencies of the CpG and polyG motifs. The underrepresentation of stimulatory CpG motifs and overrepresentation of inhibitory polyG motifs were documented in HBV genomes, whereas the DNA from other viral genomes displayed the opposite trend. Moreover, it was demonstrated that HBV could suppress the activation of IFN-α via its own DNA through the high proportion of polyG motifs. To our knowledge, this is the first demonstration of a specific role for polyG motifs in the inhibition of the IFN-α response following DNA virus infection.

Structure, mechanism and therapeutic utility of immunosuppressive oligonucleotides

Synthetic oligodeoxynucleotides that can down-regulate cellular elements of the immune system have been developed and are being widely studied in preclinical models. These agents vary in sequence, mechanism of action, and cellular target(s) but share the ability to suppress a plethora of inflammatory responses. This work reviews the types of immunosuppressive oligodeoxynucleotide (Sup ODN) and compares their therapeutic activity against diseases characterized by pathologic levels of immune stimulation ranging from autoimmunity to septic shock to cancer (see graphical abstract). The mechanism(s) underlying the efficacy of Sup ODN and the influence size, sequence and nucleotide backbone on function are considered.

Guanine-modified inhibitory oligonucleotides efficiently impair TLR7- and TLR9-mediated immune responses of human immune cells

Activation of TLR7 and TLR9 by endogenous RNA- or DNA-containing ligands, respectively, is thought to contribute to the complicated pathophysiology of systemic lupus erythematosus (SLE). These ligands induce the release of type-I interferons by plasmacytoid dendritic cells and autoreactive antibodies by B-cells, both responses being key events in perpetuating SLE. We recently described the development of inhibitory oligonucleotides (INH-ODN), which are characterized by a phosphorothioate backbone, a CC(T)XXX3-5GGG motif and a chemical modification of the G-quartet to avoid the formation of higher order structures via intermolecular G-tetrads. These INH-ODNs were equally or significantly more efficient to impair TLR7- and TLR9-stimulated murine B-cells, macrophages, conventional and plasmacytoid dendritic cells than the parent INH-ODN 2088, which lacks G-modification. Here, we evaluate the inhibitory/therapeutic potential of our set of G-modified INH-ODN on human immune cells. We report the novel finding that G-modified INH-ODNs efficiently inhibited the release of IFN-α by PBMC stimulated either with the TLR7-ligand oligoribonucleotide (ORN) 22075 or the TLR9-ligand CpG-ODN 2216. G-modification of INH-ODNs significantly improved inhibition of IL-6 release by PBMCs and purified human B-cells stimulated with the TLR7-ligand imiquimod or the TLR9-ligand CpG-ODN 2006. Furthermore, inhibition of B-cell activation analyzed by expression of activation markers and intracellular ATP content was significantly improved by G-modification. As observed with murine B-cells, high concentrations of INH-ODN 2088 but not of G-modified INH-ODNs stimulated IL-6 secretion by PBMCs in the absence of TLR-ligands thus limiting its blocking efficacy. In summary, G-modification of INH-ODNs improved their ability to impair TLR7- and TLR9-mediated signaling in those human immune cells which are considered as crucial in the pathophysiology of SLE.

Nanoparticles encapsulating hepatitis B virus cytosine-phosphate-guanosine induce therapeutic immunity against HBV infection

Infection with hepatitis B virus (HBV) is the most common cause of liver disease worldwide. However, because the current interferon (IFN)-based treatments have toxic side effects and marginal efficacy, improved antivirals are essential. Here we report that unmethylated cytosine-phosphate-guanosine oligodeoxynucleotides (CpG ODNs) from the HBV genome (HBV-CpG) induced robust expression of IFN-α by plasmacytoid dendritic cells (pDCs) in a Toll-like receptor 9 (TLR9)-dependent manner. We also identified inhibitory guanosine-rich ODNs in the HBV genome (HBV-ODN) that are capable of inhibiting HBV-CpG-induced IFN-α production. Furthermore, nanoparticles containing HBV-CpG, termed NP(HBV-CpG), reversed the HBV-ODN-mediated suppression of IFN-α production and also exerted a strong immunostimulatory effect on lymphocytes. Our results suggest that NP(HBV-CpG) can enhance the immune response to hepatitis B surface antigen (HBsAg) and skew this response toward the Th1 pathway in mice immunized with rHBsAg and NP(HBV-CpG). Moreover, NP(HBV-CpG)-based therapy led to the efficient clearance of HBV and induced an anti-HBsAg response in HBV carrier mice.

CONCLUSION

Endogenous HBV-CpG ODNs from the HBV genome induce IFN-α production so that nanoparticle-encapsulated HBV-CpG may act as an HBsAg vaccine adjuvant and may also represent a potent therapeutic agent for the treatment of chronic HBV infection.

Modulating toll-like receptor 7 and 9 responses as therapy for allergy and autoimmunity

Type I allergic diseases, such as allergic rhinitis and asthma, depend on allergen-induced T-helper type 2 (Th2) cells and IgE-secreting plasma cells. Fortunately, this harmful immune response can be modified by engaging Toll-like receptor (TLR)7 and TLR9, offering hopes to allergy sufferers. While clinical trials employing synthetic ligands for TLR7 or TLR9 are under way, one can wonder whether TLR7 or TLR9 engagements may trigger inadvertent autoreactivity and/or Th1-/Th17-mediated tissue pathology. To neutralize such danger, we have pioneered the development of potent TLR9 pathway antagonists, inhibitory oligonucleotides (INH-ODNs), which work in a sequence-specific manner. Interestingly, INH-ODNs also have TLR7-inhibitory properties; however, these effects appear to be sequence independent and phosphorothioate backbone dependent. In B cells, co-engagement of the B-cell receptor for antigen and TLR7 or TLR9 may influence how INH-ODNs impose their regulatory effects. INH-ODNs block TLR9 activation by competitively antagonizing ligand binding to proteolytically cleaved C-terminal TLR9 fragment. One may envision future use of INH-ODNs in systemic autoimmune diseases, DNA-mediated sepsis, or other situations in which chronic inflammation results from abnormal TLR7- and/or TLR9-mediated immune activation.