Effect of suppressive DNA on CpG-induced immune activation

DNA-based hydrogels for bone regeneration: A promising tool for bone organoids

DNA-based hydrogels stand out for bone regeneration due to their exceptional biocompatibility and programmability. These hydrogels facilitate the formation of spatial bone structures through bulk hydrogel fabricating, microsphere formatting, and 3D printing. Furthermore, the bone microenvironment can be finely tuned by leveraging the degradation products, nanostructure, targeting, and delivery capabilities inherent to DNA-based materials. In this review, we underscore the advantages of DNA-based hydrogels, detailing their composition, gelation techniques, and structure optimization. We then delineate three critical elements in the promotion of bone regeneration using DNA-based hydrogels: (i) osteogenesis driven by phosphate ions, plasmids, and oligodeoxynucleotides (ODNs) that enhance mineralization and promote gene and protein expression; (ii) vascularization facilitated by tetrahedral DNA nanostructures (TDNs) and aptamers, which boosts gene expression and targeted release; (iii) immunomodulation achieved through loaded factors, TDNs, and bound ions that stimulate macrophage polarization and exhibit antibacterial properties. With these advantages and properties, these DNA-based hydrogels can be used to construct bone organoids, providing an innovative tool for disease modeling and therapeutic applications in bone tissue engineering. Finally, we discuss the current challenges and future prospects, emphasizing the potential impacts and applications in regenerative medicine.

Extra-viral DNA in adeno-associated viral vector preparations induces TLR9-dependent innate immune responses in human plasmacytoid dendritic cells

Adeno-associated viral (AAV) vector suspensions produced in either human derived HEK cells or in Spodoptera frugiperda (Sf9) insect cells differ in terms of residual host cell components as well as species-specific post-translational modifications displayed on the AAV capsid proteins. Here we analysed the impact of these differences on the immunogenic properties of the vector. We stimulated human plasmacytoid dendritic cells with various lots of HEK cell-produced and Sf9 cell-produced AAV-CMV-eGFP vectors derived from different manufacturers. We found that AAV8-CMV-eGFP as well as AAV2-CMV-eGFP vectors induced lot-specific but not production platform-specific or manufacturer-specific inflammatory cytokine responses. These could be reduced or abolished by blocking toll-like receptor 9 signalling or by enzymatically reducing DNA in the vector lots using DNase. Successful HEK cell transduction by DNase-treated AAV lots and DNA analyses demonstrated that DNase did not affect the integrity of the vector but degraded extra-viral DNA. We conclude that both HEK- and Sf9-cell derived AAV preparations can contain immunogenic extra-viral DNA components which can trigger lot-specific inflammatory immune responses. This suggests that improved strategies to remove extra-viral DNA impurities may be instrumental in reducing the immunogenic properties of AAV vector preparations.

Toll-like receptor 9 antagonist suppresses humoral immunity in experimental autoimmune myasthenia gravis

Recent studies have demonstrated the important role of toll-like receptor 9 (TLR9) signalling in autoimmune diseases, but its role in myasthenia gravis (MG) has not been fully established. We show herein that blocking TLR9 signalling via the suppressive oligodeoxynucleotide (ODN) H154 alleviated the symptoms of experimental autoimmune myasthenia gravis (EAMG). With the downregulation of dendritic cells (DCs), TLR9 interruption reduced follicular helper T cells (Tfh) and germinal centre (GC) B cells, leading to decreased antibody production. In addition, TLR9⁺ B cells as well as total B cells in the spleen were inhibited by H154. These findings highlight the critical role of TLR9 in EAMG and suggest that the inhibition of the TLR9 pathway might be a potential pharmacological strategy for the treatment of myasthenia gravis.

Class A CpG Oligonucleotide Priming Rescues Mice from Septic Shock via Activation of Platelet-Activating Factor Acetylhydrolase

Sepsis is a life-threatening, overwhelming immune response to infection with high morbidity and mortality. Inflammatory response and blood clotting are caused by sepsis, which induces serious organ damage and death from shock. As a mechanism of pathogenesis, platelet-activating factor (PAF) induces excessive inflammatory responses and blood clotting. In this study, we demonstrate that a Class A CpG oligodeoxynucleotide (CpG-A₁₅₈₅) strongly induced PAF acetylhydrolase, which generates lyso-PAF. CpG-A₁₅₈₅ rescued mice from acute lethal shock and decreased fibrin deposition, a hallmark of PAF-induced disseminated intravascular coagulation. Furthermore, CpG-A₁₅₈₅ improved endotoxin shock induced by lipopolysaccharide, which comprises the cell wall of Gram-negative bacteria and inhibits inflammatory responses induced by cytokines such as interleukin-6 and tumor necrosis factor-α. These results suggest that CpG-A₁₅₈₅ is a potential therapeutic target to prevent sepsis-related induction of PAF.

The Role of Toll-Like Receptors in Autoimmune Diseases through Failure of the Self-Recognition Mechanism

Toll-like receptors (TLRs), part of the innate immune system that recognises molecular signatures, are important in the recognition of pathogenic components. However, when specific cellular contexts develop in which TLRs are inappropriately activated by self-components, this may lead to sterile inflammation and result in the occurrence of autoimmunity. This review analyses the available data regarding TLR biochemistry, the specific mechanisms which are brought about by TLR activation, and the importance of these mechanisms in the light of any existing and potential therapies in the field of autoimmunity.

Lipid Nanoparticles Loaded with an Antisense Oligonucleotide Gapmer Against Bcl-2 for Treatment of Lung Cancer

PURPOSE

Bcl-2 is an anti-apoptotic gene that is frequently overexpressed in human cancers. G3139 is an antisense oligonucleotide against bcl-2 that has shown limited efficacy in clinical trials. Here, we report the synthesis of a new antisense oligonucleotide containing additional chemical modifications and its delivery using nanoparticles.

METHODS

An oligonucleotide G3139-GAP was synthesized, which has 2'-O-methyl nucleotides at the 5' and 3' ends based on a "gapmer" design. Furthermore, G3139-GAP was incorporated into lipid nanoparticles (LNPs) composed of DOTAP/egg PC/cholesterol/Tween 80. The LNP-loaded G3139-GAP was evaluated in A549 lung cancer cells both in vitro and in a murine xenograft model for biological activity and therapeutic efficacy.

RESULTS

The LNPs showed excellent colloidal and serum stability, and high encapsulation efficiency for G3139-GAP. They have a mean particle diameter and zeta potential of 134 nm and 9.59 mV, respectively. G3139-GAP-LNPs efficiently downregulated bcl-2 expression in A549 cells, as shown by 40% and 83% reduction in mRNA and protein levels, respectively. Furthermore, G3139-GAP-LNPs were shown to inhibit tumor growth, prolong survival, and downregulate tumor bcl-2 expression in an A549 murine xenograft tumor model. These data indicate that G3139-GAP-LNPs have excellent anti-tumor efficacy and warrant further evaluation.

Suppressive oligonucleotides inhibit inflammation in a murine model of mechanical ventilator induced lung injury

BACKGROUND

Mechanical ventilation (MV) is commonly used to improve blood oxygenation in critically ill patients and for general anesthesia. Yet the cyclic mechanical stress induced at even moderate ventilation volume settings [tidal volume (Vt) <10 mL/kg] can injure the lungs and induce an inflammatory response. This work explores the effect of treatment with suppressive oligonucleotides (Sup ODN) in a mouse model of ventilator-induced lung injury (VILI).

METHODS

Balb/cJ mice were mechanically ventilated for 4 h using clinically relevant Vt and a positive end-expiratory pressure of 3 cmH₂O under 2-3% isoflurane anesthesia. Lung tissue and bronchoalveolar lavage fluid were collected to assess lung inflammation and lung function was monitored using a FlexiVent^®.

RESULTS

MV induced significant pulmonary inflammation characterized by the influx and activation of CD11c⁺/F4/80⁺ macrophages and CD11b⁺/Ly6G⁺ polymorphonuclear cells into the lung and bronchoalveolar lavage fluid. The concurrent administration of Sup ODN attenuated pulmonary inflammation as evidenced by reduced cellular influx and production of inflammatory cytokines. Oligonucleotide treatment did not worsen lung function as measured by static compliance or resistance.

CONCLUSIONS

Treatment with Sup ODN reduces the lung injury induced by MV in mice.

Epithelial-mesenchymal transition promotes reactivity of human lung adenocarcinoma A549 cells to CpG ODN

BACKGROUND

Epithelial-mesenchymal transition (EMT) is reported to promote airway remodeling in asthmatics, which is the main histological change that causes complex and severe symptoms in asthmatics. However, little is known about whether EMT also plays a role in acute exacerbations of asthma evoked by respiratory tract infections.

METHODS

A human lung adenocarcinoma line, A549, was incubated with TGF-β1 at 10 ng/ml to induce EMT. Then the cells were stimulated with CpG ODN. Expression of surface and intracellular molecules was analyzed by flow cytometry. IL-6, IL-8 and MCP-1 in the culture supernatant were measured by Cytometric Bead Assay, and the expression of mRNA was quantitated by real-time PCR. CpG ODN uptake was analyzed by flow cytometry.

RESULTS

The culture supernatant levels of IL-6, IL-8 and MCP-1 and the expression of mRNA for these cytokines in CpG ODN-stimulated A549 cells that had undergone EMT was significantly higher compared to those that had not. Addition of ODN H154, a TLR9-inhibiting DNA, significantly suppressed the CpG ODN-induced production of those cytokines. However, flow cytometry found the level of TLR9 expression to be slightly lower in A549 cells that had undergone EMT compared to those that had not. On the other hand, CpG ODN uptake was increased in cells that had undergone EMT.

CONCLUSIONS

EMT induction of A549 cells enhanced CpG ODN uptake and CpG ODN-induced production of IL-6, IL-8 and MCP-1. These results suggest that EMT plays an important role in exacerbation in asthmatics with airway remodeling by enhancing sensitivity to extrinsic pathogens.

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.

Porcine circovirus type 2 induces type I interferon production via MyD88-IKKα-IRFs signaling rather than NF-κB in porcine alveolar macrophages in vitro

Type I interferon (IFN-I) plays important roles in host antiviral responses. The interferon regulatory factor (IRF) and NF-κB transcription factors are thought to be important in the processes of viral secretion and triggering of interferon production. Recently, studies have shown that porcine circovirus type 2 (PCV2) can induce IFN-I production in vivo and in vitro, but the mechanisms underlying the production of PAMs infected with PCV2 remains unknown. Treatment of these cells with BAY11-7082, an inhibitor of NF-κB activation, allowed us to study the secretion of IFN-α and IFN-β in PAMs infected with PCV2. We found that IFN-α expression was induced following virus infection of PAMs. Notably, even after inhibitor treatment of PAMs infected with PCV2, secretion of IFN-α was significantly higher (P<0.05) compared with the PCV2 infection alone group. Our findings suggest that NF-κB plays a minor role in PCV2-induced type I interferon responses. To further characterize the signaling pathway that drives IFN-I expression in PAMs in response to PCV2, we used siRNA to silence the expression of Myeloid differentiation factor 88 (MyD88) and study the role of MyD88-IKKα-IRF signaling in IFN-I production in PAMs induced by PCV2. Our findings show that PCV2 induced IFN-α mRNA transcription, which is associated with the activities of MyD88, IRF7, and IRF3. Thus, PCV2 can induce IFN-I transcription via the MyD88-IKKα-IRF signaling axis.

Virus-like nanostructures for tuning immune response

Synthetic vaccines utilize viral signatures to trigger immune responses. Although the immune responses raised against the biochemical signatures of viruses are well characterized, the mechanism of how they affect immune response in the context of physical signatures is not well studied. In this work, we investigated the ability of zero- and one-dimensional self-assembled peptide nanostructures carrying unmethylated CpG motifs (signature of viral DNA) for tuning immune response. These nanostructures represent the two most common viral shapes, spheres and rods. The nanofibrous structures were found to direct immune response towards Th1 phenotype, which is responsible for acting against intracellular pathogens such as viruses, to a greater extent than nanospheres and CpG ODN alone. In addition, nanofibers exhibited enhanced uptake into dendritic cells compared to nanospheres or the ODN itself. The chemical stability of the ODN against nuclease-mediated degradation was also observed to be enhanced when complexed with the peptide nanostructures. In vivo studies showed that nanofibers promoted antigen-specific IgG production over 10-fold better than CpG ODN alone. To the best of our knowledge, this is the first report showing the modulation of the nature of an immune response through the shape of the carrier system.

MGN1703, an immunomodulator and toll-like receptor 9 (TLR-9) agonist: from bench to bedside

The adaptive immune system has been the main focus of immunological strategies in oncology with only more recent approaches targeting innate immunity. Endosomal toll-like receptors (TLR-7, TLR-9) activate innate immune responses by signaling damage-associated molecular patterns (DAMP) from decaying tumor cells. This has led to the development of DNA-based TLR-9 agonists, which induce antitumor activity through innate and subsequent adaptive immune responses. Early clinical trials with CpG-ODN as TLR-9 agonists were associated with unfavorable tolerability and narrow clinical efficacy, leading to failure in pivotal trials. dSLIM, the active ingredient of MGN1703, is a DNA-based, radically different molecular alternative to CpG-ODN, which results in genuine antitumor immunomodulation. Preclinical and clinical studies of MGN1703 have confirmed that this TLR-9 agonist has therapeutic potential in a variety of solid tumors, while long-term treatment with high doses was very well tolerated. A pivotal trial of first-line maintenance treatment with MGN1703 in patients with metastatic colorectal cancer is underway.

A toll-like receptor 9 antagonist reduces pain hypersensitivity and the inflammatory response in spinal cord injury

Toll-like receptors (TLRs) are mediators of the innate immune response to exogenous pathogens. They have also been implicated in sterile inflammation associated with systemic injury and non-infectious diseases via binding of endogenous ligands, possibly released by damaged cells. Emerging evidence indicates that some TLRs play a role in nervous system injury and especially in injury-elicited pain and sterile inflammation. However, no information is available about the contribution of TLR9, a member of the TLR family, to traumatic spinal cord injury (SCI). Moreover, the therapeutic potential of TLR9 ligands in the functional outcomes of SCI, including pain, has not been explored. We report, for the first time, that the intrathecal administration of a TLR9 antagonist, cytidine-phosphate-guanosine oligodeoxynucleotide 2088 (CpG ODN 2088), to mice sustaining a severe contusion SCI, diminishes injury-induced heat hypersensitivity. Investigations on the potential mechanisms underlying the reduction in pain sensitivity indicated an attenuation of the inflammatory reaction manifested by a decrease in the number of CD11b-, CD45- and CD3-immunoreactive cells and a reduction in tumor necrosis factor-α (TNF-α) expression at the epicenter. Conversely, intrathecal delivery of a TLR9 agonist, CpG ODN 1826, increased inflammatory cell numbers and TNF-α expression in the epicenter. The CpG ODN 2088 treatment did not appear to induce systemic adverse effects as shown by spleen histology and serum cytokine levels. We propose that CpG ODN 2088 dampens injury-induced heat hypersensitivity by suppressing the inflammatory response and TNF-α expression. This investigation defines a previously unreported therapeutic role for CpG ODN 2088 in SCI-induced pain.

Safety assessment of biolistic DNA vaccination

DNA-based vector systems have been widely studied as new modalities for the prevention and treatment of human diseases. As for all other medicinal products, safety is an important aspect in the evaluation of such products. In this chapter we reflect on the basic safety issues which have been raised with respect to preventive and therapeutic DNA vaccines, including insertional mutagenesis in case of chromosomal integration, possible formation of anti-DNA antibodies, induction of autoimmune responses and/or immunological tolerance. In addition, local reactions at the site of administration and adverse effects resulting from plasmid DNA spread to nontarget tissues are discussed. Most importantly, however, the benefit-risk profile of a medicinal product is crucial for a decision on providing marketing authorization or not. A product has an acceptable benefit-risk profile if the benefits of the product outweigh its risks for the treated patient.

Class I/II hybrid inhibitory oligodeoxynucleotide exerts Th1 and Th2 double immunosuppression

We designed class I/II hybrid inhibitory oligodeoxynucleotides (iODNs), called iSG, and found that the sequence 5′-TTAGGG-3′, which has a six-base loop head structure, and a 3′-oligo (dG)_3–5 tail sequence are important for potent immunosuppressive activity. Interestingly, splenocytes isolated from ovalbumin (OVA)-immunized mice and treated with iSG3 showed suppression of not only interleukin (IL)-6, IL-12p35, IL-12p40, and interferon (IFN) γ mRNA expression, but also IL-4 and IL-13 mRNA expression. Thus, both Th2 and Th1 immune responses can be strongly suppressed by iODNs in splenocytes from allergen-immunized mice, suggesting usefulness in the treatment of diseases induced by over-active immune activation.

Regulatory role of suppressive motifs from commensal DNA

The microbiota contributes to the induction of both effector and regulatory responses in the gastrointestinal (GI) tract. However, the mechanisms controlling these distinct properties remain poorly understood. We previously showed that commensal DNA promotes intestinal immunity. Here, we find that the capacity of bacterial DNA to stimulate immune responses is species specific and correlated with the frequency of motifs known to exert immunosuppressive function. In particular, we show that the DNA of Lactobacillus species, including various probiotics, is enriched in suppressive motifs able to inhibit lamina propria dendritic cell activation. In addition, immunosuppressive oligonucleotides sustain T(reg) cell conversion during inflammation and limit pathogen-induced immunopathology and colitis. Altogether, our findings identify DNA-suppressive motifs as a molecular ligand expressed by commensals and support the idea that a balance between stimulatory and regulatory DNA motifs contributes to the induction of controlled immune responses in the GI tract and gut immune homeostasis. Further, our findings suggest that the endogenous regulatory capacity of DNA motifs enriched in some commensal bacteria could be exploited for therapeutic purposes.

Vascular dysfunction following polymicrobial sepsis: role of pattern recognition receptors

AIMS

Aim was to elucidate the specific role of pattern recognition receptors in vascular dysfunction during polymicrobial sepsis (colon ascendens stent peritonitis, CASP).

METHODS AND RESULTS

Vascular contractility of C57BL/6 (wildtype) mice and mice deficient for Toll-like receptor 2/4/9 (TLR2-D, TLR4-D, TLR9-D) or CD14 (CD14-D) was measured 18 h following CASP. mRNA expression of pro- (Tumor Necrosis Factor-α (TNFα), Interleukin (IL)-1β, IL-6) and anti-inflammatory cytokines (IL-10) and of vascular inducible NO-Synthase (iNOS) was determined using RT-qPCR. Wildtype mice exhibited a significant loss of vascular contractility after CASP. This was aggravated in TLR2-D mice, blunted in TLR4-D animals and abolished in TLR9-D and CD14-D animals. TNF-α expression was significantly up-regulated after CASP in wildtype and TLR2-D animals, but not in mice deficient for TLR4, -9 or CD14. iNOS was significantly up-regulated in TLR2-D animals only. TLR2-D animals showed significantly higher levels of TLR4, -9 and CD14. Application of H154-ODN, a TLR9 antagonist, attenuated CASP-induced cytokine release and vascular dysfunction in wildtype mice.

CONCLUSIONS

Within our model, CD14 and TLR9 play a decisive role for the development of vascular dysfunction and thus can be effectively antagonized using H154-ODN. TLR2-D animals are more prone to polymicrobial sepsis, presumably due to up-regulation of TLR4, 9 and CD14.

Targeting Toll-like receptors by chloroquine protects mice from experimental cerebral malaria

Excessive production of proinflammatory cytokines, elicited mostly by Th1 cells, is an important cause of cerebral malaria (CM). Dendritic cells (DCs), a critical link between innate and adaptive immune responses, rely heavily on Toll-like receptor (TLR) signaling. Using C57BL/6 mice infected with Plasmodium berghei ANKA (PbA) as an experimental CM model, we first confirmed that inhibition of TLR9 by suppressive oligodeoxynucleotides protected mice from CM. In addition to being a well-known antimalarial, chloroquine (CQ) has been used as an immunomodulator of endocytic TLRs because it inhibits endosomal acidification. We found that immediately before and shortly after infection by PbA, treatment with a single dose of 50 mg/kg of CQ protected mice from experimental CM. Both CQ treatments significantly inhibited expression of TLR9 and MHC-II on DCs, and reduced the number of myeloid and plasmatocytoid DCs at 3 and 5 days after infection. Consequently, activation of CD4+ T cells, especially the expansion of the Th1 subsets, was dramatically inhibited in CQ treated groups, which was accompanied by a remarkable decline in the production of Th1 type proinflammatory mediators IFN-γ, TNF-α, and nitric oxide. Taken together, these results corroborated the involvement of TLR9 in CM pathogenesis and suggest that interference with the activation of this receptor is a promising strategy to prevent deleterious inflammatory response mediating pathogenesis and severity of malaria.

Structure-activity relationship of a guanine-free oligodeoxynucleotide as immunopotent inhibitor

Excessive innate immune response could contribute to the pathogenesis of inflammatory and autoimmune diseases. It is required to develop agents to inhibit the overwhelming innate immune response. SAT05f, an inhibitory ODN with CCT repeat sequence found in human microsatellite DNA, has been demonstrated to down-regulate TLR7/9-mediated innate immune response, protect mice from D-GalN/CpG ODN induced lethal shock, and reduce anti-ssDNA antibody level in the lupus-prone mice induced by chronic graft versus host disease (cGVHD). In this article, to explore the structure-activity relationship of SAT05f, we designed and synthesized a series of ODNs based on the sequence of SAT05f by changing repeat number of the CCT unit, substituting CCT unit with AAG at 3' end or 5' end or in the middle and by forming hairpin at 5' or 3' end, and tested their inhibitory effect on the CpG ODN induced proliferation and TNF-α production in murine immune cells. The results indicated that 1) at least 8 CCT units were required for a CCT repeat ODN to display its inhibitory activity; 2) CCT unit at 3' end of SAT05f was necessary for its full inhibitory activity; and 3) 5' end of SAT05f could be modified to design a more potent SAT05f derived inhibitory ODN. The data provided here would be helpful for finding a potent inhibitory ODN as a candidate medicament for the treatment of diseases associated with over-activated innate immune response.

Competition by inhibitory oligonucleotides prevents binding of CpG to C-terminal TLR9

TLR9 recognizes unmethylated CpG-containing DNA commonly found in bacteria. Synthetic oligonucleotides containing CpG-motifs (CpG ODNs) recapitulate the activation of TLR9 by microbial DNA, whereas inversion of the CG dinucleotide within the CpG motif to GC (GpC ODNs) renders such ODNs inactive. This difference cannot be attributed to binding of ODNs to the full-length TLR9 ectodomain, as both CpG and GpC ODNs bind comparably. Activation of murine TLR9 requires cleavage into an active C-terminal fragment, which binds CpG robustly. We therefore compared the ability of CpG and GpC ODNs to bind to full-length and C-terminal TLR9, and their impact on the cleavage of TLR9. We found that CpG binds better to C-terminal TLR9 when compared with GpC, despite comparably low binding of both ODNs to full-length TLR9. Neither CpG nor GpC ODNs affected TLR9 cleavage in murine RAW 264.7 cells stably expressing TLR9-Myc. Inhibitory ODNs (IN-ODNs) block TLR9 signaling, but how they do so remains unclear. We show here that inhibitory ODNs do not impede TLR9 cleavage but bind to C-terminal TLR9 preferentially, and thereby compete for CpG ODN binding both in RAW cells and in TLR9-deficient cells transduced with TLR9-Myc. Ligand binding to C-terminal fragment thus determines the outcome of activation through TLR9.

Optimal oligonucleotide sequences for TLR9 inhibitory activity in human cells: lack of correlation with TLR9 binding

Toll-like receptor (TLR)9 performs our innate response to bacterial DNA, warning us of the presence of infection. Inhibitory oligodeoxyribonucleotides (INH-ODN) have been developed that selectively block activation of mouse TLR9. Their inhibitory motif consisting of CCx(not-C)(not-C)xxGGG (x = any base) also reduces anti-DNA antibodies in lupus mice. The current study demonstrates that this motif also provides the sequences required to block TLR9 in human B cells and human embryonic kidney (HEK) cells transfected with human TLR9. However, extending the sequence by four to five bases at the 5' end enhanced activity and this enhancement was greater when a phosphorothioate (pS) backbone replaced the native phosphodiester (pO) backbone. A series of pO-backbone INH-ODN representing a 500-fold range of activity in biologic assays was shown to cover less than a 2.5-fold range of avidity for binding human TLR9-Ig fusion protein, eliminating TLR9 ectodomain binding as the explanation for sequence-specific differences in biologic activity. With few exceptions, the relative activity of INH-ODN in Namalwa cells and HEK/human TLR9 cells was similar to that seen in mouse B cells. INH-ODN activity in human peripheral blood B cells correlated significantly with the cell line data. These results favor the conclusion that although the backbone determines strength of TLR9 binding, critical recognition of the INH-ODN sequence necessary for biologic activity is performed by a molecule that is not TLR9. These studies also identify the strongest INH-ODN for human B cells, helping to guide the selection of INH-ODN sequences for therapeutics in any situation where inflammation is enhanced by TLR9.

The immunostimulatory activity of phosphorothioate CpG oligonucleotides is affected by distal sequence changes

CpG motifs in bacterial DNA activate innate immune cells via toll like receptor 9 (TLR9). Short synthetic oligodeoxynucleotides (ODN) containing a six base CpG motif can mimic the immunostimulatory activity of bacterial DNA. Phosphorothioate (PS) modification of the backbone of ODN makes them more resistant to nuclease degradation and consequently preferable for therapeutic use. Previous studies have shown that the sequence requirements for PS-ODN to have maximal stimulatory activity are more stringent than for normal phosphodiester (PO) ODN. Here we show small sequence changes distal to the CpG motif can affect the activity of PS-ODN whilst having no effect on the activity of PO-ODN. The addition of terminal dG residues and other minor changes to the potently immunostimulatory PS-ODN 1668S caused delayed signalling. The reduction in immunostimulatory activity of PS-ODN was associated with a delay in the activation of MAP kinases.

Therapeutic targeting of TLR9 inhibits cell growth and induces apoptosis in neuroblastoma

The Toll-like receptor 9 (TLR9) evolved to cope with pathogens, but it is expressed in a variety of tumors for reasons that are unclear. In this study, we report that neuroblastoma (NB) cells express functional TLR9. Liposome-complexed CpG oligonucleotides inhibited the proliferation of TLR9-expressing NB cells and induced caspase-dependent apoptotic cell death. Inhibitory oligonucleotides (iODNs) abrogated these effects. RNA interference reduced TLR9 expression but not to the level where functional responses to CpG were abolished. Compared with free CpG, liposomal formulations of NB-targeted CpG (TL-CpG) significantly prolonged the survival of mice bearing NB tumor xenografts. While CpG alone lacked antitumor efficacy in NOD/SCID/IL2rg(-/-) mice, TL-CpG retained significant efficacy related to direct effects on tumor cells. TLR9 expression in primary human NB specimens was found to correlate inversely with disease stage. Our findings establish functional expression of TLR9 in NB and suggest that TLR9 may represent a novel theranostic target in this disease.

Mammalian telomeric DNA suppresses endotoxin-induced uveitis

Telomeric regions of mammalian chromosomes contain suppressive TTAGGG motifs that inhibit several proinflammatory and Th1-biased immune responses. Synthetic oligodeoxynucleotides (ODN) expressing suppressive motifs can reproduce the down-regulatory activity of mammalian telomeric repeats and have proven effective in the prevention and treatment of several autoimmune and autoinflammatory diseases. Endotoxin-induced uveitis (EIU) is an established animal model of acute ocular inflammation induced by LPS administration. Augmented expression of proinflammatory cytokines/chemokines such as TNFalpha, IL-6, and MCP1 and bactericidal nitric oxide production mediated by LPS contribute to the development of EIU. Suppressing these mediators using agents that are devoid of undesirable systemic side effects may help prevent the development of EIU. This study demonstrates the selective down-regulatory role of suppressive ODN after (i) local or (ii) systemic treatment in EIU-induced rabbits and mice. Our results indicate that suppressive ODN down-regulate at both the transcript and protein levels of several proinflammatory cytokines and chemokines as well as nitric oxide and co-stimulatory surface marker molecules when administrated prior to, simultaneously with, or even after LPS challenge, thereby significantly reducing ocular inflammation in both rabbit and mouse eyes. These findings strongly suggest that suppressive ODN is a potent candidate for the prevention of uveitis and could be applied as a novel DNA-based immunoregulatory agent to control other autoimmune or autoinflammatory diseases.

A human microsatellite DNA-mimicking oligodeoxynucleotide with CCT repeats negatively regulates TLR7/9-mediated innate immune responses via selected TLR pathways

A human microsatellite DNA-mimicking ODN (MS ODN) composed of CCT repeats, designated as SAT05f, has been studied for its capacity of negatively regulating innate immunity induced by TLR7/TLR9 agonists in vitro and in mice. The result showed that SAT05f could down-regulate TLR7/9-dependent IFN-α production in cultured human PBMC stimulated by inactivated Flu virus PR8 or HSV-1 or CpG ODN or imiquimod, protect d-GalN-treated mice from lethal shock induced by TLR9 agonist, not by TLR3/4 agonist. In addition, SAT05f significantly inhibit IFN-α production from purified human plasmacytoid cells (pDCs) stimulated by CpG ODN. Interestingly, SAT05f could up-regulate CD80, CD86, and HLA-DR on the pDCs in vitro, implying that SAT05f-mediated inhibition on IFN-α production could be related to the activation of pDCs. The data suggest that SAT05f could be developed as a candidate medicament for the treatment of TLR7/9 activation-associated diseases by inhibiting TLR7/9 signaling pathways.

Therapeutic applications and mechanisms underlying the activity of immunosuppressive oligonucleotides

Synthetic oligodeoxynucleotides (ODN) capable of "neutralizing" or "inhibiting" immune responses have been described. This review will focus on the properties of phosphorothioate ODN that mimic the immunosuppressive activity of the repetitive TTAGGG motifs present in mammalian telomeres. These TTAGGG multimers block the production of pro-inflammatory and T helper type 1 cytokines elicited when immune cells are activated by a wide variety of Toll-like receptor ligands, polyclonal activators, and antigens. Several mechanisms contribute to the suppressive activity of such ODN. Ongoing microarray studies indicate that suppressive ODN interfere with the phosphorylation of signal transducer and activator of transcription 1 (STAT1) and STAT4, thereby blocking the inflammation mediated by STAT-associated signaling cascades. In animal models, suppressive ODN can be used to prevent or treat diseases characterized by persistent immune activation, including collagen-induced arthritis, inflammatory arthritis, systemic lupus erythematosus, silicosis, and toxic shock. These findings suggest that TTAGGG multimers may find broad use in the treatment of diseases characterized by over-exuberant/persistent immune activation.

Ex VivoProgramming of Antigen-Presenting B Lymphocytes: Considerations on DNA Uptake and Cell Activation

Plasmids used in DNA vaccination not only serve as a source of antigen, but also have an important adjuvant effect. This review focuses on recent advancements made in understanding how cells internalize DNA, and how internalized DNA activates immune response pathways. We also comment on the role of B cells in both of these processes.

The TLR9-MyD88 pathway is critical for adaptive immune responses to adeno-associated virus gene therapy vectors in mice

Recombinant adeno-associated viruses (AAVs) have been used widely for in vivo gene therapy. However, adaptive immune responses to AAV have posed a significant hurdle in clinical application of AAV vectors. Recent advances have suggested a crucial role for innate immunity in shaping adaptive immune responses. How AAV activates innate immunity, and thereby promotes AAV-targeted adaptive immune responses, remains unknown. Here we show that AAV activates mouse plasmacytoid DCs (pDCs) via TLR9 to produce type I IFNs. In vivo, the TLR9-MyD88 pathway was crucial to the activation of CD8+ T cell responses to both the transgene product and the AAV capsid, leading to loss of transgene expression and the generation of transgene product-specific and AAV-neutralizing antibodies. We further demonstrate that TLR9-dependent activation of adaptive immunity targeting AAV was mediated by type I IFNs and that human pDCs could be activated in vitro to induce type I IFN production via TLR9. These results reveal an essential role for the TLR9-MyD88-type I IFN pathway in induction of adaptive immune responses to AAV and suggest that strategies that interfere with this pathway may improve the outcome of AAV-mediated gene therapy in humans.

Type I interferon in HIV treatment: from antiviral drug to therapeutic target

Type I interferons (IFNs) are soluble molecules that exert potent antiviral activity and are currently used for the treatment of a panel of viral infections. In the case of HIV, the use of type I IFN has had limited success, and has almost been abandoned. During the last decade, a series of studies has highlighted how HIV infection may cause overactivation of type I IFN production, which contributes to the exhaustion of the immune system and to disease progression. This review describes the transition from the proposed use of type I IFN as antiviral drugs in HIV infection, to the idea that blocking their activity or production may provide an immunologic benefit of much greater importance than their antiviral activity.

Human microsatellite DNA mimicking oligodeoxynucleotides down-regulate TLR9-dependent and -independent activation of human immune cells

To develop novel immunoregulatory oligodeoxynucleotides (ODNs), we have designed a series of ODNs based on the sequences in human microsatellite (MS) DNA. The ODNs, designated as human MS DNA mimicking ODNs (MS ODNs), have been studied for their inhibitory effects on human immune cells activated by TLR9-dependent and -independent stimulations. We find for the first time that MS08, a MS ODN composed entirely of TC dinucleotide (TC) repeats, inhibits CpG ODN (TLR9 ligand)-induced human PBMCs proliferation, CD80 and CD86 expression and production of interferon. In addition, MS08 also inhibits the proliferation of human PBMCs stimulated by PHA, PMA and alloantigens in a TLR9-independent manner. The inhibition correlates with competition of binding and uptake between MS08 and CpG ODN in human PBMCs. Structurally, TC, CT or CCT are revealed as essential suppressive motifs required for the inhibition. These findings suggest that TC repeat containing MS ODN could be of therapeutic use in pathologic situations due to excessive activation of immune cells.

Excessive CpG 1668 stimulation triggers IL-10 production by cDC that inhibits IFN-alpha responses by pDC

Upon stimulation with a wide range of concentrations of CpG oligodeoxynucleotide 2216 (CpG 2216), plasmacytoid DC are induced to produce type I IFN (IFN-alpha/beta). In contrast, CpG 1668 shows a bell-shaped dose-response correlation, i.e. only intermediate but not high doses of CpG 1668 induce IFN-alpha/beta. Interestingly, high-dose CpG 1668 completely inhibited IFN-alpha responses induced by CpG 2216. Experiments using supernatant of high-dose CpG-1668-treated cells indicated that secreted inhibitor(s) mediated the IFN-alpha shut-off. Among modulating cytokines, IL-10 turned out to be one important negative regulator. In line with this, supernatants of IL-10-deficient DC cultures stimulated with high-dose CpG 1668 did not inhibit IFN-alpha production. Interestingly, high-dose CpG 1668 also inhibited IFN-alpha responses induced by the DNA-encoded mouse cytomegalovirus, whereas IFN-alpha responses induced by negative-strand RNA-encoded vesicular stomatitis virus were only marginally affected. Experiments with DC cultures devoid of TLR9 indicated that TLR9 was critically required to mediate stimulatory and modulatory signals by low and high concentrations of CpG 1668, respectively. Analysis of purified DC subsets showed that conventional DC were the main IL-10 producers, whereas plasmacytoid DC hardly produced any IL-10.

Immunoadjuvant effects of bacterial genomic DNA and CpG oligodeoxynucleotides on avian influenza virus subtype H5N1 inactivated oil emulsion vaccine in chicken

This study investigated the immunoadjuvant effects of three types of bacterial genomic DNA and CpG oligonucleotides (CpG ODN) on the avian influenza virus (AIV) subtype H5N1 inactivated oil emulsion vaccine under two immunization strategies. The genomic DNA extracted from Escherichia coli O(2), Staphylococcus aureus,Streptococcus faecalis FQ68, and synthetic CpG ODN were used as adjuvants, and their effects on the AIV oil emulsion vaccine were examined in chickens. The results indicated that when administered separately from the vaccine, adjuvants induced lower haemagglutination inhibition (HI) titres and serum IgG titres but resulted in higher concentrations of IFN-gamma and IL-10. In contrast, when combined with the oil emulsion vaccine prior to inoculation, CpG ODN induced higher HI, IgG titres and IFN-gamma concentration but resulted in lower IL-10 concentration. These data suggest that, depending on the immunization approaches, adjuvants may exert distinct immune effects in chickens receiving AIV H5N1 oil emulsion vaccine: the prior incorporation of CpG ODN into the vaccine may augment both the humoral and Th1 type immune responses, while separate inoculation of adjuvants has not shown better adjuvanticity.

Suppressive oligodeoxynucleotides inhibit silica-induced pulmonary inflammation

Inhalation of silica-containing dust particles induces silicosis, an inflammatory disease of the lungs characterized by the infiltration of macrophages and neutrophils into the lungs and the production of proinflammatory cytokines, chemokines, and reactive oxygen species (ROS). Synthetic oligodeoxynucleotides (ODN) expressing "immunosuppressive motifs" were recently shown to block pathologic inflammatory reactions in murine models of autoimmune disease. Based on those findings, the potential of suppressive ODN to prevent acute murine silicosis was examined. In vitro studies indicate that suppressive ODN blunt silica-induced macrophage toxicity. This effect was associated with a reduction in ROS production and p47phox expression (a subunit of NADPH oxidase key to ROS generation). In vivo studies show that pretreatment with suppressive (but not control) ODN reduces silica-dependent pulmonary inflammation, as manifest by fewer infiltrating cells, less cytokine/chemokine production, and lower levels of ROS (p < 0.01 for all parameters). Treatment with suppressive ODN also reduced disease severity and improved the survival (p < 0.05) of mice exposed to silica.

Chloroquine and inhibition of Toll-like receptor 9 protect from sepsis-induced acute kidney injury

Mortality from sepsis has remained high despite recent advances in supportive and targeted therapies. Toll-like receptors (TLRs) sense bacterial products and stimulate pathogenic innate immune responses. Mice deficient in the common adapter protein MyD88, downstream from most TLRs, have reduced mortality and acute kidney injury (AKI) from polymicrobial sepsis. However, the identity of the TLR(s) responsible for the host response to polymicrobial sepsis is unknown. Here, we show that chloroquine, an inhibitor of endocytic TLRs (TLR3, 7, 8, 9), improves sepsis-induced mortality and AKI in a clinically relevant polymicrobial sepsis mouse model, even when administered 6 h after the septic insult. Chloroquine administration attenuated the decline in renal function, splenic apoptosis, serum markers of damage to other organs, and prototypical serum pro- and anti-inflammatory cytokines TNF-alpha and IL-10. An oligodeoxynucleotide inhibitor (H154) of TLR9 and TLR9-deficient mice mirror the actions of chloroquine in all functional parameters that we tested. In addition, chloroquine decreased TLR9 protein abundance in spleen, further suggesting that TLR9 signaling may be a major target for the protective actions of chloroquine. Our findings indicate that chloroquine improves survival by inhibiting multiple pathways leading to polymicrobial sepsis and that chloroquine and TLR9 inhibitors represent viable broad-spectrum and targeted therapeutic strategies, respectively, that are promising candidates for further clinical development.

Synthetic oligonucleotides as modulators of inflammation

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs mimic the immunostimulatory activity of bacterial DNA. CpG ODN directly stimulate human B cells and plasmacytoid dendritic cells, promote the production of Th1 and proinflammatory cytokines, and trigger the maturation/activation of professional APC. CpG ODN are finding use in the treatment of cancer, allergy, and infection. In contrast, ODN containing multiple TTAGGG motifs mimic the immunosuppressive activity of self-DNA, down-regulating the production of proinflammatory and Th1 cytokines. Preclinical studies suggest that "suppressive" ODN may slow or prevent diseases characterized by pathologic immune stimulation, including autoimmunity and septic shock. Extensive studies in animal models suggest that the therapeutic value of CpG and TTAGGG ODN may be optimized by early administration.

Inhibitory oligodeoxynucleotide improves glomerulonephritis and prolongs survival in MRL-lpr/lpr mice

Inhibitory oligodeoxynucleotides (ODNs), which are capable of blocking CpG-induced inflammation, have been anticipated to be beneficial therapeutic agents for autoimmune diseases. In this study, we show that GpC ODN, which inverted the cytosine guanine sequence of CpG motif to guanine cytosine sequence, is an inhibitory ODN. The inhibitory effects of GpC ODN on CpG ODN-induced immune activation were confirmed by cytokine assay using splenocytes from lupus-prone MRL-lpr/lpr mice. In vivo, injecting MRL-lpr/lpr mice with GpC ODN did not reduce the deposition of IgG and C3 in the glomeruli, the serum level of IL-12, the serum level of rheumatoid factors and anti-ds DNA antibody, or alter the composition of IgG isotypes of anti-ds DNA antibody. However, the mice in the GpC group showed less proteinuria, significantly lower blood urea nitrogen levels (BUN) and significantly prolonged survival. Our results suggest that inhibitory ODNs, such as GpC ODN, have the potential to become a treatment for autoimmune diseases, like lupus nephritis.

Adjuvant effects of bacillus Calmette-Guerin DNA or CpG-oligonucleotide in the immune response to Taenia solium cysticercosis vaccine in porcine

The immune stimulation properties of CpG-oligonucleotides (CpG-ODN) containing a central unmethylated CpG motif could be useful for vaccination against parasite infection. However, the high cost of synthetic CpG-ODN has limited its use in veterinary vaccines. In this study, we investigated whether genomic DNA derived from Mycobacterium bovis bacillus Calmette-Guerin (BCG-DNA) could be used as an effective adjuvant to enhance the immunogenicity and the protective capacity of recombinant cC1 antigen (rcC1) against pig cysticercosis. Pigs were vaccinated with rcC1 plus CpG-containing DNA adjuvants (BCG-DNA or CpG-ODN) or rcC1 alone. Immunization with rcC1 alone induced a Th1-biased response, whereas coadministration of rcC1 with BCG-DNA or CpG-ODN increased levels of IgG2, IFN-gamma, percentage of CD8+ and specific proliferation of peripheral blood mononuclear cells. Four weeks after the last immunization, pigs were infected with Taenia solium eggs. A high level of protection (81%) was induced by rcC1 immunization that was not significantly increased by the CpG-containing DNA. These data indicate that coadministration of rcC1 plus BCG-DNA or CpG-ODN significantly enhanced Th1 response but did not improve the level of the protection induced.

Structural requirements and applications of inhibitory oligodeoxyribonucleotides

Synthetic oligodeoxyribonucleotides (ODN) bearing certain sequence characteristics mimic bacterial DNA by activating B cells and dendritic cells through Toll-like receptor (TLR) 9, an event that potentiates both humoral and cell-mediated immunity. ODN sharing some of the sequence characteristics of strong stimulatory (ST-) ODN, but substituting GGG for CGTT, competitively inhibit ST-ODN-driven events. An ODN with the same length and base composition as a strong ST-ODN, but lacking both ST- and IN-sequence requirements, has neither ST- nor IN-activity. Whereas, certain sequence changes strongly influence ST-ODN activity in human cells relative to mouse cells and B cells relative to non B cells, the strongest IN-ODN appear to work well in both species and multiple cell types. Converting from the natural phosphodiester backbone to a nuclease-resistant phosphorothioate backbone increases the sensitivity to ST-ODN about 2 logs and to IN-ODN 3 logs, while increasing the impact of critical base changes in ST-ODN and diminishing it in IN-ODN. Examples where IN-ODN have been used in vivo to interrupt autoimmune and other TLR-9-induced inflammatory states are described.

Inhibitory oligodeoxynucleotides downregulate herpes simplex virus-induced plasmacytoid dendritic cell type I interferon production and modulate cell function

Recognition of nucleic acids by TLR9 expressed by human plasmacytoid dendritic cells (PDC) plays a key role in the defense against viral infections. Upon microbial pathogen stimulation, PDC secrete large amounts of type I interferon and arbitrate thereby both innate and adaptive immune mechanisms. Unmethylated CpG motifs, which are an integral part of bacterial or viral DNA, are used in vitro and in vivo to activate the TLR9 pathway, whereas inhibitory oligodeoxynucleotide (iODN) are capable of depressing TLR9 signaling. In this study we demonstrate that TTAGGG motifs containing iODN efficiently block the TLR9 signaling in terms of herpes simplex virus (HSV)-induced type I interferon production by PDC. However, iODN, as well as control ODN, still promote PDC maturation with upregulated expression of costimulatory molecules, major histocompatibility complex molecules, and other signs for PDC maturation. Furthermore, iODN and control ODN incubated PDC demonstrate increased T-cell stimulatory functions. Coculture experiments with autologous T cells indicate that iODN-treated PDC induce more CD4(+)CD25(+)Foxp3(+) T regulatory cells from naive CD4(+) T cells and preincubation of HSV-stimulated PDC with iODN upregulated T cells' IFN-gamma production. These data indicate that iODN, while blocking type I interferon production by PDC, modify PDC activation and maturation as well as T-cell priming and stimulation. Knowledge about the different functions of iODN on PDC elucidated might be crucial for immunotherapeutic strategies in which iODN motifs are used to prevent the interaction of CpG-DNA with TLR9 to calm down specific immunological responses, because our data indicate that iODN might not only have inhibitory functions but also be effective activators of immune cells.

Characterization of suppressive oligodeoxynucleotides that inhibit Toll-like receptor-9-mediated activation of innate immunity

Synthetic oligodeoxynucleotides containing unmethylated CpG sequences (CpG-ODNs) stimulate Toll-like receptor-9 (TLR-9), thereby activating innate immunity. Stimulatory CpG-ODNs have been shown to be valuable in modifying immune responses in allergy, infection and cancer. Recently, it has been reported that the stimulation of TLR-9 by endogenous DNA might contribute to the pathogenesis of autoimmune diseases. We here report the identification of a suppressive, guanosine-rich ODN (G-ODN) that inhibited the activation of TLR-9 by stimulatory CpG-ODNs. The G-ODN was suppressive in murine macrophages and dendritic cells as well as in human plasmacytoid dendritic cells in vitro. G-ODN blocked the secretion of tumour necrosis factor-alpha (TNF-alpha) and interleukin-12p40 and interfered with the up-regulation of major histocompatibility complex (MHC) class II and costimulatory molecules. G-ODN was inhibitory even at a molar ratio of 1:10 (G-ODN:CpG-ODN) and when administered up to 7 hr after stimulation with CpG. G-ODN specifically inhibited TLR-9 but not other TLRs. Inhibition was dependent on a string of five guanosines. G-ODN was also inhibitory in an in vivo model of CpG/galactosamin (GalN) lethal shock. G-ODN interfered with upstream TLR-9 signalling. However, by extensive analysis we can exclude that G-ODN acts at the stage of cellular uptake. G-ODN therefore represents a class of suppressive ODNs that could be of therapeutic use in situations with pathologic TLR-9 activation, as has been proposed for certain autoimmune diseases.

Control of in vitro immune responses by regulatory oligodeoxynucleotides through inhibition of pIII promoter directed expression of MHC class II transactivator in human primary monocytes

Ag presentation is a key step in the initiation of adaptive immune responses that depends on the expression of MHC Ags and costimulatory molecules. Immune-enhancing CpG and non-CPG oligodeoxynucleotides (ODNs) stimulate Ag presentation by stimulating the expression of these molecules and by promoting dendritic cell maturation. In this report, we identify immunoregulatory orthophosphorothioate non-CpG molecules, referred to as regulatory ODNs (rODNs), by their ability to inhibit allogeneic monocyte-stimulated T cell responses and down-regulate HLA-DR in human primary monocytes. The rODNs promoted the survival of macrophages and were able to activate IL-8 secretion through a chloroquine-resistant pathway. Messenger RNAs for HLA-DR alpha and beta and the MHC CIITA were reduced by rODNs but not by stimulatory CpG ODN2006 and non-CpG ODN2006a. CIITA transcription in monocytes was controlled primarily by promoter III and not by promoter I or IV. rODNs blocked promoter III-directed transcription of CIITA in these cells. Under conditions that induced dendritic cell differentiation, rODNs also reduced HLA-DR expression. The activity of rODNs is phosphorothioate chemistry and G stretch dependent but TLR9 independent. G tetrads were detected by circular dichroism in active rODNs and associated with high m.w. multimers on nondenaturing gels. Heat treatment of rODNs disrupted G tetrads, the high m.w. aggregates, and the HLA-DR inhibitory activity of the ODNs. The inhibition of immune responses by regulatory oligodeoxynucleotides may be useful for the treatment of immune-mediated disorders including autoimmune diseases and graft rejection.

2'-O-methyl-modified RNAs act as TLR7 antagonists

RNA molecules such as single-stranded RNA (ssRNA) and small interfering RNA (siRNA) duplexes induce Toll-like receptor (TLR)-mediated immune stimulation after intracellular delivery. We have previously shown that selective incorporation of 2'-O-methyl (2'OMe) residues into siRNA abrogates cytokine production without reduction of gene silencing activity. Here we show that 2'OMe-modified RNA acts as a potent inhibitor of RNA-mediated cytokine induction in both human and murine systems. This activity does not require the direct incorporation of 2'OMe nucleotides into the immunostimulatory RNA or that the 2'OMe nucleotide-containing RNA be annealed as a complementary strand to form a duplex. Our results indicate that 2'OMe RNA acts as a potent antagonist of immunostimulatory RNA. We further show that 2'OMe RNA is able significantly to reduce both interferon-alpha (IFN-alpha) and interleukin-6 (IL-6) induction by the small-molecule TLR7 agonist loxoribine in human peripheral blood mononuclear cells (human PBMCs), in murine Flt3L dendritic cells (Flt3L DCs), and in vivo in mice. These results indicate that 2'OMe-modified RNA may have utility as an inhibitor of TLR7 with potential applications in the treatment of inflammatory and autoimmune diseases that involve TLR7-mediated immune stimulation.

TLR9 expression and function is abolished by the cervical cancer-associated human papillomavirus type 16

Cervical cancer development is linked to the persistent infection by high-risk mucosal human papillomaviruses (HPVs) types. The E6 and E7 major oncoproteins from this dsDNA virus play a key role in the deregulation of the cell cycle, apoptosis, and adaptive immune surveillance. In this study, we show for the first time that HPV type 16 (HPV16), the most carcinogenic type among the high-risk subgroup, interferes with innate immunity by affecting the expression of TLRs. Infection of human primary keratinocytes with HPV16 E6 and E7 recombinant retroviruses inhibits TLR9 transcription and hence functional loss of TLR9-regulated pathways. Similar findings were achieved in HPV16-positive cancer-derived cell lines and primary cervical cancers, demonstrating that this event occurs also in an in vivo context. Interestingly, E6 and E7 from the low-risk HPV type 6 are unable to down-regulate the TLR9 promoter. In addition, E6 and E7 from the high-risk HPV type 18, which are known to persist less competently in the host than HPV16, have reduced efficiency compared with HPV16 in inhibiting TLR9 transcription. Furthermore, a CpG motif derived from the HPV16 E6 DNA sequence activated TLR9, indicating this virus is able to initiate innate responses via the receptor it later down-regulates. This study reveals a novel mechanism used by HPV16 to suppress the host immune response by deregulating the TLR9 transcript, providing evidence that abolishing innate responses may be a crucial step involved in the carcinogenic events mediated by HPVs.

Optimization and delivery of plasmid DNA for vaccination

Vaccination with DNA is one of the most promising novel immunization techniques against a variety of pathogens and tumors, for which conventional vaccination regimens have failed. DNA vaccines are able to stimulate both arms of the immune system simultaneously, without carrying the safety risks associated with live vaccines, therefore representing not only an alternative to conventional vaccines but also significant progress in the prevention and treatment of fatal diseases and infections. However, translation of the excellent results achieved in small animals to similar success in primates or large animals has so far proved to be a major hurdle. Moreover, biosafety issues, such as the removal of antibiotic resistance genes present in plasmid DNA used for vaccination, remain to be addressed adequately. This review describes strategies to improve the design and production of conventional plasmid DNA, including an overview of safety and regulatory issues. It further focuses on novel systems for the optimization of plasmid DNA and the development of diverse plasmid DNA delivery systems for vaccination purposes.

The newly identified CpG-N ODN208 protects mice from challenge with CpG-S ODN by decreasing TNF-alpha release

Administration of an excess of oligodeoxynucleotides containing immunostimulatory CpG motifs (CpG-S ODNs) may induce systemic inflammatory response syndrome (SIRS) and sepsis. Therefore, it is important to develop neutralizing CpG ODNs (CpG-N ODNs), which can be used to reduce the release of cytokines induced by the presence of CpG-S ODNs. In the present study, CpG-N ODN208 (5'-TGCCGCGGCAGA-3'), a neutralizing twelve-oligodeoxynucleotide molecule recently identified in our laboratory, inhibited TNF-alpha release from human peripheral blood mononuclear cells (hPBMCs) and murine RAW264.7 cells induced by CpG-S ODN exposure in a dose- and time-dependent manner. Flow cytometry revealed that CpG-N ODN208 decreased cell-surface binding and internalization of 6-FAM-CpG-S ODN. However, the decreased cell-surface binding and internalization of CpG-S ODN could not completely account for the decreased TNF-alpha release. RT-PCR experiments revealed that CpG-N ODN treatment could down-regulate the CpG-S ODN-induced upregulation of Toll-like receptor 9 (TLR9) mRNA expression. This finding suggested that the decreased cytokine release following CpG-N ODN treatment might be related to decreased TLR9 mRNA expression. In in vivo experiments, no protection was found when the ratio of CpG-N ODN to CpG-S ODN delivered to mice was 3:1. However, at a 5:1 ratio, CpG-N ODN208 could protect mice from an ordinarily lethal dose of CpG-S ODN. Furthermore, we found that CpG-N ODN208 treatment decreased serum TNF-alpha levels in mice injected with sublethal doses of CpG-S ODN whether the CpG-N ODN208 was added prior to or concurrent with the CpG-S ODN. Our results demonstrated that CpG-N ODN-mediated protection against a lethal challenge by CpG-S ODN was associated with the reduction of TNF-alpha release.

TLR2 synergizes with both TLR4 and TLR9 for induction of the MyD88-dependent splenic cytokine and chemokine response to Streptococcus pneumoniae

We previously demonstrated that induction of splenic cytokine and chemokine secretion in response to Streptococcus pneumoniae (Pn) is MyD88-, but not critically TLR2-dependent, suggesting a role for additional TLRs. In this study, we investigated the role of TLR2, TLR4, and/or TLR9 in mediating this response. We show that a single deficiency in TLR2, TLR4, or TLR9 has only modest, selective effects on cytokine and chemokine secretion, whereas substantial defects were observed in TLR2(-/-)xTLR9(-/-) and TLR2(-/-)xTLR4(-/-) mice, though not as severe as in MyD88(-/-) mice. Chloroquine, which inhibits the function of intracellular TLRs, including TLR9, completely abrogated detectable cytokine and chemokine release in spleen cells from TLR2(-/-)xTLR4(-/-) mice, similar to what is observed for mice deficient in MyD88. These data demonstrate significant synergy between TLR2 and both TLR4 and TLR9 for induction of the MyD88-dependent splenic cytokine and chemokine response to Pn.

Silencing of natural interferon producing cell activation by porcine circovirus type 2 DNA

Porcine circovirus type 2 (PCV2) infection of natural interferon producing cells (NIPCs) impairs the induction of interferon (IFN)-alpha and tumour necrosis factor (TNF)-alpha by cytosine-phosphorothioate-guanine (CpG) oligodeoxynucleotides (ODNs), thereby preventing both their autocrine maturation and the paracrine maturation of myeloid dendritic cells (DCs). The present study shows that the PCV2-mediated inhibition of NIPCs was mediated by viral DNA, although it was independent of virus replication. The inhibitory effect of PCV2 DNA was more diversified than if it had simply targeted CpG-ODN-induced cytokines (IFN-alpha, TNF-alpha, interleukin-6, IL-12). A broad spectrum inhibition was noted, affecting responses induced by toll-like receptor (TLR)-7 and TLR9 agonists, as well as viruses including pseudorabies virus, transmissible gastroenteritis virus and classical swine fever virus. From these results, it would appear that PCV2 DNA can induce a dominant negative signal influencing independent pattern recognition receptor-induced activation cascades. Despite a concomitant internalization of PCV2 DNA and CpG-ODNs, no colocalization was observed, indicating that PCV2 DNA and CPG-ODNs may not target the same receptor. This study describes a novel modulation of the innate immune response, which would render the host more susceptible to secondary or concomitant microbial infections.

Signal transduction, gene transcription, and cytokine production triggered in macrophages by exposure to trypanosome DNA

Activation of a type I cytokine response is important for early resistance to infection with Trypanosoma brucei rhodesiense, the extracellular protozoan parasite that causes African sleeping sickness. The work presented here demonstrates that trypanosome DNA activates macrophages to produce factors that may contribute to this response. Initial results demonstrated that T. brucei rhodesiense DNA was present in the plasma of C57BL/6 and C57BL/6-scid mice following infection. Subsequently, the effect of trypanosome DNA on macrophages was investigated; parasite DNA was found to be less stimulatory than Escherichia coli DNA but more stimulatory than murine DNA, as predicted by the CG dinucleotide content. Trypanosome DNA stimulated the induction of a signal transduction cascade associated with Toll-like receptor signaling in RAW 264.7 macrophage cells. The signaling cascade led to expression of mRNAs, including interleukin-12 (IL-12) p40, IL-6, IL-10, cyclooxygenase-2, and beta interferon. The treatment of RAW 264.7 cells and bone marrow-derived macrophages with trypanosome DNA induced the production of NO, prostaglandin E2, and the cytokines IL-6, IL-10, IL-12, and tumor necrosis factor alpha. In all cases, DNase I treatment of T. brucei rhodesisense DNA abolished the activation. These results suggest that T. brucei rhodesiense DNA serves as a ligand for innate immune cells and may play an important contributory role in early stimulation of the host immune response during trypanosomiasis.