Necessity of oligonucleotide aggregation for toll-like receptor 9 activation

Control of A/D type CpG-ODN aggregates to a suitable size for induction of strong immunostimulant activity

Among several types of CpG-ODNs, A/D-type CpG-ODNs have potent adjuvant activity to induce Th-1 immune responses, but exhibit a propensity to aggregate. For the clinical application of A/D-type CpG-ODNs, it is necessary to control such aggregation and obtain a comprehensive understanding of the relationship between their structure and the immune responses. This study revealed that a representative A/D-type CpG ODN, D35, adopted a single-stranded structure in water, while it assembled into aggregates in response to Na+ ions. From polyacrylamide gel electrophoresis and circular dichroism analyses, D35 adopted a homodimeric form (duplex) via palindromic sequences in low-Na+-concentration conditions (10-50 mM NaCl). After replacement of the solution with PBS, quadruplexes began to form in a manner coordinated by Na+, resulting in large aggregates. The duplexes and small aggregates prepared in 50 mM NaCl showed not only high cellular uptake but also high affinity to Toll-like receptor 9 (TLR9) proteins, leading to the production of a large amount of interferon-α for peripheral blood mononuclear cells. The much larger aggregates prepared in 100 mM NaCl were incorporated into cells at a high level, but showed a low ability to induce cytokine production. This suggests that the large aggregates have difficulty inducing TLR9 dimerization, resulting in loss of the stimulation of the cells. We thus succeeded in inducing adequate innate immunity in vitro by controlling and adjusting the formation of D35 aggregates. Therefore, the findings in this study for D35 ODNs could be a vital research foundation for in vivo applications.

Nonspecific Regulation of the Number of Immunocompetent Cells Under the Influence of DT Toxoid in Children With Glomerulonephritis

Background

Studies aimed at identifying the mechanisms of the immunoregulatory effect of vaccination with diphtheria and tetanus toxoid on the parameters of adaptive immunity in children with kidney pathology are limited. The study aimed to study the effect of revaccination against diphtheria and tetanus on the proliferation and differentiation of immunocompetent cells, the formation of specific antibodies, and the course of the disease in children with glomerulonephritis (GN).

Methods

The study included 45 children with glomerulonephritis (GN) aged 5 to 15 years, in remission from 6 months up to 4 years. Of these, 25 children were revaccinated with DT toxoid (Diphtheria-Tetanus toxoid with reduced antigenic content) and 20 were in the control group (not vaccinated). The frequency of development of local and systemic reactions and the course of GN were assessed. The subpopulation structure of lymphocytes was studied in dynamics after 1-6-12 months by flow cytometry and IgG levels to diphtheria and tetanus were studied by ELISA.

Results

In 92% of children with GN, the post-vaccination period was uneventful. 8% showed a rise in temperature up to 37.3^°C, without the development of local reactions. During the year, none of the patients had an exacerbation of GN or a concomitant disease. After revaccination with DT toxoid, a significant increase in IgG antibodies against diphtheria and tetanus was revealed, which persisted after 12 months - 7.5 [5.1-10.8] IU/mL (p <0.001) and 7.2 [4.8-10.7] IU/mL (p <0.001), respectively. In the post-vaccination period, a multidirectional change in the concentration of T-lymphocytes was noted: with an initially increased level, their percentage after revaccination with DT toxoid decreases from 83 (81-86) % to 78 (76-80)% after a month (p = 0.04) and up to 75 (69-79)% after 12 months (p<0.001). In the control group, such a decrease was not observed. A similar picture was observed for T-helpers, cytotoxic T-lymphocytes, and in patients with an initially low percentage of cytotoxic T-lymphocytes, on the contrary, its increase was noted (p<0.001), which is comparable with the value of this parameter in the group of children with initially normal value (H = 0.54, p = 0.76). The same patterns were observed in the change in the content of B-cells: one month after revaccination, the relative level of B-cells in patients with an initially lowered value increased (p = 0.02) and remained for 12 months (p<0.001).

Conclusion

Revaccination with DT toxoid in children with GN not only does not cause undesirable changes in the system of immunocompetent cells but also has an immunomodulatory effect, which contributes to the favorable maintenance of the remission period of the disease.

Supramolecular Assembled Programmable Nanomedicine As In Situ Cancer Vaccine for Cancer Immunotherapy

Using nanotechnology for improving the immunotherapy efficiency represents a major research interest in recent years. However, there are paradoxes and obstacles in using a single nanoparticle to fulfill all the requirements in the complicated immune activation processes. Herein, a supramolecular assembled programmable immune activation nanomedicine (PIAN) for sequentially finishing multiple steps after intravenous injection and eliciting robust antitumor immunity in situ is reported. The programmable nanomedicine is constructed by supramolecular assembly via host-guest interactions between poly-[(N-2-hydroxyethyl)-aspartamide]-Pt(IV)/β-cyclodextrin (PPCD), CpG/polyamidoamine-thioketal-adamantane (CpG/PAMAM-TK-Ad), and methoxy poly(ethylene glycol)-thioketal-adamantane (mPEG-TK-Ad). After intravenous injection and accumulation at the tumor site, the high level of reactive oxygen species in the tumor microenvironment promotes PIAN dissociation and the release of PPCD (mediating tumor cell killing and antigen release) and CpG/PAMAM (mediating antigen capturing and transferring to the tumor-draining lymph nodes). This results in antigen-presenting cell activation, antigen presentation, and robust antitumor immune responses. In combination with anti-PD-L1 antibody, the PIAN cures 40% of mice in a colorectal cancer model. This PIAN provides a new framework for designing programmable nanomedicine as in situ cancer vaccine for cancer immunotherapy.

Toll-like receptor-mediated innate immunity against herpesviridae infection: a current perspective on viral infection signaling pathways

Background

In the past decades, researchers have demonstrated the critical role of Toll-like receptors (TLRs) in the innate immune system. They recognize viral components and trigger immune signal cascades to subsequently promote the activation of the immune system.

Main body

Herpesviridae family members trigger TLRs to elicit cytokines in the process of infection to activate antiviral innate immune responses in host cells. This review aims to clarify the role of TLRs in the innate immunity defense against herpesviridae, and systematically describes the processes of TLR actions and herpesviridae recognition as well as the signal transduction pathways involved.

Conclusions

Future studies of the interactions between TLRs and herpesviridae infections, especially the subsequent signaling pathways, will not only contribute to the planning of effective antiviral therapies but also provide new molecular targets for the development of antiviral drugs.

Polyethyleneimine-CpG Nanocomplex as an In Situ Vaccine for Boosting Anticancer Immunity in Melanoma

Cancer immunotherapy is redefining the field of cancer therapy. However, current cancer immunotherapies are limited by insufficient immune activation, which results in low response rate. Herein, polyethyleneimine-CpG nanocomplex (CpG@PEI) is reported as an in situ vaccine for boosting anticancer immunity in melanoma. CpG, a Toll-like receptor (TLR) 9 agonist, can activate antigen-presenting cells and increase the expression of costimulatory molecules, while PEI can help to enhance the stability and cellular internalization of CpG. It is proved that PEI loading can significantly enhance the cellular internalization and immune stimulation ability of CpG, and the CpG@PEI nanocomplex can effectively inhibit murine B16F10 melanoma growth after intratumoral injection. Further analysis reveals that this CpG@PEI nanocomplex therapy elicits both innate and adaptive immunity, with much increased natural killer (NK) cells and T cells infiltration in the tumor, as well as CD80 expression on the dendritic cells (DCs). This study will inspire more attempts in directly using single nanoparticle-loaded pattern recognition receptor (PRR) agonists for cancer immunotherapy.

Therapeutic Interventions into Innate Immune Diseases by Means of Aptamers

The immune system plays a crucial role in the body's defense system against various pathogens, such as bacteria, viruses, and parasites, as well as recognizes non-self- and self-molecules. The innate immune system is composed of special receptors known as pattern recognition receptors, which play a crucial role in the identification of pathogen-associated molecular patterns from diverse microorganisms. Any disequilibrium in the activation of a particular pattern recognition receptor leads to various inflammatory, autoimmune, or immunodeficiency diseases. Aptamers are short single-stranded deoxyribonucleic acid or ribonucleic acid molecules, also termed "chemical antibodies," which have tremendous specificity and affinity for their target molecules. Their features, such as stability, low immunogenicity, ease of manufacturing, and facile screening against a target, make them preferable as therapeutics. Immune-system-targeting aptamers have a great potential as a targeted therapeutic strategy against immune diseases. This review summarizes components of the innate immune system, aptamer production, pharmacokinetic characteristics of aptamers, and aptamers related to innate-immune-system diseases.

The Emerging Role of Innate Immunity in Chronic Kidney Diseases

Renal fibrosis is a common fate of chronic kidney diseases. Emerging studies suggest that unsolved inflammation will progressively transit into tissue fibrosis that finally results in an irreversible end-stage renal disease (ESRD). Renal inflammation recruits and activates immunocytes, which largely promotes tissue scarring of the diseased kidney. Importantly, studies have suggested a crucial role of innate immunity in the pathologic basis of kidney diseases. This review provides an update of both clinical and experimental information, focused on how innate immune signaling contributes to renal fibrogenesis. A better understanding of the underlying mechanisms may uncover a novel therapeutic strategy for ESRD.

A novel TLR7 agonist as adjuvant to stimulate high quality HBsAg-specific immune responses in an HBV mouse model

Background

The global burden of hepatitis B virus (HBV) infection in terms of morbidity and mortality is immense. Novel treatments that can induce a protective immune response are urgently needed to effectively control the HBV epidemic and eventually eradicate chronic HBV infection.

Methods

We designed and evaluated an HBV therapeutic vaccine consisting of a novel Toll-like receptor 7 (TLR7) agonist T7-EA, an Alum adjuvant and a recombinant HBsAg protein. We used RNA-seq, ELISA and hTLR7/8 reporting assays to characterize T7-EA in vitro and real-time PCR to evaluate the tissue-retention characteristics in vivo. To evaluate the adjuvant potential, we administrated T7-EA intraperitoneally in a formulation with an Alum adjuvant and HBsAg in normal and HBV mice, then, we evaluated the HBsAg-specific immune responses by ELISA and Elispot assays.

Results

T7-EA acted as an hTLR7-specific agonist and induced a similar gene expression pattern as an unmodified TLR7 ligand when Raw 264.7 cells were exposed to T7-EA; however, T7-EA was more potent than the unmodified TLR7 ligand. In vivo studies showed that T7-EA had tissue-retaining activity with stimulating local cytokine and chemokine expression for up to 7 days. T7-EA could induce Th1-type immune responses, as evidenced by an increased HBsAg-specific IgG2a titer and a T-cell response in normal mice compared to mice received traditional Alum-adjuvant HBV vaccine. Importantly, T7-EA could break immune tolerance and induce persistent HBsAg-specific antibody and T-cell responses in an HBV mouse model.

Conclusions

T7-EA might be a candidate adjuvant in a prophylactic and therapeutic HBV vaccine.

CpG ODN D35 improves the response to abbreviated low-dose pentavalent antimonial treatment in non-human primate model of cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) affects the lives of 0.7–1 million people every year causing lesions that take months to heal. These lesions can result in disfiguring scars with psychological, social and economic consequences. Antimonials are the first line of therapy for CL, however the treatment is lengthy and linked to significant toxicities; further, its efficacy is variable and resistant parasites are emerging. Shorter or lower dose antimonial treatment regimens, which would decrease the risk of adverse events and improve patient compliance, have shown reduced efficacy and further increase the risk emergence of antimonial-resistant strains. The progression of lesions in CL is partly determined by the immune response it elicits, and previous studies showed that administration of immunomodulatory type D CpG ODNs, magnifies the immune response to Leishmania and reduces lesion severity in nonhuman primates (NHP) challenged with Leishmania major or Leishmania amazonensis. Here we explored whether the addition of a single dose of immunomodulating CpG ODN D35 augments the efficacy of a short-course, low-dose pentavalent antimonial treatment regimen. Results show that macaques treated with D35 plus 5mg/kg sodium stibogluconate (Sb^V) for 10 days had smaller lesions and reduced time to re-epithelization after infection with Leishmania major. No toxicities were evident during the studies, even at doses of D35 10 times higher than those used in treatment. Critically, pentavalent antimonial treatment did not modify the ability of D35 to induce type I IFNs. The findings support the efficacy of D35 as adjuvant therapy for shorter, low dose pentavalent antimonial treatment.

Cutaneous leishmaniasis is a devastating disease that affects close to a million people every year. Its clinical presentation ranges from small uncomplicated lesions that heal over a few months to debilitating large chronic or recurring lesions that result in disfigurement, stigma, and economic loss. Antimonials are the first line treatment for cutaneous leishmaniasis in most countries, but the lengthy treatment schedules, significant associated toxicities, and the emergence of resistant strains, require the development of alternative strategies. As the immune response is a key determinant of disease course, immunomodulatory therapies could be harnessed to act in concert with antimonials to improve the safety and efficacy of CL treatment. Synthetic oligonucleotide D35 selectively activates plasmacytoid dendritic cells and was previously shown to reduce the severity of L. major and L. amazonensis lesions in rhesus macaques, but its activity in combination with antimonials was unknown. Our studies show that a single subcutaneous dose of innate immune modulator D35 improved the response to a low-dose abbreviated antimonial course, reducing the severity of the lesions and accelerating healing in primates. No toxicities were evident with D35 at doses ten-fold higher than the effective dose. The studies suggest that the combined therapy strategy shows clinical promise.

Lipid nanoparticles of Type-A CpG D35 suppress tumor growth by changing tumor immune-microenvironment and activate CD8 T cells in mice

Type-A CpG oligodeoxynucleotides (ODNs), which have a natural phosphodiester backbone, is one of the highest IFN-α inducer from plasmacytoid dendritic cells (pDC) via Toll-like receptor 9 (TLR9)-dependent signaling. However, the in vivo application of Type-A CpG has been limited because the rapid degradation in vivo results in relatively weak biological effect compared to other Type-B, -C, and -P CpG ODNs, which have nuclease-resistant phosphorothioate backbones. To overcome this limitation, we developed lipid nanoparticles formulation containing a Type-A CpG ODN, D35 (D35LNP). When tested in a mouse tumor model, intratumoral and intravenous D35LNP administration significantly suppressed tumor growth in a CD8 T cell-dependent manner, whereas original D35 showed no efficacy. Tumor suppression was associated with Th1-related gene induction and activation of CD8 T cells in the tumor. The combination of D35LNP and an anti-PD-1 antibody increased the therapeutic efficacy. Importantly, the therapeutic schedule and dose of intravenous D35LNP did not induce apparent liver toxicity. These results suggested that D35LNP is a safe and effective immunostimulatory drug formulation for cancer immunotherapy.

Linked Toll-Like Receptor Triagonists Stimulate Distinct, Combination-Dependent Innate Immune Responses

Traditional vaccination strategies have failed to generate effective vaccines for many infections like tuberculosis and HIV. New approaches are needed for each type of disease. The protective immunity and distinct responses of many successful vaccines come from activating multiple Toll-like receptors (TLRs). Vaccines with multiple TLRs as adjuvants have proven effective in preclinical studies, but current research has not explored two important elements. First, few multi-TLR systems explore spatial organization-a critical feature of whole-cell vaccines. Second, no multi-TLR systems to date provide systematic analysis of the combinatorial space of three TLR agonists. Here, we present the first examination of the combinatorial space of several spatially defined triple-TLR adjuvants, by synthesizing a series of five triple-TLR agonists and testing their innate activity both in vitro and in vivo. The combinations were evaluated by measuring activation of immune stimulatory genes (Nf-κB, ISGs), cytokine profiles (IL12-p70, TNF-α, IL-6, IL-10, CCL2, IFN-α, IFN-β, IFN-γ), and in vivo cytokine serum levels (IL-6, TNF-α, IL12-p40, IFN-α, IFN-β). We demonstrate that linking TLR agonists substantially alters the resulting immune response compared to their unlinked counterparts and that each combination results in a distinct immune response, particularly between linked combinations. We show that combinations containing a TLR9 agonist produce more Th1 biasing immune response profiles, and that the effect is amplified upon conjugation. However, combinations containing TLR2/6 agonist are skewed toward T_H2 biasing profiles despite the presence of TLR9. These results demonstrate the profound effects that conjugation and combinatorial administration of TLR agonists can have on immune responses, a critical element of vaccine development.

Dual Toll-Like Receptor Targeting Liposomal Spherical Nucleic Acids

Liposomal spherical nucleic acids (LSNAs) are a class of nanomaterial used broadly for biomedical applications. Their intrinsic capacity to rapidly enter cells and engage cell surface and intracellular ligands stems from their unique three-dimensional architecture, which consists of densely packed and uniformly oriented oligonucleotides on the surface of a liposomal core. Such structures are promising for therapeutics because they can carry chemical cargo within the lipid core in addition to the nucleic acids that define them, in principle enabling delivery of multiple signals to a single cell. On the basis of these traits, we have designed novel dual-targeting LSNAs that deliver a nucleic acid specific for TLR9 inhibition and a small molecule (TAK-242) that inhibits TLR4. Toll-like receptors (TLRs) play a large role in pathogen recognition and disease initiation, and TLR subtypes are differentially located within the lipid membranes of the cell surface and within intracellular endosomes. Oftentimes, in acute or chronic inflammatory conditions, multiple TLRs are activated, leading to stimulation of distinct, and sometimes overlapping, downstream pathways. As such, these inflammatory conditions may respond to attenuation of more than one initiating receptor. We show that dual targeting LSNAs, comprised of unilamellar liposomal cores, the INH-18 oligonucleotide sequence, and TAK-242 robustly inhibit TLR-9 and TLR-4 respectively, in engineered TLR reporter cells and primary mouse peritoneal macrophages. Importantly, the LSNAs exhibit up to a 10- and a 1000-fold increase, respectively, in TLR inhibition compared to the linear sequence and TAK-242 alone. Moreover, the timing of delivery is shown to be a critical factor in effecting TLR-inhibition, with near-complete TLR-4 inhibition occurring when cells were pretreated with SNAs for 4 h prior to stimulation. The most pronounced effect observed from this approach is the benefit of delivering the small molecule within the SNA via the receptor-mediated internalization pathway common to SNAs.

Immunostimulatory activity of Y-shaped DNA nanostructures mediated through the activation of TLR9

Immunostimulatory oligodeoxynucleotides (DNAs) have been widely studied in pharmaceutical and biomedical research fields for applications in cancer immunotherapy and vaccination. Toll-like receptors (TLRs) are critical for the instruction and orchestration of the host immune system composed of innate and adaptive immunity. In particular, TLR9 responds to DNAs with unmethylated deoxycytosine-deoxyguanosine (CpG) motifs, thereby inducing the activation of innate immune cells, such as dendritic cells, and consequently, adaptive immune cells. In this study, we developed two kinds of Y-shaped double-stranded DNA nanostructures (Y-DNAs), including a single unit composed of three DNA strands (Y_S-DNA) and a ligated multiunit complex formed by crosslinking each Y_S-DNA (Y_L-DNA), and investigated whether they have immunostimulatory activity in innate immune cells. Y_S-DNA and Y_L-DNA induced the production of immune cytokines such as IL-12 and TNF-α and the expression of costimulatory molecules such as CD80 and CD86 in primary mouse dendritic cells and macrophage cells (RAW264.7 cells). A Coprecipitation study demonstrated that Y_L-DNA was directly associated with TLR9. The induction of immune cytokines by Y_S-DNA and Y_L-DNA was abolished in TLR9-deficient primary mouse dendritic cells. The results demonstrated that Y-DNAs induced the activation of dendritic cells and macrophages mediated by the activation of TLR9, as shown by the expression of immune cytokines and costimulatory molecules. The results suggest that Y-DNA nanostructures provide a beneficial strategy for immunotherapy by modulating the immune system.

Complex Consisting of β-Glucan and Antigenic Peptides with Cleavage Site for Glutathione and Aminopeptidases Induces Potent Cytotoxic T Lymphocytes

The efficient induction of antigen-specific immune responses requires not only promotion of the uptake of antigens and adjuvant molecules into antigen-presenting cells but also control of their intracellular behavior. We previously demonstrated that the β-glucan schizophyllan (SPG) can form complexes with CpG oligonucleotides with attached dA₄₀ (CpG-dA/SPG), which can accumulate in macrophages in the draining inguinal lymph nodes and induce strong immune responses. In this study, we prepared various conjugates composed of antigenic peptide (OVA_257-264) and dA₄₀ and made complexes with SPG. The conjugates with a disulfide bond between OVA_257-264 and dA₄₀ were easily cleaved by glutathione. The resultant peptides with a hydrophobic amino acid at the C-terminal end was recognized by puromycin-insensitive leucine aminopeptidase (PILS-AP), which trims antigenic peptide precursors and prepares peptides of eight or nine amino acids in length, which is the optimal length for binding to major histocompatibility complex (MHC)-I. The conjugate exposed to such enzymes induced a high antigen presentation level. The antigen presentation level was almost the same before and after the complexation with SPG. Immunization with a mixture of dA-OVA_257-264/SPG and CpG-dA/SPG induced high antigen-specific cytotoxic T-lymphocyte activity at a much lower peptide dose than in previous studies. These results can be strongly ascribed to not only the cell-specific delivery by SPG but also the control of the intracellular behavior by the introduction of cleavage sites. Therefore, peptide-dA/SPG complexes could be used as potent vaccine antigens for the treatment of cancers and infectious diseases.

CpG Type A Induction of an Early Protective Environment in Experimental Multiple Sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory, demyelinating disease of the CNS that mimics human multiple sclerosis (MS), and it is thought to be driven by Th1 and Th17 myelin-reactive cells. Although adaptive immunity is clearly pivotal in the pathogenesis of EAE, with an essential role of CD4⁺ T cells, little is known of early, innate responses in this experimental setting. CpG-rich oligodeoxynucleotides (ODNs), typically found in microbial genomes, are potent activators of TLR9 in plasmacytoid dendritic cells (pDCs). In this study, we compared the effects of two types of CpG, namely, type A and type B, on EAE. We found that treatment with CpG type A ODN (CpG-A), known to induce high amounts of IFN-α in pDCs, significantly reduced disease severity in EAE, relative to controls (12.63 ± 1.86 versus 23.49 ± 1.46, resp.; p = 0.001). Treatment also delayed onset of neurological deficits and reduced spinal cord demyelination, while increasing the percentage of splenic regulatory (Foxp3⁺ CD4⁺) T cells. CpG-A likewise reduced the levels of IL-17 and IFN-γ in the CNS. Mechanistic insight into those events showed that CpG-A promoted a regulatory phenotype in pDCs. Moreover, adoptive transfer of pDCs isolated from CpG-A-treated mice inhibited CNS inflammation and induced disease remission in acute-phase EAE. Our data thus identify a link between TLR9 activation by specific ligands and the induction of tolerance via innate immunity mechanisms.

Adjuvant Activity Enhanced by Cross-Linked CpG-Oligonucleotides in β-Glucan Nanogel and Its Antitumor Effect

Cancer vaccine has the ability to directly eradicate tumor cells by creating and activating cytotoxic T lymphocytes (CTLs). To achieve efficient CTL activity and to induce Th1 responses, it is essential to administer an appropriate adjuvant as well as an antigen. CpG-ODN is known as a ligand of Toll-like receptor 9 (TLR9) and strongly induces Th1 responses. In our previous study, we developed a CpG-ODN delivery system by use of the formation of complexes between ODN and a β-glucan SPG, denoted as CpG/SPG, and demonstrated that CpG/SPG induces high Th1 responses. In this study, we created a nanogel made from CpG/SPG complexes through DNA-DNA hybridization (cross-linked (CL)-CpG). Immunization with CL-CpG induced much stronger antigen-specific Th1 responses in combination with the antigenic protein ovalbumin (OVA) than that with CpG/SPG. Mice preimmunized with CL-CpG and OVA exhibited a long delay in tumor growth and an improved survival rate after tumor inoculation. These immune inductions can be attributed to the improvement of cellular uptake by the combination of increased size and the cluster effect of the β-glucan recognition site in the nanogel structure. In other words, the particle nature of CL-CpG, instead of the semiflexible rod conformation of CpG/SPG, enhanced the efficacy of a cancer vaccine. The present results indicate that CL-CpG can be used as a potent vaccine adjuvant for the treatment of cancers and infectious diseases.

Toll-like receptor 9 ligand D-type oligodeoxynucleotide D35 as a broad inhibitor for influenza A virus replication that is associated with suppression of neuraminidase activity

The most effective drugs available to treat influenza are neuraminidase (NA) inhibitors, which provide important additional measures for the control of influenza virus infections. However, since the emergence of NA inhibitor-resistant viruses may compromise the clinical utility of this class of anti-influenza agents, it is very important to develop new anti-influenza agents which target a different region in NA responsible for its sensitivity from that for NA inhibitors and could be used to treat NA inhibitors-resistant isolates. The oligodeoxynucleotide D35, multimerized and aggregated, suppressed replication of influenza A viruses except A/WSN/33 (WSN). The suppressive viral replication by D35 depended on G-terad and multimer formation. The range of the suppressive viral replication at the late stage, including virus assembly and release from infected cells, was much larger than that at the initial stage, viral attachment and entry. D35 suppressed NA activity of influenza A viruses. Furthermore, replacing the NA gene of A/Puerto Rico/8/34 (PR8), in which viral replication was inhibited by D35 at the late stage, with the NA gene from WSN, in which viral replication was not inhibited, eliminated the D35-dependent suppression. D35 showed an additive anti-influenza effect with oseltamivir. It was also effective in vivo. These results suggest that the influenza virus NA mainly contributse to the D35-suppressible virus release from infected cells at the late stage. In addition, because administration of D35 into the virus-infected mice suppressed viral replication and weight loss, clinical application of D35 could be considered.

•

The oligodeoxynucleotide D35 suppressed replication of some influenza A viruses.

•

D35 inhibits viral replication at the late step which is dependent on NA activity.

•

Antiviral mechanism by D35 is different from that by oseltamivir.

Aptamers Against Immunologic Targets: Diagnostic and Therapeutic Prospects

The concept of in vitro selection of nucleic acid aptamers emerged 25 years ago, and since then tremendous progress has been achieved in the development of different aptamers and their applications for various bioanalytical and therapeutic purposes. Among other protein targets of aptamers, immune system proteins are of particular interest both as diagnostic markers and therapeutic targets. The present review summarizes up-to-date articles concerning the selection and design of DNA and RNA aptamers against immunologic targets such as antibodies, cytokines, and T-cell and B-cell receptors. We also discuss the prospects of employing aptamers as recognizing modules of diagnostic aptasensors, potential therapeutic candidates for the treatment of autoimmune diseases and cancer, and specific tools for functional studies of immune system proteins.

Development of Nonaggregating Poly-A Tailed Immunostimulatory A/D Type CpG Oligodeoxynucleotides Applicable for Clinical Use

Immunostimulatory CpG ODNs have been developed and utilized as TLR9-dependent innate immune activators and vaccine adjuvants. Four different types of immunostimulatory CpG ODNs (A/D, B/K, C, and P type) have been reported. A/D type ODNs are characterized by high IFN-α production but intrinsically form aggregates, hindering its good manufacturing practice grade preparation. In this study, we developed several D35-derived ODNs (a commonly used A/D type ODN), which were modified with the addition of a phosphorothioate polynucleotide tail (such as dAs40), and examined their physical properties, solubility in saline, immunostimulatory activity on human PBMCs, and vaccine adjuvant potential in monkeys. We found that two modified ODNs including D35-dAs40 and D35core-dAs40 were immunostimulatory, similar to original D35 in human PBMCs, resulting in high IFN-α secretion in a dose-dependent manner. Physical property analysis by dynamic light scattering revealed that both D35-dAs40 and D35core-dAs40 did not form aggregates in saline, which is currently impossible for the original D35. Furthermore, D35-dAs40 and D35core-dAs40 worked as better vaccine adjuvant in monkeys. These results suggested that D35-dAs40 and D35core-dAs40 are two promising prototypes of nonaggregating A/D type ODN with advantages of ease of drug preparation for clinical applications as vaccine adjuvants or IFN-α inducing immunomodifiers.

Enzymatic synthesis of modified oligonucleotides by PEAR using Phusion and KOD DNA polymerases

Antisense synthetic oligonucleotides have been developed as potential gene-targeted therapeutics. We previously reported polymerase-endonuclease amplification reaction (PEAR) for amplification of natural and 5'-O-(1-thiotriphosphate) (S)-modified oligonucleotides. Here, we extended the PEAR technique for enzymatic preparation of 2'-deoxy-2'-fluoro-(2'-F) and 2'-F/S double-modified oligonucleotides. The result showed that KOD and Phusion DNA polymerase could synthesize oligonucleotides with one or two modified nucleotides, and KOD DNA polymerase is more suitable than Phusion DNA polymerase for PEAR amplification of 2'-F and 2'-F/S double modified oligonucleotides. The composition of PEAR products were analyzed by electrospray ionization liquid chromatography mass spectrometry (ESI/LC/MS) detection and showed that the sequence of the PEAR products are maintained at an extremely high accuracy (>99.9%), and after digestion the area percent of full-length modified oligonucleotides reaches 89.24%. PEAR is suitable for synthesis of modified oligonucleotides efficiently and with high purity.

Alginate-coated chitosan nanogels differentially modulate class-A and class-B CpG-ODN targeting of dendritic cells and intracellular delivery

CpG-oligodeoxynucleotides (CpG-ODNs) interact with dendritic cells (DCs), but evidence is less clear for CpG-ODN admixed with or incorporated into vaccine delivery vehicles. We loaded alginate-coated chitosan-nanogels (Ng) with class-A or class-B CpG-ODN, and compared with the same CpG-ODNs free or admixed with empty Ng. Experiments were performed on both porcine and human blood DC subpopulations. Encapsulation of class-A CpG-ODN (loading into Ng) strongly reduced the CpG-ODN uptake and intracellular trafficking in the cytosol; this was associated with a marked deficiency in IFN-α induction. In contrast, encapsulation of class-B CpG-ODN increased its uptake and did not influence consistently intracellular trafficking into the nucleus. The choice of CpG-ODN class as adjuvant is thus critical in terms of how it will behave with nanoparticulate vaccine delivery vehicles. The latter can have distinctive modulatory influences on the CpG-ODN, which would require definition for different CpG-ODN and delivery vehicles prior to vaccine formulation.

FROM THE CLINICAL EDITOR

This basic science study investigates the role of class-A and class-B CpG-oligodeoxynucleotides loaded into alginate-coated chitosan nanogels, demonstrating differential effects between the two classes as related to the use of these nanoformulations as vaccine delivery vehicles.

RNA:DNA hybrids are a novel molecular pattern sensed by TLR9

The sensing of nucleic acids by receptors of the innate immune system is a key component of antimicrobial immunity. RNA:DNA hybrids, as essential intracellular replication intermediates generated during infection, could therefore represent a class of previously uncharacterised pathogen-associated molecular patterns sensed by pattern recognition receptors. Here we establish that RNA:DNA hybrids containing viral-derived sequences efficiently induce pro-inflammatory cytokine and antiviral type I interferon production in dendritic cells. We demonstrate that MyD88-dependent signalling is essential for this cytokine response and identify TLR9 as a specific sensor of RNA:DNA hybrids. Hybrids therefore represent a novel molecular pattern sensed by the innate immune system and so could play an important role in host response to viruses and the pathogenesis of autoimmune disease.

Biomimetic protein nanoparticles facilitate enhanced dendritic cell activation and cross-presentation

Many current cancer vaccine strategies suffer from the inability to mount a CD8 T cell response that is strong enough to overcome the low immunogenicity of tumors. Viruses naturally possess the sizes, geometries, and physical properties for which the immune system has evolved to recognize, and mimicking those properties with nanoparticles can produce robust platforms for vaccine design. Using the nonviral E2 core of pyruvate dehydrogenase, we have engineered a viral-mimicking vaccine platform capable of encapsulating dendritic cell (DC)-activating CpG molecules in an acid-releasable manner and displaying MHC I-restricted SIINFEKL peptide epitopes. Encapsulated CpG activated bone marrow-derived DCs at a 25-fold lower concentration in vitro when delivered with the E2 nanoparticle than with unbound CpG alone. Combining CpG and SIINFEKL within a single multifunctional particle induced ∼3-fold greater SIINFEKL display on MHC I by DCs over unbound peptide. Importantly, combining CpG and SIINFEKL to the E2 nanoparticle for simultaneous temporal and spatial delivery to DCs showed increased and prolonged CD8 T cell activation, relative to free peptide or peptide-bound E2. By codelivering peptide epitopes and CpG activator in a particle of optimal DC-uptake size, we demonstrate the ability of a noninfectious protein nanoparticle to mimic viral properties and facilitate enhanced DC activation and cross-presentation.

Sweeten PAMPs: Role of Sugar Complexed PAMPs in Innate Immunity and Vaccine Biology

Innate sensors play a critical role in the early innate immune responses to invading pathogens through sensing of diverse biochemical signatures also known as pathogen associated molecular patterns (PAMPs). These biochemical signatures primarily consist of a major family of biomolecules such as proteins, lipids, nitrogen bases, and sugar and its complexes, which are distinct from host molecules and exclusively expressed in pathogens and essential to their survival. The family of sensors known as pattern recognition receptors (PRRs) are germ-line encoded, evolutionarily conserved molecules, and consist of Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), NOD-like receptors (NLRs), C-type lectin-like receptors (CLRs), and DNA sensors. Sensing of PAMP by PRR initiates the cascade of signaling leading to the activation of transcription factors, such as NF-κB and interferon regulatory factors (IRFs), resulting in a variety of cellular responses, including the production of interferons (IFNs) and pro-inflammatory cytokines. In this review, we discuss sensing of different types of glycosylated PAMPs such as β-glucan (a polymeric sugar) or lipopolysaccharides, nucleic acid, and so on (sugar complex PAMPs) by different families of sensors, its role in pathogenesis, and its application in development of potential vaccine and vaccine adjuvants.

Activation of Rac1 GTPase by nanoparticulate structures in human macrophages

Inflammatory activation of alveolar macrophages by ambient particles can be facilitated via Toll-like receptors (TLR). The action of TLR agonists and antagonists has been reported to depend on the formation of nanoparticulate structures. Aim of the present study was to identify the signaling pathways induced by nanoparticulate structures in human macrophages, which might be critical for inflammatory cell activation.

METHODS

Studies were performed in primary human alveolar macrophages or in differentiated THP-1 macrophages. Silica nanoparticles were prepared by Stöber synthesis and characterized by dynamic light scattering and scanning electron microscopy. Mycobacterial DNA was isolated from Mycobacterium bovis BCG, and nanoparticle formation was assessed by atomic force microscopy and dynamic light scattering. Actin polymerization was measured by phalloidin-TRITC staining, and cell activation was determined by reverse transcription quantitative PCR analysis, L929 cytotoxicity assay (cytokine induction), and pull-down assays (Rho GTPases).

RESULTS

In contrast to immune stimulatory sequence ISS 1018, BCG DNA spontaneously formed nanoparticulate structures and induced actin polymerization as did synthetic silica nanoparticles. Co-incubation with silica nanoparticles amplified the responsiveness of macrophages toward the TLR9 ligand ISS 1018. The activation of Rac1 was induced by silica nanoparticles as well as BCG DNA and is suggested as the critical signaling event inducing both cytoskeleton changes as well as inflammatory cell activation.

CONCLUSION

Nanoparticles can induce signaling pathways, which amplify an inflammatory response in macrophages.

CpG oligodeoxynucleotides with double stem-loops show strong immunostimulatory activity

Based on the current understanding of TLR9 recognition of CpG ODN, we have tried to design a series of CpG ODNs that display double stem-loops when being analyzed for their secondary structures using 'mfold web server'. Proliferation of human PBMC and bioassay for IFN production were used as technical platforms in primary screening. Interestingly, two of them, designated as DSL01 and D-SL03, belonging to B class CpG ODN and C class CpG ODN respectively, showed vigorous immunostimulatory activity and were chosen for further tests. Flow cytometry analysis showed that both of them could activate human B cells, NK cells, mononuclear cells and T cells and up-regulate expression of CD80, CD86 and HLA-DR on the surface of subsets in human PBMCs. Furthermore, we demonstrated that those two ODNs potently stimulated proliferation of PBMC/splenocytes obtained from diverse vertebrate species. Noticeably, both of them displayed anti-breast cancer effect in mice when administered by peritumoral injection.

Self-assembled multivalent DNA nanostructures for noninvasive intracellular delivery of immunostimulatory CpG oligonucleotides

Designed oligonucleotides can self-assemble into DNA nanostructures with well-defined structures and uniform sizes, which provide unprecedented opportunities for biosensing, molecular imaging, and drug delivery. In this work, we have developed functional, multivalent DNA nanostructures by appending unmethylated CpG motifs to three-dimensional DNA tetrahedra. These small-sized functional nanostructures are compact, mechanically stable, and noncytotoxic. We have demonstrated that DNA nanostructures are resistant to nuclease degradation and remain substantially intact in fetal bovine serum and in cells for at least several hours. Significantly, these functional nanostructures can noninvasively and efficiently enter macrophage-like RAW264.7 cells without the aid of transfection agents. After they are uptaken by cells, CpG motifs are recognized by the Toll-like receptor 9 (TLR9) that activates downstream pathways to induce immunostimulatory effects, producing high-level secretion of various pro-inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-12. We also show that multivalent CpG motifs greatly enhance the immunostimulatory effect of the nanostructures. Given the high efficacy of these functional nanostructures and their noncytotoxic nature, we expect that DNA nanostructures will become a promising tool for targeted drug delivery.

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

Toll-like receptor 9 (TLR9) is an endosomal DNA sensor that warns us of the presence of infectious danger and triggers a rapid pro-inflammatory response in dendritic cells, macrophages, and B cells. The consequences of uncontrolled TLR9 activation can be detrimental for the host, contributing to the pathogenesis of bacterial septic shock or autoimmune diseases, such as systemic lupus erythematosus. Therefore, we need to develop TLR9 antagonists. We and others have created inhibitory oligonucleotides (INH-ODN) that are capable of sequence-dependent inhibition of TLR9-induced activation in both human and mouse cells. However, it is not clear whether marked differences in INH-ODN activity related to base sequence derived from polymerization of INH-ODNs or their ability to complex with stimulatory CpG-oligonucleotides (ST-ODN). Furthermore, the 5' end of INH-ODNs may assume a particular loop configuration that may be needed for binding to a critical site on TLR9. Here, we show that 1) G-tetrads required for ODN stacking were compatible with INH-ODN activity but were not necessary; 2) there was no relationship between activity and self-association at endosomal pH; 3) there was no evidence for direct binding between ST-ODNs and INH-ODNs; 4) when a 3G sequence was disrupted, despite a preserved stem-loop formation, INH-ODN activity was abolished. These results support the conclusion that certain features of the primary linear sequence are critical for TLR9 inhibition, but changes in secondary structure or in ODN aggregation are irrelevant.

Human serum amyloid P functions as a negative regulator of the innate and adaptive immune responses to DNA vaccines

The utility of DNA vaccines has been limited by their failure to elicit sufficiently potent immune responses in many human applications, whereas DNA vaccinations in mice have been very successful. However, the underlying mechanisms remain unknown. We hypothesize that serum amyloid P component (SAP), which has a species-specific, DNA-binding ability, contributes to the differences between human and mice and then limits DNA vaccine's efficacy in vivo. In our study, DNA vaccine-induced adaptive immune responses were also significantly decreased in the human SAP (hSAP) transgenic mice. Using human promonocytic cell line THP-1-derived macrophages as a cell model, we found that cells incubated with a hSAP-DNA complex showed significant defects in innate immune activations, whereas mouse SAP had similar, albeit very weak, activities. hSAP also significantly inhibited the functions of two identified DNA sentinels, high-mobility group B protein 1 and antimicrobial peptide LL37, and redirected DNA update to FcRs leading to endocytosis and endosomal degradation. We also found that a chemical SAP inhibitor strongly recovered the suppressed innate immune responses to DNA in the presence of human serum and enhanced the immunogenicity of DNA vaccines in vivo. Our data indicated that SAP is a key negative regulator for innate immune responses to DNA and may be partly responsible for the insufficient immune responses after DNA vaccinations in humans. SAP suppression may be a novel strategy for improving efficacy of human DNA vaccines and requires further clinical investigations.

5'-Phosphate oligodeoxynucleotides enhance the phosphodiester-CpG DNA-induced inflammatory response in macrophages

Dying cells release genomic DNA into the surroundings where the DNA is first degraded to oligodeoxynucleotides, then to nucleotides, nucleosides and so on. Given that the unmethylated CpG dinucleotide (CpG motif), which is characteristic of bacterial DNA, is also contained in mammalian DNA and has been reported to be involved in the exacerbation of DNA-associated autoimmune diseases, we investigated whether nucleotides and nucleosides affect immune responses to phosphodiester (PO)-CpG DNA. Addition of non-CpG DNA to RAW264.7, murine macrophage-like cells, induced no significant TNF-α production irrespective of treatment with DNase I; however, DNase I-treated, but not untreated, non-CpG DNA increased the PO-CpG DNA-mediated TNF-α production. This increase was not observed with phosphorothioate-CpG DNA or ligands for TLR3, TLR4 or TLR7. Deoxynucleotides with a 5'-phosphate showed similar effects to those of DNase I-treated non-CpG DNA, but DNase II-treated DNA or deoxynucleosides did not. Subcutaneous injection of PO-CpG DNA into the mouse footpad induced little swelling of the paw; however, significant swelling was observed when DNase I-treated DNA was co-injected with PO-CpG DNA. These results imply that PO-CpG DNA-dependent inflammatory responses are increased by DNA molecules with a 5'-phosphate; such molecules could therefore be considered as exacerbating factors for CpG motif-related inflammation.

Enhanced cytokine secretion from primary macrophages due to Dectin-1 mediated uptake of CpG DNA/β-1,3-glucan complex

Unmethylated CpG sequences (CpG DNA) can induce Th1 response and thus become a potential immunotherapeutic agent. A key step in the treatment is to transport CpG DNA to its receptor TLR9 located in the endocytosis pathway of target immune cells. For the effective transport, we prepared a novel complex from a β-1,3-glucan schizophyllan (SPG) and CpG DNA, and administered the complex to murine peritoneal macrophages that had been previously activated by thioglycollate and expressed a major β-1,3-glucan receptor Dectin-1 on the cellular surface. Flow cytometric analysis and microscopic observation showed that the complex was taken up by the macrophage through Dectin-1 mediated pathway. Indeed, ELISA demonstrated that IL-12 production was increased sigmoidally with increasing SPG/CpG DNA ratio in the complexation, and reached the maximum at the SPG-rich composition. In the present work, we describe a new approach to deliver CpG DNA to immune cells by use of a β-1,3-glucan/DNA complex.

Higher order structure of short immunostimulatory oligonucleotides studied by atomic force microscopy

Immunostimulatory CpG-DNA activates the innate immune system by binding to Toll-like receptor 9. Structurally different CpG-containing oligonucleotides trigger a different type of immune response while activating the same receptor. We therefore investigated the higher order structure of two different classes of immunostimulatory CpG-DNA. Class A, which contains a partly self-complementary sequence and poly-G ends, forms duplexes and nanoparticles in salt solution, while class B, which does not contain these features and is purely linear, does not form a duplex or nanoparticles. Results obtained here by high-resolution atomic force microscopy of classes A and B CpG-DNA, reflect these differences in secondary structure. Detailed structural analysis of the atomic force microscopy topographs is presented for two different sample preparation methods.

Immune Mechanisms and Therapeutic Potential of CpG Oligodeoxynucleotides

Unmethylated CpG motifs in bacterial DNA and synthetic oligodeoxynucleotides activate immune cells that express Toll-like Receptor 9. Activation through this receptor triggers cellular signaling that leads to production of a proinflammatory and a Th1-type, antigen-specific immune response. The immunostimulatory effects of CpG oligodeoxynucleotides confer protection against infectious disease, allergy and cancer in animal models, and clinical trials have been initiated. However, CpG oligodeoxynucleotides may exacerbate disease in some situations. We will review current concepts in the mechanisms of activating Toll-like Receptor 9 with CpG oligodeoxynucleotides and highlight opportunities for using large animal models to better determine the mechanisms of action.

Immunostimulatory sequence oligdeoxynucleotide/cholera toxin B conjugate: a novel allergen-independent intranasal vaccine for allergic rhinitis

BACKGROUND

Recent studies have shown that by acting as strong TH1 response-inducing adjuvants, DNA immunostimulatory sequence oligdeoxynucleotides (ISS-ODNs) can be used in the treatment of allergic diseases, and efforts are being made to enhance these TH1 adjuvant actions.

OBJECTIVE

To determine whether intranasally delivered ISS-ODN/cholera toxin B (CTB) conjugate has enhanced antiallergic effects in an allergic rhinitis mouse model.

METHODS

BALB-c mice were sensitized with ovalbumin. Chemical conjugation of ISS-ODN and CTB was performed. After a single local intranasal administration of 50 microg of ISS-ODN or high- and low-dose (50- and 5-microg) ISS-ODN/CTB conjugate, we measured the allergic response in terms of sneezing events, eosinophil infiltration in the nasal mucosa, serum ovalbumin specific IgE and IgG2a levels, and TH1 and TH2 cytokine levels in nasal lavage fluid and spleen cell cultures.

RESULTS

A single local administration of 50 microg of ISS-ODN did not suppress the allergic phenotype. However, 50 and 5 microg of ISS-ODN/CTB conjugate significantly attenuated allergic symptoms, eosinophil infiltration in the nasal mucosa, and interleukin 4 production from nasal lavage fluid and cultured splenocyte supernatant compared with the allergic control. Serum specific IgG2a and interleukin 12 production in nasal lavage fluid and spleen cell cultures was significantly increased.

CONCLUSIONS

In a mouse model of allergic rhinitis, a single intranasal delivery of low-dose ISS-ODN/CTB conjugate effectively protects previously sensitized mice from allergic hypersensitivity responses. With further research, ISS-ODN/CTB conjugate may serve as a new allergen-independent intranasal vaccine for the treatment of allergic rhinitis.

Discovery and development of the G-rich oligonucleotide AS1411 as a novel treatment for cancer

Certain guanine-rich (G-rich) DNA and RNA molecules can associate intermolecularly or intramolecularly to form four stranded or "quadruplex" structures, which have unusual biophysical and biological properties. Several synthetic G-rich quadruplex-forming oligodeoxynucleotides have recently been investigated as therapeutic agents for various human diseases. We refer to these biologically active G-rich oligonucleotides as aptamers because their activities arise from binding to protein targets via shape-specific recognition (analogous to antibody-antigen binding). As therapeutic agents, the G-rich aptamers may have some advantages over monoclonal antibodies and other oligonucleotide-based approaches. For example, quadruplex oligonucleotides are non-immunogenic, heat stable and they have increased resistance to serum nucleases and enhanced cellular uptake compared to unstructured sequences. In this review, we describe the characteristics and activities of G-rich oligonucleotides. We also give a personal perspective on the discovery and development of AS1411, an antiproliferative G-rich phosphodiester oligonucleotide that is currently being tested as an anticancer agent in Phase II clinical trials. This molecule functions as an aptamer to nucleolin, a multifunctional protein that is highly expressed by cancer cells, both intracellularly and on the cell surface. Thus, the serendipitous discovery of the G-rich oligonucleotides also led to the identification of nucleolin as a new molecular target for cancer therapy.

Enhanced cytokine secretion owing to multiple CpG side chains of DNA duplex

Unmethylated CpG sequences (CpG ODN) stimulate Toll-like receptor 9 (TLR9) to activate innate immunity. We made DNA duplexes from poly(dT)320 and CpG ODN with (dA)40 attached at the 3' end. Circular dichroism and gel electrophoresis indicated that the CpG parts turned outward from the duplex. When we changed the CpG ODN/poly(dT) molar ratio, the amount of IL-12 secreted from J774A.1 cells (murine macrophage-like) reached the maximum at the compositions with two to four CpG portions in one duplex, while the maximum loading was eight CpG ODNs per one poly(dT)320. When the residual free dT parts were hybridized with its control GpC ODN with (dA)40 tail or just (dA)40, the maximum disappeared and the secretion increased with increasing the CpG molar ratio. These results indicated that there is a particular DNA higher-order structure to activate TLR9 more efficiently than single CpG ODN.

Structural basis of pattern recognition by innate immune molecules

The importance of the innate immune system as a first line defence against pathogenic challenge has long been recognised. Over the last decade the identity of many of the key molecules mediating innate host defence have been clarified and a model of self/ nonself discrimination by families of pattern recognition receptors (PRRs) has emerged. Although a large amount of information is now available concerning the action of these innate immune molecules at the level of the cell and organism, little is known about the molecular interface between pathogens and innate immune recognition molecules. In this chapter the molecular basis for innate immune discrimination of a wide variety of pathogen derived molecules is discussed in the context of the emerging literature.

Toll-like receptor 9 mediates CpG oligonucleotide-induced cellular invasion

Toll-like receptor 9 (TLR9) belongs to the innate immune system and recognizes microbial and vertebrate DNA. We showed previously that treatment with the TLR9-agonistic ODN M362 (a CpG sequence containing oligonucleotide) induces matrix metalloproteinase-13-mediated invasion in TLR9-expressing human cancer cell lines. Here, we further characterized the role of the TLR9 pathway in this process. We show that CpG oligonucleotides induce invasion in macrophages from wild-type C57/B6 and MyD88 knockout mice and in human MDA-MB-231 breast cancer cells lacking MyD88 expression. This effect was significantly inhibited in macrophages from TLR9 knockout mice and in human MDA-MB-231 breast cancer cells stably expressing TLR9 small interfering RNA or dominant-negative tumor necrosis factor receptor-associated factor 6 (TRAF6). Sequence modifications to the CpG oligonucleotides that targeted the stem loop and other secondary structures were shown to influence the invasion-inducing effect in MDA-MB-231 cells. In contrast, methylation of the cytosine residues of the parent CpG oligonucleotide did not affect the TLR9-mediated invasion compared with the unmethylated parent CpG oligonucleotide. Finally, expression of TLR9 was studied in clinical breast cancer samples and normal breast epithelium with immunohistochemistry. TLR9 staining localized in epithelial cells in both cancer and normal samples. The mean TLR9 staining intensity was significantly increased in the breast cancer cells compared with normal breast epithelial cells. In conclusion, our results suggest that TLR9 expression is increased in breast cancer and CpG oligonucleotide-induced cellular invasion is mediated via TLR9 and TRAF6, independent of MyD88. Further, our findings suggest that the structure and/or stability of DNA may influence the induction of TLR9-mediated invasion in breast cancer.

Immunostimulatory CpG oligonucleotides form defined three-dimensional structures: results from an NMR study

The DNA eicosamer 5'-TCCATGACGTTCCTGATGCT-3' is known to stimulate the innate immune system of vertebrae. The immunostimulatory activity is based on the activation of Toll-like receptor 9 (TLR9). While it is known that the CG dinucleotide of the eicosamer has to be unmethylated, the structural basis of the recognition of the DNA through the receptor remains unclear. Oligodeoxynucleotides containing the sequence of the eicosamer, or a portion thereof, ranging in length from hexamer to pentaeicosamer were studied by (1)H NMR spectroscopy. Based on two-dimensional NMR spectra, a number of resonances could be unambiguously assigned. For all oligonucleotides, structural transitions were detected upon heating, as monitored by the line width and chemical shift of low-field resonances. This includes the TC dinucleotide of the 5'-terminal portion, which does not have any clear base-pairing partners. The melting transitions, together with the NOESY cross-peaks, demonstrate that structure formation occurs well beyond the core hexamer 5'-GACGTT-3', a fact that may be important for understanding the molecular recognition by the Toll-like receptors of the innate immune system.

Attenuated activation of macrophage TLR9 by DNA from virulent mycobacteria

Alveolar macrophages are the first line of host defence against mycobacteria, but an insufficient host response allows survival of bacteria within macrophages. We aimed to investigate the role of Toll-like receptor 9 (TLR9) activation in macrophage defence against mycobacteria. Human in vitro differentiated macrophages as well as human and mouse alveolar macrophages showed TLR9 mRNA and protein expression. The cells were markedly activated by DNA isolated from attenuated mycobacterial strains (H37Ra and Mycobacterium bovis BCG) as assessed by measuring cytokine expression by real-time PCR, whereas synthetic phosphorothioate-modified oligonucleotides had a much lower potency to activate human macrophages. Intracellular replication of H37Ra was higher in macrophages isolated from TLR9-deficient mice than in macrophages from wild-type mice, whereas H37Rv showed equal survival in cells from wild-type or mutant mice. Increased bacterial survival in mouse macrophages was accompanied by altered cytokine production as determined by Luminex bead assays. In vivo infection experiments also showed differential cytokine production in TLR9-deficient mice compared to wild-type animals. Both human monocyte-derived macrophages as well as human alveolar macrophages showed reduced activation upon treatment with DNA isolated from bacteria from virulent (M. bovis and H37Rv) compared to attenuated mycobacteria. We suggest attenuated TLR9 activation contributes to the insufficient host response against virulent mycobacteria.

In vivo efficacy of a phosphodiester TLR-9 aptamer and its beneficial effect in a pulmonary anthrax infection model

Immunostimulatory oligonucleotide (ISS-ODN) used as adjuvants are commonly modified with phosphorothioate (PS). The PS backbone prevents nuclease degradation, but confers undesired side effects, including systemic cytokine release. Previously, R10-60, a phosphodiester (PO) ISS-ODN, was structurally optimized as an intracellular Toll-like receptor-9 agonist. Here intravenous, intradermal and intranasal administration of PO R10-60 elicit local or adaptive immune responses with minimal systemic effects compared to a prototypic PS ISS-ODN in mice. Furthermore, prophylactic intranasal administration of PO R10-60 significantly delayed death in mice exposed to respiratory anthrax comparable to the PS ISS-ODN. The pattern of cytokine release suggested that early IL-1beta production might contribute to this protective effect, which was replicated with recombinant IL-1beta injections during infection. Hence, the transient effects from a PO TLR-9 agonist may be beneficial for protection in a bacterial bioterrorism attack, by delaying the onset of systemic infection without the induction of a cytokine syndrome.

Therapeutic applications of synthetic CpG oligodeoxynucleotides as TLR9 agonists for immune modulation

Vertebrate toll-like receptors (TLRs) sense invading pathogens by recognizing bacterial and viral structures and, as a result, activate innate and adaptive immune responses. Ten human functional TLRs have been reported so far; three of these (TLR7, 8, and 9) are expressed in intracellular compartments and respond to single-stranded nucleic acids as natural ligands. The pathogen structure selectively recognized by TLR9 in bacterial or viral DNA was identified to be CpG dinucleotides in specific sequence contexts (CpG motifs). Short phosphorothioate-stabilized oligodeoxynucleotides (ODNs) containing such motifs are used as synthetic TLR9 agonists, and different classes of ODN TLR9 agonists have been identified with distinct immune modulatory profiles. The TLR9-mediated activation of the vertebrate immune system suggests using such TLR9 agonists as effective vaccine adjuvants for infectious disease, and for the treatment of cancer and asthma/allergy. Immune activation by CpG ODNs has been demonstrated to be beneficial in animal models as a vaccine adjuvant and for the treatment of a variety of viral, bacterial, and parasitic diseases. Antitumor activity of CpG ODNs has also been established in numerous mouse models. In clinical vaccine trials in healthy human volunteers or in immunocompromised HIV-infected patients, CpG ODNs strongly enhanced vaccination efficiency. Most encouraging results in the treatment of cancers have come from human phase I and II clinical trials using CpG ODNs as a tumor vaccine adjuvant, monotherapy, or in combination with chemotherapy. Therefore, CpG ODNs represent targeted immune modulatory drugs with a broad range of potential applications.

Altered degradation of circulating nucleic acids and oligonucleotides in diabetic patients

Foreign, infection-associated or endogenously generated circulating nucleotide motifs may represent the critical determinants for the activation of the Toll-like receptors (TLRs), leading to immune stimulation and cytokine secretion. The importance of circulating nucleases is to destroy nucleic acids and oligonucleotides in the blood stream and during cell entry. Patients with juvenile insulin-dependent diabetes, adult patients with insulin-dependent diabetes and adult patients with type 2 diabetes were allocated to the study, together with the age-matched control subjects. Plasma RNase and nuclease activity were examined, in relation to different substrates-TLRs response modifiers, and circulating RNA and oligonucleotides were isolated. The fall in enzyme activity in plasma was obtained for rRNA, poly(C), poly(U), poly(I:C), poly(A:U) and CpG, especially in juvenile diabetics. In order to test the non-enzymatic glycation, commercial RNase (E.C.3.1.27.5) and control plasma samples were incubated with increasing glucose concentrations (5, 10, 20 and 50 mmol/l). The fall of enzyme activity was expressed more significantly in control plasma samples than for the commercial enzyme. Total amount of purified plasma RNA and oligonucleotides was significantly higher in diabetic patients, especially in juvenile diabetics. The increase in the concentration of nucleotides corresponded to the peak absorbance at 270 nm, similar to polyC. The electrophoretic bands shared similar characteristics between controls and each type of diabetic patients, except that the bands were more expressed in diabetic patients. Decreased RNase activity and related increase of circulating oligonucleotides may favor the increase of nucleic acid "danger motifs", leading to TLRs activation.

Enhanced immunostimulatory activity of oligodeoxynucleotides by Y-shape formation

DNA containing unmethylated CpG dinucleotides (CpG DNA) is a potent activator of innate and acquired immune responses. Although the sequence-specific immunostimulatory activity of CpG DNA has been extensively explored, little information is available about the importance of the stereochemical properties of CpG DNA. In this study, Y-shaped oligodeoxynucleotides (Y-ODNs) were prepared using three ODNs with the halves of each ODN being partially complementary to a half of the other two ODNs. Y-ODN induced greater amounts of tumour necrosis factor-alpha and interleukin-6 from RAW264.7 macrophage-like cells than did conventional single-stranded ODN (ssODN) or double-stranded ODN (dsODN). The Y-ODN was less stable in serum than dsODN, but greater amounts of Y-ODN were taken up by macrophage-like cells compared with dsODN. A newly designed Y-ODN containing three potent CpG motifs generated significantly higher levels of cytokines compared with dsODN containing the identical sequences. These results indicate that the Y-shaped form of ODN is a novel, reproducible and reliable approach to enhancing the immunostimulatory activity of ODNs.