Phosphorothioate backbone modification modulates macrophage activation by CpG DNA

Mn2+/CpG Oligodeoxynucleotides Codecorated Black Phosphorus Nanosheet Platform for Enhanced Antitumor Potency in Multimodal Therapy

Manganese ions (Mn2+)-coordinated nanoparticles have emerged as a promising class of antitumor nanotherapeutics, capable of simultaneously disrupting the immunosuppressive tumor microenvironment (TME) and triggering the stimulator of interferon genes (STING) pathway-dependent antitumor immunity. However, the activation of STING signaling by Mn2+-based monotherapies is suboptimal for comprehensive stimulation of antigen presenting cells and reversal of immunosuppression in the TME. Here, we report the design of a Mn2+/CpG oligodeoxynucleotides (ODNs) codecorated black phosphorus nanosheet (BPNS@Mn2+/CpG) platform based on the Mn2+ modification of BPNS and subsequent adsorption of synthetic CpG ODNs. The coordination of Mn2+ significantly improved the stability of BPNS and the adsorption of CpG ODNs. The acidic TME and endosomal compartments can disrupt the Mn2+ coordination, triggering pH-responsive release of CpG ODNs and Mn2+ to effectively activate the Toll-like receptor 9 and STING pathways. As a result, M2-type macrophages and immature dendritic cells were strongly stimulated in the TME, thereby increasing T lymphocyte infiltration and reversing the immunosuppression within the TME. Phototherapy and chemodynamic therapy, utilizing the BPNS@Mn2+/CpG platform, have demonstrated efficacy in inducing immunogenic cell death upon 808 nm laser irradiation. Importantly, the treatment of BPNS@Mn2+/CpG with laser irradiation exhibited significant therapeutic efficacy against the irradiated primary tumor and effectively suppressed the growth of nonirradiated distant tumor. Moreover, it induced a robust immune memory, providing long-lasting protection against tumor recurrence. This study demonstrated the enhanced antitumor potency of BPNS@Mn2+/CpG in multimodal therapy, and its proof-of-concept application as a metal ion-modified BPNS material for effective DNA/drug delivery and immunotherapy.

Approaches of the Innate Immune System to Ameliorate Adaptive Immunotherapy for B-Cell Non-Hodgkin Lymphoma in Their Microenvironment

A dominant paradigm being developed in immunotherapy for hematologic malignancies is of adaptive immunotherapy that involves chimeric antigen receptor (CAR) T cells and bispecific T-cell engagers. CAR T-cell therapy has yielded results that surpass those of the existing salvage immunochemotherapy for patients with relapsed/refractory diffuse large B-cell lymphoma (DLBCL) after first-line immunochemotherapy, while offering a therapeutic option for patients with follicular lymphoma (FL) and mantle cell lymphoma (MCL). However, the role of the innate immune system has been shown to prolong CAR T-cell persistence. Cluster of differentiation (CD) 47-blocking antibodies, which are a promising therapeutic armamentarium for DLBCL, are novel innate immune checkpoint inhibitors that allow macrophages to phagocytose tumor cells. Intratumoral Toll-like receptor 9 agonist CpG oligodeoxynucleotide plays a pivotal role in FL, and vaccination may be required in MCL. Additionally, local stimulator of interferon gene agonists, which induce a systemic anti-lymphoma CD8⁺ T-cell response, and the costimulatory molecule 4-1BB/CD137 or OX40/CD134 agonistic antibodies represent attractive agents for dendritic cell activations, which subsequently, facilitates initiation of productive T-cell priming and NK cells. This review describes the exploitation of approaches that trigger innate immune activation for adaptive immune cells to operate maximally in the tumor microenvironment of these lymphomas.

Tilsotolimod: an investigational synthetic toll-like receptor 9 (TLR9) agonist for the treatment of refractory solid tumors and melanoma

INTRODUCTION

Cancer immunotherapy has seen tremendous strides in the past 15 years, with the introduction of several novel immunotherapeutic agents. Nevertheless, as clinical practice has shown, significant challenges remain with a considerable number of patients responding sub-optimally to available therapeutic options. Research has demonstrated the important immunoregulatory role of the tumor microenvironment (TME), with the potential to either hinder or promote an effective anti-tumor immune response. As such, scientific efforts have focused on investigating novel candidate immunomodulatory agents with the potential to alter the TME toward a more immunopotentiating composition.

AREAS COVERED

Herein, we discuss the novel investigational toll-like receptor 9 agonist tilsotolimod currently undergoing phase II and III clinical trials for advanced refractory cancer, highlighting its mode of action, efficacy, tolerability, and potential future applications in the treatment of cancer. To this effect, we conducted an exhaustive Web of Science and PubMed search to evaluate available research on tilsotolimod as of August 2021.

EXPERT OPINION

With encouraging early clinical results demonstrating extensive TME immunomodulation and abscopal effects on distant tumor lesions, tilsotolimod has emerged as a potential candidate immunomodulatory agent with the possibility to augment currently available immunotherapy and provide novel avenues of treatment for patients with advanced refectory cancer.

Elucidating the Motif for CpG Oligonucleotide Binding to the Dendritic Cell Receptor DEC-205 Leads to Improved Adjuvants for Liver-Resident Memory

DEC-205 is a cell-surface receptor that transports bound ligands into the endocytic pathway for degradation or release within lysosomal endosomes. This receptor has been reported to bind a number of ligands, including keratin, and some classes of CpG oligodeoxynucleotides (ODN). In this study, we explore in detail the requirements for binding ODNs, revealing that DEC-205 efficiently binds single-stranded, phosphorothioated ODN of ≥14 bases, with preference for the DNA base thymidine, but with no requirement for a CpG motif. DEC-205 fails to bind double-stranded phosphodiester ODN, and thus does not bind the natural type of DNA found in mammals. The ODN binding preferences of DEC-205 result in strong binding of B class ODN, moderate binding to C class ODN, minimal binding to P class ODN, and no binding to A class ODN. Consistent with DEC-205 binding capacity, induction of serum IL-12p70 or activation of B cells by each class of ODN correlated with DEC-205 dependence in mice. Thus, the greater the DEC-205 binding capacity, the greater the dependence on DEC-205 for optimal responses. Finally, by covalently linking a B class ODN that efficiently binds DEC-205, to a P class ODN that shows poor binding, we improved DEC-205 binding and increased adjuvancy of the hybrid ODN. The hybrid ODN efficiently enhanced induction of effector CD8 T cells in a DEC-205-dependent manner. Furthermore, the hybrid ODN induced robust memory responses, and was particularly effective at promoting the development of liver tissue-resident memory T cells.

Activation of Innate Immune Responses by a CpG Oligonucleotide Sequence Composed Entirely of Threose Nucleic Acid

Recent advances in synthetic biology have led to the development of nucleic acid polymers with backbone structures distinct from those found in nature, termed xeno-nucleic acids (XNAs). Several unique properties of XNAs make them attractive as nucleic acid therapeutics, most notably their high resistance to serum nucleases and ability to form Watson-Crick base pairing with DNA and RNA. The ability of XNAs to induce immune responses has not been investigated. Threose nucleic acid (TNA), a type of XNA, is recalcitrant to nuclease digestion and capable of undergoing Darwinian evolution to produce high affinity aptamers; thus, TNA is an attractive candidate for diverse applications, including nucleic acid therapeutics. In this study, we evaluated a TNA oligonucleotide derived from a cytosine-phosphate-guanine oligonucleotide sequence known to activate toll-like receptor 9-dependent immune signaling in B cell lines. We observed a slight induction of relevant mRNA signals, robust B cell line activation, and negligible effects on cellular proliferation.

Identification of new CpG oligodeoxynucleotide motifs that induce expression of interleukin-1β and nitric oxide in avian macrophages

Unmethylated CpG motifs are known to stimulate mammalian toll-like receptor-9 expressing cells such as macrophages. However, the magnitude of immune-stimulation by CpG-motif can be sequence- and host-specific, implying the importance of identifying new immune-stimulatory motifs. This study aimed to determine the frequency distribution of 256 unique hexamers CpG-motifs in the Salmonella genome and to characterize their immune-stimulatory activity in avian host. We synthesized 256 CpG oligodeoxynucleotides (CpG-ODNs) each containing triplicates of a unique hexamer CpG-motif and tested their ability to induce expression of pro-inflammatory cytokine IL-1β in avian macrophages using q-RT PCR in four rounds of screening assays. CpG-ODNs that induced significantly higher IL-1β expression were also subjected to Griess assay to determine their ability to induce nitric oxide (NO) production in avian macrophages. This analysis resulted in identification of 7 CpG-ODNs that consistently induced IL-1β expression and NO production in avian macrophages at a level similar to the expression achieved using commercially available PTO-CpG-ODN 2007 and LPS derived from Salmonella. To the best of our knowledge, this is the first report showing comprehensive screening of all possible unique CpG hexamer (n=256) motifs for their ability to induce IL-1β expression and NO production in avian macrophages. We also show that the newly identified CpG-motifs with high immune-stimulatory activity are widely distributed in Salmonella genome. The CpG-ODNs identified in this study may serve as promising immunoprophylactics to potentiate innate responses in chickens against Salmonella and other infectious agents.

T cell-dependent antigen adjuvanted with DOTAP-CpG-B but not DOTAP-CpG-A induces robust germinal center responses and high affinity antibodies in mice

The development of vaccines for infectious diseases for which we currently have none, including HIV, will likely require the use of adjuvants that strongly promote germinal center responses and somatic hypermutation to produce broadly neutralizing antibodies. Here we compared the outcome of immunization with the T-cell dependent antigen, NP-conjugated to chicken gamma globulin (NP-CGG) adjuvanted with the toll-like receptor 9 (TLR9) ligands, CpG-A or CpG-B, alone or conjugated with the cationic lipid carrier, DOTAP. We provide evidence that only NP-CGG adjuvanted with DOTAP-CpG-B was an effective vaccine in mice resulting in robust germinal center responses, isotype switching and high affinity NP-specific antibodies. The effectiveness of DOTAP-CpG-B as an adjuvant was dependent on the expression of the TLR9 signaling adaptor MyD88 in immunized mice. These results indicate DOTAP-CpG-B but not DOTAP-CpG-A is an effective adjuvant for T cell-dependent protein antigen-based vaccines.

Immunomodulatory nanoparticles ameliorate disease in the Leishmania (Viannia) panamensis mouse model

Leishmania (Viannia) panamensis (L. (V.) panamensis) is a species of protozoan parasites that causes New World leishmaniasis, which is characterized by a hyper-inflammatory response. Current treatment strategies, mainly chemotherapeutic, are suboptimal due to adverse effects, long treatment regimens, and increasing drug resistance. Recently, immunotherapeutic approaches have shown promise in preclinical studies of leishmaniasis. As NPs may enable broad cellular immunomodulation through internalization in phagocytic and antigen-presenting cells, we tested the therapeutic efficacy of biodegradable NPs encapsulating a pathogen-associated molecular pattern (PAMP), CpG-rich oligonucleotide (CpG; NP-CpG), in mice infected with L. (V.) panamensis. NP-CpG treatment reduced lesion size and parasite burden, while neither free CpG nor empty NP showed therapeutic effects. NP-encapsulation led to CpG persistence at the site of infection along with an unexpected preferential cellular uptake by myeloid derived suppressor cells (MDSCs; CD11b(+)Ly6G(+)Ly6C(-)) as well as CD19(+) dendritic cells. This corresponded with the suppression of the ongoing immune response measured by the reduction of pathogenic cytokines IL-10 and IL-13, as well as IL-17 and IFNγ, in comparison to other treatment groups. As chronic inflammation is generally associated with the accumulation of MDSCs, this study may enable the rational design of cost-effective, safe, and scalable delivery systems for the treatment of inflammation-mediated diseases.

Effects of KLK Peptide on Adjuvanticity of Different ODN Sequences

Endosomal Toll-like receptors (TLR) such as TLR3, 7, 8 and 9 recognize pathogen associated nucleic acids. While DNA sequence does influence degree of binding to and activation of TLR9, it also appears to influence the ability of the ligand to reach the intracellular endosomal compartment. The KLK (KLKL5KLK) antimicrobial peptide, which is immunostimulatory itself, can translocate into cells without cell membrane permeabilization and thus can be used for endosomal delivery of TLR agonists, as has been shown with the IC31 formulation that contains an oligodeoxynucleotide (ODN) TLR9 agonist. We evaluated the adjuvant activity of KLK combined with CpG or non-CpG (GpC) ODN synthesized with nuclease resistant phosphorothioate (S) or native phosphodiester (O) backbones with ovalbumin (OVA) antigen in mice. As single adjuvants, CpG(S) gave the strongest enhancement of OVA-specific immunity and the addition of KLK provided no benefit and was actually detrimental for some readouts. In contrast, KLK enhanced the adjuvant effects of CpG(O) and to a lesser extent of GpC (S), which on their own had little or no activity. Indeed while CD8 T cells, IFN-γ secretion and humoral response to vaccine antigen were enhanced when CpG(O) was combined with KLK, only IFN-γ secretion was enhanced when GpC (S) was combined to KLK. The synergistic adjuvant effects with KLK/ODN combinations were TLR9-mediated since they did not occur in TLR9 knock-out mice. We hypothesize that a nuclease resistant ODN with CpG motifs has its own mechanism for entering cells to reach the endosome. For ODN without CpG motifs, KLK appears to provide an alternate mechanism for accessing the endosome, where it can activate TLR9, albeit with lower potency than a CpG ODN. For nuclease sensitive (O) backbone ODN, KLK may also provide protection from nucleases in the tissues.

Synergy of anti-CD40, CpG and MPL in activation of mouse macrophages

Activation of macrophages is a prerequisite for their antitumor effects. Several reagents, including agonistic anti-CD40 monoclonal antibody (anti-CD40), CpG oligodeoxynucleotides (CpG) and monophosphoryl lipid A (MPL), can stimulate activation of macrophages. Our previous studies showed synergy between anti-CD40 and CpG and between anti-CD40 and MPL in macrophage activation and antitumor efficacy in mice. In the present study, we asked whether there was synergy among these three reagents. The activation of adherent peritoneal exudate cells (PEC) obtained from mice injected with anti-CD40 and then treated with CpG and/or MPL in vitro was determined by their ability to suppress proliferation of tumor cells and to produce various cytokines and chemokines in vitro. Cell sorting and histology followed by functional testing showed that macrophages were the main cell population in PEC activated by CD40 ligation in vivo. A combination of anti-CD40, CpG or MPL activated PEC to suppress proliferation of B16 cells and produce nitric oxide far greater than the single reagents or any of the double combinations of these reagents. In addition, the combination of all three reagents activated PEC to secrete IL-12, IFN-γ and MCP-1 to a greater degree than any single reagent or any two combined reagents. These results demonstrate that macrophages can be synergistically activated by anti-CD40, CpG and MPL, suggesting that this novel combined approach might be further investigated as potential cancer therapy.

Inhibitory/suppressive oligodeoxynucleotide nanocapsules as simple oral delivery devices for preventing atopic dermatitis in mice

Here, we report a simple and low-cost oral oligodeoxynucleotide (ODN) delivery system targeted to the gut Peyer's patches (PPs). This system requires only Dulbecco's modified eagle's medium, calcium chloride, ODNs, and basic laboratory equipment. ODN nanocapsules (ODNcaps) were directly delivered to the PPs through oral administration and were taken up by macrophages in the PPs, where they induced an immune response. Long-term continuous oral dosing with inhibitory/suppressive ODNcaps (iODNcaps, "iSG3caps" in this study) was evaluated using an atopic dermatitis mouse model to visually monitor disease course. Administration of iSG3caps improved skin lesions and decreased epidermal thickness. Underlying this effect is the ability of iSG3 to bind to and prevent phosphorylation of signal transducer and activator of transcription 6, thereby blocking the interleukin-4 signaling cascade mediated by binding of allergens to type 2 helper T cells. The results of our iSG3cap oral delivery experiments suggest that iSG3 may be useful for treating allergic diseases.

DEC-205 is a cell surface receptor for CpG oligonucleotides

We have recently demonstrated that synthetic CpG oligonucleotides (ODNs), which function as potent immunostimulators, bind to the multi-lectin receptor DEC-205, resulting in their internalization. DEC-205-deficient mice exhibit impaired dendritic-cell and B-cell maturation, impaired cytokine responses and suboptimal cytotoxic T-cell responses. As murine and human DEC-205 are highly conserved, CpG ODNs destined to clinical applications should be designed to maximize DEC-205 binding.

Phosphorothioate-modified CpG oligodeoxynucleotide (CpG ODN) induces apoptosis of human hepatocellular carcinoma cells independent of TLR9

Toll-like receptors (TLRs) expressed on cancer cells are closely associated with tumor development. In this study, we investigated the biological functions of the TLR9 ligand, CpG oligodeoxynucleotide (CpG ODN), on TLR9 expressed in the cytoplasm of hepatocellular carcinoma (HCC) cells. In vitro, human HCC cell lines were transfected with phosphorothioate-modified oligodeoxynucleotides TLR9 agonist OND M362 and its negative control ODN M362 ctrl, which inhibited the proliferation of HCC cells by inducing apoptosis without altering the cell cycle. Interestingly, ODN M362 and ODN M362 Ctrl displayed a similar proapoptotic effect on HCC, possibly related to phosphorothioate modification of the structure of CpG ODN. Although both of them resulted in the upregulation of the TLR9 receptor, their effect on HCC apoptosis was independent of TLR9. They also upregulated inflammatory cytokines, but did not activate the NF-κB signaling pathway. Finally, the activities of ODN M362 and ODN M362 Ctrl were demonstrated in nude mice inoculated with HCC cells. These findings suggest that the phosphorothioate-modified TLR9 agonist ODN M362, and its control, elicit antitumor activity in HCC cells and may serve as a novel therapeutic target for HCC therapy.

Traditional biochemical assays for studying toll-like receptor 9

Understanding the mechanistic basis of receptor activation and regulation can offer therapeutic targets for disease treatment. Evidence is emerging for a role of the normally foreign responsive Toll-like receptors (TLRs) in the development of autoimmunity through response to self-patterns. Regulatory mechanisms governing this class of receptors are poorly understood, and failures within this system likely contribute to development of autoimmunity. In this article, we review biochemical assays used to study one of the self-pattern responsive TLRs, TLR9, and suggest that these studies are critical for development of new targets for autoimmune therapies.

DEC-205 is a cell surface receptor for CpG oligonucleotides

Synthetic CpG oligonucleotides (ODN) have potent immunostimulatory properties exploited in clinical vaccine trials. How CpG ODN are captured and delivered to the intracellular receptor TLR9, however, has been elusive. Here we show that DEC-205, a multilectin receptor expressed by a variety of cells, is a receptor for CpG ODN. When CpG ODN are used as an adjuvant, mice deficient in DEC-205 have impaired dendritic cell (DC) and B-cell maturation, are unable to make some cytokines such as IL-12, and display suboptimal cytotoxic T-cell responses. We reveal that DEC-205 directly binds class B CpG ODN and enhances their uptake. The CpG-ODN binding function of DEC-205 is conserved between mouse and man, although human DEC-205 preferentially binds a specific class B CpG ODN that has been selected for human clinical trials. Our findings identify an important receptor for class B CpG ODN and reveal a unique function for DEC-205.

The pharmacokinetics of Toll-like receptor agonists and the impact on the immune system

Toll-like receptor (TLR) ligation activates both the innate and adaptive immune systems, and plays an important role in antiviral and anti-tumor immunity. Therefore, a significant amount of effort has been devoted to exploit the therapeutic potential of TLR agonists. Depending on the therapeutic purpose, either as adjuvants to vaccine, chemotherapy or standalone therapy, TLR agonists have been administered via different routes. Both preclinical and clinical studies have suggested that the route of administration has significant effects on pharmacokinetics, and that understanding these effects is critical to the success of TLR agonist drug development. This article will summarize the pharmacokinetics of TLR agonists with different administration routes, with an emphasis on clinical studies of TLR ligands in oncologic applications.

DNA inhibits dsRNA-induced secretion of pro-inflammatory cytokines by gingival fibroblasts

Nucleic acids interacting with pattern-recognizing receptors (PRRs), such as Toll-like-(TLRs), RIG-I-like receptors (RLRs) and dsDNA-receptors activate innate immune response in non-professional immune cells and thus the production of pro-inflammatory cytokines. Along with bacterial and viral nucleic acids, endogenous cell-free and cell-surface-bound extracellular DNA (exDNA and csbDNA) could interact with PRRs and possess immunomodulating activity. To elucidate if exDNA influence innate immunity a comparative study of exDNA, genomic and plasmid DNA on interleukin production in gingival fibroblasts (GF) has been done. All DNA tested have no effect on IL secretion in a broad concentration range (10 ng/ml-1 μg/ml). Simultaneous treatment of cells with DNA and dsRNA analog poly(I:C) leads to inhibition of poly(I:C)-activated secretion of IL-6 and IL-8. Cell-surface-bound DNA possesses two times stronger inhibiting effect as compared to genomic DNA indicating the enrichment of csbDNA in sequences providing such activity. Effects of several recently found specific DNA sequences tightly bound with cell surface have been tested. Joint stimulation of GF with poly(I:C) and deoxyribooligonucleotides (ODN), containing such sequences, demonstrates that both ssODN and dsODN possess sequence-dependent inhibiting effect. Inhibition of IL production after colipofection of ODN and poly(I:C) into cells indicates the involvement of RLRs or other cytoplasmic factors in the effect. The data obtained indicate that endogenous DNA might be involved in regulation of antiviral immune response and sequence-specific ODNs are potential inhibitors of the inflammation induced by viral infection.

DNA binding to proteolytically activated TLR9 is sequence-independent and enhanced by DNA curvature

Toll-like receptor 9 (TLR9) recognizes microbial DNA in endolysosomal compartments. The ectodomain of TLR9 must be proteolytically cleaved by endosomal proteases to produce the active receptor capable of inducing an innate immune signal. We show that the cleaved TLR9 ectodomain is a monomer in solution and that DNA ligands with phosphodiester backbones induce TLR9 dimerization in a sequence-independent manner. Ligands with phosphorothioate (PS) backbones induce the formation of large TLR9-DNA aggregates, possibly due to the propensity of PS ligands to self-associate. DNA curvature-inducing proteins including high-mobility group box 1 and histones H2A and H2B significantly enhance TLR9 binding, suggesting that TLR9 preferentially recognizes curved DNA backbones. Our work sheds light on the molecular mechanism of TLR9 activation by endogenous protein-nucleic acid complexes, which are associated with autoimmune diseases including systemic lupus erythematosus.

Efficacy of QCDCR formulated CpG ODN 2007 in Nile tilapia against Streptococcus iniae and identification of upregulated genes

The potential of using a QCDCR (quilA:cholesterol:dimethyl dioctadecyl ammonium bromide:carbopol:R1005 glycolipid) formulated CpG oligodeoxynucleotide (ODN), ODN 2007, to confer protection in Nile tilapia against Streptococcus iniae infection was evaluated in this study. At two days post treatment, QCDCR formulated ODN 2007 elicited significant (P<0.05) protection to Nile tilapia, with relative percent survival of 63% compared to fish treated by QCDCR alone. To understand the molecular mechanisms involved in the protective immunity elicited by ODN 2007, suppression subtractive cDNA hybridization technique was used to identify upregulated genes induced by ODN 2007. A total of 69 expressed sequence tags (ESTs) were identified from the subtractive cDNA library. Quantitative PCR revealed that 44 ESTs were significantly (P<0.05) upregulated by ODN 2007, including 29 highly (>10-fold) and 15 moderately (<10-fold) upregulated ESTs. Of all ESTs, putative peroxisomal sarcosine oxidase was upregulated the highest. The 69 ESTs only included six genes that had putative functions related to immunity, of which only two (putative glutaredoxin-1 and carboxypeptidase N catalytic chain) were confirmed to be significantly upregulated. Our results suggest that the protection elicited by ODN 2007 is mainly through innate immune responses directly or indirectly related to immunity.

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.

Stimulatory type A CpG-DNA induces a Th2-like response in human endothelial cells

Unmethylated CpG-DNA motifs from pathogens are detected by the pattern recognition receptor toll-like receptor 9 (TLR9), eliciting an inflammatory immune response. These DNA sequences have been identified as potent immune modifiers and are used as adjuvants in vaccine research. Since we previously found TLR9 expression and function in human endothelial cells, we have here investigated whether endothelial cells play a role in the recognition of respective ligands and whether their response might contribute to vaccination success. We determined the effect of CpG-DNA on the inflammatory response of human endothelial cells of aortic or skin microvascular origin (HAoEC, HDMEC and HMEC-1) and compared the effects to those of two identically treated human macrophage cell lines. Using the same CpG-DNA D19(chimera) sequence in both cell types, we find the known up-regulation of pro-inflammatory cytokines in macrophages but consistent and significant inhibition of the pro-inflammatory response (IL-6, IL-8, and IFN-beta1) in endothelial cells. This inhibition is accompanied by enhanced proliferation and an increase in IL-10 gene expression. This anti-inflammatory response persists even in the presence of pro-inflammatory cytokines and low LPS concentrations, and is overruled only in the presence of relatively high concentrations of LPS. By testing different sequences, we find the strongest response with phosphorothioate bonds. Our results demonstrate an important regulatory function of endothelial cells in inflammatory responses, and the apparent Th2-like endothelial response in the human system may contribute significantly to the adjuvant activity of CpG-DNA.

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.

Oligonucleotide motifs that disappear during the evolution of influenza virus in humans increase alpha interferon secretion by plasmacytoid dendritic cells

CpG motifs in an A/U context have been preferentially eliminated from classical H1N1 influenza virus genomes during virus evolution in humans. The hypothesis of the current work is that CpG motifs in a uracil context represent sequence patterns with the capacity to induce an immune response, and the avoidance of this immunostimulatory signal is the reason for the observed preferential decline. To analyze the immunogenicity of these domains, we used plasmacytoid dendritic cells (pDCs). pDCs express pattern recognition receptors, including Toll-like receptor 7 (TLR7), which recognizes guanosine- and uridine-rich viral single-stranded RNA (ssRNA), including influenza virus ssRNA. The signaling through TLR7 results in the induction of inflammatory cytokines and type I interferon (IFN-I), an essential process for the induction of specific adaptive immune responses and for mounting a robust antiviral response mediated by IFN-α. Secretion of IFN-α is also linked to the activation of other immune cells, potentially amplifying the effect of an initial IFN-α secretion. We therefore also examined the role of IFN-α-driven activation of NK cells as another source of selective pressure on the viral genome. We found direct evidence that CpG RNA motifs in a U-rich context control pDC activation and IFN-α-driven activation of NK cells, likely through TLR7. These data provide a potential explanation for the loss of CpG motifs from avian influenza viruses as they adapt to mammalian hosts. The selective decrease of CpG motifs surrounded by U/A may be a viral strategy to avoid immune recognition, a strategy likely shared by highly expressed human immune genes.

Toll-like receptor 9 agonists as cancer therapeutics

INTRODUCTION

Toll-like receptor 9 (TLR9) agonists, commonly referred to as CpG oligodeoxynucleotides (ODN), have been added to the arsenal of anti-cancer drugs as monotherapy or in combination with chemotherapy, radiotherapy and other immunotherapeutic approaches as they increase antigen presentation and boost anti-tumor T- and B-cell responses. Several synthetic TLR9 agonists have been developed for clinical grade use and displayed substantial efficacy in the preclinical and clinical models.

AREAS COVERED

This review summarizes TLR9 signaling and the impact of TLR9 agonists on the immune response. The most recent experimental and clinical data are analyzed as well as the development of new TLR9 agonists in current clinical trials.

EXPERT OPINION

Application of TLR9 agonists, in particular, combination strategies with chemo- or radiotherapy seem a promising and efficient immunotherapeutic approach in cancer patients even with refractory disease. Simultaneous application of TLR9 agonists aims at supporting the patient's immune response and overcoming specific immunosuppressant strategies developed by tumors. Combinatory approaches of the future might also seek for synergism of TLR9 agonists with other immunomodulatory strategies such as B-cell activation using the CD40-CD40L system.

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.

B cells do not take up bacterial DNA: an essential role for antigen in exposure of DNA to toll-like receptor-9

Murine dendritic cells (DC) and macrophages respond to bacterial CpG DNA through toll-like receptor 9 (TLR9). Although it is frequently assumed that bacterial DNA is a direct stimulus for B cells, published work does not reliably show responses of purified B cells. Here we show that purified splenic B cells did not respond to Escherichia coli DNA with induction of CD86, despite readily responding to single-stranded (ss) phosphodiester CpG oligodeoxynucleotides (ODN). This was due to a combination of weak responses to both long and double-stranded (ds) DNA. B-cell DNA uptake was greatly reduced with increasing DNA length. This contrasts with macrophages where DNA uptake and subsequent responses were enhanced with increasing DNA length. However, when DNA was physically linked to hen egg lysozyme (HEL), HEL-specific B cells showed efficient uptake of DNA, and limited proliferation in response to the HEL-DNA complex. We propose that, in the absence of other signals, B cells have poor uptake and responses to long dsDNA to prevent polyclonal activation. Conversely, when DNA is physically linked to a B-cell receptor (BCR) ligand, its uptake is increased, allowing TLR9-dependent B-cell activation in an antigen-specific manner. We could not generate fragments of E. coli DNA by limited DNaseI digestion that could mimic the stimulatory effect of ss CpG ODN on naïve B cells. We suggest that the frequently studied polyclonal B-cell responses to CpG ODN are relevant to therapeutic applications of phosphorothioate-modified CpG-containing ODN, but not to natural responses to foreign or host dsDNA.

CpG-ODN 2006 and human parvovirus B19 genome consensus sequences selectively inhibit growth and development of erythroid progenitor cells

Recent studies have shown that anemia is commonly observed after exposure to pathogens or pathogen-derived products, which are recognized via Toll-like receptor 9 (TLR9). In the current study, we demonstrate that CpG oligodeoxynucleotide-2006, a TLR9 ligand with phosphodiester (PO; 2006-PO) but not with the phosphorothioate backbone, selectively inhibits the erythroid growth derived from human CD34(+) cells. The 2006-PO was internalized by the erythroid progenitors within 30 minutes; however, expression of TLR9 mRNA was not detected in these cells. The 2006-PO directly inhibited burst-forming unit-erythroid growth, resulted in the accumulation of cells in S and G(2)/M phases, and increased cell size and frequency of apoptotic cells. These features were similar to those observed in erythroid progenitors infected with human parvovirus B19 that causes pure red cell aplasia. The consensus sequence of 2006-PO was defined as 5'-GTTTTGT-3', which was located in the P6-promoter region of B19 and inhibited erythroid growth in a sequence-specific manner and down-regulated expression of erythropoietin receptor (EPOR) mRNA and EPOR. B19 genome extracted from serum also inhibited erythroid growth and down-regulated expression of EPOR on glycophorin A(+) cells. These results provide a possible insight into our understanding of the mechanisms of human parvovirus B19-mediated inhibition of erythropoiesis.

Murine J774 macrophages recognize LPS/IFN-g, non-CpG DNA or two-CpG DNA-containing sequences as immunologically distinct

Specific bacterial lipopolysaccharides (LPS), IFN-gamma, and unmethylated cytosine or guanosine-phosphorothioate containing DNAs (CpG) activate host immunity, influencing infectious responses. Macrophages detect, inactivate and destroy infectious particles, and synthetic CpG sequences invoke similar responses of the innate immune system. Previously, murine macrophage J774 cells treated with CpG induced the expression of nitric oxide synthase 2 (NOS2) and cyclo-oxygenase 2 (COX2) mRNA and protein. In this study murine J774 macrophages were exposed to vehicle, interferon gamma+lipopolysaccharide (IFN-g/LPS), non-CpG (SAK1), or two-CpG sequence-containing DNA (SAK2) for 0-18h and gene expression changes measured. A large number of immunostimulatory and inflammatory changes were observed. SAK2 was a stronger activator of TNFalpha- and chemokine expression-related changes than LPS/IFN-g. Up regulation included tumor necrosis factor receptor superfamily genes (TNFRSF's), IL-1 receptor signaling via stress-activated protein kinase (SAPK), NF-kappaB activation, hemopoietic maturation factors and sonic hedgehog/wingless integration site (SHH/Wnt) pathway genes. Genes of the TGF-beta pathway were down regulated. In contrast, LPS/IFN-g-treated cells showed increased levels for TGF-beta signaling genes, which may be linked to the observed up regulation of numerous collagens and down regulation of Wnt pathway genes. SAK1 produced distinct changes from LPS/IFN-g or SAK2. Therefore, J774 macrophages recognize LPS/IFN-g, non-CpG DNA or two-CpG DNA-containing sequences as immunologically distinct.

LL-37 promotes rapid sensing of CpG oligodeoxynucleotides by B lymphocytes and plasmacytoid dendritic cells

LL-37 is a cationic antimicrobial peptide derived from neutrophils and keratinocytes. It plays an important role in protection against bacterial infection in the skin and mucosal surfaces. However, its role within the blood compartment remains unclear given that serum inhibits its bactericidal property. In this study, we show that LL-37 promotes very rapid and highly efficient sensing of CpG motifs in bacterial DNA by human B lymphocytes and plasmacytoid dendritic cells (pDCs) in serum-containing media and in whole blood. LL-37 allowed detection of CpG oligodeoxynucleotide (ODN) within minutes of exposure. Without LL-37, 20-30 times more CpG was required to produce the same effect. The promotion of CpG detection by LL-37 was independent of the backbone of the ODN, as the effect was observed not only in ODNs with modified phosphorothioate backbone, but also in ODNs with natural phosphodiester backbone, as found in genomic DNA. Unmethylated CpG motifs within the phosphodiester ODN and LL-37-mediated delivery are required for pDCs to respond. In keeping with the above, cells responded to CpG-rich bacterial DNA and LL-37, but not to human DNA and LL-37. The ability of LL-37 to enhance delivery of CpG to stimulate immune cells is independent of its amphipathic structure and its bactericidal property. LL-37 aids the delivery of CpG to B cells and pDCs, but not T cells. These findings are pertinent to rapid recognition of microbial DNA and are highly relevant to contemporary studies of CpG/TLR9 agonists in vaccines and cancer therapy.

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.

Immunotherapeutic applications of CpG oligodeoxynucleotide TLR9 agonists

Toll-like receptor 9 (TLR9) agonists have demonstrated substantial potential as vaccine adjuvants, and as mono- or combination therapies for the treatment of cancer and infectious and allergic diseases. Commonly referred to as CpG oligodeoxynucleotides (ODN), TLR9 agonists directly induce the activation and maturation of plasmacytoid dendritic cells and enhance differentiation of B cells into antibody-secreting plasma cells. Preclinical and early clinical data support the use of TLR9 agonists as vaccine adjuvants, where they can enhance both the humoral and cellular responses to diverse antigens. In mouse tumor models TLR9 agonists have shown activity not only as monotherapy, but also in combination with multiple other therapies including vaccines, antibodies, cellular therapies, other immunotherapies, antiangiogenic agents, radiotherapy, cryotherapy, and some chemotherapies. Phase I and II clinical trials have indicated that these agents have antitumor activity as single agents and enhance the development of antitumor T-cell responses when used as therapeutic vaccine adjuvants. CpG ODN have shown benefit in multiple rodent and primate models of asthma and other allergic diseases, with encouraging results in some early human clinical trials. Although their potential clinical contributions are enormous, the safety and efficacy of these TLR9 agonists in humans remain to be determined.

Sequence independent interferon-alpha induction by multimerized phosphodiester DNA depends on spatial regulation of Toll-like receptor-9 activation in plasmacytoid dendritic cells

Single-stranded versus multimeric phosphorothioate-modified CpG oligodeoxynucleotides (ODNs) undergo differential endosomal trafficking upon uptake into plasmacytoid dendritic cells (pDCs), correlating with Toll-like receptor-9-dependent pDC maturation/activation (single-stranded B-type CpG ODN) or interferon-alpha (IFN-alpha) induction (multimeric A-type CpG ODN), respectively. As was recently shown, IFN-alpha production, other than by CpG ODNs, can also be induced in a sequence-independent manner by phosphodiester (PD) ODNs multimerized by 3' poly-guanosine (poly-G) tails. We investigate here the type of endosomal trafficking responsible for IFN-alpha induction by natural PD ODN ligands. We show that 3' extension with poly-G tails leads to multimerization of single-stranded PD ODNs and to enhanced cellular uptake into pDCs. While monomeric PD ODNs, which induce CpG-dependent Toll-like receptor-9 stimulation and pDC maturation/activation, localized to late endosomal/lysosomal compartments, the poly-G multimerized PD ODNs, which induce CpG-independent IFN-alpha production, located to vesicles with a distinct, 'early' endosomal phenotype. We conclude that poly-G-mediated multimerization of natural PD ODNs allows for sequence-independent, Toll-like receptor-9-dependent IFN-alpha induction in pDCs by combining three distinct effects: relative protection of sensitive PD ODNs from extracellular and intracellular DNase degradation, enhanced cellular uptake and preferential early endosomal compartmentation.

The DNA sugar backbone 2' deoxyribose determines toll-like receptor 9 activation

CpG motifs within phosphorothioate (PS)-modified DNA drive Toll-like receptor 9 (TLR9) activation, but the rules governing recognition of natural phosphodiester (PD) DNA are less understood. Here, we showed that the sugar backbone determined DNA recognition by TLR9. Homopolymeric, base-free PD 2' deoxyribose acted as a basal TLR9 agonist as it bound to and activated TLR9. This effect was enhanced by DNA bases, even short of CpG motifs. In contrast, PS-modified 2' deoxyribose homopolymers acted as TLR9 and TLR7 antagonists. They displayed high affinity to both TLRs and did not activate on their own, but they competitively inhibited ligand-TLR interaction and activation. Although addition of random DNA bases to the PS 2' deoxyribose backbone did not alter these effects, CpG motifs transformed TLR9-inhibitory to robust TLR9-stimulatory activity. Our results identified the PD 2' deoxyribose backbone as an important determinant of TLR9 activation by natural DNA, restrict CpG-motif dependency of TLR9 activation to synthetic PS-modified ligands, and define PS-modified 2' deoxyribose as a prime effector of TLR9 and TLR7 inhibition.

CpG ODN mediated prevention from ovalbumin-induced anaphylaxis in mouse through B cell pathway

Allergic inflammation is induced by type 2 T helper cell (Th2) and Th2 cytokines such as interleukin (IL)-4, IL-5 and IL-13. These cytokines induce the production of allergen-specific immunoglobulin (Ig)E by B cells, and the ensuing degranulation of mast cells via IgE cross-linking leads to most clinical manifestations of allergic diseases. We examined the ability of immunomodulatory unmethylated CpG oligodeoxynucleotides (ODN), which are potent inducers of Th1 cytokines, to prevent allergic symptoms in mice immunized and sensitized with allergen. Coadministration of CpG ODN with ovalbumin (OVA) before OVA sensitization substantially prevented mice from allergic anaphylaxis representing enhanced circulating concentrations of OVA-specific IgE and histamine, and decreased body temperature. Although CpG ODN provokes an abundance of Th1-skewing cytokines, including IL-12, interferon (IFN)-alpha and IFN-gamma, administration of CpG ODN in IFN-gamma deficient mice inhibited IgE production and prevented from OVA-induced anaphylaxis, indicating a dispensable role of IFN-gamma in mediating these protective effects. In vitro analysis revealed that CpG ODN inhibited class switching from IgM to IgE and IgG1 in response to CD40 and IL-4 in B cells, and this effect did not correlate with up-regulation of IFN-alpha production. These results imply a B cell-intrinsic, T cell-independent mechanism by which CpG ODN directly acts on B cells and inhibits IgE and IgG1 production leading to cause prevention from allergic symptoms.

Alpha 2-macroglobulin binds CpG oligodeoxynucleotides and enhances their immunostimulatory properties by a receptor-dependent mechanism

CpG oligodeoxynucleotides (ODN) stimulate the immune system and are under evaluation as treatments and vaccine adjuvants for infectious diseases, cancer, and immune system disorders. Although they have shown promising results in numerous clinical trials, the ultimate use of CpG ODN-based therapeutics may hinge on improved pharmacokinetics and reduced systemic side-effects. CpG ODN efficacy and potency might be enhanced greatly by packaging them into particles that protect them from degradation and specifically target them for uptake by immune-competent cells. The plasma proteinase inhibitor alpha 2-macroglobulin (alpha 2M) binds numerous biologically active macromolecules, including cytokines, chemokines, and growth factors, and can modulate their activity. Molecules bound to alpha 2M are protected from interactions with neighboring macromolecules and are targeted for receptor-mediated uptake by immune-competent cells. Here, we report that activated alpha 2M (alpha 2M*) binds CpG ODN and enhances their immunostimulatory properties significantly. Murine macrophages treated with alpha 2M*-ODN complexes respond more rapidly and produce a greater cytokine response than induced by free CpG ODN. Using human PBMC, alpha 2M*-ODN complexes exhibit fourfold enhanced potency and 15-fold greater efficacy for stimulating production of inflammatory cytokines. alpha 2M* targets delivery of CpG ODN specifically to immune-competent cells, which endocytose the complexes sixfold more rapidly than free CpG ODN. CpG ODN bound to alpha 2M* are also protected from degradation by nucleases. This novel targeting technology may improve CpG ODN-based therapeutics by increasing efficacy at reduced doses, thus reducing side-effects and cost.

Structure-efficacy relationships of immunostimulatory activity of CpG-containing oligodeoxynucleotides on mouse spleen cells

AIM

To study the relationship between primary structures of oligodeoxynucleotides (ODN) containing unmethylated deoxycytidyldeoxyguanosine (CpG) dinucleotide motifs and their immunostimulatory activities in mouse spleen cells.

METHODS

A series of CpG ODN with different primary structures were synthesized. Their capabilities to stimulate mouse spleen cell proliferation were determined by [3H]thymidine incorporation assay. Cytokine (interleukin [IL]-6, IL-12, and IFN-alpha) secretion spectra induced by CpG ODN were assessed by ELISA. The ability of CpG ODN to activate natural killer cells was evaluated by standard 4 h (51)Cr-release assay. Flow cytometry was utilized to examine the expressions of various lymphocyte surface molecules on diverse immunocytes. An effective CpG ODN for murine, ODN1826, was set as the template of modification and the positive control.

RESULTS

The immunostimulatory activities of CpG ODN with different sequences and compositions varied markedly, both in character and in extent. It was useless for improving the immunostimulatory activity of ODN1826 by simply increasing the functional hexameric CpG motif number, modifying the site of CpG motifs, or changing the distance between multi-CpG motifs. However, an addition of a self-complementary palindrome structure at the 3'-end, but not the 5'-end of CpG ODN, aroused marked improvement in its activity. Several designed ODN had superior comprehensive immunostimulatory properties compared to ODN1826.

CONCLUSION

The immunostimulatory activity of a CpG ODN was relevant to its primary structure. It was useless for promoting immunostimulatory activity to simply change CpG motif number, space, or distance. The 3'-end palindrome structure of CpG ODN is associated with enhanced immunostimulatory activity.

CpG oligodeoxynucleotides up-regulate antibacterial systems and induce protection against bacterial challenge in rainbow trout (Oncorhynchus mykiss)

The effects of unmethylated CpG oligodeoxynucleotides (ODN) on the mammalian immune system are relatively well studied but much less is known of their effects on the immune systems of different fish species. Here we show that CpG ODNs significantly enhance the survival of rainbow trout (Oncorhynchus mykiss) following bacterial challenge when used both as stand-alone prophylactic agents, or as adjuvants to a commercially available vaccine. They are also capable of increasing serum lysozyme activity in vivo and stimulating the production of chemoattractant factors for rainbow trout head kidney (HK) leucocytes in vitro.

Translocation of bacterial DNA from Gram-positive microorganisms is associated with a species-specific inflammatory response in serum and ascitic fluid of patients with cirrhosis

Translocation of bacterial-DNA in patients with cirrhosis and ascites triggers an innate immune response. Identification of characteristics to which this response is sensitive is relevant from a clinical standpoint. The aim of this study has been to determine if the proinflammatory immune response established in vivo in cirrhotic patients with ascites as a consequence of bacterial-DNA translocation is related to the identified bacterial species and their frequency of cytosine-guanosine content in serum and ascitic fluid. Patients with advanced cirrhosis and ascites were included in the study and distributed into groups I and II according to the absence or presence of bacterial-DNA translocation, respectively. Serum and ascitic fluid levels of proinflammatory cytokines after normalization of bacterial-DNA concentration and the activated form of nuclear factor-kappa B in ascitic fluid pellets were measured by enzyme-linked immunosorbent assay techniques. Translocation of bacterial-DNA with higher cytosine-guanosine content induced the highest cytokine response, which was higher than that in patients without bacterial-DNA translocation. The activated form of nuclear factor-kappa B in ascitic fluid pellets of patients with bacterial-DNA translocation was greater in patients with higher bacterial-DNA cytosine-guanosine content, whereas the amount of total nuclear factor-kappa B remained unaltered. Bacterial-DNA translocation induces a marked immune reaction in vivo in patients with advanced cirrhosis and ascites which is related, among other factors, to the bacterial-DNA cytosine-guanosine content. Therefore, the host's immune response to bacterial-DNA translocation constitutes a species-specific phenomenon.

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.

A protective allergy vaccine based on CpG- and protamine-containing PLGA microparticles

PURPOSE

Allergen-specific immunotherapy (SIT) requires dozens of subcutaneous injections over 3 to 5 years in order to control IgE-mediated hypersensitivity, which is a T-helper 2 (Th2)-associated pathology. This study investigates the use of poly(lactide-co-glycolide) (PLGA) microparticles combined with immunostimulatory oligodeoxynucleotide (CpG), as well as protamine in SIT.

MATERIALS AND METHODS

We prepared microparticle formulations with the major allergen of bee venom, phospholipase A2 (PLA2), and analyzed the effect of co-encapsulated or admixed CpG in both naïve and bee venom allergic mice.

RESULTS

Mice immunized with microparticles containing only PLA2 induced weak antibody responses. In contrast, the combination with CpG resulted in strong PLA2-specific antibody responses. The presence of CpG was required for the induction of the Th1-associated isotype IgG2a, and the titers of IgG2a in sensitized mice correlated with a better protection against an allergen challenge. The effect of CpG was further strengthened when protamine was co-encapsulated for complexation of CpG.

CONCLUSIONS

This study shows that allergen-specific immunotherapy with a PLGA-based allergen-delivery system in combination with CpG enhanced the induction of protective IgG2a immune responses. This may improve SIT compliance and shorten its duration.

Improvement of Adjuvant Systems to Obtain a Cost-Effective Production of High Levels of Specific IgY

Incomplete Freund's adjuvant (IFA) is used as standard adjuvant for the production of specific antibodies. In this study, we evaluated the ability of supplementation of IFA with 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] or C-phosphate-guanosine-oligodeoxynucleotide (CpG-ODN) to enhance the quantity of specific IgY found in the eggs of hyperimmunized laying hens. In this comparative study, the fimbrial adhesin F4 of porcine enterotoxigenic Escherichia coli was used as prototype immunogen. Hens of 3 groups received by i.m. injection 20 microg of purified F4 adhesin emulsified with 1 of the following adjuvants: 0.5 mL of IFA alone (F4-IFA group), 0.5 mL of IFA supplemented with 285.6 ng of 1alpha,25(OH)(2)D(3) (F4-IFA-D(3) group), or 0.5 mL of IFA supplemented with 10 microg of CpG-ODN (F4-IFA-CpG group). Hens of 2 control groups received PBS or purified F4 alone. Immunization was repeated after 2 and 5 or 7 wk. Eggs were collected at 3- to 4-d intervals from preimmunization to d 79, and whole eggs were tested to measure the quantity of anti-F4 IgY by a standardized indirect ELISA. The quantity of specific anti-F4 IgY present in eggs from immunized hens of the F4-IFA group increased from d 13 to 79, corresponding to the end of the experiment. The values for this group at each time were considered as 100%. Results obtained for the other adjuvants were expressed in relation to this reference method. Supplementation of IFA with 1alpha,25(OH)(2)D(3) did not result in any enhancement of the quantity of anti-F4 IgY present in the eggs. On the other hand, supplementation of IFA with CpG-ODN resulted in an enhancement of yield up to 942% of the F4-specific antibody response. Moreover, the use of CpG-ODN is a cost-effective and ethical refinement for the production of specific antibodies, permitting a reduction in the number of immunizations needed. In conclusion, this study provides strong evidence for the use of IFA supplemented with CpG-ODN rather than IFA alone for the production of high levels of specific antibody in laying hens.

Nucleic acids exert a sequence-independent cooperative effect on sequence-dependent activation of Toll-like receptor 9

Toll-like receptor 9 (TLR9) activates the innate immune system in response to microbial DNA or mimicking oligodeoxynucleotides. Although cell stimulation experiments demonstrate the preferential activation of TLR9 by CpG-containing nucleic acids, direct binding investigations have reached contradictory conclusions with respect to the ability of this receptor to bind nucleic acids in a sequence-specific manner. To address this apparent discrepancy, we report the purification of the soluble ectodomain of human TLR9 with characterization of its ligand binding properties. We observe that TLR9 has a high degree of specificity in its ability to bind nucleic acids that contain CpG dinucleotides as well as higher order motifs that mediate species-specific activation. However, TLR9 is also functionally influenced by nucleic acids in a sequence-independent fashion as both stimulatory and nonstimulatory nucleic acids sensitize TLR9 for in vitro ligand binding as well as in vivo activation. We propose a model in which receptor activation is achieved in a sequence-dependent manner, and sensitivity is modulated by the absolute concentration of nucleic acids in a sequence-independent fashion. This model bears resemblance to that recently proposed for Toll in that activation is a two-step process in which formation of a ligand-bound monomer precedes formation of the activated dimer. In each model receptor sensitivity is determined within the second step with the crucial distinction that Toll undergoes negative cooperativity, whereas TLR9 is sensitized through a positive cooperative effect.

Response of nitric oxide production to CpG oligodeoxynucleotides in turkey and chicken peripheral blood monocytes

We evaluated the innate immune response to various synthetic CpG-containing oligodeoxynucleotides (CpG ODNs) by measuring nitric oxide production in the peripheral blood monocytes from turkey poults. The results indicate that the presence of the CpG dinucleotide in ODNs was a prerequisite for activation of turkey monocytes and induction of nitric oxide (NO) synthesis. CpG motifs and sequence structure of the ODNs were also found to influence stimulatory activity greatly. The most potent CpG ODN to induce NO synthesis in turkey monocytes was human-specific CpG ODN M362, followed by CpG ODN 2006 (human), CpG ODN#17 (chicken) and CpG ODN 1826 (mouse). The optimal CpG motif for NO induction was GTCGTT. Phosphorothioate modification of CpG ODNs also significantly increased stimulatory activity. Compared with chicken monocytes, turkey monocytes appeared to be less sensitive to CpG motif variation, whereas chicken monocytes were found to respond more strictly to human-specific CpG ODNs or ODNs that contain GTCGTT motifs.

A hexanucleotide selected for increased cellular uptake in cis contains a highly active CpG-motif in human B cells and primary peripheral blood mononuclear cells

The relationship between immunostimulation of human B cells by cytosine-phosphate-guanosine (CpG) -containing oligonucleotides and their physical cellular uptake is of mechanistic interest and a prerequisite for rational improvements of the therapeutic potential of CpG-harbouring oligonucleotides. Here, a combinatorial approach was used to identify nucleotide sequence motifs that facilitate increased cellular uptake in mammalian cells. Oligonucleotides harbouring the selected hexanucleotide TCGTGT in cis show increased cellular uptake. This motif contains a CpG dinucleotide within a sequence context that shows a very strong CpG-specific stimulatory activity on human B cells. Here we describe the influence of concentration, length and sequence position of the unmethylated CpG dinucleotide on immunostimulation. A comparison between phosphorothioate-derivatives and unmodified TCGTGT-containing oligonucleotides strongly indicates a great CpG-specificity for the unmodified CpG-harbouring oligonucleotides but not for the phosphorothioate versions. This work describes a link between the physical cellular uptake of naked oligonucleotides harbouring the selected cellular uptake motif TCGTGT, its strong CpG-specific stimulation of human B cells and its relationship with the sequence context of CpG and its cellular uptake.

Structure-activity relationship studies on the immune stimulatory effects of base-modified CpG toll-like receptor 9 agonists

Synthetic oligodeoxynucleotides containing unmethylated deoxycytidylyl-deoxyguanosine dinucleotide (CpG) motifs are able to stimulate potent immune responses through a signaling pathway involving Toll-like receptor 9 (TLR9). We have investigated the structure-activity relationship (SAR) of base-modified CpG oligonucleotides with TLR9 by measuring TLR9 activation by 20-mer oligonucleotides having just a single human recognition motif (5'-GTCGTT-3') in functional cell-based TLR9 assays. Substitution of guanine by hypoxanthine and 6-thioguanine resulted in activity similar to the unmodified parent molecule, whereas purine, 2-aminopurine, 2,6-diaminopurine, and 8-oxo-7,8-dihydroguanine substitution resulted in approximately 40-60 % reduction in activity, and 7-deazaguanine substitution led to the strongest (80 %) reduction in TLR9 stimulation. Furthermore, none of the investigated modifications at C5 and N4 of cytosine were well tolerated with respect to human TLR9 stimulation. Our results are compatible with a SAR model in which guanine is recognized by the Hoogsteen site, and C5 is most critical for recognition of cytosine. In addition, we found significant species-specific differences between human and murine TLR9 recognition, which demonstrates the importance of choosing appropriate assay systems for SAR studies.