In vitro inhibition of murine IFN gamma production by phosphorothioate deoxyguanosine oligomers

Interfering with baffled B cells at the lupus tollway: Promises, successes, and failed expectations

B cells play an important role in systemic lupus erythematosus by acting not only as precursors of autoantibody-producing cells but also as antigen-presenting, cytokine-secreting, and regulatory cells. Unopposed activation of B cells through their B-cell receptor for antigen, as seen in B cells lacking Lyn kinase, results in systemic autoimmunity. The B-cell activating factor of the TNF family (BAFF), nucleic acid-sensing Toll-like receptors (TLRs), and type I interferon can affect B-cell survival and decrease their threshold for activation. Herein we discuss both direct and indirect strategies aimed at targeting B cells in patients with lupus by blocking BAFF, type I interferon, or TLR7 to TLR9. Although BAFF-depleting therapy with belimumab achieved approval for lupus, other BAFF inhibitors were much less beneficial in clinical trials. Inhibitors of the B-cell receptor for antigen signaling and antibodies against type I interferon are in the pipeline. The TLR7 to TLR9 blocker hydroxychloroquine has been in use in patients with lupus for more than 50 years, but oligonucleotide-based inhibitors of TLR7 to TLR9, despite showing promise in animal models of lupus, have not reached the primary end point in a recent phase 1 trial. These data point toward possible redundancies in B-cell signaling/survival pathways, which must be better understood before future clinical trials are executed.

Structure, mechanism and therapeutic utility of immunosuppressive oligonucleotides

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

In vivo TLR9 inhibition attenuates CpG-induced myocardial dysfunction

The involvement of toll-like receptor 9 (TLR9), a receptor for bacterial DNA, in septic cardiac depression has not been clarified in vivo. Thus, the aim of the study was to test possible TLR9 inhibitors (H154-thioate, IRS954-thioate, and chloroquine) for their ability to protect the cardiovascular system in a murine model of CpG oligodeoxynucleotide- (ODN-) dependent systemic inflammation. Sepsis was induced by i.p. application of the TLR9 agonist 1668-thioate in C57BL/6 wild type (WT) and TLR9-deficient (TLR9-D) mice. Thirty minutes after stimulation TLR9 antagonists were applied i.v. Survival was monitored up to 18 h after stimulation. Cardiac mRNA expression of inflammatory mediators was analyzed 2 h and 6 h after stimulation with 1668-thioate and hemodynamic parameters were monitored at the later time point. Stimulation with 1668-thioate induced a severe sepsis-like state with significant drop of body temperature and significantly increased mortality in WT animals. Additionally, there was a time-dependent increase of inflammatory mediators in the heart accompanied by development of septic heart failure. These effects were not observed in TLR9-D mice. Inhibition of TLR9 by the suppressive ODN H154-thioate significantly ameliorated cardiac inflammation, preserved cardiac function, and improved survival. This suppressive ODN was the most efficient inhibitor of the tested substances.

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

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

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

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

An oligodeoxynucleotide capable of lessening acute lung inflammatory injury in mice infected by influenza virus

Infection of influenza virus could induce acute lung inflammatory injury (ALII) that was at least partially caused by excessive innate immune responses. To study whether down-regulating Toll-like receptor (TLR)-mediated innate immune response could lessen influenza virus-induced ALII, a microsatellite DNA mimicking oligodeoxynucleotide (MS ODN), named as SAT05f capable of inhibiting TLR7/9-activation in vitro, was used to treat mice infected with FM1 virus. In parallel, two MS ODNs confirmed with less or no in vitro activities, named as MS19 and MS33, were used as controls. Unexpectedly, SAT05f failed to lessen ALII in the mice, whereas MS19 significantly inhibited the weight loss and displayed dramatic effect on lessening the ALII by reducing consolidation, hemorrhage, intra-alveolar edema and neutrophils infiltration in lungs of the mice. Meanwhile, MS19 could decrease the mortality of influenza virus infected mice and down-regulate TNF-α production in their lungs. The data suggest that MS19 might display its therapeutic role on ALII induced by influenza virus by reducing over-production of TNF-α.

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

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

Suppression of immune responses by nonimmunogenic oligodeoxynucleotides with high affinity for high-mobility group box proteins (HMGBs)

The activation of innate immune responses by nucleic acids is central to the generation of host responses against pathogens; however, nucleic acids can also trigger the development and/or exacerbation of pathogenic responses such as autoimmunity. We previously demonstrated that the selective activation of nucleic acid-sensing cytosolic and Toll-like receptors is contingent on the promiscuous sensing of nucleic acids by high-mobility group box proteins (HMGBs). From this, we reasoned that nonimmunogenic nucleotides with high-affinity HMGB binding may function as suppressing agents for HMGB-mediated diseases, particularly those initiated and/or exacerbated by nucleic acids. Here we characterize an array of HMGB-binding, nonimmunogenic oligodeoxynucleotides (ni-ODNs). Interestingly, we find that binding affinity is rather independent of nucleotide sequence, but is instead dependent on length and structure of the deoxyribose backbone. We further show that these ni-ODNs can strongly suppress the activation of innate immune responses induced by both classes of nucleic acid-sensing receptors. We also provide evidence for the suppressive effect of an ni-ODN, termed ISM ODN, on the induction of adaptive immune responses and in mouse models of sepsis and autoimmunity. We discuss our findings in relation to the critical role of HMGBs in initiating immune responses and the possible use of these ni-ODNs in therapeutic interventions.

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.

Inhibition of a C-rich oligodeoxynucleotide on activation of immune cells in vitro and enhancement of antibody response in mice

To explore the possibility that human mitochondrial genomic DNA-mimicking oligodeoxynucleotides could regulate the immune response, a series of mitochondrial DNA-based oligodeoxynucleotides (MTODNs) were designed and studied to determine their immunoregulatory effects on immune cells activated by toll-like receptor (TLR) stimulation. The results showed that a C-rich MTODN, designated MT01, was able to inhibit the proliferation of human peripheral blood mononuclear cells (PBMCs) induced by cytosine-phosphate-guanosine (CpG) oligodeoxynucleotides (ODNs) and the production of type I interferon (IFN) from human PBMCs stimulated by TLR agonists, including inactivated influenza virus, imiquimod, inactivated herpes simplex virus-1 (HSV-1) and CpG ODNs. In addition, MT01 inhibited the CpG ODN-enhanced antibody response and this inhibition could be related to the antagonism of TLR9-activation pathways in B cells. Notably, unlike the G-rich suppressive ODNs reported, MT01 is composed of ACCCCCTCT repeats. These data imply that MT01 represents a novel class of immunosuppressive ODNs that could be candidate biologicals with therapeutic use in TLR activation-associated diseases.

Classification, mechanisms of action, and therapeutic applications of inhibitory oligonucleotides for Toll-like receptors (TLR) 7 and 9

Our immune defense depends on two specialized armed forces. The innate force acts as an alarm mechanism that senses changes in the microenvironment through the recognition of common microbial patterns by Toll-like receptors (TLR) and NOD proteins. It rapidly generates an inflammatory response aimed at neutralizing the intruder at the mucosal checkpoint. The innate arm also communicates this message with more specialized adaptive forces represented by pathogen-specific B cells and T cells. Interestingly, B cells also express some innate sensors, like TLR7 and TLR9, and may respond to bacterial hypomethylated CpG motifs and single-stranded RNA viruses. Intracellular nucleic acid sensing TLRs play an important role in the pathogenesis of Systemic Lupus Erythematosus (SLE). In this review, we describe recent achievements in the development of oligonucleotide—(ODN)-based inhibitors of TLR9 and/or TLR7 signaling. We categorize these novel therapeutics into Classes G, R, and B based on their cellular and molecular targets. Several short ODNs have already shown promise as pathway-specific therapeutics for animal lupus. We envision their future use in human SLE, microbial DNA-dependent sepsis, and in other autoinflammatory diseases.

Nucleic acid sensing receptors in systemic lupus erythematosus: development of novel DNA- and/or RNA-like analogues for treating lupus

Double-stranded (ds) DNA, DNA- or RNA-associated nucleoproteins are the primary autoimmune targets in SLE, yet their relative inability to trigger similar autoimmune responses in experimental animals has fascinated scientists for decades. While many cellular proteins bind non-specifically negatively charged nucleic acids, it was discovered only recently that several intracellular proteins are involved directly in innate recognition of exogenous DNA or RNA, or cytosol-residing DNA or RNA viruses. Thus, endosomal Toll-like receptors (TLR) mediate responses to double-stranded RNA (TLR-3), single-stranded RNA (TLR-7/8) or unmethylated bacterial cytosine (phosphodiester) guanine (CpG)-DNA (TLR-9), while DNA-dependent activator of IRFs/Z-DNA binding protein 1 (DAI/ZBP1), haematopoietic IFN-inducible nuclear protein-200 (p202), absent in melanoma 2 (AIM2), RNA polymerase III, retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) mediate responses to cytosolic dsDNA or dsRNA, respectively. TLR-induced responses are more robust than those induced by cytosolic DNA- or RNA- sensors, the later usually being limited to interferon regulatory factor 3 (IRF3)-dependent type I interferon (IFN) induction and nuclear factor (NF)-kappaB activation. Interestingly, AIM2 is not capable of inducing type I IFN, but rather plays a role in caspase I activation. DNA- or RNA-like synthetic inhibitory oligonucleotides (INH-ODN) have been developed that antagonize TLR-7- and/or TLR-9-induced activation in autoimmune B cells and in type I IFN-producing dendritic cells at low nanomolar concentrations. It is not known whether these INH-ODNs have any agonistic or antagonistic effects on cytosolic DNA or RNA sensors. While this remains to be determined in the future, in vivo studies have already shown their potential for preventing spontaneous lupus in various animal models of lupus. Several groups are exploring the possibility of translating these INH-ODNs into human therapeutics for treating SLE and bacterial DNA-induced sepsis.

Therapeutic applications and mechanisms underlying the activity of immunosuppressive oligonucleotides

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

DNA-like class R inhibitory oligonucleotides (INH-ODNs) preferentially block autoantigen-induced B-cell and dendritic cell activation in vitro and autoantibody production in lupus-prone MRL-Fas(lpr/lpr) mice in vivo

INTRODUCTION

B cells have many different roles in systemic lupus erythematosus (SLE), ranging from autoantigen recognition and processing to effector functions (for example, autoantibody and cytokine secretion). Recent studies have shown that intracellular nucleic acid-sensing receptors, Toll-like receptor (TLR) 7 and TLR9, play an important role in the pathogenesis of SLE. Dual engagement of rheumatoid factor-specific AM14 B cells through the B-cell receptor (BCR) and TLR7/9 results in marked proliferation of autoimmune B cells. Thus, strategies to preferentially block innate activation through TLRs in autoimmune B cells may be preferred over non-selective B-cell depletion.

METHODS

We have developed a new generation of DNA-like compounds named class R inhibitory oligonucleotides (INH-ODNs). We tested their effectiveness in autoimmune B cells and interferon-alpha-producing dendritic cells in vitro and in lupus-prone MRL-Faslpr/lpr mice in vivo.

RESULTS

Class R INH-ODNs have 10- to 30-fold higher inhibitory potency when autoreactive B cells are synergistically activated through the BCR and associated TLR7 or 9 than when stimulation occurs via non-BCR-engaged TLR7/9. Inhibition of TLR9 requires the presence of both CCT and GGG triplets in an INH-ODN, whereas the inhibition of the TLR7 pathway appears to be sequence-independent but dependent on the phosphorothioate backbone. This difference was also observed in the MRL-Faslpr/lpr mice in vivo, where the prototypic class R INH-ODN was more effective in curtailing abnormal autoantibody secretion and prolonging survival.

CONCLUSIONS

The increased potency of class R INH-ODNs for autoreactive B cells and dendritic cells may be beneficial for lupus patients by providing pathway-specific inhibition yet allowing them to generate protective immune response when needed.

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

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

Synthetic oligonucleotides as modulators of inflammation

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

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

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

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

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

Nucleic acid-sensing TLRs as modifiers of autoimmunity

The immune system requires precise regulation of activating and inhibitory signals so that it can mount effective responses against pathogens while ensuring tolerance to self-components. Some of the most potent activation signals are triggered by innate immune molecules, particularly those in the TLR family. Recent studies have shown that engagement of TLRs plays a significant role in both innate and adaptive immunity. This review focuses on the ways that TLR function might contribute to the etiology of lupus-like syndromes in the context of an autoimmune-prone environment. By considering the sources, localization, and expression of both nucleic acids and the molecules that bind them, we discuss several ways that innate immunity can play a role in the development of systemic autoimmunity.

Targeting Toll-like receptor signaling in plasmacytoid dendritic cells and autoreactive B cells as a therapy for lupus

This review focuses on the role of Toll-like receptors (TLRs) in lupus and on possibilities to treat lupus using TLR modulating inhibitory oligodeoxynucleotides (INH-ODNs). TLRs bridge innate and adaptive immune responses and may play an important role in the pathogenesis of systemic lupus erythematosus. Of particular interest are TLR3, -7, -8, and -9, which are localized intracellularly. These TLRs recognize single-stranded or double-stranded RNA or hypomethylated CpG-DNA. Exposure to higher order CpG-DNA ligands or to immune complexed self-RNA triggers activation of autoreactive B cells and plasmacytoid dendritic cells. INH-ODNs were recently developed that block all downstream signaling events in TLR9-responsive cells. Some of these INH-ODNs can also target TLR7 signaling pathways. Based on their preferential cell reactivity, we classify INH-ODNs into class B and class R. Class B ('broadly reactive') INH-ODNs target a broad range of TLR-expressing cells. Class R ('restricted') INH-ODNs easily form DNA duplexes or higher order structures, and are preferentially recognized by autoreactive B cells and plasmacytoid dendritic cells, rather than by non-DNA specific follicular B cells. Both classes of INH-ODNs can block animal lupus. Hence, therapeutic application of these novel INH-ODNs in human lupus, particularly class R INH-ODNs, may result in more selective and disease-specific immunosuppression.

The immunostimulatory activity of CpG oligonucleotides on microglial N9 cells is affected by a polyguanosine motif

Oligonucleotides (ODN) with hexameric motifs containing central unmethylated CpG dinucleotides are immunostimulatory. Also ODN with continuous guanosines (polyG motif) show a wide range of immunological activity. Depending on the position, the chemical property of the ODN backbone and the cell type, polyG motifs have either an enhancing or a suppressing effect on the immunostimulatory activity of the CpG-ODN. Microglial cells are central components of the innate immune system of the brain and are activated by CpG-ODN in vitro and in vivo. Here we present the analysis of the immunomodulatory effects of CpG-ODN carrying a polyG motif on the microglial cell line N9. Our data show that N9 cells express Toll-like receptor 9 (TLR9) and are activated by CpG-ODN, which leads to expression of interleukin-12p40 (IL12p40), tumor necrosis factor-alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS). A 3'-end polyG motif inhibits phosphothioate (PS) CpG-ODN immunostimulatory activity but enhances the immunostimulatory activity of phosphodiester (PE) CpG-ODN. Correspondingly, a 3'-end polyG motif improves the cellular uptake of PE CpG-ODN but does not change their cellular distribution pattern. Furthermore, PE CpG-ODN with a 3'-end polyG motif interact with a much higher number of cellular proteins than PE CpG-ODN. These data indicate that the 3'-end polyG motif could enhance the immunostimulatory activity of PE CpG-ODN in microglial N9 cells through increasing interaction with cellular proteins. Therefore PE CpG-ODN containing a 3'-end polyG motif resulting in increased immunostimulatory activity might be promising alternate analogues for studies in the central nervous system.

Suppressive oligodeoxynucleotides protect mice from lethal endotoxic shock

Endotoxic shock is a life-threatening condition caused by exposure to bacterial LPS. LPS triggers the release of acute phase, proinflammatory, and Th1 cytokines that facilitate the development of endotoxic shock. Synthetic oligodeoxynucleotides (ODN) expressing suppressive TTAGGG motifs effectively down-regulate the production of proinflammatory and Th1 cytokines elicited by a variety of immune stimuli. The current results demonstrate that suppressive ODN protect mice from LPS-induced endotoxic shock. Underlying this protective effect is the ability of suppressive ODN to bind to and prevent the phosphorylation of STAT1 and STAT4, thereby blocking the signaling cascade mediated by LPS-induced IFN-beta and IL-12. These findings suggest that suppressive ODN might be of use in the treatment of endotoxic shock.

Inhibitory oligodeoxynucleotides - therapeutic promise for systemic autoimmune diseases?

Recent studies have shed new light on a possible link between the innate activation of plasmocytoid dendritic cells and marginal zone B cells and the pathogenesis of systemic lupus erythematosus. Animal studies have identified that this response requires the Toll-like receptor 9 (TLR9). Engagement of the TLR9 by various ligands, including non-canonical CpG-motifs, can cause or aggravate pathogenic autoantibody production and cytokine secretion in lupus. Attempts to neutralize this activity either by blocking the acidification of the endosomal compartment with chloroquine and related compounds, or by preventing the interaction between the CpG-DNA sequences and TLR9 using inhibitory oligonucleotides could be a promising therapeutic option for lupus.

Suppressive oligodeoxynucleotides inhibit Th1 differentiation by blocking IFN-gamma- and IL-12-mediated signaling

Repetitive TTAGGG motifs present at high frequency in mammalian telomeres can suppress Th1-mediated immune responses. Synthetic oligonucleotides (ODN) containing TTAGGG motifs mimic this activity and have proven effective in the prevention/treatment of certain Th1-dependent autoimmune diseases. This work explores the mechanism by which suppressive ODN block the induction of Th1 immunity. Findings indicate that these ODN inhibit IFN-gamma-induced STAT1 phosphorylation and IL-12-induced STAT3 and STAT4 phosphorylation. As a result, T-bet expression is reduced as is the maturation of naive CD4+ cells into Th1 effectors. These changes indirectly support the generation of Th2-dominated immune responses. Suppressive ODN may thus represent a novel approach to influence the Th1:Th2 balance in vivo.

The arthritogenic and immunostimulatory properties of phosphorothioate oligodeoxynucleotides rely on synergy between the activities of the nuclease-resistant backbone and CpG motifs

Experiments with immunostimulatory unmethylated CpG-containing DNA are usually conducted with nuclease-protected phosphorothioate oligodeoxynucleotides (S-ODNs), rather than phosphodiester oligodeoxynucleotides (O-ODNs). We compared the murine immune responses to S-ODNs and O-ODNs that either contained or lacked CpG motifs. Both CpG and non-CpG S-ODNs induced synovitis, as did sequence-matched CpG O-ODN, but not GpC O-ODN. There was a minimum length requirement for arthritogenic S-ODNs since a CpC dinucleotide S-ODN did not induce arthritis. There were both sequence- (CpG > non-CpG) and backbone-dependent (S-ODN > O-ODN) differences in the levels of DNA-induced arthritis upon intra-articular injection with the ODNs. However, CpG O-ODN being an exception, induced more severe arthritis than the GpC S-ODN. The levels of in vitro proliferation and production of IL-6, TNF-alpha, IL-12, and RANTES by splenocytes following exposure to CpG S-ODN were significantly higher than those induced by CpG O-ODN. In addition, both proliferative responses and cytokine production induced by S-ODN-stimulated splenocytes increased significantly when the S-ODN contained a CpG motif. Transcription factor NFkappaB was activated by both CpG S-ODN and CpG O-ODN but interestingly not by GpC S-ODN. This indicates that the NFkappaB signal pathway modulates CpG-mediated immunostimulation, while sequence-independent immune activation by the phosphorothioate backbone is probably signalled via a different pathway.

Regulation of CpG-induced immune activation by suppressive oligodeoxynucleotides

Bacterial DNA and synthetic oligodeoxynucleotides (ODN) containing unmethylated "CpG motifs" stimulate an innate immune response characterized by the production of cytokines, chemokines, and polyreactive Igs that promote host survival following infectious challenge. Yet CpG-driven immune activation can have deleterious consequences, such as increasing the host's susceptibility to autoimmune disease. The immunomodulatory activity of CpG DNA can be blocked by DNA containing "suppressive" motifs. This work explores the rules governing cellular recognition of stimulatory and suppressive motifs, and the resultant modulation of the immune system. Results suggest that both CpG and suppressive ODN may find use as therapeutic agents.

Structural characterization of the inhibitory DNA motif for the type A (D)-CpG-induced cytokine secretion and NK-cell lytic activity in mouse spleen cells

Oligodeoxynucleotides (ODN) with the CpG motif have been shown to be potent stimulators of innate immunity. A theoretical concern is that uncontrolled stimulation of the innate immune system through the TLR-9 receptor could induce, or worsen, some autoimmune diseases such as adjuvant arthritis or systemic lupus erythematosus. Safe therapeutic use of such ODN could be enhanced if one could regulate some of their stimulatory activities. We have designed a group of synthetic ODNs, which were able to inhibit the induction of NK lytic activity, IL-12p40 and IFN-gamma cytokine secretion by type A (D)-CpG-ODNs. Inhibition occurred in both DNA-sequence and dose-dependent fashion. Fifty percent inhibition was achieved with ~10-nM concentration of the most potent inhibitory ODNs. Delayed addition of these ODNs for up to 2 h was still able to profoundly affect CpG-induced IL-12p40 production at 18 h. Inhibitory DNA motif consists of two nucleotide triplets, a proximal pyrimidine-rich CCT sequence and a more distal GGG triplet. Optimal distance between these blocks is between three to five nucleotides. The linker sequence between the CCT and GGG blocks can additionally modify the activity of inhibitory ODNs, in both a positive and in negative way. When the order of CCT and GGG blocks is reversed, inhibition is completely lost. These findings suggest that CpG regulation of innate immunity can itself be regulated by particular motifs, which could be of therapeutic benefit in autoimmune diseases.

Effect of suppressive DNA on CpG-induced immune activation

Bacterial DNA and synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs stimulate a strong innate immune response. This stimulation can be abrogated by either removing the CpG DNA or adding inhibitory/suppressive motifs. Suppression is dominant over stimulation and is specific for CpG-induced immune responses (having no effect on LPS- or Con A-induced activation). Individual cells noncompetitively internalize both stimulatory and suppressive ODN. Studies using ODN composed of both stimulatory and suppressive motifs indicate that sequence recognition proceeds in a 5'-->3' direction, and that a 5' motif can block recognition of immediately 3' sequences. These findings contribute to our understanding of the immunomodulatory activity of DNA-based products and the rules that govern immune recognition of stimulatory and suppressive motifs.

Antitumor mechanisms of oligodeoxynucleotides with CpG and polyG motifs in murine prostate cancer cells: decrease of NF-kappaB and AP-1 binding activities and induction of apoptosis

Previous studies have shown that CpG oligodeoxynucleotides (ODNs) have substantial immunostimulatory effects with anticancer applications. The antitumor applications that have been described previously are mediated through the CpG-induced activation of the host immune system, not through direct antitumor effects. Using cytostasis and cell proliferation assays, we demonstrated that specific ODNs inhibit the proliferation of RM-1 cells, a murine prostate cancer cell line. Flow cytometry analysis using propidium iodide (PI) nuclear staining confirmed the direct proapoptotic effect of ODNs on prostate cancer cells. This effect was dose dependent. Further studies using Western blot analysis and electrophoresis mobility shift assay (EMSA) revealed that the treatment of prostate cancer cells with specific ODNs activated the caspase pathway(s) and decreased the binding activities of AP-1 and NF-kappaB in a time-dependent manner. Evaluation of a panel of ODNs containing different DNA motifs demonstrated that the optimal proapoptotic sequences required polyG sequences but that CpG motifs were not essential. Finally, in vivo antitumor studies showed that the proapoptotic polyG motifs significantly inhibited prostate tumor growth. PolyG motifs inhibited tumor growth, and the effects were enhanced by CpG immune activating sequences. ODN containing both polyG and CpG motifs may have enhanced efficacy in tumor therapy through multiple mechanisms of action, including direct antitumor activities and immune activation.

Highly immunostimulatory CpG-free oligodeoxynucleotides for activation of human leukocytes

Synthetic oligodeoxynucleotides (ODNs) bearing CpG dinucleotides can mimic the immunostimulatory effects of bacterial DNA in vertebrates. Besides the known CpG motifs, no other sequence motif has been shown to have independent immunostimulatory effects. Several past investigators have demonstrated that the nucleotide content or the phosphorothioate (PS) backbone may have effects independently of the sequence. However, the effect of both nucleotide content and PS backbone to stimulate human leukocytes is not well understood. We investigated the immunostimulatory activity of 34 PS-ODNs with different nucleotide contents, lengths, and methylation status on human leukocytes. The thymidine content showed strong CpG-independent contribution to immunostimulation. In contrast, ODNs rich in other nucleotides (guanosine, cytosine, or adenosine) induced no or much lower levels of immunostimulation. The observed effects were highly dependent on the PS backbone chemistry. In addition to the base content and the backbone chemistry, the length of the PS-ODN was directly related to the magnitude of its stimulatory effects, especially on B cells. In addition, methylation of CpG dinucleotides did not always cause an abrogation of the immunostimulation. Immunostimulatory effects could be observed with methylated CpG ODNs, specifically as the ODN length was increased from 18 to 24 or more nucleotides (nt). In contrast, PS-ODNs with inverted CpG dinucleotides showed some but only weak immunostimulation. Our results demonstrate that non-CpG ODNs rich in thymidine or ODNs with methylated CpG motifs have length-dependent immunostimulatory effects. Such ODNs can induce effects similar to those seen with CpG ODNs but are much less efficient in stimulating human immune cells.

Role of the heat shock protein 90 in immune response stimulation by bacterial DNA and synthetic oligonucleotides

To elucidate the mechanisms of immunostimulation by bacterial DNA and synthetic oligonucleotides, the effects of heat shock protein 90 (Hsp90) inhibitors on the activation of murine spleen cells and macrophages by these molecules were investigated. Murine spleen cells and J774 and RAW264.7 macrophages responded to a CpG-containing oligodeoxynucleotide (CpG ODN) and Escherichia coli DNA by increased production of interleukin 6 (IL-6), IL-12, tumor necrosis factor alpha, and nitric oxide (NO). Pretreatment with any of the three Hsp90 inhibitors geldanamycin, radicicol, and herbimycin A resulted in a dose-dependent suppression of cytokine production from the spleen cells and macrophages and of NO from macrophages stimulated with CpG ODN or E. coli DNA. These Hsp90 inhibitors, however, had no effect on Staphylococcus aureus Cowan strain 1-induced IL-12 production from either the murine spleen cells or macrophages. CpG ODN and E. coli DNA induced increased intracellular levels of phosphorylated extracellular signal-regulated kinases (ERK1 and -2), which are members of the mitogen-activated protein (MAP) kinase family, while geldanamycin and radicicol blocked the phosphorylation of ERK1 and -2 in J774 and RAW264.7 cells. These data indicate that DNA-induced activation of murine spleen cells and macrophages is mediated by Hsp90 and that Hsp90 inhibitor suppression of DNA-induced macrophage activation is associated with disruption of the MAP kinase signaling pathway. Our findings suggest that Hsp90 inhibitors may provide a useful means of elucidating the mechanisms of immunostimulation by bacterial DNA and CpG ODN as well as a strategy for preventing adverse effects of bacterial DNA as well as lipopolysaccharide.

CpG stimulation of primary mouse B cells is blocked by inhibitory oligodeoxyribonucleotides at a site proximal to NF-kappaB activation

Bacterial DNA and CpG-oligodeoxyribonucleotides (ODN) are powerful B cell activators, inducing apoptosis protection, cell cycle entry, proliferation, costimulatory molecule expression, immunoglobulin (Ig) and interleukin-6 (IL-6) secretion. However, proximal events in B cell activation by ODN are only partially characterized, including the translocation of NF-kappaB to the nucleus. In this paper, we provide evidence that CpG-ODN-induced cell cycle entry and apoptosis protection are blocked by SN50 or gliotoxin and thus require NF-kappaB activation. NF-kappaB activation occurred within 30 minutes of stimulation of murine B cells with a phosphorothioate (S) CpG-ODN and persisted for up to 40 hours, with p50, p65, and c-Rel as the major components. Similar to other NF-kappaB inducers, CpG-ODN caused an early IkappaBalpha and IkappaBbeta degradation plus cleavage of the p50 precursor and subsequent NF-kappaB nuclear translocation. A group of closely related S-ODN, which specifically blocked CpG-induced B cell activation at submicromolar concentrations, also prevented NF-kappaB DNA binding and transcriptional activation. These inhibitory S-ODN differed from stimulatory S-ODN by having 2-3 G substitutions in the central motif. As inhibitory S-ODN did not directly interfere with the NF-kappaB DNA binding but prevented CpG-induced NF-kappaB nuclear translocation of p50, p65, and c-Rel and blocked p105, IkappaBalpha, and IkappaBbeta degradation, we concluded that their putative target must lie upstream of inhibitory kinase (IKK) activation.

Inhibition of murine macrophage IL-12 production by natural and synthetic DNA

DNA is a complex macromolecule whose immunological properties vary with sequence and structure. To determine whether DNA can inhibit immune responses, the effects of mammalian DNA and synthetic phosphodiester (Po) and phosphorothioate (Ps) oligonucleotides (ODNs) on IL-12 production were tested using murine macrophages. With bacterial DNA as a stimulant, calf thymus DNA and human placenta DNA blocked IL-12 production by splenic and bone marrow macrophages. A (dG)(30) Po ODN and all single-base Ps 30 mer ODNs were also effective inhibitors. The Ps ODNs also blocked IL-12 production induced by lipopolysaccharide (LPS) and a stimulatory Ps ODN. With the J774 cell line, single-base Ps ODNs inhibited IL-12 production induced by bacterial DNA, LPS, and a stimulatory Ps ODN. Together, these results indicate that DNA has inhibitory properties, suggesting that mammalian DNA could limit immune activation during inflammation and counteract the effects of bacterial DNA.

An overview of cancer immunotherapy

The survival of patients with cancer has improved steadily but incrementally over the last century, with the advent of effective anticancer treatments such as chemotherapy and radiotherapy. However, the majority of patients with metastatic disease will not be cured by these measures and will eventually die of their disease. New and more effective methods of treating these patients are required urgently. The immune system is a potent force for rejecting transplanted organs or microbial pathogens, but effective spontaneous immunologically induced cancer remissions are very rare. In recent years, much has been discovered about the mechanisms by which the immune system recognizes and responds to cancers. The specific antigens involved have now been defined in many cases. Improved adjuvants are available. Means by which cancer cells overcome immunological attack can be exploited and overcome. Most importantly, the immunological control mechanisms responsible for initiating and maintaining an effective immune response are now much better understood. It is now possible to manipulate immunological effector cells or antigen-presenting cells ex vivo in order to induce an effective antitumour response. At the same time, it is possible to recruit other aspects of the immune system, both specific (e.g. antibody responses) and innate (natural killer cells and granulocytes).

Delineation of a CpG phosphorothioate oligodeoxynucleotide for activating primate immune responses in vitro and in vivo

Oligodeoxynucleotides (ODN) containing unmethylated CpG dinucleotides within specific sequence contexts (CpG motifs) are detected, like bacterial or viral DNA, as a danger signal by the vertebrate immune system. CpG ODN synthesized with a nuclease-resistant phosphorothioate backbone have been shown to be potent Th1-directed adjuvants in mice, but these motifs have been relatively inactive on primate leukocytes in vitro. Moreover, in vitro assays that predict in vivo adjuvant activity for primates have not been reported. In the present study we tested a panel of CpG ODN for their in vitro and in vivo immune effects in mice and identified in vitro activation of B and NK cells as excellent predictors of in vivo adjuvant activity. Therefore, we tested >250 phosphorothioate ODN for their capacity to stimulate proliferation and CD86 expression of human B cells and to induce lytic activity and CD69 expression of human NK cells. These studies revealed that the sequence, number, and spacing of individual CpG motifs contribute to the immunostimulatory activity of a CpG phosphorothioate ODN. An ODN with a TpC dinucleotide at the 5' end followed by three 6 mer CpG motifs (5'-GTCGTT-3') separated by TpT dinucleotides consistently showed the highest activity for human, chimpanzee, and rhesus monkey leukocytes. Chimpanzees or monkeys vaccinated once against hepatitis B with this CpG ODN adjuvant developed 15 times higher anti-hepatitis B Ab titers than those receiving vaccine alone. In conclusion, we report an optimal human CpG motif for phosphorothioate ODN that is a candidate human vaccine adjuvant.

Influence of backbone chemistry on immune activation by synthetic oligonucleotides

Depending on base sequence, DNA displays immunological activities relevant to the design of novel therapeutic agents. To determine the influence of backbone structure on these activities, we tested a series of synthetic phosphodiester and phosphorothioate oligonucleotides in in vitro cultures of murine spleen cells. These compounds were 30 bases long and consisted of either a single base or an immunostimulatory sequence (AACGTT) flanked on 5' and 3' ends by 12 nucleotides of each base. Cell activation was assessed by both thymidine incorporation and expression of cell surface CD69; production of interleukin-6 and interleukin-12 was used as a measure of cytokine stimulation. In these assays, phosphorothioate oligonucleotides induced much higher levels of proliferation, CD69 expression, and cytokine production than the comparable phosphodiester compounds and had activity at lower concentrations. The sequence for optimal stimulation by phosphorothioates varied among responses, however. For example, whereas compounds containing an immunostimulatory sequence all induced similar levels of proliferation and CD69 expression, cytokine production was greatest with compounds with dA and dT flanks. Furthermore, while single base dG oligonucleotides stimulated proliferation as both phosphodiesters and phosphorothioates, they failed to stimulate cytokine production. Together, these findings indicate that base sequence as well as backbone chemistry influence immune activation by synthetic oligonucleotides, with the effects varying among responses. While suggesting differences in the structure-function relationships of nucleic acids in their immune activities, these findings also raise the possibility of the design of agents with specific patterns of immune modulation.

Mechanisms and applications of immune stimulatory CpG oligodeoxynucleotides

Immune stimulation has been widely recognized as an undesirable side effect of certain antisense oligodeoxynucleotides (ODN) which can interfere with their therapeutic application. It is now clear that these dose-dependent immune stimulatory effects primarily result from the presence of an unmethylated CpG dinucleotide in particular base contexts ('CpG motif). The sequence-specific immune activation is not just an experimental artifact, but is actually a highly evolved immune defense mechanism whose actual 'goal' is the detection of microbial nucleic acids. In contrast to vertebrate DNA, in which CpG dinucleotides are 'suppressed' and are highly methylated, microbial genomes do not generally feature CpG suppression or methylation [1]. Immune effector cells such as B cells, macrophages, dendritic cells, and natural killer cells appear to have evolved pattern recognition receptors (PRR) that by binding the microbe-restricted structure of CpG motifs, trigger protective immune responses. Although the specific immune activation appears to have a variety of potential therapeutic applications, it is generally undesirable in antisense ODN. Immune stimulation may be avoided in antisense oligos by the selection of CpG-free target sequences, by the use of ODN backbones that do not support immune stimulation, or by selective modifications of the cytosine in any CpG dinucleotides.

Oligodeoxynucleotides Containing Palindrome Sequences with Internal 5′-CpG-3′ Act Directly on Human NK and Activated T Cells to Induce IFN-γ Production In Vitro

Previous studies have shown that the action of bacterial or synthetic oligodeoxynucleotide (oligo-DNA) on mouse NK cells to produce IFN-γ is mediated mostly by monocytes/macrophages activated by olig-DNA. However, its action on human IFN-γ-producing cells has not been well investigated. In the present study, we examined the effect of oligo-DNAs on highly purified human NK and T cells. Bacillus Calmette-Guérin-derived or synthetic oligo-DNAs induced NK cells to produce IFN-γ with an increased CD69 expression, and the autocrine IFN-γ enhanced their cytotoxicity. The response of NK cells to oligo-DNAs was enhanced when the cells were activated with IL-2, IL-12, or anti-CD16 Ab. T cells did not produce IFN-γ in response to oligo-DNAs but did respond independently of IL-2 when they were stimulated with anti-CD3 Ab. In the action of oligo-DNAs, the palindrome sequence containing unmethylated 5′-CpG-3′ motif(s) appeared to play an important role in the IFN-γ-producing ability of NK cells. The changes of base composition inside or outside the palindrome sequence altered its activity: The homooligo-G-flanked GACGATCGTC was the most potent IFN-γ inducer for NK cells. The CG palindrome was also important for activated NK and T cells in their IFN-γ production, although certain nonpalindromes acted on them. Among the sequences tested, cell activation- or cell lineage-specific sequences were likely; i.e., palindrome ACCGGT and nonpalindrome AACGAT were favored by activated NK cells but not by unactivated NK cells or activated T cells. These results indicate that oligo-DNAs containing CG palindrome act directly on human NK cells and activated T cells to induce IFN-γ production.

Cutting Edge: Rapid Induction of Mitogen-Activated Protein Kinases by Immune Stimulatory CpG DNA

Unmethylated CpG motifs in bacterial DNA or synthetic oligodeoxynucleotides (CpG DNA) rapidly activate B cells and monocyte-derived cells; however, the intracellular signaling pathways involved in this process are unclear. Here, we demonstrate that CpG DNA induces the activation of c-Jun NH2-terminal kinase and p38 but does not activate the extracellular receptor kinase in murine B and monocyte-like cell lines. CpG DNA also induces the phosphorylation of activating transcription factor-2, c-Jun, and mitogen-activated protein kinase (MAPK)-activated protein kinase 2 as well as the activation of activator protein-1 (AP-1) DNA binding. Inhibition of p38 led to the suppression of CpG DNA-induced AP-1 DNA-binding activity and cytokine production, indicating that the p38 pathway is required for mediating these immune stimulatory effects of CpG DNA. Chloroquine, an endosomal acidification inhibitor, selectively abolished CpG DNA-mediated MAPK activation. Our results indicate that CpG DNA activates the p38 and c-Jun NH2-terminal kinase MAPK and leads to the activation of AP-1 via a pathway which is sensitive to chloroquine.

Animal models of antisense oligonucleotides: lessons for use in humans

The ability of oligonucleotides to inhibit genetic expression in a sequence-specific manner has been well documented. Because of their potential for exquisite specificity, oligonucleotides have been proposed as therapeutic agents for a variety of human diseases, including cancers, microbial infections and autoimmune disorders. Approximately 16 clinical trials are currently in progress. However, relatively little is known about the in vivo behaviour of oligonucleotides. Extrapolations from in vitro studies to predict in vivo pharmacokinetics and effects in humans might be difficult and inappropriate. Animal models still remain an essential tool in the development of oligonucleotides as efficient drugs in humans.