Stimulation of in vitro proliferation of murine lymphocytes by synthetic oligodeoxynucleotides

Phosphorothioated antisense oligodeoxynucleotide suppressing interleukin-10 is a safe and potent vaccine adjuvant

While vaccination is highly effective for the prevention of many infectious diseases, the number of adjuvants licensed for human use is currently very limited. The aim of this study was to evaluate the safety, efficacy, and to clarify the mechanism of a phosphorothioated interleukin (IL)-10-targeted antisense oligonucleotide (ASO) as an immune adjuvant in intradermal vaccination. The cytotoxicity of IL-10 ASO and its ability to promote T cell proliferation were assessed by Cell Counting Kit-8 (CCK-8) assay. The contents of IL-6, IL-8, TNF-α, IL-1β, and IL-10 in inoculated local tissue and the antigen-specific antibody titers in mouse serum samples were determined by ELISA. The target cells of IL-10 ASO were observed using immunofluorescent staining. The results showed that the specific antibody titer of ovalbumin (OVA), a model antigen, was increased 100-fold upon addition of IL-10 ASO as an adjuvant compared to that of OVA alone. IL-10 ASO showed an immunopotentiation efficacy similar to that of Freund's incomplete adjuvant, with no detectable cell or tissue toxicity. In vitro and in vivo experiments confirmed that IL-10 ASO enhances immune responses by temporarily suppressing IL-10 expression from local dendritic cells and consequently promoting T cell proliferation. In conclusion, IL-10 ASO significantly enhances immune responses against co-delivered vaccine antigens with high efficacy and low toxicity. It has the potential to be developed into a safe and efficient immune adjuvant.

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

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

PU.1 and ICSBP control constitutive and IFN-gamma-regulated Tlr9 gene expression in mouse macrophages

Macrophages are activated by unmethylated CpG-containing DNA (CpG DNA) via TLR9. IFN-gamma and LPS can synergize with CpG DNA to enhance proinflammatory responses in murine macrophages. Here, we show that LPS and IFN-gamma up-regulated Tlr9 mRNA in murine bone marrow-derived macrophages (BMM). The ability of LPS and IFN-gamma to induce Tlr9 mRNA expression in BMM was dependent on the presence of the growth factor, CSF-1, which is constitutively present in vivo. However, there were clear differences in mechanisms of Tlr9 mRNA induction. LPS stimulation rapidly removed the CSF-1 receptor (CSF-1R) from the cell surface, thereby blocking CSF-1-mediated transcriptional repression and indirectly inducing Tlr9 mRNA expression. By contrast, IFN-gamma activated the Tlr9 promoter directly and only marginally affected cell surface CSF-1R expression. An approximately 100-bp proximal promoter of the murine Tlr9 gene was sufficient to confer basal and IFN-gamma-inducible expression in RAW264.7 cells. A composite IFN regulatory factor (IRF)/PU.1 site upon the major transcription start site was identified. Mutation of the binding sites for PU.1 or IRF impaired basal promoter activity, but only the IRF-binding site was required for IFN-gamma induction. The mRNA expression of the IRF family member IFN consensus-binding protein [(ICSBP)/IRF8] was coregulated with Tlr9 in macrophages, and constitutive and IFN-gamma-inducible Tlr9 mRNA expression was reduced in ICSBP-deficient BMM. This study therefore characterizes the regulation of mouse Tlr9 expression and defines a molecular mechanism by which IFN-gamma amplifies mouse macrophage responses to CpG DNA.

Novel immunostimulatory agent based on CpG oligodeoxynucleotide linked to the nontoxic B subunit of cholera toxin

In this study, we report the development of a novel, rationally designed immunostimulatory adjuvant based on chemical conjugation of CpG oligodeoxynucleotide (ODN) to the nontoxic B subunit of cholera toxin (CTB). We demonstrate that the immunostimulatory effects of CpG can be dramatically enhanced by conjugation to CTB. Thus, CpG ODN linked to CTB (CTB-CpG) was shown to be a more potent stimulator of proinflammatory cytokine and chemokine responses in murine splenocytes and human PBMCs than those of CpG ODN alone in vitro. The presence of CpG motif, but not modified phosphorothioate ODN backbone, was found to be critical for the enhanced immunostimulatory effects of CTB-CpG. Our mode-of-action studies, including studies on cells from specifically gene knockout mice suggest that similar to CpG, CTB-CpG exerts its immunostimulatory effects through a TLR9/MyD88- and NF-kappaB-dependent pathway. Surprisingly, and as opposed to CpG ODN, CTB-CpG-induced immunity was shown to be independent of endosomal acidification and resistant to inhibitory ODN. Furthermore, preincubation of CTB-CpG with GM1 ganglioside reduced the immunostimulatory effects of CTB-CpG to those of CpG ODN alone. Interestingly, conjugation of CpG ODN to CTB confers an enhanced cross-species activity to CpG ODN. Furthermore, using tetanus toxoid as a vaccine Ag for s.c. immunization, CTB-CpG markedly enhanced the Ag-specific IgG Ab response and altered the specific pattern of Ab isotypes toward a Th1 type response. To our knowledge, CTB is the first nontoxic derivative of microbial toxins discovered that when chemically linked to CpG remarkably augments the CpG-mediated immune responses.

Oral administration of second-generation immunomodulatory oligonucleotides induces mucosal Th1 immune responses and adjuvant activity

CpG DNA induces potent Th1 immune responses through Toll-like receptor 9. In the present study, we used oligonucleotides consisting of a novel 3'-3'-linked structure and synthetic stimulatory motifs, referred as second-generation immunomodulatory oligonucleotides (IMOs). The stimulatory motifs included: CpR, YpG, or R'pG (R = 2'-deoxy-7-deazaguanosine, Y = 2'-deoxy-5-hydroxy-cytidine, and R' = 1-[2'-deoxy-beta-d-ribofuranosyl]-2-oxo-7-deaza-8-methyl-purine). We evaluated the stability of orally administered IMOs in the gastrointestinal (GI) environment and their ability to induce mucosal immune responses in mice, and compared these characteristics with those of a conventional CpG DNA. The IMOs were significantly more stable than CpG DNA following oral administration, and IMOs induced stronger local and systemic immune responses as determined by MIP-1beta, MCP-1, IP-10, and IL-12 production. Mice orally immunized with ovalbumin (OVA) and IMO had higher levels of IgG2a antibodies in serum and IgA antibodies in intestinal mucosa than did mice immunized with OVA and CpG DNA. These studies demonstrate that IMOs are more stable than CpG DNA in the GI tract and can induce more potent mucosal Th1 adjuvant responses. IMOs may prove to be effective oral adjuvants, able to promote strong systemic and mucosal immune responses to oral vaccines and antigens for therapeutic and prophylactic applications.

Cutting edge: species-specific TLR9-mediated recognition of CpG and non-CpG phosphorothioate-modified oligonucleotides

Different DNA motifs are required for optimal stimulation of mouse and human immune cells by CpG oligodeoxynucleotides (ODN). These species differences presumably reflect sequence differences in TLR9, the CpG DNA receptor. In this study, we show that this sequence specificity is restricted to phosphorothioate (PS)-modified ODN and is not observed when a natural phosphodiester backbone is used. Thus, human and mouse cells have not evolved to recognize different CpG motifs in natural DNA. Nonoptimal PS-ODN (i.e., mouse CpG motif on human cells and vice versa) gave delayed and less sustained phosphorylation of p38 MAPK than optimal motifs. When the CpG dinucleotide was inverted to GC in each ODN, some residual activity of the PS-ODN was retained in a species-specific, TLR-9-dependent manner. Thus, TLR9 may be responsible for mediating many published CpG-independent responses to PS-ODN.

Single-base oligodeoxyguanosine-binding proteins on nonspecific cytotoxic cells: identification of a new class of pattern-recognition receptors

The present study was designed to identify a possible new class of pathogen-recognition proteins that bind single-base oligodeoxynucleotide (ODN) ligands. Binding by the teleost natural killer cell equivalent [referred to as nonspecific cytotoxic cells (NCC)] was compared with mammalian cells (mouse RAW264.7 cells and human THP-1 cells). The ODN analysed were composed of 20-mers of guanosine (dG20), adenosine (dA20), thymidine (dT20) or cytosine (dC20). Binding studies first determined the 50% saturation levels for NCC (1.25 microg/ml), RAW264.7 (0.2 microg/ml) and THP-1 (0.8 microg/ml). Binding by dG20 to all the three cell types was saturable. Ligand blots of NCC membrane lysates with biotinylated dG20 revealed two different major molecular weight species (16-18 and 29 kDa) of binding proteins. The 29-kDa protein was identified with the help of Western blot analysis using a polyclonal antibody specific to an NCC antimicrobial protein (ncamp-1). The membrane expression of the 29-kDa ncamp-1 was determined by the binding of surface-biotinylated NCC membrane proteins with digoxigenin dG20 followed by immunoprecipitation using anti-digoxigenin agarose beads. The 29 and 14-18 kDa NCC membrane proteins were cross-reactive using Western blot examination with a polyclonal anti-histone 1 antibody. Function studies revealed that dG20 activated a twofold upregulation of membrane binding by homologous dG20-biotin. dG20 also stimulated NCC-increased membrane expression of NCC receptor protein 1. Additional experiments were performed to determine the DNase sensitivity of the different ODN. dG20 appeared to be more resistant to DNase treatment, compared to dC20, dA20 and dT20. The single-base ODN-binding proteins may represent a new class of pattern-recognition receptors that are involved in innate anti-bacterial resistance mediated by NCC.

Self-stabilized CpG DNAs optimally activate human B cells and plasmacytoid dendritic cells

We recently showed that 5'-terminal secondary structures in CpG DNA affect activity significantly more than those at the 3'-end [Biochem. Biophys. Res. Commun. 306 (2003) 948]. The need for an accessible 5'-end of CpG DNA for activity suggested that the receptor reads the DNA sequence from this end. In continuation of these studies, we have designed immunomodulatory oligonucleotides (IMOs), consisting of a nine-mer stimulatory domain, containing a CpG motif and a hairpin-loop structure at the 3'-end, referred to as self-stabilized CpG DNAs. We studied the ability of self-stabilized CpG DNAs to stimulate human B-cell proliferation and interferon-alpha (IFN-alpha) secretion in plasmacytoid dendritic cell (pDC) culture assays. Self-stabilized CpG DNAs activated human B cells and induced plasmacytoid dendritic cells to secrete high levels of IFN-alpha. While both stimulatory and secondary structures in CpG DNAs were required for pDC activation, CpG motifs were sufficient to activate B cells. Interestingly, CpG motifs were not required for activity in the hairpin duplex region. Further modifications of the hairpin duplex region with a mixture of oligodeoxynucleotides and oligo-2'-O-methylribonucleotides in a heteroduplex formation permitted activation of both human B cells and pDCs.

Immunoregulatory activity of CpG oligonucleotides in humans and nonhuman primates

Oligodeoxynucleotides (ODN) containing CpG motifs mimic the ability of microbial DNA to activate the innate immune system. The resultant response limits the early spread of infectious organisms while promoting the development of adaptive immunity. CpG ODN show promise as vaccine adjuvants and in the treatment of asthma, allergy, infection, and cancer. Due to evolutionary divergence in CpG recognition between species, CpG ODN that are most active in rodents are poorly immunostimulatory in primates. Thus, evidence that CpG ODN have therapeutic activity in mice must be confirmed in primates. Two distinct types of CpG ODN were identified that stimulate primate PBMC. D-type ODN trigger plasmacytoid DC to secrete IFNalpha, monocytes to mature into functionally active DC, and NK cells to secrete IFNgamma. K-type ODN stimulate B cells and monocytes to proliferate and secrete IgM, IL-10, and/or IL-6. In vivo studies in nonhuman primates indicate that proinflammatory or humoral immune responses can be selectively facilitated by judicious use of these distinct types of ODN.

Secondary structures in CpG oligonucleotides affect immunostimulatory activity

Oligodeoxynucleotides containing CpG dinucleotides in specific sequence contexts activate the vertebrate immune system. Our previous studies showed that the 5(')-end of a CpG oligonucleotide should be accessible for receptor recognition and subsequent immune stimulation. Activity is abrogated if this end is blocked by joining two CpG oligos through 5(')-5(') linkage. It was not known whether a similar effect would arise from secondary structures at either end of a CpG oligo, such as hairpin loops or terminal dimers. In the present study we found that 5(')-terminal secondary structures affect activity significantly more than those at the 3(')-end. The need for an open 5(')-end suggests that the receptor responsible for immune stimulation reads the DNA sequence from this end. These results may also provide insights to place CpG motifs appropriately in DNA vaccines to induce additional Th1 type responses.

Potent CpG oligonucleotides containing phosphodiester linkages: in vitro and in vivo immunostimulatory properties

Bacterial and synthetic DNAs, containing CpG dinucleotides in specific sequence contexts, activate the vertebrate immune system. Unlike phosphorothioate (PS) CpG DNAs, phosphodiester (PO) CpG DNAs require either palindromic sequences and/or poly(dG) sequences at the 3(')-end for activity. Here, we report 'PO-immunomers' having two PO-CpG DNA molecules joined through their 3(')-ends. These PO-imunomers permitted us, for the first time, to assess immunostimulatory properties of PO-CpG DNAs in vitro and in vivo without the need for palindromic and/or poly(dG) sequences. In medium containing 10% fetal bovine serum, PO-immunomers were more resistant than PO-CpG DNAs to nucleases. Compared to PS-CpG DNA in BALB/c and C3H/HeJ mice spleen cell culture assays, PO-immunomers showed increased IL-12 secretion and minimal amounts of IL-6 secretion. PO-immunomers activated NF-kappa B and induced cytokine secretion in J774 cell cultures. In addition, PO-immunomers showed antitumor activity in nude mice bearing human breast (MCF-7) and prostate (DU145) cancer xenografts.

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.

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.

Beyond danger: unmethylated CpG dinucleotides and the immunopathogenesis of disease

Oligonucleotide sequences containing unmethylated cytidine phosphate guanosine (CpG) motifs are known to have significant immunostimulatory properties. Because of these immunostimulatory effects, unmethylated CpG oligonucleotides are thought to act as 'danger signals' that produce a favorable immune response by alerting the host to the presence of invading organisms or abnormal cells. In contrast to this concept, we review the evidence that unmethylated CpG sequences derived either from microbial agents or from endogenous CpG-rich Alu motifs promote disease progression by inducing an aberrant or autoreactive immune response. Recognition of the negative effect of unmethylated CpG dinucleotides should lead to more effective immune strategies to combat infectious, inflammatory, autoimmune and malignant diseases.

Stimulation of thymocyte proliferation by phosphorothioate DNA oligonucleotides

DNA is a complex macromolecule the immunological properties of which depend on short sequence motifs called CpG motifs or immunostimulatory sequences (ISS). These sequences are mitogenic for B cells and can stimulate macrophage cytokine production. While these sequences do not directly activate T cells, they can augment effects of stimulation via the TCR. Furthermore, ISS can affect T cells because of macrophage production of IL-12 and IFN-alpha/beta. In these studies, we further evaluated the immune effects of DNA on T cells, testing the possibility that certain T cell populations can respond directly to this stimulus. We therefore tested the in vitro responses of thymocytes to a series of phosphodiester (Po) and phosphorothioate (Ps) oligonucleotides (ODNs) varying in sequence. In in vitro cultures, phosphorothioate ODNs (sODNs) containing CpG motifs induced significant proliferation of murine thymocytes, although phosphodiester compounds lacked activity. The magnitude of stimulation varied with sequences flanking the CpG motifs, as both dA and dT sequences enhanced the stimulatory capacity of the CpG motif. Furthermore, CpG sODNs were strong costimulators of anti-CD3-mediated thymocyte activation, increasing proliferation compared to anti-CD3 in the absence of DNA. This activation was only partially inhibited by cyclosporine A and was not dependent on a calcium influx. Together, these results indicate that phosphorothioate oligonucleotides containing CpG motifs can directly induce thymocyte proliferation as well as augment TCR activation. These observations thus extend the range of actions of CpG DNA and suggest additional mechanisms for its function as an immunomodulatory agent or 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.

The influence of base sequence on the immunostimulatory properties of DNA

DNA is a complex macromolecule whose immunological properties vary with base sequences. As shown with synthetic oligonucleotides, potent immune stimulation results from six base motifs called CpG motifs or immunostimulatory sequences (ISS). These sequences center on an unmethylated CpG dinucleotide and occur much more commonly in bacterial DNA than mammalian DNA. As such, CpG motifs may function as a danger signal to stimulate B cell activation and cytokine production. In addition to CpG motifs, runs of deoxyguanosine (dG) residues in DNA can induce B cell activation and promote macrophage cytokine expression by adjacent CpG motifs. The array of these sequences may determine the overall immune activity of a DNA molecule and affect such processes as host defense against infection as well as the use of plasmids and synthetic oligonucleotides to treat disease.

MHC Class I-Restricted Presentation of Maleylated Protein Binding to Scavenger Receptors

Pathways for loading exogenous protein-derived peptides on MHC class I are thought to be present mainly in monocyte-lineage cells and to involve phagocytosis- or macropinocytosis-mediated antigenic leakage into either cytosol or extracellular milieu to give peptide access to MHC class I. We show that maleylation of OVA enhanced its presentation to an OVA-specific MHC class I-restricted T cell line by both macrophages and B cells. This enhanced presentation involved uptake through receptors of scavenger receptor (SR)-like ligand specificity, was TAP-1-independent, and was inhibited by low levels (2 mM) of ammonium chloride. No peptide loading of bystander APCs by maleylated (maleyl) OVA-pulsed macrophages was detected. Demaleylated maleyl-OVA showed enhanced MHC class I-restricted presentation through receptor-mediated uptake and remained highly sensitive to 2 mM ammonium chloride. However, if receptor binding of maleyl-OVA was inhibited by maleylated BSA, the residual presentation was relatively resistant to 2 mM ammonium chloride. Maleyl-OVA directly introduced into the cytosol via osmotic lysis of pinosomes was poorly presented, confirming that receptor-mediated presentation of exogenous maleyl-OVA was unlikely to involve a cytosolic pathway. Demaleylated maleyl-OVA was well presented as a cytosolic Ag, consistent with the dependence of cytosolic processing on protein ubiquitination. Thus, receptor-specific delivery of exogenous protein Ags to APCs can result in enhanced MHC class I-restricted presentation, suggesting that the exogenous pathway of peptide loading for MHC class I may be a constitutive property dependent mainly on the quantity of Ag taken up by APCs.

Immunostimulatory properties of genomic DNA from different bacterial species

Bacterial DNA has potent immunological properties because of its content of immunostimulatory sequences centering on CpG motifs. To investigate whether DNA from various bacterial species differ in these properties, the activity of a panel of DNA was assessed in in vitro cultures of murine spleen cells. This panel varied in base composition and included DNA from Clostridium perfringens (CP), Escherichia coli (EC), Micrococcus lysodeikticus (MC), Staphylococcus aureus (SA), and, as a mammalian DNA control, calf thymus (CT) DNA. In assays of IL-12 and IFN-gamma production as well as B cell mitogenesis, these DNA showed marked differences in their immunostimulatory activity. For both cytokine and B cell responses, EC DNA demonstrated the highest activity while CP DNA had the lowest activity among the bacterial DNA. To determine whether differences in stimulatory capacity resulted from differences in cell uptake, the activity of DNA complexed with lipofectin was tested. While the addition of lipofectin to DNA increased stimulation by all DNA, it did not change the relative potency of the DNA tested. These results indicate that bacterial DNA differ in their immunostimulatory capacity, most likely reflecting their content of CpG motifs. These differences could affect the induction of innate immunity as well as the consequences of infection.

DNA and a CpG oligonucleotide derived from Babesia bovis are mitogenic for bovine B cells

DNAs from bacteria and variety of nonvertebrate organisms, including nematodes, mollusks, yeasts, and insects, cause polyclonal activation of murine B lymphocytes. Similar studies have not been reported for bovine B cells, and to date no studies have reported mitogenic properties of protozoal DNA for any species. However, we and others have observed that protozoal parasite antigens can induce the proliferation of lymphocytes from nonexposed donors. Extending these studies, we now show that the mitogenic property of protozoal antigen preparations is in part attributable to parasite DNA and that Babesia bovis DNA is directly mitogenic for bovine B cells. DNase treatment of B. bovis extracts abrogated B. bovis-induced proliferation of peripheral blood mononuclear cells from nonexposed cattle. Like DNAs from other organisms that were mitogenic for murine B cells, B. bovis DNA is largely nonmethylated and induced a dose-dependent proliferation of bovine B cells, which was reduced upon methylation. Furthermore, B. bovis and E. coli DNAs enhanced immunoglobulin secretion by cultured B cells, inducing moderate increases in immunoglobulin G1 and stronger increases in immunoglobulin G2. Because certain nonmethylated CpG motifs present in bacterial DNA are known to stimulate proliferation of murine and human B cells, an 11-kb fragment of B. bovis DNA was analyzed for CG dinucleotide content and for the presence of known immunostimulatory sequences (ISS) centered on a CG motif. The frequency of CG dinucleotides was approximately one-half of the expected frequency, and several CpG hexameric sequences with known activity for murine B cells were identified. An oligodeoxynucleotide containing one of these ISS (AACGTT), which is present within the rhoptry-associated protein-1 (rap-1) open reading frame, was shown to stimulate B-cell proliferation. These ISS may be involved in host immune modulation during protozoal infection and may be useful as vaccine adjuvants.

The influence of base sequence on the immunological properties of defined oligonucleotides

To assess the influence of base sequence on the immunostimulatory activities of DNA, cell binding and mitogenicity of a series of 30-mer phosphodiester oligonucleotides were tested using murine spleen cells. These compounds consisted of either a single base or a six base CpG motif in the context of 5' and 3' flanking sequences of each base. Among fluoresceinated oligonucleotides, (dG)30 had the highest binding of single base compounds tested while the presence of dG flanks increased binding of compounds with six base motifs, whether active on inactive. In assays of mitogenesis including incorporation of thymidine and uridine as well as expression of cell surface CD69, (dG)30 induced the highest responses among single base compounds. Among compounds with an active six base motif, the extent of proliferation varied with flanking sequence, with dG flanks producing the greatest stimulation in all assays tested. Together, these findings indicate that a variety of base sequences may affect the immunomodulatory properties of DNA, with the activity of dG sequences perhaps resulting from the formation of variant DNA structures.

Bacterial DNA as an evolutionary conserved ligand signalling danger of infection to immune cells

During infection, the innate limb of the immune system senses danger (pathogens) via constitutively expressed pattern-recognition receptors, and responds with activation and secretion of pro-inflammatory cytokines. Cell-wall components of gram-positive and gram-negative bacteria, such as peptidoglycan, endotoxin or lipoteichoic acid, activate via CD14, a prototypic pattern-recognition receptor for carbohydrates. This review article focuses on an alternative recognition system of the innate immune system for the recognition of bacterial DNA. Bacterial DNA differs from eukaryotic DNA in its frequency of the dinucleotides CG and its lack of methylation. These structural differences appear to be sensed by cells of the innate immune system such as antigen-presenting cells. As a consequence bacterial DNA serves as an alternate ligand to signal danger of infection. Bacterial DNA and (synthetic) oligonucleotides (ODN) derived thereof are as efficient as endotoxin in activating macrophages and dendritic cells and in triggering release of pro-inflammatory cytokines. In mice sensitized with D-galactosamine (D-GalN), high doses of bacterial DNA from either gram-positive or gram-negative pathogens induce a lethal cytokine syndrome (lethal shock). Therefore, bacterial DNA may represent a hitherto unrecognized pathophysiological entity in host-parasite interactions. Moreover, recent evidence suggests that bacterial DNA or immunostimulating ODN triggers the immunostimulation of antigen-presenting cells, and can be utilized as adjuvant to enhance immune responses of the adaptive immune system towards poorly immunogenic antigens. In fact, foreign DNA might be useful as immunotherapeutically active adjuvant to direct adaptive immune responses towards Thl-dominated immune reactions. If these findings are operative in humans, immunostimulating ODN might be used to influence Th2-dominated diseases such as allergy.

The influence of DNA sequence on the immunostimulatory properties of plasmid DNA vectors

To determine the influence of DNA sequence on immunostimulatory properties of vaccine vectors, we tested the induction of in vitro and in vivo immune responses by plasmids modified to contain extended runs of dG sequences. Studies with oligonucleotides indicate that dG sequences can directly stimulate B cells as well as enhance the activity of immunostimulatory CpG motifs because of interaction with the macrophage scavenger receptor (MSR); this receptor can bind a variety of polyanions including dG sequences. To modify vectors, we introduced stretches of 20-60 dG residues into the pCMV-beta and pSG5rab.gp vectors and measured the ability of these plasmids to induce IL-12 and IFN-gamma production by murine splenocytes. The induction of in vivo antibody responses to rabies glycoprotein was also assessed with the pSG5rab.gp vectors. In in vitro cultures, cytokine production induced by plasmids with and without dG sequences was similar. Furthermore, the addition of dG sequences to pSG5rab.gp vectors failed to enhance the anti-rabies glycoprotein response to immunization. To assess further mechanisms by which plasmids stimulate macrophages, we measured the effects of MSR ligands on in vitro cytokine induction. In in vitro cultures, poly(G), dG30, and fucoidan inhibited IL-12 induction by plasmids. IL-12 induction was also inhibited by mammalian DNA but was unaffected by polyanions that are not MSR ligands. Together, these results suggest that the addition of 20 to 60-base dG sequences to plasmids does not significantly affect their properties as immunostimulators or vaccines. Furthermore, these results suggest that MSR ligands can block cytokine induction by plasmid DNA whether or not the plasmid contains extended runs of dG.

IFN-gamma primes macrophage responses to bacterial DNA

Macrophages recognize and are activated by unmethylated CpG motifs in bacterial DNA. Here we demonstrate that production of nitric oxide (NO) from murine RAW 264 macrophages and bone marrow-derived macrophages (BMM) in response to bacterial DNA is absolutely dependent on interferon-gamma (IFN-gamma) priming. Similarly, arginine uptake and expression of the inducible nitric oxide synthase (iNOS) gene in response to bacterial DNA in BMM occurred only after IFN-gamma priming. In contrast, mRNA for the cationic amino acid transporter, CAT2, was induced by plasmid DNA alone, and priming with IFN-gamma had no effect on this response. Tumor necrosis factor-alpha (TNF-alpha) release from RAW 264 and BMM in response to bacterial DNA was augmented by IFN-gamma pretreatment. In a stably transfected HIV-1 long terminal repeat (LTR) luciferase RAW 264 cell line, IFN-gamma and bacterial DNA synergized in activation of the HIV-1 LTR. Bacterial DNA has been shown to induce IFN-gamma production in vivo as an indirect consequence of interleukin-12 (IL-12) and TNF-alpha production from macrophages. The results herein suggest the existence of a self-amplifying loop that may have implications for therapeutic applications of bacterial DNA.

Rapid induction of Jak2 and Sp1 in T cells by phosphorothioate oligonucleotides

Phosphorothioate-modified ODNs ([S]ODNs) are known to exert a variety of sequence-independent effects that are mediated in part by rapid induction of the Sp1 transcription factor. An unidentified tyrosine kinase was implicated in this Sp1 induction. In the present study, antisense [S]ODNs, initially designed to target three signaling molecules in the prolactin (PRL)-responsive rat Nb2 T cell line rapidly elevated Jak2 tyrosine kinase and Sp1 protein levels. The [S]ODN-mediated elevation of Jak2 peaked (3-fold to 6.5-fold above controls) at 15 minutes and returned to basal levels by 1 hour, whereas elevation of Sp1 (about 2-fold above controls) peaked at 1 hour. The [S]ODN-mediated induction of Sp1, but not Jak2, was abrogated by AG 490, a Jak2-specific inhibitor. In the presence of submaximal doses of PRL (0.18-0.36 ng/ml), [S]ODN-mediated induction of Jak2 and Sp1 was sustained for 72 hours. Furthermore, the [S]ODNs alone significantly increased Nb2 cell growth and enhanced the growth stimulatory effects of PRL on these cells. In contrast, unmodified ODNs had no effect on Jak2 or Sp1 protein levels and did not stimulate Nb2 cell growth. In conclusion, [S]ODNs stimulate the coordinate induction of Jak2 and Sp1 and stimulate Nb2 T cell proliferation in a sequence-independent manner. The abrogation of Sp1 induction by AG 490 indicates that Jak2 tyrosine kinase is required for [S]ODN-mediated induction of Sp1 in these cells. These results may help to explain some of the nonspecific effects of [S]ODNs, particularly in cytokine-dependent immune cells.

Evaluation of the toxicity of ISIS 2302, a phosphorothioate oligonucleotide, in a 4-week study in CD-1 mice

The subchronic toxicity of ISIS 2302 and ISIS 3082, phosphorothioate oligonucleotides with antisense activity against human and murine ICAM-1 mRNA, respectively, was investigated in CD-1 mice. ISIS 2302 is currently in clinical trials as an anti-inflammatory agent. Because of the differences in mRNA sequence targets between humans and mice, ISIS 2302 has no pharmacologic activity in mice. ISIS 3082 was specifically designed to inhibit murine ICAM-1 and was included in this study to evaluate the effects of prolonged ICAM-1 inhibition. The oligonucleotides were administered by bolus i.v. injection (via tail vein) every other day for 27 days (14 doses) at dose levels of 0, 0.8, 4, 20, and 100 mg/kg per injection ISIS 2302 or 20 mg/kg per injection ISIS 3082. The basic group size consisted of 10 male and 10 female mice, which were sacrificed 2 days after the last dose and an additional 5 mice per sex in vehicle control and 100 mg/kg ISIS 2302 dose groups, which remained on study for a 28-day treatment-free period. No treatment-related deaths occurred during this study, and there were no effects of either oligonucleotide on body weight gain or food consumption. The most common changes observed in this study included a mixed mononuclear cell infiltrate seen in a number of organs or tissues, splenomegaly, and lymphoid hyperplasia at dose levels of > or = 20 mg/kg ISIS 2302. In the group that received the highest dose level of ISIS 2302 (100 mg/kg), there were alterations in serum chemistry parameters that appeared to be related to perturbations in the liver, including 3- to 4-fold increases in aspartate and alanine aminotransferase and smaller changes in bilirubin, alkaline phosphatase, cholesterol, triglycerides, and albumin levels. Treatment-related effects on hematologic parameters were limited to the 100 mg/kg ISIS 2302 dose group and included slight monocytosis and thrombocytopenia. None of the effects observed appeared to be life threatening. Complete or partial reversal of all effects was evident in the remaining high-dose ISIS 2302 animals at the end of the 4-week recovery period. Comparison of the effects produced by the same dose level (20 mg/kg) of ISIS 2302 and ISIS 3082 did not reveal any differences that could be attributed to exaggerated pharmacology. In conclusion, treatment-related alterations were observed primarily at the 100 mg/kg dose level, including immune stimulation and hepatic alterations, which were partially reversed following a 4-week treatment-free period.

A "stealth" approach to inhibition of lymphocyte activation by oligonucleotide complementary to the putative G0/G1 switch regulatory gene G0S30/EGR1/NGFI-A

The putative G0/G1 switch regulatory gene G0S30/EGR1/NFGI-A show increased expression shortly after adding concanavalin-A (ConA) to cultured T lymphocytes. However, it is reported that lymphocytes from mice in which the gene has been deleted proliferate normally in response to ConA. This suggests that G0S30 expression is not critical for the response. Paradoxically, others report that proliferation of ConA-stimulated rat lymphocytes is inhibited by an antisense oligonucleotide complementary to G0S30. Because the G0S30 sequence is highly conserved between species, we used a similar oligonucleotide (differing by 1 base) to show for humans that the response to ConA is also inhibited. However, no oligonucleotide-induced changes in the concentrations of G0S30 protein or mRNA are detectable. This suggests that the oligonucleotide is not acting by influencing the expression of G0S30, and may be targeting another gene. The phosphorothioated oligonucleotide was maximally inhibitory at a 50 nM concentration, which is near to the "physiological" concentration found with CpG-containing oligonucleotides to activate mouse B lymphocytes. In the present work, increasing the concentration above 50 nM, or adding further quantities of control oligonucleotides, decreased the inhibition. It is suggested that by using low oligonucleotide concentrations (the "stealth" approach), one may avoid "tripping" an endogenous defense system directed against exogenous oligonucleotides, yet still get sufficient uptake to inhibit lymphocyte activation.

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

Phosphorothioate (PT) oligonucleotides are designed as specific agents for antisense therapy although they have been reported to exert non-specific immunomodulatory effects. To elucidate further their actions, the effect of PT deoxyguanosine oligomers (S-oligo(dG)) on in vitro cytokine production by mouse splenocytes was studied. S-oligo(dG)20 inhibited production of INF gamma induced by Con A, E. coli DNA or the combination of PMA and calcium ionophore A23187. The diester analogue was inactive, and of PT homo-oligomers tested, S-oligo(dG)20 was the most active. PT compounds with as few as 5 dG residues could also block INF gamma production. These results indicate that base composition and length, as well as the PT backbone, contribute to the inhibition of INF gamma production and extend the range of immunomodulatory effects of PT compounds.