Novel chimeric immunomodulatory compounds containing short CpG oligodeoxyribonucleotides have differential activities in human cells

Subunit vaccines for Acinetobacter baumannii

Acinetobacter baumannii is a gram-negative bacterium and a crucial opportunistic pathogen in hospitals. A. baumannii infection has become a challenging problem in clinical practice due to the increasing number of multidrug-resistant strains and their prevalence worldwide. Vaccines are effective tools to prevent and control A. baumannii infection. Many researchers are studying subunit vaccines against A. baumannii. Subunit vaccines have the advantages of high purity, safety, and stability, ease of production, and highly targeted induced immune responses. To date, no A. baumannii subunit vaccine candidate has entered clinical trials. This may be related to the easy degradation of subunit vaccines in vivo and weak immunogenicity. Using adjuvants or delivery vehicles to prepare subunit vaccines can slow down degradation and improve immunogenicity. The common immunization routes include intramuscular injection, subcutaneous injection, intraperitoneal injection and mucosal vaccination. The appropriate immunization method can also enhance the immune effect of subunit vaccines. Therefore, selecting an appropriate adjuvant and immunization method is essential for subunit vaccine research. This review summarizes the past exploration of A. baumannii subunit vaccines, hoping to guide current and future research on these vaccines.

Enhanced Immunostimulatory Activity of Covalent DNA Dendrons

The present study focused on the design and synthesis of covalent DNA dendrons bearing multivalent cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODNs) that can stimulate the immune system through the activation of TLR9. These dendrons were synthesized using branching trebler phosphoramidite containing three identical protecting groups that enabled the simultaneous synthesis of multiple strands on a single molecule. Compared with linear ODNs, covalent DNA dendrons were found to be more resistant to nuclease degradation and were more efficiently taken up by macrophage-like RAW264.7 cells. Cellular uptake was suggested to be mediated by macrophage scavenger receptors. The covalent DNA dendrons composed of multivalent immunostimulatory branches enhanced the secretion of proinflammatory cytokines TNF-α and IL-6 from RAW264.7 cells, and 9-branched DNA dendrons showed the highest enhancement. Given their enhanced efficacy, we expect covalent DNA dendrons to be useful structures of oligonucleotide medicines.

CpG Adjuvant in Allergen-Specific Immunotherapy: Finding the Sweet Spot for the Induction of Immune Tolerance

Prevalence and incidence of IgE-mediated allergic diseases have increased over the past years in developed and developing countries. Allergen-specific immunotherapy (AIT) is currently the only curative treatment available for allergic diseases that has long-term efficacy. Although AIT has been proven successful as an immunomodulatory therapy since its beginnings, it still faces several unmet needs and challenges today. For instance, some patients can experience severe side effects, others are non-responders, and prolonged treatment schedules can lead to lack of patient adherence and therapy discontinuation. A common strategy to improve AIT relies on the use of adjuvants and immune modulators to boost its effects and improve its safety. Among the adjuvants tested for their clinical efficacy, CpG oligodeoxynucleotide (CpG-ODN) was investigated with limited success and without reaching phase III trials for clinical allergy treatment. However, recently discovered immune tolerance-promoting properties of CpG-ODN place this adjuvant again in a prominent position as an immune modulator for the treatment of allergic diseases. Indeed, it has been shown that the CpG-ODN dose and concentration are crucial in promoting immune regulation through the recruitment of pDCs. While low doses induce an inflammatory response, high doses of CpG-ODN trigger a tolerogenic response that can reverse a pre-established allergic milieu. Consistently, CpG-ODN has also been found to stimulate IL-10 producing B cells, so-called B regulatory cells (Bregs). Accordingly, CpG-ODN has shown its capacity to prevent and revert allergic reactions in several animal models showing its potential as both preventive and active treatment for IgE-mediated allergy. In this review, we describe how CpG-ODN-based therapies for allergic diseases, despite having shown limited success in the past, can still be exploited further as an adjuvant or immune modulator in the context of AIT and deserves additional attention. Here, we discuss the past and current knowledge, which highlights CpG-ODN as a potential adjuvant to be reevaluated for the enhancement of AIT when used in appropriate conditions and formulations.

Development of the CpG Adjuvant 1018: A Case Study

The development of aluminum salts (alum) as vaccine adjuvants was an empirical process with little understanding of the mechanism of action and, with decades of use, it has become clear that there is a need for alternatives where alum-based adjuvants are suboptimal. Oligonucleotides containing unmethylated CpG sequences represent one alternative as they are potent stimulators of the vertebrate innate immune system through activation of Toll-like receptor-9. This chapter outlines the methods used by Dynavax Technologies to progress a CpG-containing oligonucleotide sequence termed 1018 through preclinical and clinical testing as an adjuvant for immunization against hepatitis B virus (HBV). 1018 is a short (22-mer) oligonucleotide sequence containing CpG motifs active in both rodents and primates. Preclinical testing of hepatitis B surface antigen (HBsAg) + 1018 in comparison to HBsAg + alum demonstrated induction of substantially higher antibody titers and a favorable safety profile for 1018. Most importantly, clinical studies with HBsAg vaccination consistently demonstrate more rapid induction of protective antibody titers with 1018 compared to alum in all populations studied, including groups that are harder to immunize such as the elderly and immunocompromised individuals. These studies represent the basis for use of the CpG-motif-containing oligonucleotide 1018 as an improved adjuvant for HBsAg immunogenicity. HBsAg + 1018 (HEPLISAV-B^™) is currently in late-stage clinical testing for prophylactic immunization against HBV.

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

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

Optimization, Production, and Characterization of a CpG-Oligonucleotide-Ficoll Conjugate Nanoparticle Adjuvant for Enhanced Immunogenicity of Anthrax Protective Antigen

We have synthesized and characterized a novel phosphorothioate CpG oligodeoxynucleotide (CpG ODN)-Ficoll conjugated nanoparticulate adjuvant, termed DV230-Ficoll. This adjuvant was constructed from an amine-functionalized-Ficoll, a heterobifunctional linker (succinimidyl-[(N-maleimidopropionamido)-hexaethylene glycol] ester) and the CpG-ODN DV230. Herein, we describe the evaluation of the purity and reactivity of linkers of different lengths for CpG-ODN-Ficoll conjugation, optimization of linker coupling, and conjugation of thiol-functionalized CpG to maleimide-functionalized Ficoll and process scale-up. Physicochemical characterization of independently produced lots of DV230-Ficoll reveal a bioconjugate with a particle size of approximately 50 nm and covalent attachment of more than 100 molecules of CpG per Ficoll. Solutions of purified DV230-Ficoll were stable for at least 12 months at frozen and refrigerated temperatures and stability was further enhanced in lyophilized form. Compared to nonconjugated monomeric DV230, the DV230-Ficoll conjugate demonstrated improved in vitro potency for induction of IFN-α from human peripheral blood mononuclear cells and induced higher titer neutralizing antibody responses against coadministered anthrax recombinant protective antigen in mice. The processes described here establish a reproducible and robust process for the synthesis of a novel, size-controlled, and stable CpG-ODN nanoparticle adjuvant suitable for manufacture and use in vaccines.

Adjuvants: Classification, Modus Operandi, and Licensing

Vaccination is one of the most efficient strategies for the prevention of infectious diseases. Although safer, subunit vaccines are poorly immunogenic and for this reason the use of adjuvants is strongly recommended. Since their discovery in the beginning of the 20th century, adjuvants have been used to improve immune responses that ultimately lead to protection against disease. The choice of the adjuvant is of utmost importance as it can stimulate protective immunity. Their mechanisms of action have now been revealed. Our increasing understanding of the immune system, and of correlates of protection, is helping in the development of new vaccine formulations for global infections. Nevertheless, few adjuvants are licensed for human vaccines and several formulations are now being evaluated in clinical trials. In this review, we briefly describe the most well known adjuvants used in experimental and clinical settings based on their main mechanisms of action and also highlight the requirements for licensing new vaccine formulations.

A CpG-Ficoll Nanoparticle Adjuvant for Anthrax Protective Antigen Enhances Immunogenicity and Provides Single-Immunization Protection against Inhaled Anthrax in Monkeys

Nanoparticulate delivery systems for vaccine adjuvants, designed to enhance targeting of secondary lymphoid organs and activation of APCs, have shown substantial promise for enhanced immunopotentiation. We investigated the adjuvant activity of synthetic oligonucleotides containing CpG-rich motifs linked to the sucrose polymer Ficoll, forming soluble 50-nm particles (DV230-Ficoll), each containing >100 molecules of the TLR9 ligand, DV230. DV230-Ficoll was evaluated as an adjuvant for a candidate vaccine for anthrax using recombinant protective Ag (rPA) from Bacillus anthracis. A single immunization with rPA plus DV230-Ficoll induced 10-fold higher titers of toxin-neutralizing Abs in cynomolgus monkeys at 2 wk compared with animals immunized with equivalent amounts of monomeric DV230. Monkeys immunized either once or twice with rPA plus DV230-Ficoll were completely protected from challenge with 200 LD50 aerosolized anthrax spores. In mice, DV230-Ficoll was more potent than DV230 for the induction of innate immune responses at the injection site and draining lymph nodes. DV230-Ficoll was preferentially colocalized with rPA in key APC populations and induced greater maturation marker expression (CD69 and CD86) on these cells and stronger germinal center B and T cell responses, relative to DV230. DV230-Ficoll was also preferentially retained at the injection site and draining lymph nodes and produced fewer systemic inflammatory responses. These findings support the development of DV230-Ficoll as an adjuvant platform, particularly for vaccines such as for anthrax, for which rapid induction of protective immunity and memory with a single injection is very important.

Enhancement of the Immunostimulatory Activity of a TLR7 Ligand by Conjugation to Polysaccharides

Toll-like receptors (TLRs) in the innate immune system recognize specific pathogen-associated molecular patterns derived from microbes. Synthetic small molecule TLR7 agonists have been extensively evaluated as topical agents for antiviral and anticancer therapy, and as adjuvants for vaccine. However, safe and reproducible administration of synthetic TLR7 ligands has been difficult to achieve due to undesirable pharmacokinetics and unacceptable side effects. Here, we conjugated a versatile low molecular weight TLR7 ligand to various polysaccharides in order to improve its water solubility, enhance its potency, and maintain low toxicity. The synthetic TLR7 ligand, 2-methoxyethoxy-8-oxo-9-(4-carboxy benzyl)adenine, designated 1V209, was stably conjugated to primary amine functionalized Ficoll or dextran using benzoic acid functional groups. The conjugation ratios using specified equivalents of TLR7 ligand were dose responsive and reproducible. The zeta potential value of the polysaccharides was decreased in inverse proportion to the ratio of conjugated TLR7 ligand. These conjugates were highly water-soluble, stable for at least 6 months at room temperature in aqueous solution, and easy to lyophilize and reconstitute without altering potency. In vitro studies with murine mononuclear leukocytes showed that the TLR7 agonist conjugated to polysaccharides had 10- to 1000-fold higher potencies than the unconjugated TLR7 ligand. In vivo pharmacodynamics studies after injection indicate that the conjugates induced systemic cytokine production. When the conjugates were used as vaccine adjuvants, they enhanced antigen specific humoral and cellular immune responses to a much greater extent than did unconjugated TLR7 ligands. These results indicated that small molecule TLR7 ligands conjugated to polysaccharides have improved immunostimulatory potency and pharmacodynamics. Polysaccharides can be conjugated to a variety of molecules such as antigens, peptides, and TLR ligands. Therefore, such conjugates could represent a versatile platform for the development of vaccines against cancer and infectious diseases.

Vaccinating captive chimpanzees to save wild chimpanzees

Infectious disease has only recently been recognized as a major threat to the survival of Endangered chimpanzees and Critically Endangered gorillas in the wild. One potentially powerful tool, vaccination, has not been deployed in fighting this disease threat, in good part because of fears about vaccine safety. Here we report on what is, to our knowledge, the first trial in which captive chimpanzees were used to test a vaccine intended for use on wild apes rather than humans. We tested a virus-like particle vaccine against Ebola virus, a leading source of death in wild gorillas and chimpanzees. The vaccine was safe and immunogenic. Captive trials of other vaccines and of methods for vaccine delivery hold great potential as weapons in the fight against wild ape extinction.

Structure-dependent immunostimulatory effect of CpG oligodeoxynucleotides and their delivery system

Unmethylated cytosine-phosphate-guanosine (CpG) oligodeoxynucleotides (ODNs) are recognized by Toll-like receptor 9 (TLR9) found in antigen-presenting cells and B cells and can activate the immune system. Using CpG ODNs as an adjuvant has been found to be effective for treating infectious diseases, cancers, and allergies. Because natural ODNs with only a phosphodiester backbone are easily degraded by nuclease (deoxyribonuclease [DNase]) in serum, CpG ODNs with a phosphorothioate backbone have been studied for clinical application. CpG ODNs with a phosphorothioate backbone have raised concern regarding undesirable side effects; however, several CpG ODNs with only a phosphodiester backbone have been reported to be stable in serum and to show an immunostimulatory effect. In recent years, research has been conducted on delivery systems for CpG ODNs using nanoparticles (NPs). The advantages of NP-based delivery of CpG ODN include (1) it can protect CpG ODN from DNase, (2) it can retain CpG ODN inside the body for a long period of time, (3) it can improve the cellular uptake efficiency of CpG ODN, and (4) it can deliver CpG ODN to the target tissues. Because the target cells of CpG ODN are cells of the immune system and TLR9, the receptor of CpG ODN is localized in endolysosomes, CpG ODN delivery systems are required to have qualities different from other nucleic acid drugs such as antisense DNA and small interfering RNA. Studies until now have reported various NPs as carriers for CpG ODN delivery. This review presents DNase-resistant CpG ODNs with various structures and their immunostimulatory effects and also focuses on delivery systems of CpG ODNs that utilize NPs. Because CpG ODNs interact with TLR9 and activate both the innate and the adaptive immune system, the application of CpG ODNs for the treatment of cancers, infectious diseases, and allergies holds great promise.

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

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

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

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

Broad-spectrum drugs against viral agents

Development of antivirals has focused primarily on vaccines and on treatments for specific viral agents. Although effective, these approaches may be limited in situations where the etiologic agent is unknown or when the target virus has undergone mutation, recombination or reassortment. Augmentation of the innate immune response may be an effective alternative for disease amelioration. Nonspecific, broad-spectrum immune responses can be induced by double-stranded (ds)RNAs such as poly (ICLC), or oligonucleotides (ODNs) containing unmethylated deocycytidyl-deoxyguanosinyl (CpG) motifs. These may offer protection against various bacterial and viral pathogens regardless of their genetic makeup, zoonotic origin or drug resistance.

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

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

Immunostimulatory DNA as a vaccine adjuvant

Immunostimulatory DNA containing unmethylated CpG motifs is recognized by Toll-like receptor 9, resulting in the activation of innate immune responses that subsequently amplify the adaptive-immune response. Advances in the characterization of Toll-like receptor 9 signaling have identified immunostimulatory sequences (ISS) with distinct biological activities. Numerous animal models have demonstrated that synthetic ISS are effective adjuvants that enhance both humoral and cellular immune responses in diverse indications, ranging from infectious disease to cancer and allergy. An added benefit supporting the use of ISS as a vaccine adjuvant is that the specific activation of a pathway critical to the regulation of the immune response results in minimal toxicity. To date, clinical testing has largely affirmed the potency and safety of ISS-adjuvanted vaccines.

Combination treatment with omalizumab and rush immunotherapy for ragweed-induced allergic rhinitis: Inhibition of IgE-facilitated allergen binding

BACKGROUND

The combination of anti-IgE (omalizumab) therapy with ragweed injection immunotherapy for seasonal allergic rhinitis results in a significant reduction in systemic side effects and enhanced efficacy compared with immunotherapy alone. One proposed mechanism of immunotherapy is to induce regulatory antibodies that inhibit facilitated antigen presentation.

OBJECTIVES

We sought to determine whether the combination protocol has a cumulative effect on inhibition of facilitated antigen presentation both during and after discontinuation of treatment.

METHODS

Ragweed allergen immunotherapy with and without omalizumab therapy was tested in a 4-arm, double-blind, placebo-controlled study. Flow cytometry was used to detect serum inhibitory activity for IgE-facilitated CD23-dependent allergen binding to B cells as a surrogate marker for facilitated antigen presentation. Serum ragweed-specific IgG4 was measured by means of ELISA.

RESULTS

Immunotherapy alone resulted in partial inhibition of allergen-IgE binding after 5 to 19 weeks of treatment compared with baseline (P < .01). Complete inhibition of allergen-specific IgE binding was observed in both treatment groups receiving omalizumab (P < .001). Allergen-specific IgG4 levels were only increased after immunotherapy (P < .05), both in the presence and absence of anti-IgE treatment. Combined treatment resulted in the induction of long-lasting inhibitory antibody function for up to 42 weeks compared with either treatment alone.

CONCLUSION

Ragweed immunotherapy induced serum regulatory antibodies that partially blocked binding of allergen-IgE complexes to B cells. Additional treatment with anti-IgE, by directly blocking IgE binding to CD23, completely inhibited allergen-IgE binding.

CLINICAL IMPLICATIONS

The combination of ragweed immunotherapy and anti-IgE resulted in prolonged inhibition of allergen-IgE binding compared with either treatment alone, events that might contribute to enhanced efficacy.

Properties regulating the nature of the plasmacytoid dendritic cell response to Toll-like receptor 9 activation

Human plasmacytoid dendritic cells (PDCs) can produce interferon (IFN)-α and/or mature and participate in the adaptive immune response. Three classes of CpG oligonucleotide ligands for Toll-like receptor (TLR)9 can be distinguished by different sequence motifs and different abilities to stimulate IFN-α production and maturation of PDCs. We show that the nature of the PDC response is determined by the higher order structure and endosomal location of the CpG oligonucleotide. Activation of TLR9 by the multimeric CpG-A occurs in transferrin receptor (TfR)-positive endosomes and leads exclusively to IFN-α production, whereas monomeric CpG-B oligonucleotides localize to lysosome-associated membrane protein (LAMP)-1–positive endosomes and promote maturation of PDCs. However, CpG-B, when complexed into microparticles, localizes in TfR-positive endosomes and induces IFN-α from PDCs, whereas monomeric forms of CpG-A localize to LAMP-1–positive endosomes accompanied by the loss of IFN-α production and a gain in PDC maturation activity. CpG-C sequences, which induce both IFN-α and maturation of PDCs, are distributed in both type of endosomes. Encapsulation of CpG-C in liposomes stable above pH 5.75 completely abrogated the IFN-α response while increasing PDC maturation. This establishes that the primary determinant of TLR9 signaling is not valency but endosomal location and demonstrates a strict compartmentalization of the biological response to TLR9 activation in PDCs.

Therapeutic potential of Toll-like receptor 9 activation

In the decade since the discovery that mouse B cells respond to certain unmethylated CpG dinucleotides in bacterial DNA, a specific receptor for these 'CpG motifs' has been identified, Toll-like receptor 9 (TLR9), and a new approach to immunotherapy has moved into the clinic based on the use of synthetic oligodeoxynucleotides (ODN) as TLR9 agonists. This review highlights the current understanding of the mechanism of action of these CpG ODN, and provides an overview of the preclinical data and early human clinical trial results using these drugs to improve vaccines and treat cancer, infectious disease and allergy/asthma.

Inhibitors of TLR-9 act on multiple cell subsets in mouse and man in vitro and prevent death in vivo from systemic inflammation

In parallel with the discovery of the immunostimulatory activities of CpG-containing oligodeoxynucleotides, several groups have reported specific DNA sequences that could inhibit activation by CpG-containing oligodeoxynucleotides in mouse models. We show that these inhibitory sequences, termed IRS, inhibit TLR-9-mediated activation in human as well as mouse cells. This inhibitory activity includes proliferation and IL-6 production by B cells, and IFN-alpha and IL-12 production by plasmacytoid dendritic cells. Our studies of multiple cell types in both mice and humans show the optimal IRS to contain a GGGG motif within the sequence, and the activity to require a phosphorothioate backbone. Although the GGGG motif readily itself leads to formation of a tetrameric oligodeoxynucleotide structure, inhibitory activity resides exclusively in the single-stranded form. When coinjected with a CpG oligodeoxynucleotide in vivo, IRS were shown to inhibit inflammation through a reduction in serum cytokine responses. IRS do not need to be injected at the same site to inhibit, demonstrating that rapid, systemic inhibition of TLR-9 can be readily achieved. IRS can also inhibit a complex pathological response to ISS, as shown by protection from death after massive systemic inflammation induced by a CpG-containing oligodeoxynucleotides.

Immunomodulatory oligonucleotides containing a cytosine-phosphate-2'-deoxy-7-deazaguanosine motif as potent toll-like receptor 9 agonists

Bacterial DNA and synthetic oligomers containing CpG dinucleotides activate the immune system through Toll-like receptor (TLR) 9. Here, we compare the immunostimulatory activity of three immunomers with different nucleotide sequences containing a synthetic cytosine-phosphate-2'-deoxy-7-deazaguanosine dinucleotide (CpR), called immunomodulatory oligonucleotides (IMOs), in mouse, human, and monkey systems. IMOs induced IL-12 and IFN-gamma secretion more than a control non-CpG IMO in mice. All three IMOs activated HEK293 cells expressing TLR9 but not TLR3, -7, or -8. IMOs induced human B-cell proliferation and enhanced expression of CD86 and CD69 surface markers on B cells. The three IMOs induced CD86 expression on human plasmacytoid dendritic cells, but only IMOs that contained a 5'-terminal TCR nucleotide sequence induced IFN-alpha secretion. A sequence that forms a duplex structure also was required for IFN-alpha induction in human peripheral blood mononuclear cell cultures. IMOs induced chemokine and cytokine gene expression in human peripheral blood mononuclear cells. In monkeys, all three IMOs induced transient changes in peripheral blood leukocytes and lymphocytes and activated B and T lymphocytes. All three IMOs induced IFN-alpha in vivo in monkeys; the IMO sequence that forms a stable secondary structure induced the highest levels of IFN-alpha. These studies are, to our knowledge, the first comprehensive studies to compare the activity of IMOs containing synthetic stimulatory CpR dinucleotides in mouse, monkey, and human systems. These results suggest that IMOs induce strong and rapid immunostimulation and that the CpR dinucleotide is recognized by TLR9, leading to immune-cell activation and cytokine secretion in vitro and in vivo.

Superior activity of the type C class of ISS in vitro and in vivo across multiple species

CpG-C are a novel class of CpG motif-containing immunostimulatory sequences (ISS) that includes both a 5'-TCG element and a CpG-containing palindrome. CpG-C drive all known ISS activities and, in particular, are potent enhancers of IFN-alpha from plasmacytoid dendritic cells (PDCs). In our examination of CpG-C sequence requirements, we determined that optimal IFN-alpha-inducing activity could be achieved with longer palindromes. Longer palindromes also correlated with maintenance of the double-stranded (ds) form despite concentration and pH changes, indicating a preference for ds oligodeoxynucleotides (ODNs) by the ISS-induced signaling mechanism for IFN-alpha synthesis. This correlation did not hold for all arms of the ISS-induced immune response, since we did not observe increased B cell activity with the longer palindrome CpG-C ODNs. We further demonstrated that CpG-C retained activity in an in vitro primate system and induced the expression of several cytokines and IFN-alpha-inducible genes when CpG-C were administered in vivo to mice and primates. In conclusion, we have shown CpG-C to exert several types of immune functions across multiple species, and this novel class is thus an attractive candidate for ISS-based therapeutic strategies.

New approaches in immunotherapy: allergen vaccination with immunostimulatory DNA

Despite its success, conventional immunotherapy is saddled with a number of encumbrances. An allergenic vaccine that could reduce allergenicity, maintain immunogenicity, and be given in a few doses would have important therapeutic implications, as millions of patients with poorly controlled allergic rhinitis and asthma would be candidates for such a form of immunomodulation. This article addresses a specific adjuvant approach to immunotherapy in which highly active immunostimulatory phosphorothioate oligodeoxyribonucleotide moieties are linked to the principal allergenic moiety of a relevant aeroallergen.

Adjuvants for allergen immunotherapy: experimental results and clinical perspectives

PURPOSE OF REVIEW

Inclusion of adjuvants in immunotherapy vaccines are important to enhance immune responses to allergens. This article will cover the recent advances in adjuvant formulations described in published articles primarily over the past 2 years.

RECENT FINDINGS

Traditionally, allergen immunotherapy preparations utilize aluminium hydroxide as an adjuvant. These have generally proved efficacious and have a good safety profile. However, recent advances in the understanding of immunological mechanisms underlying immunotherapy and in the design of new adjuvants may allow a more rational approach to adjuvant use. One approach is to use adjuvants such as immunostimulatory sequences or monophosphoryl lipid A, which can deviate allergy-associated Th2 immune responses towards a Th1 phenotype. Both of these adjuvants have been used in pilot controlled clinical trials which have demonstrated clinical efficacy and the induction of protective IgG antibodies. Other approaches to improve immunotherapy vaccines include microencapsulation of allergen to allow delivery of the allergen directly to the gut in order to induce immunological tolerance and vaccination with heat-killed mycobacteria.

SUMMARY

There is great interest in newly designed adjuvants to improve the efficacy and safety of allergen immunotherapy. A better understanding of immunological mechanisms and further clinical trials utilizing new adjuvants are needed.

Mucosal immunization with attenuated Shigella flexneri harboring an influenza hemagglutinin DNA vaccine protects mice against a lethal influenza challenge

Mucosal surfaces are important for the induction of immunity against influenza virus. In a murine intranasal immunization model, we demonstrated that the attenuated Shigella flexneri Deltaasd strain 15D, carrying a DNA construct encoding the influenza virus hemagglutinin (HA), induces protective immunity against a lethal respiratory challenge with influenza A/WSN/33. Influenza virus-specific IFN-gamma T cells were detected among splenocytes, and anti-HA IgG was detected in serum post-immunization, albeit at low levels. Following influenza virus challenge, an accelerated anti-HA IgA antibody response was detected in bronchoalveolar lavage (BAL) washings from mice vaccinated with attenuated shigella containing the HA construct. These results suggest that S. flexneri Deltaasd strain 15D is a promising vector for mucosal DNA vaccine immunization against influenza virus and other mucosal pathogens.

Polymyxin B enhances ISS-mediated immune responses across multiple species

The immunostimulatory effects of bacterial DNA on mammalian cells have been localized to unmethylated CpG motifs, and synthetic CpG-containing oligodeoxynucleotides that mimic these effects are known as immunostimulatory sequences (ISS). We have found that the polycationic antibiotic, polymyxin B (PMXB), associates with ISS and serum albumin in vitro and forms microparticles that greatly increase the activity of ISS on plasmacytoid dendritic cells (PDCs). Specifically, ISS/PMXB greatly enhanced IFN-alpha production from PDCs and other activities downstream of IFN-alpha, including IFN-gamma secretion, NK lytic activity, and the expression of genes dependent upon IFN-alpha/IFN-gamma. This amplification was specific for the IFN-alpha pathway since other ISS activities, including B cell proliferation, B cell IL-6 secretion, and PDC maturation, were not affected by PMXB. Both the polycationic peptide and lipophilic fatty acid side chain domains of PMXB, as well as the presence of a third party stabilizing agent such as albumin or Tween 85, were required for particle formation and enhanced ISS activity. The ISS-enhancing activity of PMXB was observed across multiple species (human, primate, and mouse) and in vivo (primate, mouse). These data illustrate the usefulness of formulating ISS with a cationic lipopeptide such as PMXB, which focuses and greatly amplifies the ISS-induced pathway of IFN-alpha-mediated responses.