Oligodeoxynucleotides containing CpG motifs modulate the allergic TH2 response of BALB/c mice to Bet v 1, the major birch pollen allergen

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.

Metalloproteinases and their Inhibitors under the Course of Immunostimulation by CPG-ODN and Specific Antigen Inhalation in Equine Asthma

Objectives

Inhalation of immunostimulatory bacterial DNA segments (cytosine-phosphate-guanosine-oligodeoxynucleotides, CpG-ODN) normalizes clinical and cytologic parameters in severe equine asthma. We hypothesized that CpG-ODN inhalation also reduces the misbalance of elastinolytic activity in asthmatic horses.

Methods

Twenty asthmatic horses diagnosed by clinical examinations using a scoring system were included. All horses inhaled CpG-ODNs for 14 days in 2-day intervals. Matrix metalloproteinase (MMP-2/-9) and tissue inhibitors of metalloproteinase (TIMP-1/-2) concentrations were measured in tracheal aspirates using equine sandwich ELISAs before and 2 and 6 weeks after CpG-ODN inhalation.

Results

MMP and TIMP concentrations correlated with the results of clinical scoring in all stages of equine asthma. Inhalation therapy led to significant reductions in clinical scores. MMP-2, MMP-9, and TIMP-2 concentrations were significantly reduced immediately, and all MMP and TIMP concentrations 6 weeks after therapy.

Discussion

In equine asthma, overexpression of MMPs contributes to pathological tissue destruction, while TIMPs counteract MMPs with overexpression leading to fibrosis formation. The results of this study show that CpG-ODN inhalation may be an effective therapy to address a misbalance in equine asthma.

Conclusions

Misbalance of elastinolytic activity seems to improve by CpG-ODN inhalation for at least 6 weeks posttherapy, which may reduce the remodeling of the extracellular matrix. Further studies should evaluate this effect in comparison to glucocorticoid inhalation therapy.

Significance

CpG-ODN inhalation may be an effective therapy in the prevention of pulmonary fibrosis formation in equine asthma.

Suppression of Allergic Response by CpG Motif Oligodeoxynucleotide–House-Dust Mite Conjugate in Animal Model of Allergic Rhinitis

Background

Although there have been many therapeutic options for allergic disease, the true allergen desensitization remains a challenging goal. The classic immunotherapy has a limited efficacy, is inconvenient, and has a risk of anaphylaxis. Recent reports revealed that immunostimulatory DNA sequences (ISS-oligdeoxynucleotide [ODN], CpG motif) act as a strong Th1 response–inducing adjuvants and that DNA-based vaccination might be an effective therapeutic option. In this study, we investigate whether ISS-ODN/Dermatophagoides farinae (Der f) conjugate has antiallergic effects in the allergic rhinitis mouse model, sensitive to house-dust mites. Der f is the most common allergen-inducing allergic rhinitis in Korea.

Methods

C57BL/6 mice were sensitized with crude extract of Der f. After injection of ISS-ODN or ISS-ODN/Der f conjugate, several parameters of allergic response were evaluated.

Results

Scratching and sneezing symptoms and eosinophilic infiltration into nasal mucosa were suppressed by injection with ISS-ODN only and ISS-ODN/Der f conjugate. Interleukin-5 level was decreased and interferon γ level was increased in nasal lavage fluid by injection of ISS-ODN/Der f conjugate. Der f–specific immunoglobulin E was decreased by injection of ISS-ODN or Der f /ISS-ODN conjugate; however, these were not statistically significant. Transforming growth factor β1 secreted by cultured splenocyte was increased significantly in ISS-ODN/Der f conjugate group.

Conclusion

These results suggest ISS-ODN/Der f conjugate induces an antiallergic effect and induces an increase in transforming growth factor β1 level in the allergic rhinitis model using Der f allergen. Allergic response developed by Der f allergen could be more effectively reduced by injection with ISS-ODN/Der f conjugate than by injection with ISS-ODN only.

A comparison of nanoparticullate CpG immunotherapy with and without allergens in spontaneously equine asthma-affected horses, an animal model

INTRODUCTION

New therapeutic strategies to modulate the immune response of human and equine allergic asthma are still under extensive investigation. Immunomodulating agents stimulating T-regulatory cells offer new treatment options beyond conventional symptomatic treatment or specific immunotherapy for human and equine allergic airway diseases, with the goal of a homoeostatic T-helper cell balance. The aim of this study was to evaluate the effects of a nebulized gelatin nanoparticle-CpG formulation (CpG-GNP) with and without specific allergens for the treatment of spontaneous allergic equine asthma as a model for human asthma.

METHODS

Twenty equine asthma-affected horses were treated either with CpG-GNP alone or CpG-GNP with allergens. Two specific allergens were selected for each horse based on history and an in-vitro test. Each horse received seven administrations of the respective nebulized composition and was examined before treatment, immediately after and 6 weeks after the treatment course.

RESULTS

Clinical parameters such as breathing rate, indirect interpleural measurement, arterial blood gases, amount of tracheal mucus and percentage of neutrophils and cytokines in tracheal washes and serum samples were evaluated. Treatment with CpG-GNP alone as well as in combinations with relevant allergens resulted in clinical improvement of nasal discharge, breathing rate, amount of secretion and viscosity, neutrophil percentage and partial oxygen pressure directly after and 6 weeks after treatment. There were no significant differences between the two treatments in clinical parameters or local cytokine profiles in the tracheal wash fluid (IL-10, IFN-g, and IL-17). IL-4 concentrations decreased significantly in both groups.

CONCLUSION

Nonspecific CpG-GNP-based immunotherapy shows potential as a treatment for equine and possibly also human allergic asthma.

Allergen immunotherapy for birch pollen-allergic patients: recent advances

As of today, allergen immunotherapy is performed with aqueous natural allergen extracts. Recombinant allergen vaccines are not yet commercially available, although they could provide patients with well-defined and highly consistent drug substances. As Bet v 1 is the major allergen involved in birch pollen allergy, with more than 95% of patients sensitized to this allergen, pharmaceutical-grade recombinant Bet v 1-based vaccines were produced and clinically tested. Herein, we compare the clinical results and modes of action of treatments based on either a birch pollen extract or recombinant Bet v 1 expressed as hypoallergenic or natural-like molecules. We also discuss the future of allergen immunotherapy with improved drugs intended for birch pollen-allergic patients suffering from rhinoconjunctivitis.

A limited CpG-containing oligodeoxynucleotide therapy regimen induces sustained suppression of allergic airway inflammation in mice

BACKGROUND

CpG-containing oligodeoxynucleotides (CpG-ODNs) are potent inhibitors of T helper 2 mediated allergic airway disease in sensitised mice challenged with allergen. A single treatment has transient effects but a limited series of treatments has potential to achieve clinically meaningful sustained inhibition of allergic airway disease.

OBJECTIVE

To optimise the treatment regimen for sustained efficacy and to determine the mechanisms of action in mice of an inhaled form of CpG-ODN being developed for human asthma treatment.

METHODS

We set up a chronic allergic-asthma model using ragweed-sensitised mice exposed weekly to intranasal ragweed. Using this model, the effects of a limited series of weekly intranasal 1018 ISS (CpG-ODN; B-class) treatments were evaluated during treatment and for several weeks after treatments had stopped but weekly allergen exposures continued. Treatment efficacy was evaluated by measuring effects on lung T helper 2 cytokines and eosinophilia, and lung dendritic cell function and T-cell responses.

RESULTS

Twelve intranasal 1018 ISS treatments induced significant suppression of bronchoalveolar lavage eosinophilia and interleukin 4, 5 and 13 levels. This suppression of allergic T helper 2 parameters was maintained through 13 weekly ragweed exposures administered after treatment cessation. Subsequent experiments demonstrated that at least five treatments were required for lasting suppression. Although CpG-ODN induced moderate T helper 1 responses, suppression of allergic airway disease did not require interferon γ but was associated with induction of a regulatory T-cell response.

CONCLUSIONS

A short series of CpG-ODN treatments results in sustained suppression of allergic lung inflammation induced by a clinically relevant allergen.

Perspectives in vaccine adjuvants for allergen-specific immunotherapy

The design of more powerful adjuvants is a tool of crucial interest to ameliorate vaccination strategies to reduce injections and/or dose of antigen, induce local immunity and obtain better protection. Effective anti-infectious vaccines should elicit protective TH1 responses, cytotoxic CD8+ cells and antibody-forming cells. However, cytokine microenvironment is a key point also in targeted therapeutic vaccinations, such as allergen-specific immunotherapy, where the interference with an already-existing but inappropriate immunity is required. In this case, safe, appropriately conditioning and potentially orally available adjuvants together with delivery to appropriate subsets of dendritic cells would be highly appreciated to properly boost innate immune cells. In fact, aluminium hydroxide, although safe, has been classically associated with the induction of a TH2 response to co-formulated antigens. Thus, detoxified lipopolysaccaride (MPL-A), CpG oligonucleotides, imidazoquinolines and adenine derivatives acting via innate sensors may represent improvements in therapeutic vaccinations for allergy as able to interfere with pathogenic TH2 cells with eventual induction of TH1 differentiation.

A prophylactic effect of an oligodeoxynucleotide containing a cytidine-guanosine motif against Japanese cedar pollen-induced T-helper type 2 allergic response

BACKGROUND

Over 10% of entire population in Japan suffer from allergic diseases induced by Japanese cedar pollen (JCP) every spring. In terms of preventive medicine, it has become a matter of urgency to establish successful prophylactic and therapeutic strategies for controlling the disorders. The effect of an oligodeoxynucleotide containing a cytidine-guanosine motif (CpG ODN) on the regulation of immune responses induced by JCP was investigated in this study.

METHODS

BALB/c mice were inoculated with CpG ODN intraperitoneally before intranasal sensitization to JCP. Cellular infiltration in the lung of BALB/c mice after treatment with CpG ODN or JCP was performed by hematoxylin and eosin (H&E) staining. Antibody titers and cytokines levels were determined by ELISA.

RESULTS

Intranasal inoculation of BALB/c mice with JCP induced a T-helper type 2 (Th2-type) dominant immune response, as characterized by the production of interleukin (IL)-4 and IL-5 in the lung and of JCP-specific IgE antibody in serum. Prior intraperitoneal administration of CpG ODN to mice suppressed the subsequent JCP-induced antibody production and infiltration of inflammatory cells in the lung. The inhibitory mechanism of CpG ODN seemed to be attributable to a CpG ODN-induced Th1-type dominant environment, which down-regulated Th2-type response subsequently induced by JCP allergen sensitization. Furthermore, administration with CpG ODN decreased the production of JCP-induced IL-17, which has been found to play a pivotal role in several inflammatory diseases including allergic asthma. The decreased production of IL-17, together with reduced secretion of IL-4 and IL-5, may contribute to diminish the inflammation in the lung of JCP-sensitized mice.

CONCLUSION

This work provides evidence that the CpG ODN has a prophylactic effect on the JCP-induced Th2-type allergic responses by establishing or restoring a Th1-type shift of immune environments.

Immunotherapy for allergies and asthma: present and future

Allergen immunotherapy (IT) is a proven approach for treating allergic rhinitis and allergic asthma that has been practiced since 1911 and has undergone significant development in the past two decades. As currently practiced, IT involves subcutaneous or sublingual administration of allergens, both methods of which have been extensively investigated. In addition to allergen IT, a number of additional nonspecific IT approaches are being used or are in phase II/phase III clinical trials, which may be available in clinics within the next one to three years. Such therapies include anti-IgE antibodies and the soluble IL-4 receptor. Other experimental IT approaches are at the preclinical research stage and may proceed to clinical trials and the clinic within the next five to ten years. This review discusses the pros and cons of recent developments in both currently practiced and experimental IT approaches.

Impaired lung dendritic cell migration and T cell stimulation induced by immunostimulatory oligonucleotides contribute to reduced allergic airway inflammation

CpG-containing oligonucleotides (CpG) have been shown to reduce key features of allergic airway inflammation in mouse models. Given the inhibitory effects of CpG treatment on Ag presentation of subsequently encountered Ags via MHC class I and II molecules by dendritic cells (DC), we hypothesized that intranasal CpG treatment would lead to reduced Ag-specific T cell stimulation in the lung-draining lymph nodes, thereby reducing the inflammatory response in sensitized mice. Intranasal CpG administration led to phenotypic maturation of lung and mediastinal lymph node DC as determined by expression of MHC class II, CD80, and CD86. This was accompanied by a significant reduction in the proliferation of adoptively transferred Ag-specific CD4(+) and CD8(+) T cells in mediastinal lymph nodes, when CpG was given before inhalative OVA challenges. DC obtained from mediastinal lymph nodes of CpG-treated mice before OVA inhalation led to reduced T cell stimulation via MHC class I and II molecules. In addition, CpG diminished airway eosinophilia and pulmonary infiltration after sensitization or following adoptive transfer of Ag-specific Th2 cells. These results were explained by reduced CCL21 expression and inhibition of lung DC migration following CpG administration, which could be restored by transfer of bone marrow-derived DC, because CpG had no major impact on the constitutive MHC class II Ag presentation of protein-derived Ag by lung tissue-derived DC. We conclude that CpG treatment can effectively impair the DC-mediated Ag transport from the lungs to the lymph nodes, resulting in reduced T cell activation and blunted airway inflammation.

Systemic administration of olygodeoxynucleotides with CpG motifs at priming phase reduces local Th2 response and late allergic rhinitis in BALB/c mice

Oligodeoxynucleotides (ODN) with CpG motifs (CpG ODN) induce T helper (Th)1-type reaction. We aimed to evaluate the therapeutic effect of CpG ODN in the development of late allergic rhinitis induced by ovalbumin (OVA), which is one of Th2 diseaes, in BALB/c mice. Effects of a single dose of synthetic CpG-ODN (50 microg) intraperitoneally (i.p.) at the priming phase (on day 0) by OVA on the development of late eosinophilic rhinitis at respiratory areas were compared to the control mice treated with its vehicle (ODN without CpG motifs; 50 microg). Animals were again sensitized by OVA (on day 10) i.p., and 4 days after second sensitization animals were challenged by OVA intranasally (on day 14). Four days after challenge, eosinophilic reactions, nasal lesions and local cytokine values were examined. Compared to the control group, the CpG ODN-administration increased production of OVA-specific Th1 cytokine (interferon-gamma) and decreased productions of ovalubmin-specific Th2 cytokines [interleukin (IL)-5 and IL-13] in nasal cavity fluids, supernatants of splenocytes and/or sera. Also, eosinophilia and increased total IgE values were decreased in mice treated with the CpG ODN compared to the control group. Moreover, nasal lesions with infiltration of eosinophils were prominently reduced by the CpG ODN-treatment compared to the control mice. The present study suggests that the systemic administration of CpG ODN at the priming phase may reduce local OVA-specific Th2 responses, resulting in decreased nasal pathology in the late allergic eosinophilic rhinitis.

Immunostimulatory oligonucleotides in therapy of allergic diseases

At present, the improvement of hygienic life standards is considered as an environmental condition, increasing the prevalence of allergic diseases, as early contact with some pathogens is, according to the hygiene hypothesis, required for maturation of the immune system. The recognition of microbial components involves acquired and innate immunity mechanisms. Recently, the link between innate and acquired immunity has been discovered. It involves the evolutionarily old Toll-like receptor (TLR) system. Ligands recognised by TLRs include unmethylated deoxycytidil-deoxyguanosine (CpG) motif-containing microbial DNA. TLR-mediated signalling induces expression of cytokines preferentially promoting a Th1-directed response. Therefore, synthetic CpG motif-containing immunostimulatory oligonucleotides could be employed in causal allergy treatment. This review discusses some molecular aspects of the TLR system, as well as results of animal studies and early experiences, including treatment safety, from human clinical trials with immunostimulatory CpG motif-containing oligonucleotides.

Immunostimulatory oligonucleotides block allergic airway inflammation by inhibiting Th2 cell activation and IgE-mediated cytokine induction

A single treatment with a CpG-containing immunostimulatory DNA sequence (ISS) given before allergen challenge can inhibit T helper type 2 cell (Th2)–mediated airway responses in animal models of allergic asthma; however, the mechanism of this inhibition remains largely undefined. Here, we demonstrate that airway delivery of ISS before allergen challenge in Th2-primed mice acts in two distinct ways to prevent the allergic responses to this challenge. The first is to prevent induction of cytokines from allergen-specific Th2 cells, as demonstrated by the nearly complete inhibition of Th2 cytokine production, Th2-dependent functional responses, and gene induction patterns. ISS inhibits the Th2 response by rendering lung antigen-presenting cells (APCs) unable to effectively present antigen to Th2 cells, but not to Th1 cells. This loss of APC function correlates with a reduced expression of costimulatory molecules, including programmed cell death ligand (PD-L)1, PD-L2, CD40, CD80, CD86, and inducible T cell costimulator, and of major histocompatibility complex class II on CD11c⁺APCs from the airways of ISS-treated mice. The second important action of ISS is inhibition of immunoglobulin E–dependent release of Th2 cytokines, especially interleukin 4, from basophils and/or mast cells in the airways of Th2-primed mice. Thus, inhibition by ISS of allergic responses can be explained by two novel mechanisms that culminate in the inhibition of the principal sources of type 2 cytokines in the airways.

Targeting memory Th2 cells for the treatment of allergic asthma

Th2 memory cells play an important role in the pathogenesis of allergic asthma. Evidence from patients and experimental models indicates that memory Th2 cells reside in the lungs during disease remission and, upon allergen exposure, become activated effectors involved in disease exacerbation. The inhibition of memory Th2 cells or their effector functions in allergic asthma influence disease progression, suggesting their importance as therapeutic targets. They are allergen specific and can potentially be suppressed or eliminated using this specificity. They have distinct activation, differentiation, cell surface phenotype, migration capacity, and effector functions that can be targeted singularly or in combination. Furthermore, memory Th2 cells residing in the lungs can be treated locally. Capitalizing on these unique attributes is important for drug development for allergic asthma. The aim of this review is to present an overview of therapeutic strategies targeting Th2 memory cells in allergic asthma, emphasizing Th2 generation, differentiation, activation, migration, effector function, and survival.

Cotranslational endoplasmic reticulum assembly of FcepsilonRI controls the formation of functional IgE-binding receptors

The human high affinity receptor for IgE (FcepsilonRI) is a cell surface structure critical for the pathology of allergic reactions. Human FcepsilonRI is expressed as a tetramer (alphabetagamma(2)) on basophils or mast cells and as trimeric (alphagamma(2)) complex on antigen-presenting cells. Expression of the human alpha subunit can be down-regulated by a splice variant of FcepsilonRIbeta (beta(var)). We demonstrate that FcepsilonRIalpha is the core subunit with which the other subunits assemble strictly cotranslationally. In addition to alphabetagamma(2) and alphagamma(2), we demonstrate the presence of alphabeta and alphabeta(var)gamma(2) complexes that are stable in the detergent Brij 96. The role of individual FcepsilonRI subunits for the formation of functional, immunoglobulin E-binding FcepsilonRI complexes during endoplasmic reticulum (ER) assembly can be defined as follows: beta and gamma support ER insertion, signal peptide cleavage and proper N-glycosylation of alpha, whereas beta(var) allows accumulation of alpha protein backbone. We show that assembly of FcepsilonRI in the ER is a key step for the regulation of surface expression of FcepsilonRI. The ER quality control system thus regulates the quantity of functional FcepsilonRI, which in turn controls onset and persistence of allergic reactions.

An antigen-independent but not antigen-specific T(H)1 response provides protection in the murine airway inflammation model

BACKGROUND

Atopic disorders are associated with an imbalanced T(H) cell response biased toward a strong T(H)2 type, resulting in excessive production of IgE antibodies, eosinophil recruitment and activation, and mast cell degranulation. Restoring the T(H)1-T(H)2 balance by increasing the antigen-specific T(H)1 response has been pursued for specific allergy immunotherapy. Synthetic oligodeoxynucleotides containing unmethylated CG dinucleotides (CpG) are strong T(H)1 adjuvants and are being investigated for allergy immunotherapy.

OBJECTIVE

This study was designed to investigate the protective role of antigen-specific T(H)1 responses induced by epidermal powder immunization with ovalbumin (OVA) and CpG in a murine airway inflammation model.

METHODS

An allergy model was used in which BALB/c mice were sensitized and then challenged with OVA. Mice received prophylactic or therapeutic immunizations with OVA, CpG, or both. After challenge, pulmonary inflammation and cell infiltration were measured on the basis of BAL cell counts and lung histology. Immune response was determined by measuring the levels of lavage cytokines and serum antibodies.

RESULTS

Coadministration of OVA and CpG by means of subcutaneous injection or epidermal powder immunization, although inducing a strong T(H)1 response, neither suppressed T(H)2 cytokines nor offered protection against pulmonary eosinophilia and histopathology in a mouse challenge model. However, when CpG was used as a stand-alone treatment of previously sensitized animals, protection against allergic airway inflammation was observed. After challenge with OVA, eosinophilia was suppressed in the lungs of the CpG-treated mice.

CONCLUSION

This finding argues against the approach of boosting an allergen-dependent T(H)1 response and favors induction of an antigen-independent T(H)1 response for allergy immunotherapy.

CpG-DNA as immune response modifier

Toll-like receptors (TLRs) have been recognized to play a fundamental role in the recognition of microbial pathogens and the activation of innate immunity. However, it has also turned out that triggering of TLRs with purified compounds or synthetic ligands represents a powerful means to modulate innate as well as adaptive immune responses. Among the substances currently under investigation as immune response modifiers CpG-DNA has gained particular interest. One reason for this is the feasibility to easily synthesize and modify immunostimulatory CpG-containing oligodeoxynucleotides (CpG-ODNs). This review deals with the structural needs of CpG-ODNs. CpG-ODNs are discussed as being composed of distinct building blocks (e.g. sequence strings, backbone modifications) giving rise to a concept of structural modules within CpG-ODNs.

Animal models of type I allergy using recombinant allergens

Various animal models including guinea pigs, monkeys, dogs, rats, and mice have been established in an attempt to provide insights into the complex immunological and pathophysiological mechanisms of human type I allergic diseases. The detailed knowledge of the murine genome, the various components of the murine immune system, and the generation of engineered mice has made the murine system the most attractive among all animal models. The availability of multitude technologies and reagents to characterize and manipulate immunological pathways and mediators adds to the outstanding opportunities to assess the pathology of allergic diseases and to develop novel therapeutic strategies in mice. Numerous sensitization protocols with food and aero-allergens are used to establish an allergic/asthma-like phenotype in mice. Requirements for an appropriate murine model include a close resemblance to the pathology of the disease in humans, the objective measurement of the physiologic parameters, as well as reliability and reproducibility of the experimental data. With respect to reproducible experimental conditions, it has been recognized that extract preparations from natural allergen sources can vary in their allergen-content and -composition. This might influence the degree of sensitization or the outcome of treatment strategies in dependence of the applied extract preparation. The use of recombinant allergens in experimental in vivo and in vitro systems can overcome these problems. Another aspect, that has become obvious from the experimental studies, is that allergens can differ in their immunogenicity as well as in their capacity to act as tolerogens. Therefore, it seems important that the efficacy of the different allergen-molecules to act as therapeutic agents is individually examined. In this review, examples of animal models are described, in which recombinant allergens have been used for sensitization and/or treatment of allergic responses and how they have been used to enhance our understanding of the pathology of allergic diseases.

Allergen-immunostimulatory oligodeoxynucleotide conjugate: a novel allergoid for immunotherapy

PURPOSE OF REVIEW

To summarize the data of both preclinical studies and initial clinical trials of a novel allergoid for allergen specific immunotherapy. This allergoid consists of allergen covalently coupled to immunostimulatory oligodeoxynucleotide DNA sequences.

RECENT FINDINGS

Recently, immunostimulatory oligodeoxynucleotide sequences, also called unmethylated cytosin-guanine dinucleotide motifs, have been discovered that act as strong T helper 1 response inducing adjuvants in mice. Although mixing allergens with immunostimulatory DNA sequences induces T helper 1 responses in T helper 2 biased mice, the allergens in such mixes could still cause anaphylactic reactions when used in humans which is one of the reasons why immunotherapy has gradually been falling out of favor. Therefore, we made allergen-immunostimulatory oligodeoxynucleotide conjugates and investigated their immunogenicity and allergenicity in animal models of allergy. These conjugates were highly immunogenic for inducing T helper 1-like antiallergen responses and reversed T helper 2 responses and symptoms of asthma in mouse models. They were also less allergenic, as shown by the reaction with human immunoglobulin E antibodies and by histamine release from basophils of allergic patients. Preliminary phase I and II trials in ragweed allergic patients showed that allergen-immunostimulatory oligodeoxynucleotide conjugates are well tolerated, less allergenic and induce immunoglobulin G antiallergen antibodies more rapidly than allergen extracts without significantly increasing the immunoglobulin E titer.

SUMMARY

Allergen-immunostimulatory DNA conjugates induce T helper 1 and down regulate preexisting T helper 2 anti-allergen responses in mice. Initial phase I and II trials in ragweed allergic patients showed that ragweed allergen-DNA conjugates are well tolerated and induce a rapid immunoglobulin G but not E response. The data show that allergen-DNA conjugates are a novel type of allergoid that have great potential for a safe and potent form of allergen specific immunotherapy.

Mucosal co-application of lactic acid bacteria and allergen induces counter-regulatory immune responses in a murine model of birch pollen allergy

Recent epidemiological studies and clinical trials suggest a possible role of certain lactic acid bacteria (LAB) strains in the prevention of allergic diseases. In this study, we aimed at evaluating the immunomodulatory potential of two LAB strains, Lactococcus lactis and Lactobacillus plantarum, for prophylaxis and therapy of allergic immune responses. Both LAB strains-induced high levels of IL-12 and IFN-gamma in naive murine spleen cell cultures. Intranasal co-application with recombinant Bet v 1, the major birch pollen allergen, prior or after allergic sensitization, led to increased levels of allergen-specific IgG2a antibodies and in vitro IFN-gamma production, indicating a shift towards Th1 responses. Successful immunomodulation by the mucosal pre-treatment was further demonstrated by suppression of allergen-induced basophil degranulation. We conclude that these LAB strains in combination with an allergen could be promising candidates for mucosal vaccination against type I allergy.

Efficacy of local nasal immunotherapy for Dp2-induced airway inflammation in mice: Using Dp2 peptide and fungal immunomodulatory peptide

BACKGROUND

Local nasal immunotherapy (LNIT) is an effective immunotherapy. Peptides derived from the group 2 allergen of Dermatophagoides pteronyssinus, Dp2 28-40 and Dp2 28-40A, and fungal immunomodulatory peptide (FIP) have been shown to act as T(H)1 potential and response-inducing adjuvant. LNIT by the use of Dp2 peptides in conjunction with FIP were investigated.

OBJECTIVE

We sought to determine whether Dp2-induced airway inflammation in mice could be downregulated by Dp2 peptides or a mixture of Dp2 peptides with FIP.

METHOD

Mice were sensitized with rDp2 followed by LNIT with Dp2 peptides, FIP, or FIP and a mixture of Dp2 peptides. After intratracheal challenge with rDp2, the airway inflammation and hyperresponsiveness were determined by bronchoalveolar lavage fluid (BALF) analysis and methacholine challenge.

RESULTS

Both Dp2 peptides and FIP were able to inhibit rDp2-induced airway inflammation and airway hyperresponsiveness. An increase in IFN-gamma and a decrease in IL-5 in BALF and sera were found after LNIT with Dp2 peptides, FIP, and mixtures of both. Serum levels of TGF-beta were reduced after LNIT with FIP and Dp2 28-40. Penh values were significantly decreased after methacholine challenge in both the early and late phase.

CONCLUSIONS

LNIT with allergen-derived peptides and FIP can produce an anti-inflammatory effect on allergen-induced airway inflammation. LNIT with selected peptides and FIP might be a good alternative therapy for allergic airway disease.

Identification of a novel CpG DNA class and motif that optimally stimulate B cell and plasmacytoid dendritic cell functions

Recent reports have identified two major classes of CpG motif-containing oligodeoxynucleotide immunostimulatory sequences (ISS): uniformly modified phosphorothioate (PS) oligodeoxyribonucleotides (ODNs), which initiate B cell functions but poorly activate dendritic cells (DCs) to make interferon (IFN)-alpha, and chimeric PS/phosphodiester (PO) ODNs containing runs of six contiguous guanosines, which induce very high levels of plasmacytoid DC (PDC)-derived IFN-alpha but poorly stimulate B cells. We have generated the first reported ISS, C274, which exhibits very potent effects on all human immune cells known to recognize ISS. C274 is a potent inducer of IFN-gamma/IFN-alpha from peripheral blood mononuclear cells and exhibits accelerated kinetics of activity compared with standard ISS. This ODN also effectively stimulates B cells to proliferate, secrete cytokines, and express costimulatory antigens. In addition, C274 specifically activates PDCs to undergo maturation and secrete cytokines, including very high levels of IFN-alpha. Sequence variation studies based on C274 were used to identify the general motif requirements for this novel and distinct class of ISS. In contrast, chimeric PO/PS CpG-containing ODNs with polyguanosine sequences exert a differential pattern of ISS activity compared with C274, perhaps in part as a result of their greatly different structural nature. This pattern is composed of high IFN-alpha/IFN-gamma induction and low DC maturation in the absence of B cell stimulation. In conclusion, we have generated a novel class of ISS that transcends the limitations ascribed to classes described previously in that it provides excellent stimulation of B cells and simultaneously activates PDCs to differentiate and secrete large amounts of type I IFN.

Immunopharmacology of CpG DNA

Recognition of danger of infection by innate immune cells is a prerequisite to combat infections and to activate T and B cells. Pathogen-associated molecular patterns (PAMP) play a fundamental role in this process. PAMPs are sensed by at least ten different Toll-like receptors (TLR). Within the realm of PAMPs, CpG DNA that is recognized by TLR-9 has an outstanding propensity to induce a milieu that favors activation of T lymphocytes and biases Th1-dominated immune responses. Therefore CpG DNA has become a promising immuno-therapeutical candidate to assist and to direct immune responses such as in vaccination or modulation of allergic responses. As opposed to other PAMPs, CpG DNA can be synthesized with defined purity and base composition. Moreover, chemical substitutions can confer new qualities to synthetic CpG DNA.

CpG motifs in bacterial DNA and their immune effects

Unmethylated CpG motifs are prevalent in bacterial but not vertebrate genomic DNAs. Oligodeoxynucleotides (ODN) containing CpG motifs activate host defense mechanisms leading to innate and acquired immune responses. The recognition of CpG motifs requires Toll-like receptor (TLR) 9, which triggers alterations in cellular redox balance and the induction of cell signaling pathways including the mitogen activated protein kinases (MAPKs) and NF kappa B. Cells that express TLR-9, which include plasmacytoid dendritic cells (PDCs) and B cells, produce Th1-like proinflammatory cytokines, interferons, and chemokines. Certain CpG motifs (CpG-A) are especially potent at activating NK cells and inducing IFN-alpha production by PDCs, while other motifs (CpG-B) are especially potent B cell activators. CpG-induced activation of innate immunity protects against lethal challenge with a wide variety of pathogens, and has therapeutic activity in murine models of cancer and allergy. CpG ODN also enhance the development of acquired immune responses for prophylactic and therapeutic vaccination.

Distribution of intranasal instillations in mice: effects of volume, time, body position, and anesthesia

Intranasal instillation techniques are used to deliver various substances to the upper and lower respiratory tract (URT and LRT) in mice. Here, we quantify the relative distribution achieved with intranasal delivery of a nonabsorbable tracer, (99m)Tc-labeled sulfide-colloid. Relative distribution was determined by killing mice after instillation and quantifying the radioactivity in dissected tissues using gamma scintigraphy. A significant effect of delivery volume on relative distribution was observed when animals were killed 5 min after instillation delivered under gas anesthesia. With a delivery volume of 5 microl, no radiation was detected in the LRT; this increased to a maximum of 55.7 +/- 2.5% distribution to the LRT when 50 microl were delivered. The majority of radiation not detected in the LRT was found in the URT. Over the course of the following 1 h, radiation in the LRT remained constant, while that in the URT decreased and appeared in the gastrointestinal tract. Instillation of 25 microl into anesthetized mice resulted in 30.1 +/- 6.9% distribution to the LRT, while only 5.3 +/- 1.5% (P < 0.05) of the same volume was detected in the LRT of awake mice. Varying the body position of mice did not affect relative distribution. When using intranasal instillation, the relative distribution between the URT and LRT and the gastrointestinal tract is heavily influenced by delivery volume and level of anesthesia.

Amb a 1-linked CpG oligodeoxynucleotides reverse established airway hyperresponsiveness in a murine model of asthma

BACKGROUND

Recently, it has been demonstrated that immunostimulatory DNA sequences (ISS) containing CpG motifs prevent the development of allergic airway responses in murine models of disease. However, few studies have addressed the issue of whether these agents will reverse established Tm(H)2-driven allergic airway responses.

OBJECTIVE

The aim of this study was to determine whether intradermal delivery of an immunogenic protein of ragweed pollen linked to an immunostimulatory DNA sequence could reverse an established allergic response in the mouse lung.

METHODS

Mice sensitized and challenged with ragweed pollen extract were treated intradermally twice at 1-week intervals with an ISS chemically linked to Amb a 1 (Amb a 1-ISS). One week after the Amb a 1-ISS treatment, mice were rechallenged intratracheally with ragweed extract, and airway responses were assessed.

RESULTS

Amb a 1-ISS treatment of ragweed-sensitized and ragweed-challenged mice significantly reversed allergen-induced airway hyperresponsiveness and suppressed the total number of eosinophils in bronchoalveolar lavage fluid. The inhibitory effect of Amb a 1-ISS was associated with a marked increase in IFN-gamma levels by Amb a 1-stimulated splenocytes and a shift in the antibody profile from a T(H)2-directed IgG1 response to a T(H)1-directed IgG2a response. Interestingly, the inhibitory effect of Amb a 1-ISS on allergen-driven airway hyperresponsiveness was independent of suppression of T(H)2 cytokine production.

CONCLUSION

These results demonstrate that intradermal delivery of allergen-specific DNA conjugates can reverse established allergic responses in the murine lung, supporting their potential use in the treatment of human asthma.

Mucosal tolerance as therapy of type I allergy: intranasal application of recombinant Bet v 1, the major birch pollen allergen, leads to the suppression of allergic immune responses and airway inflammation in sensitized mice

BACKGROUND

Several studies have demonstrated that mucosal administration of soluble antigens can prevent the onset or reduce the severity of certain autoimmune diseases or allergies. Few studies exist showing the efficacy of mucosal tolerance for therapy of such diseases.

OBJECTIVE

The aim of the present study was to modulate an allergic immune response by intranasal antigen administration in an already sensitized organism.

METHODS

A murine model of allergic asthma to birch pollen (BP) and its major allergen Bet v 1 was utilized. Sensitized mice were intranasally treated with recombinant (r)Bet v 1 in different concentrations and at different intervals. On the day the mice were killed, blood and bronchoalveolar lavage fluids were taken and immediate type I skin tests were performed. T cell proliferation and cytokine production (interleukin (IL)-5, interferon (IFN)-gamma) were measured in spleen and lung cell cultures.

RESULTS

Mucosal treatment with rBet v 1 (3 x 50 microg in 4 day intervals) led to a reduction of type I skin reactions, suppressed immunoglobulin (Ig)G1/IgE antibody levels and markedly decreased IL-5 and IFN-gamma production in vitro in spleen and lung cell cultures. Moreover, lung inflammation (i.e. eosinophilia and IL-5 levels in bronchoalveolar lavage fluids) was significantly suppressed by the treatment.

CONCLUSION

Our results demonstrate that intranasal treatment with rBet v 1 reduced systemic allergic immune responses as well as airway inflammation in BP-sensitized mice. We therefore suggest that mucosal tolerance induction with recombinant allergens could be a promising concept for the therapy of allergic diseases.

Mucosal immunization of mice using CpG DNA and/or mutants of the heat-labile enterotoxin of Escherichia coli as adjuvants

Cholera toxin (CT) and the Escherichia coli heat-labile enterotoxin (LT) are potent mucosal adjuvants in animals associated, at least in part, with their ability to induce cAMP. While toxicity generally precludes their use in humans, a number of different subunit or genetically detoxified mutants of CT and LT have been developed. Another type of adjuvant that has been shown to be effective at mucosal surfaces comprises synthetic oligodeoxynucleotides (ODN) containing immunostimulatory CpG motifs (CpG ODN). We have previously demonstrated a synergy between CpG ODN and native toxins after intranasal (IN) administration to mice, and herein have examined whether this synergy is linked to the cAMP activity. The adjuvanticity of CpG ODN was evaluated with IN and oral delivery of tetanus toxoid or the hepatitis B surface antigen, relative to and in combination with native LT holotoxin (LTh), three active site mutants (LTS61F, LTA69G, LTE112K), a protease site mutant (LTR192G), and the B subunit of LT (LTB). At an equivalent dose, the adjuvants could generally be divided into two groups: one that included CpG ODN, LTh, LTR192G, and LTA69G which acted as strong adjuvants; and the second which comprised LTB, LTS61F, and LTE112K, which produced significantly weaker immune responses. When CpG ODN was co-administered with bacterial toxin-derivatives, in most cases, no synergy between CpG and the LT derivatives was found for strength of the humoral response. Nevertheless, for both routes and antigens, CpG ODN combined with any LT derivative induced a more Type 1-like response than LT derivative alone. These results suggest that while the synergy seen previously with native toxins may have been due in part to inherent cAMP activity, it may have also depended on the particular antigen used and the route of immunization.

Systemic administration of immunostimulatory DNA sequences mediates reversible inhibition of Th2 responses in a mouse model of asthma

This study investigated whether immunostimulatory DNA sequences (ISS) induce a transient or sustained inhibition of Th2 responses to inhaled antigen. We sensitized mice with subcutaneous injections to develop a Th2 response to ovalbumin (ova) and then administered a dose of ISS prior to ova inhalation challenge. Mice were then rechallenged with ova by inhalation a second time at varying time points after the first ova inhalation (1 to 8 weeks later) to determine whether the ISS dose administered prior to the first ova inhalation protected against a subsequent second ova inhalation challenge. A single dose of ISS inhibited the Th2 response to the first inhalation of ova antigen, as well as 4 weeks later to the second inhalation of ova. However, ISS did not inhibit a Th2 response to the second inhalation of ova 8 weeks later. The reversible inhibition of Th2 responses at 8 weeks suggests the need for repeated ISS administration at monthly intervals.

Oligodeoxynucleotides containing CpG motifs induce low levels of TNF-alpha in human B lymphocytes: possible adjuvants for Th1 responses

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) represent potential adjuvants for specific immunotherapy of type I allergies because they foster Th1-like immune responses. However, previous work has shown that CpG-ODN induce systemically active levels of TNF-alpha in murine macrophages. The goal of the present study was to evaluate the release of TNF-alpha in human cells by a CpG-ODN proven to induce Th1 immune responses in cells from atopic individuals and in mice. CpG-ODN induced TNF-alpha in cells from atopic and healthy individuals. However, the amounts were low, as determined by comparison with commonly used Ags. Intracellular cytokine staining of PBMC revealed that CpG-ODN-induced TNF-alpha derived exclusively from B lymphocytes. TNF-alpha contributed to the CpG-ODN-augmented proliferation and Ig synthesis in PBMC, but was not involved in IFN-gamma synthesis. In conclusion, our findings indicate that certain CpG-ODN induce low amounts of TNF-alpha in human B lymphocytes and may therefore be used to modulate Th2-biased immune responses in allergic patients.

CpG oligodeoxynucleotide vaccination suppresses IgE induction but may fail to down-regulate ongoing IgE responses in mice

Antigen-specific IgE plays an important role in the pathogenesis of allergic disorders. Immunostimulatory CpG motifs (CpG) in bacterial DNA or synthesized oligodeoxynucleotides (ODN) are gaining recognition as potential immunomodulators for switching on protectiveT(h)1-mediated immunity and preventing or potentially inhibiting T(h)2-dependent allergic responses. To date, allergic models used in CpG ODN studies have been established by immunization of mice with allergen in the presence of adjuvant. This, in addition to failure to assess specific IgE production in most of the studies, has limited understanding of the role of CpG ODN vaccination in allergic responses. Here, we examine the effects of synthesized CpG ODN on both developing and ongoing IgE responses in mice sensitized using a recombinant mosquito salivary antigen (rAed a 2) without adjuvant. Pretreatment of mice with CpG ODN mixed with rAed a 2 successfully inhibited subsequent induction of serum rAed a 2-specific IgE (but not IgG1) and antigen-induced IL-4 and IL-5 production in spleen cells. This was associated with an increase of serum IgG2a and IL-12, and increased IFN-gamma and IL-12 production by spleen cells. In this model, however, co-administration of CpG ODN with rAed a 2 to presensitized mice failed to down-regulate ongoing IgE responses despite significant up-regulation of serum IL-12 and specific IgG2a. Strikingly, a transient skin delayed-type hypersensitivity reaction occurred in CpG ODN-treated mice. These observations provide a new insight into the potential therapeutic application of CpG ODN to allergic disorders.

Immunotherapy of asthma and allergic diseases

The goals of therapy for allergic disease and asthma, which have increased dramatically during the past 2 decades, are to relieve and prevent symptoms. Currently, allergen immunotherapy is the only available treatment that can reduce symptoms, alter the natural course of disease, and induce long-term clinical remission effectively and safely in patients with allergic rhinitis, asthma, and insect venom anaphylaxis. Allergen immunotherapy may even prevent the evolution towards polysensitization and prevent the development of asthma in allergic children. In the long run, it is more cost-effective than pharmacotherapy and environmental control measures alone. Future developments, such as using alternate routes of administration, peptide fragments of allergen, adjuvants, and DNA vaccines, may improve its efficiency in inducing long-term clinical relief of symptoms.

CpG oligodeoxynucleotides can reverse Th2-associated allergic airway responses and alter the B7.1/B7.2 expression in a murine model of asthma

CpG oligodeoxynucleotides (CpG-ODN) administered during Ag sensitization or before Ag challenge can inhibit allergic pulmonary inflammation and airway hyperreactivity in murine models of asthma. In this study, we investigated whether CpG-ODN can reverse an ongoing allergic pulmonary reaction in a mouse model of asthma. AKR mice were sensitized with conalbumin followed by two intratracheal challenges at weekly intervals. CpG-ODN was administered 24 h after the first Ag challenge. CpG-ODN administration reduced Ag-specific IgE levels, bronchoalveolar lavage fluid eosinophils, mucus production, and airway hyperreactivity. We found that postchallenge CpG-ODN treatment significantly increased IFN-gamma concentrations and decreased IL-13, IL-4, and IL-5 concentrations in bronchoalveolar lavage fluids and spleen cell culture supernatants. Postchallenge CpG-ODN treatment also increased B7.1 mRNA expression and decreased B7.2 mRNA expression in lung tissues. These results suggest that CpG-ODN may have potential for treatment of allergic asthma by suppressing Th2 responses during IgE-dependent allergic airway reactions. The down-regulation of Th2 responses by CPG-ODN may be associated with regulation of the costimulatory factors B7.1 and B7.2.

Exposure to endotoxin or other bacterial components might protect against the development of atopy

BACKGROUND

Several recent studies have shown that growing up on a farm confers significant protection against the development of atopy. These findings point particularly towards the importance of exposure to stable dust and farm animals. It has furthermore been reported that endotoxin, an intrinsic part of the outer membrane of gram negative bacteria, is abundant in environments where livestock and poultry is kept. The aim of this study was therefore to measure the level of environmental endotoxin exposure in homes of farmers' children, children with regular contact to livestock and control children with no contact to farm animals.

METHODS

Eighty-four farming and nonfarming families were identified in rural areas in Southern Germany and Switzerland. Samples of settled and airborne dust were collected in stables, and of settled dust indoors from kitchen floors and the children's mattresses. Endotoxin concentrations were determined by a kinetic Limulus assay.

RESULTS

Endotoxin concentrations were highest in stables of farming families, but were also significantly higher indoors in dust from kitchen floors (143 EU/mg vs 39 EU/mg, P < 0.001) and children's mattresses (49479 EU/m2 vs 9383 EU/m2, P < 0.001) as compared to control children from nonfarming families. In addition, endotoxin levels were also significantly higher in mattresses and dust from kitchen floors in households where children had regular contact to farm animals (38.6 EU/mg and 23340 EU/m2, respectively) as compared to control subjects.

CONCLUSION

We propose that the level of environmental exposure to endotoxin and other bacterial wall components is an important protective determinant for the development of atopic diseases in childhood.

Conjugation of immunostimulatory DNA to the short ragweed allergen amb a 1 enhances its immunogenicity and reduces its allergenicity

BACKGROUND

Allergen immunotherapy is inconvenient and associated with the risk of anaphylaxis. Efforts to improve the safety of immunotherapy by means of chemical modification of allergens have not been successful because it greatly reduced their antigenicity. Recently, immunostimulatory DNA sequences (ISS or CpG motifs) have been shown to act as strong T(H)1 response-inducing adjuvants.

OBJECTIVE

We sought to determine whether conjugation of ISS to the major short ragweed allergen Amb a 1 results in enhanced immunotherapeutic potential in mice and decreased allergenicity in human subjects.

METHODS

A 22-mer ISS oligodeoxynucleotide (ISS-ODN) was coupled to Amb a 1 and used for immunization of mice, rabbits, and monkeys.

RESULTS

In mice the Amb a 1-ISS conjugate induced a T(H)1 response (IFN-gamma secretion), whereas Amb a 1 induced a T(H)2 response (IL-5 secretion). The T(H)1 response was not observed with an Amb a 1-non-ISS conjugate. Coinjection of Amb a 1 with ISS-ODN was much less effective in inducing a T(H)1 response. In mice primed for a T(H)2 response, injection with Amb a 1-ISS conjugate induced a de novo T(H)1 response and suppressed IgE antibody formation after challenge with Amb a 1. Amb a 1-ISS conjugate induced high-titer anti-Amb a 1 IgG antibodies in rabbits and cynomolgus monkeys, whereas Amb a 1 alone or Amb a 1 coinjected with ISS-ODN did not induce a detectable response. Amb a 1-ISS conjugate was less allergenic than Amb a 1 alone, as shown by a 30-fold lower histamine release from human basophils of patients with ragweed allergy, whereas mixing ISS-ODN with Amb a 1 did not reduce histamine release.

CONCLUSION

Amb a 1-ISS conjugate has an enhanced T(H)1-biased immunogenicity and reduced allergenicity. It may offer a more effective and safer approach for allergen immunotherapy than currently available methods.