Local immunological mechanisms of sublingual immunotherapy

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.

DC-targeted gold nanoparticles as an efficient and biocompatible carrier for modulating allergic responses in sublingual immunotherapy

BACKGROUND

Sublingual immunotherapy (SLIT) was introduced to deliver allergens in an effective and non-invasive route, which can be considered as an alternative for allergen-specific subcutaneous immunotherapy (SCIT). On the other hand, the use of gold nanoparticles (AuNPs) in allergen delivery has beneficial effects on sublingual immunotherapy. In addition, the molecular targeting agents like aptamers (Apt), have been widely applied for targeted drug delivery. Therefore, the current study aimed to evaluate the effects of dendritic cells (DCs)-specific Aptamer-modified AuNPs coated with ovalbumin (OVA) on the improvement of the SLIT outcome in the mouse model of allergy.

MATERIAL AND METHODS

AuNPs with approximately 15 nm diameter were prepared by citrate reduction of HAuCl4. Afterward, Apt-modified AuNP complex was prepared and OVA was then loaded onto this complex. Following sensitization of Balb/c mice to OVA, SLIT was performed with Apt-AuNPs containing 5 µg OVA twice a week for a 2-month period. Allergen-specific IgE in serum, as well as cytokines secretion of spleen cells, were analyzed using ELISA. Also, nasopharyngeal lavage Fluid (NALF) was collected for total and eosinophil counts. Moreover, the lungs were removed for histopathological examination.

RESULTS

SLIT with Apt-modified AuNPs complex containing 5 μg OVA, decreased the IgE levels compared to the other groups. Also, IL-4 production has significantly decreased in spleen cells, while TGF-β and IFN-γ have significantly increased. The assessment of NALF in the group treated by this complex showed a decrease in total cell as well as in eosinophil count. Also, the examination of lung tissues revealed that, in the group treated by this complex, inflammation and perivascular infiltration were lesser than the other groups, which were observed in only one vessel of tissue.

CONCLUSION

It was shown that, Sublingual immunotherapy with DC specific Apt-modified AuNPs containing 5 μg OVA can improve the Th1 and Treg immunomodulatory responses.

Effects of diet on skin sensitization by nickel, poison ivy, and sesquiterpene lactones

Skin contact or exposure to sensitizers often occurs as a consequence of occupational exposures (e.g. poison ivy in forestry), wearing jewelry (e.g. nickel), or use of cosmetics (e.g. fragrances). However, many of the known skin sensitizers or their chemical variants are also consumed orally through foods or other sources. Since oral exposure to antigenic substances can lead to tolerance, consumption of sensitizers may impact the development and potency of skin sensitization, especially if the sensitizer is consumed early in life, prior to the first skin contact. To address this issue, we have reviewed human clinical and epidemiological literature relevant to this subject and evaluated whether early oral exposures to relevant sensitizers, or their chemical variants, are associated with reduced prevalence of skin sensitization to three main allergic sensitizers - nickel, urushiols of poison ivy, and sesquiterpene lactones of chrysanthemum and other plants.

Oral myeloid cells uptake allergoids coupled to mannan driving Th1/Treg responses upon sublingual delivery in mice

BACKGROUND

Polymerized allergoids coupled to nonoxidized mannan (PM-allergoids) may represent novel vaccines targeting dendritic cells (DCs). PM-allergoids are better captured by DCs than native allergens and favor Th1/Treg cell responses upon subcutaneous injection. Herein we have studied in mice the in vivo immunogenicity of PM-allergoids administered sublingually in comparison with native allergens.

METHODS

Three immunization protocols (4-8 weeks long) were used in Balb/c mice. Serum antibody levels were tested by ELISA. Cell responses (proliferation, cytokines, and Tregs) were assayed by flow cytometry in spleen and lymph nodes (LNs). Allergen uptake was measured by flow cytometry in myeloid sublingual cells.

RESULTS

A quick antibody response and higher IgG2a/IgE ratio were observed with PM-allergoids. Moreover, stronger specific proliferative responses were seen in both submandibular LNs and spleen cells assayed in vitro. This was accompanied by a higher IFNγ/IL-4 ratio with a quick IL-10 production by submandibular LN cells. An increase in CD4⁺ CD25^high FOXP3⁺ Treg cells was detected in LNs and spleen of mice treated with PM-allergoids. These allergoids were better captured than native allergens by antigen-presenting (CD45⁺ MHC-II⁺ ) cells obtained from the sublingual mucosa, including DCs (CD11b⁺ ) and macrophages (CD64⁺ ). Importantly, all the differential effects induced by PM-allergoids were abolished when using oxidized instead of nonoxidized PM-allergoids.

CONCLUSION

Our results demonstrate for the first time that PM-allergoids administered through the sublingual route promote the generation of Th1 and FOXP3⁺ Treg cells in a greater extent than native allergens by mechanisms that might well involve their better uptake by oral antigen-presenting cells.

Enhanced efficacy of sublingual immunotherapy by liposome-mediated delivery of allergen

Immunotherapy by sublingual administration of allergens provides high patient compliance and has emerged as an alternative to subcutaneous immunotherapy for the treatment of IgE-associated allergic diseases. However, sublingual immunotherapy (SLIT) can cause adverse events. Development of allergen delivery systems enabling more efficient delivery and hence lower allergen load might reduce the adverse events. In the present study, we have investigated neutral and cationic liposomes as delivery systems of ovalbumin (OVA), as a model allergen, in an OVA-induced allergic airway inflammation model. We investigated the liposome carriers' ability to improve tolerance induction of antigens compared to the corresponding dose of free OVA. Mice were treated sublingually over 2 weeks with free or liposome encapsulated OVA followed by intraperitoneal injections and intranasal challenge. Mice sublingually treated with OVA-liposomes showed a significant reduction of airway eosinophilia and splenocyte proliferation in comparison to free OVA. A similar nonsignificant pattern was seen for OVA-specific IgE antibodies. In addition, reduced levels of interferon-γ and interleukin-5 were observed in spleen cell culture supernatants from OVA-liposome-treated mice compared to the sham-treated group. In conclusion, in vivo efficacy data showed that prophylactic SLIT with OVA-liposomes is significantly more effective in preventing allergic inflammation than the corresponding dose of free OVA.

Comparative phenotypic and functional analysis of migratory dendritic cell subsets from human oral mucosa and skin

Antigen exposure to oral mucosa is generally thought to lead to immune tolerance induction. However, very little is known about the subset composition and function of dendritic cells (DC) migrating from human oral mucosa. Here we show that migratory DC from healthy human gingival explants consist of the same phenotypic subsets in the same frequency distribution as DC migrating from human skin. The gingival CD1a+ Langerhans cell and interstitial DC subsets lacked CXCR4 expression in contrast to their cutaneous counterparts, pointing to different migration mechanisms, consistent with previous observations in constructed skin and gingival equivalents. Remarkably, without any exogenous conditioning, gingival explants released higher levels of inflammatory cytokines than human skin explants, resulting in higher DC migration rates and a superior ability of migrated DC to prime allogeneic T cells and to induce type-1 effector T cell differentiation. From these observations we conclude that rather than an intrinsic ability to induce T cell tolerance, DC migrating from oral mucosa may have a propensity to induce effector T cell immunity and maintain a high state of alert against possible pathogenic intruders in the steady state. These findings may have implications for oral immunization strategies.

Characterization of oral immune cells in birch pollen-allergic patients: impact of the oral allergy syndrome and sublingual allergen immunotherapy on antigen-presenting cells

BACKGROUND

A detailed characterization of human oral immune cells is needed to better understand local mechanisms associated with allergen capture following oral exposure.

METHODS

Oral immune cells were characterized by immunohistology and immunofluorescence in biopsies obtained from three healthy individuals and 23 birch pollen-allergic patients with/without oral allergy syndrome (OAS), at baseline and after 5 months of sublingual allergen immunotherapy (AIT).

RESULTS

Similar cell subsets (i.e., dendritic cells, mast cells, and T lymphocytes) were detected in oral tissues from healthy and birch pollen-allergic individuals. CD207+ Langerhans cells (LCs) and CD11c+ myeloid dendritic cells (DCs) were found in both the epithelium and the papillary layer of the Lamina propria (LP), whereas CD68+ macrophages, CD117+ mast cells, and CD4+ /CD8+ T cells were rather located in both the papillary and reticular layers of the LP. Patterns of oral immune cells were identical in patients with/without OAS, except lower numbers of CD207+ LCs found in oral tissues from patients with OAS, when compared to OAS- patients (P < 0.05). A 5-month sublingual AIT had a limited impact on oral immune cells, with only a significant increase in IgE+ cells in patients from the active group. Colocalization experiments confirmed that such IgE-expressing cells mostly encompass CD68+ macrophages located in the LP, and to a lesser extent CD207+ LCs in the epithelium.

CONCLUSION

Two cell subsets contribute to antigen/allergen uptake in human oral tissues, including (i) CD207+ LCs possibly involved in the physiopathology of OAS and (ii) CD68+ macrophages likely critical in allergen capture via IgE-facilitated mechanisms during sublingual AIT.

Tools and methods for identification and analysis of rare antigen-specific T lymphocytes

T lymphocytes are essential as effector and memory cells for immune defense against infections and as regulatory T cells in the establishment and maintenance of immune tolerance. However, they are also involved in immune pathology being effectors in autoimmune and allergic diseases or suppressors of immunity in cancer, and they often cause problems in transplantation. Therefore, strategies are being developed that allow the in vivo amplification or isolation, in vitro expansion and genetic manipulation of beneficial T cells for adoptive cell therapies or for the tolerization, or elimination of pathogenic T cells. The major goal is to make use of the exquisite antigen specificity of T cells to develop targeted strategies and to develop techniques that allow for the identification and depletion or enrichment of very often rare antigen-specific naïve as well as effector and memory T cells. Such techniques are very useful for immune monitoring of T cell responses in diagnostics and vaccination and for the development of T cell-based assays for the replacement of animal testing in immunotoxicology to identify contact allergens and drugs that cause adverse reactions.

Grass tablet sublingual immunotherapy downregulates the TH2 cytokine response followed by regulatory T-cell generation

BACKGROUND

Sublingual administration of Phleum pratense allergen immunotherapy (SLIT) tablets is a clinically efficient treatment for grass pollen-induced rhinoconjunctivitis. This immunotherapy downregulates TH2 immune responses, induces tolerogenic pathways, and increases regulatory T cells. However, associated immune response markers of allergen desensitization remain undefined.

OBJECTIVE

We sought to characterize the kinetics of individual changes in the immunologic response to grass tablet SLIT.

METHODS

We evaluated the systemic effects of SLIT in a longitudinal analysis of humoral and cellular immune parameters in peripheral blood samples.

RESULTS

Grass tablet SLIT administration induced a 2-phase systemic humoral and cellular response. The TH2 response was initially exacerbated and detected as increased allergen-specific IgE (sIgE) and IgG4 (sIgG4) levels and an increase in IL-4-producing cells, followed by downregulation of the TH2 response with a shift toward a TH1 cytokine profile. T cells with a regulatory phenotype were also elicited. Statistical correlations between immunologic measurements for each patient throughout therapy indicated that TH2 response downregulation and reduction of the immediate SLIT-induced IgE response were associated with increased allergen-specific IgG4 synthesis early in therapy. TH2 response downregulation by month 4 correlated with increased frequency of CD4(+) T cells with a regulatory phenotype by 12 months.

CONCLUSION

Changes in sIgE levels after therapy were linked to a specific IgG4 response, and production of blocking antibodies correlated with TH2 response downregulation. Reduced IL-4(+) cell frequency was linked to an increase in the frequency of CD4(+) T cells with a regulatory phenotype. Changes in sIgE levels and reduced IL-4 and blocking antibody levels could thus be used as indicators of a patient's immune response to therapy.

Efficacy of sublingual vectorized recombinant Bet v 1a in a mouse model of birch pollen allergic asthma

BACKGROUND

Second generation sublingual allergy vaccines based upon recombinant allergens combined with vector systems are being developed as an alternative to conventional allergen extracts. Herein, we evaluated the efficacy of a recombinant form of the major allergen Bet v 1a (rBet v 1a) formulated as a mucoadhesive particle in a preclinical model of birch pollen (BP) respiratory allergy.

MATERIALS AND METHODS

BALB/c mice were sensitized to BP extracts by intraperitoneal injections followed by aerosol exposures. Sensitized mice underwent sublingual immunotherapy (SLIT) twice a week for eight weeks with either a BP extract or rBet v 1a formulated in amylopectin-based microparticles (MPA). SLIT efficacy was assessed using whole body plethysmography, lung histology and cell counts in broncho-alveolar lavages (BAL) as read outs. BP and/or rBet v 1a-specific T cell and antibody responses were monitored in lung and serum, respectively. IgA levels were measured in saliva.

RESULTS

Mice sensitized to BP exhibit chronic airway hyperresponsiveness (AHR), lung inflammation (documented by compliance and resistance measurements), eosinophil infiltrates in BAL, as well as Bet v 1-specific Th2 biased responses. Both SLIT with soluble rBet v 1a (50μg/dose) and BP extract (equivalent to 50μg rBet v 1 per dose) lead to a significant reduction in AHR, lung eosinophilia and Th2 responses. A sub-optimal dose of 5μg of rBet v 1a displays a similar level of efficacy with a significant decrease of Th2 responses when formulated with MPA microparticles. In addition, allergen vectorization with mucoadhesive particles allows a faster reduction in AHR in sensitized animals.

CONCLUSION

We demonstrate in a murine model of chronic BP respiratory allergy the efficacy of SLIT with vectorized rBet v 1a. Thus, combining recombinant allergens with mucoadhesive vector systems paves the ground for improved second generation sublingual allergy vaccines.

Comparing subcutaneous and sublingual ımmunotherapy: what do we know?

PURPOSE OF REVIEW

Although allergen-specific sublingual (SLIT) and subcutaneous immunotherapy (SCIT) have been demonstrated to be clinically effective with similar immunological responses, head-to-head studies comparing those two modes of allergen administration in terms of onset of clinical improvement along with simultaneous immunological responses and underlying mechanisms of preventive effect are scarce. The present review will update current data on this issue.

RECENT FINDINGS

Compared with SLIT, SCIT provides a rapid onset of clinical improvement by eliciting a simultaneous surge in production of T helper 1 (Th1) and T regulatory cell (Treg) cytokines and blocking antibodies. Similar immunological and clinical responses are evoked quite later, with no effect on Immunoglobulin G (IgG)4 levels during SLIT. Increases in TGFβ secretion due to nonrelevant allergens during SLIT may explain the preventive effect on new sensitizations.

SUMMARY

SLIT and SCIT are both clinically effective in the treatment of respiratory allergic diseases with slight differences in the early phase in terms of onset of clinical efficacy and simultaneous immunological responses. Both SLIT and SCIT induce similar T-cell responses in time, but specific IgG4-blocking antibody responses are more prevalent following SCIT. Further head-to-head studies addressing the preventive effect of monotherapy and the efficacy and immunological responses of nonrelated multiallergen immunotherapy in polysensitized patients are warranted.

[Clinical symptoms and diagnostic workup of allergic reactions on the oral mucosa]

Contact allergies at the oral mucosa are associated with diverse symptoms. In this article we focus on the contact allergy of delayed type. Oral mucosa changes including stomatitis or lichenoid inflammation can give first evidence for such a contact allergy. Subjective symptoms including pain, burning or dryness of the oral mucosa can be associated with a contact allergy but may also occur in other diseases which need to be excluded. The first step in the diagnosis of a contact allergy is the complete examination of the oral mucosa. Additionally, a careful history of the patient's oral care products, drugs and dental materials is important. If mucosal changes are present, a patch test is recommended for the diagnostic work up for contact allergy of delayed type. In case of a positive patch test reaction, a careful check for the clinical relevance is needed in order to have a clear recommendation for both patient and dentist e.g. if replacement of prosthetic materials is needed.