Cell-based therapy in allergy

Past, present, and future of allergen immunotherapy vaccines

Allergen-specific immunotherapy (AIT) is an allergen-specific form of treatment for patients suffering from immunoglobulin E (IgE)-associated allergy; the most common and important immunologically mediated hypersensitivity disease. AIT is based on the administration of the disease-causing allergen with the goal to induce a protective immunity consisting of allergen-specific blocking IgG antibodies and alterations of the cellular immune response so that the patient can tolerate allergen contact. Major advantages of AIT over all other existing treatments for allergy are that AIT induces a long-lasting protection and prevents the progression of disease to severe manifestations. AIT is cost effective because it uses the patient´s own immune system for protection and potentially can be used as a preventive treatment. However, broad application of AIT is limited by mainly technical issues such as the quality of allergen preparations and the risk of inducing side effects which results in extremely cumbersome treatment schedules reducing patient´s compliance. In this article we review progress in AIT made from its beginning and provide an overview of the state of the art, the needs for further development, and possible technical solutions available through molecular allergology. Finally, we consider visions for AIT development towards prophylactic application.

Frontline Science: TLR3 activation inhibits food allergy in mice by inducing IFN-γ+ Foxp3+ regulatory T cells

The pathologic feature of food allergy (FA) is the aberrant Th2-biased immune response in the intestine. Regulatory T cells (Tregs) play an important role in the suppression of aberrant immune response. The activities of the TLRs regulate multiple cell functions. This study aims to investigate the role of TLR3 activation in the regulation of Th2-biased immune response in the intestine by the generation of inducible Tregs (iTregs). In this study, polyinosinic polycytidylic acid (polyI:C) was used as an activator of TLR3. An FA mouse model was developed to establish the Th2-biased inflammation in the intestine. The effects of TLR3 activation on the generation of iTreg were tested in the culture and in mice. We observed that exposure to polyI:C induced IFN-γ⁺ Foxp3⁺ iTregs in mouse intestine and in the culture. The IFN-γ⁺ Foxp3⁺ iTregs showed immune suppressive functions. Exposure to polyI:C increased T-bet levels in CD4⁺ T cells. The T-bet formed a complex with GATA3 to dissociate Foxp3 from GATA3/Foxp3 complex in CD4⁺ T cells. The Foxp3 thus gained the opportunity to move to TGF-β promoter to generate iTregs. Administration with polyI:C prevented the development of FA and inhibited existing FA. In conclusion, activation of TLR3 induces IFN-γ⁺ Foxp3⁺ Tregs, which can prevent FA development and inhibit existing FA in mice.

Newly identified T cell subsets in mechanistic studies of food immunotherapy

Allergen-specific immunotherapy has shown promise for the treatment of food allergy and is currently being evaluated in clinical trials. Although immunotherapy can induce desensitization, the mechanisms underlying this process are not completely understood. Recent advances in high-throughput technologies along with concomitant advances in data analytics have enabled monitoring of cells at the single-cell level and increased the research focus on upstream cellular factors involved in the efficacy of immunotherapy, particularly the role of T cells. As our appreciation of different T cell subsets and their plasticity increases, the initial simplistic view that restoring Th1/Th2 balance by decreasing Th2 or increasing Th1 responses can ameliorate food allergy is being enhanced by a more complex model involving other T cell subsets, particularly Tregs. In this Review, we focus on the current understanding of T cell functions in food allergy, tolerance, and immunotherapy.

Next-Generation of Allergen-Specific Immunotherapies: Molecular Approaches

PURPOSE OF REVIEW

The aim of this article is to discuss how allergen-specific immunotherapy (AIT) can be improved through molecular approaches. We provide a summary of next-generation molecular AIT approaches and of their clinical evaluation. Furthermore, we discuss the potential of next generation molecular AIT forms for the treatment of severe manifestations of allergy and mention possible future molecular strategies for the secondary and primary prevention of allergy.

RECENT FINDINGS

AIT has important advantages over symptomatic forms of allergy treatment but its further development is limited by the quality of the therapeutic antigen preparations which are derived from natural allergen sources. The field of allergy diagnosis is currently undergoing a dramatic improvement through the use of molecular testing with defined, mainly recombinant allergens which allows high-resolution diagnosis. Several studies demonstrate that molecular testing in early childhood can predict the development of symptomatic allergy later on in life. Clinical studies indicate that molecular AIT approaches have the potential to improve therapy of allergic diseases and may be used as allergen-specific forms of secondary and eventually primary prevention for allergy.

Homogeneous expansion of human T-regulatory cells via tumor necrosis factor receptor 2

T-regulatory cells (T(regs)) are a rare lymphocyte subtype that shows promise for treating infectious disease, allergy, graft-versus-host disease, autoimmunity, and asthma. Clinical applications of T(regs) have not been fully realized because standard methods of expansion ex vivo produce heterogeneous progeny consisting of mixed populations of CD4 + T cells. Heterogeneous progeny are risky for human clinical trials and face significant regulatory hurdles. With the goal of producing homogeneous T(regs), we developed a novel expansion protocol targeting tumor necrosis factor receptors (TNFR) on T(regs). In in vitro studies, a TNFR2 agonist was found superior to standard methods in proliferating human T(regs) into a phenotypically homogeneous population consisting of 14 cell surface markers. The TNFR2 agonist-expanded T(regs) also were functionally superior in suppressing a key T(reg) target cell, cytotoxic T-lymphocytes. Targeting the TNFR2 receptor during ex vivo expansion is a new means for producing homogeneous and potent human T(regs) for clinical opportunities.

Engraftment of retrovirally transduced Bet v 1-GFP expressing bone marrow cells leads to allergen-specific tolerance

Molecular chimerism is a promising strategy to induce tolerance to disease-causing antigens expressed on genetically modified haematopoietic stem cells. The approach was employed successfully in models of autoimmunity and organ transplantation. Recently, we demonstrated that molecular chimerism induces robust and lasting tolerance towards the major grass pollen allergen Phl p 5. Since allergens are a group of antigens differing widely in their function, origin and structure we further examined the effectiveness of molecular chimerism using the Phl p 5-unrelated major birch pollen allergen Bet v 1, co-expressed with the reporter GFP. Besides, inhibition of CD26 was used to promote engraftment of modified stem cells. Retrovirus VSV-Betv1-GFP was generated to transduce 5-FU-mobilized BALB/c hematopoietic cells to express membrane-bound Bet v 1 (VSV-GFP virus was used as control). Myeloablated BALB/c mice received Betv1-GFP or GFP expressing bone marrow cells, pre-treated with a CD26 inhibitor. Chimerism was followed by flow cytometry. Tolerance was assessed by measuring allergen-specific isotype levels in sera, RBL assays and T-cell proliferation assays. Mice transplanted with transduced BMC developed multi-lineage molecular chimerism which remained stable long-term (>8 months). After repeated immunizations with Bet v 1 and Phl p 5 serum levels of Bet v 1-specific antibodies (IgE, IgG1, IgG2a, IgG3 and IgA) remained undetectable in Betv1-GFP chimeras while high levels of Phl p 5-specific antibodies developed. Likewise, basophil degranulation was induced in response to Phl p 5 but not to Bet v 1 and specific non-responsiveness to Bet v 1 was observed in proliferation assays. These data demonstrate successful tolerization towards Bet v 1 by molecular chimerism. Stable long-term chimerism was achieved under inhibition of CD26. These results provide evidence for the broad applicability of molecular chimerism as tolerance strategy in allergy.

Molecular chimerism in IgE-mediated allergy: B-and T-cell tolerance toward highly immunogenic exogenous antigens

Specific immunotherapy is the only curative treatment currently available for IgE-mediated allergy and preventive strategies are lacking altogether. We have recently reported that molecular chimerism induces durable tolerance in experimental models of allergy, thus potentially providing a new approach for the treatment and prevention of allergic diseases. Molecular chimerism is a gene-therapy approach for tolerance induction toward defined disease-causing antigens. In proof-of-concept studies, we introduced a clinically relevant grass pollen allergen into hematopoietic stem cells and transplanted those modified cells into preconditioned syngeneic mice. Long-lasting and robust tolerance toward the allergen was achieved. In our most recent studies published in Clinical and Experimental Allergy we demonstrated that milder, non-myeloablative conditioning is sufficient to induce tolerance. Our results revealed that, in contrast to other rodent models of chimerism, persistent microchimerism suffices to induce lasting tolerance at the T cell, B cell and effector cell levels in IgE-mediated allergy. This article addendum provides a summary of the recent paper and its implications.

Allergen-specific immunotherapy: from therapeutic vaccines to prophylactic approaches

Immunoglobulin E-mediated allergies affect more than 25% of the population. Allergen exposure induces a variety of symptoms in allergic patients, which include rhinitis, conjunctivitis, asthma, dermatitis, food allergy and life-threatening systemic anaphylaxis. At present, allergen-specific immunotherapy (SIT), which is based on the administration of the disease-causing allergens, is the only disease-modifying treatment for allergy. Current therapeutic allergy vaccines are still prepared from relatively poorly defined allergen extracts. However, with the availability of the structures of the most common allergen molecules, it has become possible to produce well-defined recombinant and synthetic allergy vaccines that allow specific targeting of the mechanisms of allergic disease. Here we provide a summary of the development and mechanisms of SIT, and then review new forms of therapeutic vaccines that are based on recombinant and synthetic molecules. Finally, we discuss possible allergen-specific strategies for prevention of allergic disease.

Vaccines for allergy

Vaccines aim to establish or strengthen immune responses but are also effective for the treatment of allergy. The latter is surprising because allergy represents a hyper-immune response based on immunoglobulin E production against harmless environmental antigens, i.e., allergens. Nevertheless, vaccination with allergens, termed allergen-specific immunotherapy is the only disease-modifying therapy of allergy with long-lasting effects. New forms of allergy diagnosis and allergy vaccines based on recombinant allergen-derivatives, peptides and allergen genes have emerged through molecular allergen characterization. The molecular allergy vaccines allow sophisticated targeting of the immune system and may eliminate side effects which so far have limited the use of traditional allergen extract-based vaccines. Successful clinical trials performed with the new vaccines indicate that broad allergy vaccination is on the horizon and may help to control the allergy pandemic.