Oral immunotherapy with omalizumab reverses the Th2 cell-like programme of regulatory T cells and restores their function.

BACKGROUND: Oral immunotherapy (OIT) successfully desensitizes patients with food allergies, but the immune mechanisms mediating its efficacy remain obscure. OBJECTIVES: We tested the hypothesis that allergen-specific regulatory T (Treg) cell function is impaired in food allergy and is restored by anti-IgE antibody (omalizumab)-supplemented OIT. METHODS: Peanut-specific T effector (Teff) and Treg cell proliferative responses, activation markers and cytokine expression were analysed by flow cytometry in 13 peanut-allergic subjects before the start of omalizumab-supplemented OIT and periodically in some subjects thereafter for up to 2 years. Peripheral blood regulatory T cells (Treg cells) were analysed for their peanut-specific suppressor function before and at 1 year following OIT. This study was registered on ClinicalTrials.gov (NCT01290913). RESULTS: Proliferation of allergen-specific Teff and Treg cells precipitously declined following the initiation of omalizumab therapy prior to OIT, followed by partial recovery after the initiation of OIT. At baseline, peanut-specific Treg cells exhibited a Th2 cell-like phenotype, characterized by increased IL-4 expression, which progressively reversed upon OIT. Peanut-specific Treg cell suppressor activity was absent at the start of omalizumab/OIT therapy but became robust following OIT. Absent peanut-specific Treg cell function could also be recovered by the acute blockade of IL-4/IL-4R receptor signalling in Treg cells, which inhibited their IL-4 production. CONCLUSIONS AND CLINICAL RELEVANCE: OIT supplemented by omalizumab promotes allergen desensitization through an initial omalizumab-dependent step that acutely depletes allergen-reactive T cells, followed by an increase in allergen-specific Treg cell activity due to the reversal of their Th2 cell-like programme. Improved Treg cell function may be a key mechanism by which OIT ameliorates food allergy.

TIM-4, expressed by medullary macrophages, regulates respiratory tolerance by mediating phagocytosis of antigen-specific T cells.

Respiratory exposure to antigen induces T cell tolerance via several overlapping mechanisms that limit the immune response. While the mechanisms involved in the development of Treg cells have received much attention, those that result in T cell deletion are largely unknown. Herein, we show that F4/80(+) lymph node medullary macrophages expressing TIM-4, a phosphatidylserine receptor, remove antigen-specific T cells during respiratory tolerance, thereby reducing secondary T cell responses. Blockade of TIM-4 inhibited the phagocytosis of antigen-specific T cells by TIM-4 expressing lymph node medullary macrophages, resulting in an increase in the number of antigen-specific T cells and the abrogation of respiratory tolerance. Moreover, specific depletion of medullary macrophages inhibited the induction of respiratory tolerance, highlighting the key role of TIM-4 and medullary macrophages in tolerance. Therefore, TIM-4-mediated clearance of antigen specific T cells represents an important previously unrecognized mechanism regulating respiratory tolerance.

Changes in antigen-specific T-cell number and function during oral desensitization in cow's milk allergy enabled with omalizumab.

Food allergy is a major public health problem, for which there is no effective treatment. We examined the immunological changes that occurred in a group of children with significant cow's milk allergy undergoing a novel and rapid high-dose oral desensitization protocol enabled by treatment with omalizumab (anti-immunoglobulin (Ig)E monoclonal antibodies). Within a week of treatment, the CD4(+) T-cell response to milk was nearly eliminated, suggesting anergy in, or deletion of, milk-specific CD4(+) T cells. Over the following 3 months while the subjects remained on high doses of daily oral milk, the CD4(+) T-cell response returned, characterized by a shift from interleukin-4 to interferon-γ production. Desensitization was also associated with reduction in milk-specific IgE and a 15-fold increase in milk-specific IgG4. These studies suggest that high-dose oral allergen desensitization may be associated with deletion of allergen-specific T cells, without the apparent development of allergen-specific Foxp3(+) regulatory T cells.

99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: microbes, apoptosis and TIM-1 in the development of asthma.

Asthma is a complex disorder which has increased dramatically in prevalence over the past three decades. Current therapies, based on the T helper type 2 (Th2) paradigm, have not been able to control this disease. Epidemiological studies have demonstrated an association between infection with the hepatitis A virus (HAV) and protection against the development of asthma, and genetic studies have shown that the HAV receptor, TIM-1 (T cell, immunoglobulin domain and mucin domain), is an important atopy susceptibility gene. Furthermore, recent studies indicate that TIM-1 is a receptor for phosphatidylserine, an important marker of apoptotic cells. These studies together suggest that HAV and TIM-1 may potently regulate asthma through novel non-Th2-mediated mechanisms. Further study of the immunobiology of TIM-1 and its involvement in the clearance of apoptotic cells is likely to provide important insight into the mechanisms that lead to, and those that protect against, asthma, and how infection affects immunity and the development of asthma.

PD-L1 and PD-L2 modulate airway inflammation and iNKT-cell-dependent airway hyperreactivity in opposing directions.

Interactions of the inhibitory receptor programmed death-1 (PD-1) with its ligands, programmed death ligand (PD-L)1 and PD-L2, regulate T-cell activation and tolerance. In this study, we investigated the role of PD-L1 and PD-L2 in regulating invariant natural killer T (iNKT)-cell-mediated airway hyperreactivity (AHR) in a murine model of asthma. We found that the severity of AHR and airway inflammation is significantly greater in PD-L2(-/-) mice compared with wild-type mice after either ovalbumin (OVA) sensitization and challenge or administration of alpha-galactosylceramide (alpha-GalCer). iNKT cells from PD-L2(-/-) mice produced significantly more interleukin (IL)-4 than iNKT cells from control mice. Moreover, blockade of PD-L2 interactions of wild-type iNKT cells in vitro with monoclonal antibodies (mAbs) resulted in significantly enhanced levels of IL-4 production. In contrast, PD-L1(-/-) mice showed significantly reduced AHR and enhanced production of interferon-gamma (IFN-gamma) by iNKT cells. iNKT-deficient Jalpha18(-/-) mice reconstituted with iNKT cells from PD-L2(-/-) mice developed high levels of AHR, whereas mice reconstituted with iNKT cells from PD-L1(-/-) mice developed lower levels of AHR compared with control. As PD-L2 is not expressed on iNKT cells but rather is expressed on lung dendritic cells (DCs), in which its expression is upregulated by allergen challenge or IL-4, these findings suggest an important role of PD-L2 on lung DCs in modulating asthma pathogenesis. These studies also indicate that PD-L1 and PD-L2 have important but opposing roles in the regulation of AHR and iNKT-cell-mediated activation.

Natural killer T cells and the regulation of asthma.

A crucial role has been suggested for invariant natural killer T cells (iNKT) in regulating the development of asthma, a complex and heterogeneous disease characterized by airway inflammation and airway hyperreactivity (AHR). iNKT cells constitute a unique subset of T cells responding to endogenous and exogenous lipid antigens, rapidly secreting a large amount of cytokines, which amplify both innate and adaptive immunity. Herein, we review recent studies showing a requirement for iNKT cells in various models of asthma in mice and monkeys as well as studies in human patients. Surprisingly, in several different murine models of asthma, distinct subsets of iNKT cells were required, suggesting that iNKT cells serve as a common critical pathogenic element for many different forms of asthma. The importance of iNKT cells in both allergic and non-allergic forms of asthma, which are independent of adaptive immunity and associated with airway neutrophils, may explain situations previously found to be incompatible with the Th2 paradigm of asthma.

TIM gene family and their role in atopic diseases.

The TIM gene family was discovered seven years ago by positional cloning in a mouse model of asthma and allergy. Three of the family members (TIM-1, TIM-3, and TIM-4) are conserved between mouse and man, and have been shown to critically regulate adaptive immunity. In addition, TIM-1 has been shown to play a major role as a human susceptibility gene for asthma, allergy and autoimmunity. Recently, TIM-4 has been identified as a ligand of phosphatidylserine and to control the uptake of apoptotic cells. These studies together suggest that the TIM gene family evolved to regulate immune responses by managing survival and cell death of hematopoetic cells.

iNKT cells in allergic disease.

Recent studies indicate that invariant TCR+ CD1d-restricted natural killer T (iNKT) cells play an important role in regulating the development of asthma and allergy. iNKT cells can function to skew adaptive immunity toward Th2 responses, or can act directly as effector cells at mucosal surfaces in diseases such as ulcerative colitis and bronchial asthma. In mouse models of asthma, NKT cell-deficient strains fail to develop allergen-induced airway hyperreactivity (AHR), a cardinal feature of asthma, and NKT cells are found in the lungs of patients with chronic asthma, suggesting a critical role for NKT cells in the development of AHR. However, much work remains in characterizing iNKT cells and their function in asthma, and in understanding the relationship between the iNKT cells and conventional CD4+ T cells.

Allergen immunotherapy with heat-killed Listeria monocytogenes alleviates peanut and food-induced anaphylaxis in dogs.

BACKGROUND: Heat-killed Listeria monocytogenes (HKL) potently stimulates interferon (IFN)-gamma production in CD4 T-lymphocytes, and when used as adjuvant for immunotherapy, reduces immunoglobulin (Ig)E production and reverses established allergen-induced airway hyperreactivity (AHR) in a murine model of asthma. We asked if such treatment could decrease established peanut-induced anaphylaxis or cow's milk-induced food allergy in highly food-allergic dogs. METHODS: We therefore studied four 4-year-old atopic colony dogs extremely allergic to peanut (Group I), as well as five 7-year-old dogs very allergic to wheat, milk and other foods (Group II). All dogs experienced marked allergic symptoms, including vomiting and diarrhea on oral challenge with the relevant foods. The dogs were then vaccinated once subcutaneously with peanut or milk and wheat with HKL emulsified in incomplete Freund's adjuvant. RESULTS: Following vaccination of the allergic dogs with HKL and allergen, oral challenges with peanut (Group I) or milk (Group II) elicited only minor or no symptoms. In addition, skin test end-point titrations showed marked reductions for >10 weeks after treatment, and levels of Ara h 1-specific IgE in serum of peanut sensitive dogs, as demonstrated by immunoblotting, were greatly reduced by treatment with HKL plus peanut allergen. CONCLUSIONS: Thus, HKL plus allergen treatment markedly improved established food allergic responses in dogs, suggesting that such an immunotherapy strategy in humans might greatly improve individuals with food allergy and anaphylaxis.

Identification of Tapr (an airway hyperreactivity regulatory locus) and the linked Tim gene family.

To simplify the analysis of asthma susceptibility genes located at human chromosome 5q23-35, we examined congenic mice that differed at the homologous chromosomal segment. We identified a Mendelian trait encoded by T cell and Airway Phenotype Regulator (Tapr). Tapr is genetically distinct from known cytokine genes and controls the development of airway hyperreactivity and T cell production of interleukin 4 (IL-4) and IL-13. Positional cloning identified a gene family that encodes T cell membrane proteins (TIMs); major sequence variants of this gene family (Tim) completely cosegregated with Tapr. The human homolog of TIM-1 is the hepatitis A virus (HAV) receptor, which may explain the inverse relationship between HAV infection and the development of atopy.

Critical role for IL-13 in the development of allergen-induced airway hyperreactivity.

Airway hyperresponsiveness to a variety of specific and nonspecific stimuli is a cardinal feature of asthma, which affects nearly 10% of the population in industrialized countries. Eosinophilic pulmonary inflammation, eosinophil-derived products, as well as Th2 cytokines IL-13, IL-4, and IL-5, have been associated with the development of airway hyperreactivity (AHR), but the specific immunological basis underlying the development of AHR remains controversial. Herein we show that mice with targeted deletion of IL-13 failed to develop allergen-induced AHR, despite the presence of vigorous Th2-biased, eosinophilic pulmonary inflammation. However, AHR was restored in IL-13(-/-) mice by the administration of recombinant IL-13. Moreover, adoptive transfer of OVA-specific Th2 cells generated from TCR-transgenic IL-13(-/-) mice failed to induce AHR in recipient SCID mice, although such IL-13(-/-) Th2 cells produced high levels of IL-4 and IL-5 and induced significant airway inflammation. These studies definitively demonstrate that IL-13 is necessary and sufficient for the induction of AHR and that eosinophilic airway inflammation in the absence of IL-13 is inadequate for the induction of AHR. Therefore, treatment of human asthma with antagonists of IL-13 may be very effective.

Pulmonary dendritic cells producing IL-10 mediate tolerance induced by respiratory exposure to antigen.

Respiratory exposure to allergen induces T cell tolerance and protection against the development of airway hyperreactivity and asthma. However, the specific mechanisms by which tolerance is induced by respiratory allergen are not clear. We report here that pulmonary dendritic cells (DCs) from mice exposed to respiratory antigen transiently produced interleukin 10 (IL-10). These phenotypically mature pulmonary DCs, which were B-7(hi) as well as producing IL-10, stimulated the development of CD4(+) T regulatory 1--like cells that also produced high amounts of IL-10. In addition, adoptive transfer of pulmonary DCs from IL-10(+/+), but not IL-10(-/-), mice exposed to respiratory antigen induced antigen-specific unresponsiveness in recipient mice. These studies show that IL-10 production by DCs is critical for the induction of tolerance, and that phenotypically mature pulmonary DCs mediate tolerance induced by respiratory exposure to antigen.

Il-18 gene transfer by adenovirus prevents the development of and reverses established allergen-induced airway hyperreactivity.

We examined the role of IL-18 in preventing the development of and in reversing established allergen-induced airway inflammation and airway hyperreactivity (AHR), the cardinal features of asthma. IL-18, which potently induces IFN-gamma, was administered into the respiratory tract as cDNA in a replication-deficient adenovirus (Adv). Treatment of OVA-sensitized mice with the IL-18-expressing Adv reduced allergen-specific IL-4 production, airway eosinophilia, and mucus production, increased IFN-gamma production, and prevented the development of AHR. The effects of the IL-18 Adv treatment were dependent on the presence of IFN-gamma and IL-12. Moreover, administration of the IL-18 Adv to mice with established AHR greatly reduced AHR and IL-4 production and increased IFN-gamma production. These results demonstrate that IL-18, when administered by Adv into the respiratory tract, effectively reduces AHR and replaces an established Th2-biased immune response with a Th1-biased response.

Human alveolar macrophages induce functional inactivation in antigen-specific CD4 T cells.

BACKGROUND: Alveolar macrophages (AMCs) are the most abundant phagocytic cells in the lung, but they present antigen poorly to T cells. OBJECTIVES: The objectives of our studies were to more clearly define the mechanisms by which AMCs present antigen to T cells and to determine whether AMCs actively inhibit T-cell activation. METHODS: We studied purified human CD4 T cells and compared the capacity of allogeneic AMCs and peripheral blood monocytes to induce T-cell proliferation and cytokine production. RESULTS: We previously demonstrated that human AMCs fail to upregulate expression of B7-1 and B7-2 on stimulation with IFN-gamma. We now demonstrate that AMCs actively induce T-cell unresponsiveness (functional inactivation) in an antigen-specific manner and reduce the capacity of CD4 T cells to respond on secondary stimulation. The induction of unresponsiveness was reversed by the addition of CD28 costimulation or IL-2. However, interruption of Fas/Fas ligand interactions or of B7/CTLA-4 interactions did not prevent unresponsiveness, indicating that neither CTLA-4 triggering nor Fas-induced apoptosis was involved in the induction of T-cell unresponsiveness. CONCLUSIONS: These studies indicate that AMCs actively tolerize CD4 T cells in an antigen-specific fashion. We propose that AMCs mediate a form of immune privilege in the lungs that effectively limits immune responses in the pulmonary compartment but has little effect on systemic immunity.

Vaccination with allergen-IL-18 fusion DNA protects against, and reverses established, airway hyperreactivity in a murine asthma model.

Vaccination with naked DNA encoding a specific allergen has been shown previously to prevent, but not reverse, the development of allergen-induced airway hyperresponsiveness (AHR). To enhance the effectiveness of DNA vaccine therapies and make possible the treatment of established AHR, we developed a DNA vaccination plasmid containing OVA cDNA fused to IL-18 cDNA. Vaccination of naive mice either with this fusion DNA construct or with an OVA cDNA-containing plasmid protected the mice from the subsequent induction of AHR. Protection from AHR correlated with increased IFN-gamma production and reduced OVA-specific IgE production. The protection appeared to be mediated by IFN-gamma and CD8(+) cells because treatment of mice with neutralizing anti-IFN-gamma mAb or with depleting anti-CD8 mAb abolished the protective effect. Moreover, vaccination of mice with preexisting AHR with the OVA-IL-18 fusion DNA, but not with the OVA cDNA plasmid, reversed established AHR, reduced allergen-specific IL-4, and increased allergen-specific IFN-gamma production. Thus, combining IL-18 cDNA with OVA cDNA resulted in a vaccine construct that protected against the development of AHR, and that was unique among cDNA constructs in its capacity to reverse established AHR.

Allergen immunotherapy: novel approaches in the management of allergic diseases and asthma.

Currently available pharmacotherapies for allergic diseases and asthma, which are serious public health problems, are aimed primarily at neutralizing effector molecules and inflammatory mediators such as histamine and leukotrienes or at inhibiting the function of inflammatory cells such as eosinophils and Th2 lymphocytes. While this approach is effective in controlling symptoms, these therapies have a limited capacity to alter the natural course of allergic diseases and asthma, and discontinuation of medications results in the redevelopment of symptoms on reexposure to the offending allergens. In contrast, immune-based allergen immunotherapies modify and correct the underlying pathological immune responses in allergy and asthma in an antigen-specific manner. These immunotherapies replicate the regulatory processes that occur in nonallergic individuals and allow patients to tolerate exposure to allergens. Current and future methodologies for immunotherapy involve immunization with allergen, modified allergen, peptides of allergen, cDNA of allergen, with adjuvants, including immunostimulatory DNA sequences, cytokines, and bacterial products such as Listeria monocytogenes. This form of therapy can provide a long-lasting cure for allergic diseases without the need for continuous therapeutic intervention and without causing generalized immunosuppression or immune augmentation.

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.

Allergen-induced airway hyperreactivity is diminished in CD81-deficient mice.

We demonstrated previously that CD81(-/-) mice have an impaired Th2 response. To determine whether this impairment affected allergen-induced airway hyperreactivity (AHR), CD81(-/-) BALB/c mice and CD81(+/+) littermates were sensitized i.p. and challenged intranasally with OVA. Although wild type developed severe AHR, CD81(-/-) mice showed normal airway reactivity and reduced airway inflammation. Nevertheless, OVA-specific T cell proliferation was similar in both groups of mice. Analysis of cytokines secreted by the responding CD81(-/-) T cells, particularly those derived from peribronchial draining lymph nodes, revealed a dramatic reduction in IL-4, IL-5, and IL-13 synthesis. The decrease in cytokine production was not due to an intrinsic T cell deficiency because naive CD81(-/-) T cells responded to polyclonal Th1 and Th2 stimulation with normal proliferation and cytokine production. Moreover, there was an increase in T cells and a decrease in B cells in peribronchial lymph nodes and in spleens of immunized CD81(-/-) mice compared with wild-type animals. Interestingly, OVA-specific Ig levels, including IgE, were similar in CD81(-/-) and CD81(+/+) mice. Thus, CD81 plays a role in the development of AHR not by influencing Ag-specific IgE production but by regulating local cytokine production.

Respiratory infection with influenza A virus interferes with the induction of tolerance to aeroallergens.

Viral respiratory infections have been implicated in influencing allergen sensitization and the development of asthma, but their exact role remains controversial. Because respiratory exposure to Ag normally engenders T cell tolerance and prevents the development of airway hyperreactivity (AHR) and inflammation, we examined the effects of influenza A virus infection on tolerance induced by exposure to intranasal (i.n.) OVA and the subsequent development of AHR. We found that concurrent infection with influenza A abrogated tolerance induced by exposure to i.n. OVA, and instead led to the development of AHR accompanied by the production of OVA-specific IgE, IL-4, IL-5, IL-13, and IFN-gamma. When both IL-4 and IL-5 were neutralized in this system, AHR was still induced, suggesting that influenza-induced cytokines such as IL-13, or mechanisms unrelated to cytokines, might be responsible for the development of AHR. The length of time between influenza A infection and i.n. exposure to OVA was crucial, because mice exposed to i.n. OVA 15-30 days after viral inoculation developed neither AHR nor OVA-specific tolerance. These mice instead acquired Th1-biased OVA-specific immune responses associated with vigorous OVA-induced T cell proliferation, and reduced production of OVA-specific IgE. The protective effect of influenza A on AHR was dependent on IFN-gamma, because protection was abrogated with a neutralizing anti-IFN-gamma mAb. These results suggest that viral respiratory infection interferes with the development of respiratory allergen-induced tolerance, and that the time interval between viral infection and allergen exposure is critical in determining whether viral infection will enhance, or protect against, the development of respiratory allergen sensitization and AHR.

Mechanisms preventing allergen-induced airways hyperreactivity: role of tolerance and immune deviation.

BACKGROUND: Aeroallergens continuously enter the respiratory tract of atopic individuals and provoke the development of asthma characterized by airway hyperreactivity (AHR) and inflammation. By contrast, nonatopic individuals are exposed to the same aeroallergens, but airway inflammation does not develop. However, the mechanisms that prevent allergen-induced respiratory diseases in nonatopic subjects are poorly characterized. OBJECTIVE: In this study we compared the role of allergen-specific T-cell tolerance and immune deviation in conferring protection against the development of allergen-induced AHR. METHODS: We exposed mice to intranasal ovalbumin (OVA) to induce T-cell tolerance and examined its effects on the subsequent development of AHR and inflammation. RESULTS: We demonstrated that exposure of mice to intranasal OVA resulted in peripheral CD4(+) T-cell unresponsiveness that very efficiently prevented not only the development of AHR but also greatly inhibited airway inflammation and OVA-specific IgE production. The induction of peripheral T-cell tolerance and protection against AHR were not dependent on the presence of IFN-gamma or IL-4. The development of AHR was also prevented by an OVA-specific T(H)1-biased immune response induced by inhalation of OVA in the presence of IL-12. However, the OVA-specific T(H)1 response was associated with a significant degree of pulmonary inflammation. CONCLUSION: These results indicate that both allergen-specific T-cell tolerance and T(H)1-biased immune deviation prevent the development of AHR, but T(H)1 responses are associated with significantly greater inflammation in the lung than is associated with T-cell unresponsiveness. Therefore CD4(+) T-cell unresponsiveness critically regulates immune responses to aeroallergens and protects against the development of allergic disease and asthma.