Oral Immunotherapy (OIT) Induces Clinical Tolerance in Peanut-Allergic Children

Targeting type 2 immunity and the future of food allergy treatment

IgE-mediated food allergy affects 6-8% of the population in the United States. Type 2 immune responses are central to the pathogenesis of food allergy, but type 2 CD4+ T cell responses have been found to be heterogeneous in food allergy suggesting a division of labor between Tfh13 and peTH2 cells in promotion of IgE class switching, modulation of intestinal barrier function, and regulation of mast cell expansion. Oral immunotherapy for the treatment of food allergy incompletely targets subsets of type 2 immunity in a transient manner, but new therapeutics targeting different levels of type 2 immunity are in current or planned trials for food allergy. These new treatments and the basis for their use are the focus of this review.

A Practical, Stepwise Approach to Peanut Oral Immunotherapy in Clinical Practice: Benefits and Risks

Food allergies are common, affecting 6–8% of the children in the United States. There is a significant burden on the quality of life of allergic children and their caregivers, due to multiple dietary, social and psychological restrictions. Peanut allergy affects approximately 2–5% of the school-age children. Despite the recommended dietary avoidance, reactions tend to occur due to unintentional exposures and the fear of accidental ingestions potentially resulting in anaphylaxis and death, which creates a lot of anxiety in peanut-allergic individuals. Peanut oral immunotherapy (POIT) has emerged as a form of active treatment and has shown high efficacy in research trials with the majority of participants achieving desensitization and protection from trace exposures. An improved quality of life has also been noted following successful POIT. The risks of POIT should be balanced against the benefits resulting from successful treatment for each individual. Rates of allergic reactions and anaphylaxis are reported to be higher in individuals pursuing therapy, but most subjects will experience mild or moderate reactions during treatment. The landscape of peanut allergy management is changing and the future offers more options for patients than were previously available. Shared decision-making, which is the process of how to choose between different available options, becomes an ongoing discussion between the clinician and the patient, which will ensure achievement of the best possible outcome for the peanut-allergic child. This is a multistep process that evaluates the benefits and risks of therapy or no therapy, as well as patient and family preferences and we review it in detail in this manuscript with the aim to provide clinicians with a practical approach.

Recent advances in immunotherapy and vaccine development for peanut allergy

Peanut allergy is a common problem and can be the cause of severe, life-threatening allergic reactions. It rarely resolves, with the majority of patients carrying the disease onto adulthood. Peanut allergy poses a significant burden on the quality of life of sufferers and their families, which results mainly from the fear of accidental peanut ingestion, but is also due to dietary and social restrictions. Current standard management involves avoidance, patient education and provision of emergency medication, for use in allergic reactions, when they occur. Efforts have been made to develop a vaccine for peanut allergy. Recent developments have also highlighted the use of immunotherapy, which has shown promise as an active form of treatment and may present a disease-modifying therapy for peanut allergy. So far, results, especially from oral immunotherapy studies, have shown good efficacy in achieving desensitization to peanut with a good safety profile. However, the capacity to induce long-term tolerance has not been demonstrated conclusively yet and larger, phase III studies are required to further investigate safety and efficacy of this intervention. Peanut immunotherapy is not currently recommended for routine clinical use or outside specialist allergy units.

Developing therapies for peanut allergy

Peanut allergy is an IgE-mediated, persisting immune disorder that is of major concern worldwide. Currently, no routine immunotherapy is available to treat this often severe and sometimes fatal food allergy. Traditional subcutaneous allergen immunotherapy with crude peanut extracts has proven not feasible due to the high risk of severe systemic side effects. The allergen-specific approaches under preclinical and clinical investigation comprise subcutaneous, oral, sublingual and epicutaneous immunotherapy with whole-peanut extracts as well as applications of hypoallergenic peanut allergens or T cell epitope peptides. Allergen-nonspecific approaches include monoclonal anti-IgE antibodies, TCM herbal formulations and Toll-like receptor 9-based immunotherapy. The potential of genetically engineered plants with reduced allergen levels is being explored as well as the beneficial influence of lactic acid bacteria and soybean isoflavones on peanut allergen-induced symptoms. Although the underlying mechanisms still need to be elucidated, several of these strategies hold great promise. It can be estimated that individual strategies or a combination thereof will result in a successful immunotherapy regime for peanut-allergic individuals within the next decade.

Peanut immunotherapy

Peanut allergy is common and can be a cause of severe, life-threatening reactions. It is rarely outgrown like other food allergies, such as egg and milk. Peanut allergy has a significant effect on the quality of life of sufferers and their families, due to dietary and social restrictions, but mainly stemming from fear of accidental peanut ingestion. The current management consists of strict avoidance, education and provision of emergency medication, but a disease- modifying therapy is needed for peanut allergy. Recent developments involve the use of immunotherapy, which has shown promise as an active form of treatment. Various routes of administration are being investigated, including subcutaneous, oral, sublingual and epicutaneous routes. Other forms of treatment, such as the use of vaccines and anti-IgE molecules, are also under investigation. So far, results from immunotherapy studies have shown good efficacy in achieving desensitisation to peanut with a good safety profile. However, the issue of long-term tolerance has not been fully addressed yet and larger, phase III studies are required to further investigate safety and efficacy. An assessment of cost/benefit ratio is also required prior to implementing this form of treatment. The use of immunotherapy for peanut allergy is not currently recommended for routine clinical use and should not be attempted outside specialist allergy units.

Can we produce true tolerance in patients with food allergy?

Immune tolerance is defined as nonresponsiveness of the adaptive immune system to antigens. Immune mechanisms preventing inappropriate immune reactivity to innocuous antigens include deletion of reactive lymphocytes and generation of regulatory T (Treg) cells. The normal response to food antigens is the generation of antigen-specific Treg cells. In patients with food allergy, the dominant immune response is a T(H)2-skewed T-cell response and the generation of food-specific IgE antibodies from B cells. It is not known whether a failure of the Treg cell response is behind this inappropriate immune response, but interventions that boost the Treg cell response, such as mucosal immunotherapy, might lead to a restoration of immune tolerance to foods. Tolerance has been notoriously difficult to restore in animal disease models, but limited data from human trials suggest that tolerance (sustained nonresponsiveness) can be re-established in a subset of patients. Furthermore, studies on the natural history of food allergy indicate that spontaneous development of tolerance to foods over time is not uncommon. The current challenge is to understand the mechanisms responsible for restoration of natural or induced tolerance so that interventions can be developed to more successfully induce tolerance in the majority of patients with food allergy.

Serological and clinical characteristics of children with peanut sensitization in an Asian community

In the past two decades, peanut allergy prevalence has increased in the West but has been perceived as having remained low in Asia. To review the clinical presentation of Asian children with peanut hypersensitivity and measure their IgE responses to major peanut allergens. We enrolled 31 children presenting with various allergies and a positive skin prick test to peanut from the Children's hospital outpatient allergy clinic in Singapore. A detailed questionnaire was completed by parents. The children's serum IgE specific to native Ara h 1, native Ara h 2, and recombinant Ara h 3 were detected using ELISA. Of the 31 patients, 19 had previously documented reactions to peanuts, while 12 had no previous clinical reaction. Most, 89.5% (17/19) of first reactions featured skin changes (urticaria, erythema, angioedema), but only 36.8% (7/19) involved skin symptoms alone. Respiratory symptoms and GI symptoms occurred in 42.1% and 26.3% of patients respectively and did not occur as the sole manifestation of reaction. The most common GI manifestation was emesis, present in 26.3% (5/19) of subjects. Two children experienced impaired consciousness with systemic, anaphylactic events. Although most sought treatment for their first peanut reaction only one patient received epinephrine. Half of our patients reported a subsequent accidental ingestion after the diagnosis of peanut allergy, with a median time from diagnosis to first accidental ingestion of 4 months and a reported increased severity of reaction in approximately half of the repeat exposures. Eighty-seven percent of children had specific IgE directed against at least one of the major peanut allergens. Among all patients, 87.1% had IgE specific to both Ara h 1 and Ara h 2 and 54.8% to rAra h 3. Asian children with peanut sensitization have clinically similar presentations and respond to the same major allergenic proteins as their Western counterparts. The perceived differences between the populations in this context do not stem from divergent clinical or immunological responses.

An update on food allergy

PURPOSE OF REVIEW

The present review serves to address food allergy, which is a common problem encountered by the general pediatrician. Between 4 and 6% of US children have an allergic reaction to at least one food, and the prevalence of some food allergies appears to be increasing.

RECENT FINDINGS

A combination of genetic influences, characteristics of food antigen processing, and timing of food introduction may influence the development of food allergy. Avoidance of highly allergenic foods beyond 4-6 months may not be effective at preventing the development of food allergy in most children, and the effect of specific early introduction of allergenic foods is being investigated. Oral immunotherapy is under investigation but may be limited in future use by several factors, including a significant rate of allergic reactions.

SUMMARY

Current management of food allergy focuses on accurate diagnosis, appropriate counseling regarding strict allergen avoidance with review of available educational resources, emergency preparedness, instruction on the use of self-injectable epinephrine, and ongoing surveillance for the possible development of tolerance.