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Monday, February 3, 2014

Peanut oral immunotherapy increases Tregs and epigenetically modifies FOXP3

The mechanisms contributing to clinical immune tolerance are largely unknown. The objective of Syed et al was to study the changes associated with clinical immune tolerance in antigen induced T cells, basophils, and antibodies in subjects undergoing oral immunotherapy (OIT) for peanut allergy (J Allergy Clin Immunol 2014; 133(2): 500-510). The induction of regulatory T (Treg) cells has been a potential mechanism of maintaining immune tolerance, with Treg deficiencies implicated in the development of allergies.  Fork head box protein 3 (Foxp3) is a transcription factor that regulates Tregs, including natural regulatory Tregs (nTregs) and induced regulatory Tregs (iTregs). Epigenetic modifications to regions within the Foxp3 locus have been associated with stable Foxp3 expression and Treg cell-suppressive function.  

The authors investigated whether antigen-induced Tregs (aiTregs) and humoral and basophil immune markers are induced by OIT in clinically immune tolerant (IT) versus non-tolerant (NT) patients after OIT.  20 participants (with 20 peanut allergic controls undergoing standard avoidance therapy) successfully completed 24 months of OIT, tolerating up to 4g of peanut protein after maintenance therapy.   After 3 months of peanut avoidance, only 7 of 20 participants were defined as IT participants; these 7 avoided peanut for an additional 3 months and only 3 of 7 remained clinically nonreactive (IT).  The peanut induced basophil response was reduced in the OIT participants with a trend of more reduction in the IT group. The IT participants had higher numbers of ai-Treg cells with greater suppressive function and with higher levels of FOXP3 hypomethalation compared with NT and control participants.  The population of ai-Tregs the authors identified during OIT had a marked increase in Foxp3 expression and associated increases in both chemotaxis toward intestinal epithelial cells and suppressive function toward antigen-induced effector T cells (Teff).  Furthermore, dendritic cells (DCs) isolated after OIT therapy significantly decreased the methylation of Foxp3 in Teff cells.

These data suggest that ai-Treg cells are a key regulatory cell type modulating the immune response during OIT and that epigenetic regulation of these T cells might contribute to the induction of such immune tolerance. Although larger phase 2 clinical trials in OIT are justified and feasible, the results may be predictive of a state of operationally defined clinical immune tolerance during peanut OIT and contribute to providing safe and effective therapy for patients with peanut allergy.

Below are some questions posed to the authors regarding their article and the authors’ responses:

Why do there seem to be mixed results about the presence of Treg in food oral immunotherapy in humans?
The gating and definition of Treg is very important. Some labs report CD4+CD25+Foxp3+ cells as Treg but Treg should best be defined by suppression assays on the functional level if there is enough blood sample. In addition, the presence of Foxp3 can indicate an activated CD4+ T cell, not necessarily a Treg and Treg don't have to have Foxp3 to be a Treg.

Is there potential for Type 2 cytokines to be immune markers in IT vs NT participants?
We have examined some Th2 markers by flow cytometry and intracellular staining with no specific trends showing a difference between IT vs NT but further studies are underway.

What if any data is available about ILC2 activation during food allergy?
We are currently examining ILC2 cells in the periphery of food allergic patients.

What could be a potential outcome if patients did not avoid peanut after OIT therapy and included it in their diets?
There are several trials around the world examining this and we will be conducting mechanistic studies to try to understand differences in desensitization vs sustained unresponsiveness long term.

Food allergy: clinical advances and updates

The prevalence of food allergy is on the rise with up to 10% of the population afflicted, though remarkable advances have occurred in understanding and managing food allergies.  In their review article, Sicherer and Sampson focus on advances and updates in epidemiology, pathogenesis, diagnosis and treatment of food allergy (J Allergy Clin Immunol 2014; 133(2): 291-307).  They explain that numerous genetic and environmental risk factors have been identified, with rectifiable risk factors such as vitamin D insufficiency, excess dietary fat, obesity, increased hygiene and timing of exposure to foods as being potential targets to address in prevention for the future.  Interesting clinical insights on route of sensitization, allergen characterization and immune response provide guidance for diagnosis and treatment. Allergen avoidance and emergency treatment remain the current management option for patients, although numerous clinical trials are underway for more definitive therapies.

 A major change in approach to management stems from the observation that many children with milk or egg allergy tolerate heat denatured forms of these foods and that ingestion of these foods by children able to do so may speed allergy recovery.   Furthermore, recommendations about prevention of food allergy and atopic disease through diet have changed radically, with rescinding of many recommendations about extensive and prolonged allergen avoidance. 

There is a wide spectrum of disease caused by food allergy and diagnosis depends on combining a knowledge of pathophysiology and epidemiology with patient history and test results. The authors explain that numerous clinical trials are underway for more definitive therapies, as is basic science research using novel approaches in animal models.  

With a deeper understanding of genetics and the microbiome, incorporation of bioinformatics and numerous approaches to treatment, the next several years show promise of a revolution in the clinical approach to food allergy. 

Questions for the authors:
What impact does the modern world have on food allergy, such as the American diet, lack of exercise, and stress that aren’t discussed in this review?  Are there clinical trials in place that use a more natural approach to improving outcomes?

There are a number of studies underway looking at a more natural approach to introducing foods to the diet (earlier).  The review discusses how modern living may affect allergy outcomes (e.g., lower vitamin D due to sunscreens and indoor activities, obesity, etc., and a study showing a “healthy diet” may be important to reduce allergy.  The role of stress has not been extensively studied but a review of this topic is in press:

Schreier HM, Wright RJ. Stress and food allergy: mechanistic considerations. Ann Allergy Asthma Immunol. 2013 Aug 28. pii: S1081-1206(13)00561-9. doi: 10.1016/j.anai.2013.08.002. [Epub ahead of print]

Insights provided by mouse models relating to food allergy

Food allergy is a growing public health concern due to its increasing prevalence and life threatening potential.  Mouse models of food allergy have become useful tools for identifying the mechanisms involved in the sensitization of food allergens which are normally harmless as well as delineating the critical immune components of the effector phase of allergic reactions to food. In their review, Oyoshi et al have summarized the importance of animal models in food allergy research contrary to concerns regarding the relevance murine models have in understanding human disease (J Allergy Clin Immunol 2014; 133(2): 309-317). 

Mouse models have been exceedingly useful in the study of atopic dermatitis (AD) and asthma, paving the way for food allergy research.  For example, allergic sensitization or tolerance can be induced to specific allergens under controlled environmental conditions within defined genetic backgrounds that cannot be matched in human studies. The importance of Treg cells in the development of tolerance has been established in both mouse and humans in which deficiency of forkhead box protein 3 (foxp3)+ T cells leads to increased allergic disorders such as AD and food allergy.  These T cells have been found to be reduced in antibiotic treated mice which exhibit a predisposition towards allergic sensitization.  Furthermore, administration of commensal microbiota to these mice promoted Treg cells and limited allergic responses to foods. 

The authors explain how animal models of food allergy are invaluable tools for dissecting etiology, mechanisms and preventive strategies, as well as assisting in the identification, validation and development of therapies before they progress towards patients. While the application of animal models to human disease requires careful and thorough consideration and interpretation, their utility in facilitating truly translational discoveries has been demonstrated repeatedly and on many levels. Particularly in the setting of food allergy, where risks of adverse reactions to therapy are a major issue for patients, animal models will be indispensable to effectively and ethically develop new treatments. Mechanistically, the recent discoveries of the  roles of microbiota on the etiology of food allergy, derived from studies of animal models, provides an excellent example of how lessons learned from experimental animals can provide new breakthrough areas that educate future studies of host factors in human patients with food allergy. 

Question for the authors:
What effects on food allergy research do you anticipate from the significant cuts in basic science research funding that may reduce overall animal research?

Short-time decisions of the budget cuts in basic research funding in a time of financial crisis may lead to an abrupt slow of growth of basic science with severe long-term consequences. Particularly in the area of food allergy, where animal models are indispensible to perform mechanistic studies that are often not feasible in humans because of ethical, technical, and even financial reasons, cuts in basic science funding will leave researchers with fewer opportunities to try novel and innovative ideas that could have a high return. In addition, many of young basic scientists with limited budgets cannot survive even short term cuts. The annual costs to pediatric food allergy have been estimated at $25 billion. In today’s environment, I believe that the continued careful and coordinative work of basic and clinical science with strong support will lead to effective development of new treatment for food allergy.