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.