M. Cecilia Berin

The double‐blind placebo‐controlled oral food challenge (DBPCFC) has been the “gold standard” for diagnosing IgE‐mediated food allergy for the past 50 years. Despite tremendous strides in our understanding of basic mechanisms and clinical features of food allergy, we remain dependent on refinements of old technologies, i.e., skin tests and serum IgE measurements, to complement clinical history in making an accurate diagnosis of food allergies. However, recent technical advances in two effector cell assays, i.e., the basophil and mast cell activation tests, may soon bring these diagnostic biomarkers to the clinic. In addition, new advances in antibody assays, T‐cell assays, transcriptomics, and metabolomics in conjunction with machine learning and artificial intelligence may soon enable us to diagnose food allergy and accurately monitor immunotherapeutic outcomes without the need for an oral food challenge.

The double-blind placebo-controlled oral food challenge (DBPCFC) has been the “gold standard” for diagnosing IgE-mediated food allergy for the past 50 years. Despite tremendous strides in our understanding of basic mechanisms and clinical features of food allergy, we remain dependent on refinements of old technologies, i.e. skin tests and serum IgE measurements, to complement clinical history in making an accurate diagnosis of food allergies. However, recent technical advances in two effector cell assays, i.e. the basophil and mast cell activations tests, may soon bring these diagnostic biomarkers to the clinic. In addition, new advances in antibody assays, T-cell assays, transcriptomics, and metabolomics in conjunction with machine learning and artificial intelligence may soon enable us to diagnose food allergy and accurately monitor immunotherapeutic outcomes without the need for an oral food challenge.

Approved therapeutics for peanut allergy are not designed for the many patients with allergic reactions to more than one peanut. We randomly assigned (1:1) participants 4 to 14 years of age reacting to a challenge of between 443 mg and 5043 mg of peanut protein to peanut oral immunotherapy (P-OIT) using home-measured peanut butter versus peanut avoidance. The primary end point was the difference between groups in the proportion tolerating a two-dose-level increase or 9043 mg of peanut protein. For ingestion participants tolerating 9043 mg, sustained unresponsiveness (tolerance off treatment) was tested after 16 weeks of ad lib ingestion followed by 8 weeks of abstinence. Of 73 participants, 38 were randomly assigned to P-OIT and 35 to avoidance. Thirty-two of 38 participants in the ingestion group (84.2%) and 30 of 35 in the avoidance group (85.7%) underwent the primary outcome food challenge. The primary analysis with prespecified multiple imputation for missing values showed 100% success for ingestion versus 21.0% for avoidance (between-group difference, 79.0 percentage points; 95% confidence interval [CI], 64.6 to 93.5; P<0.001). All 32 treated and 3 out of 30 avoiders (10%) tolerated 9043 mg. In the intention-to-treat analysis, sustained unresponsiveness occurred in 68.4% (26/38) on P-OIT versus 8.6% (3/35) tolerating 9043 mg among those avoiding (between-group difference, 59.9 percentage points; 95% CI, 42.4 to 77.3). No dosing reactions were greater than grade 1 severity, and no serious adverse events were reported. In this trial of P-OIT using store-bought, home-measured peanut versus peanut avoidance in high-threshold peanut allergy, those treated achieved significantly higher rates of desensitization with a durable response off treatment. (Funded by the National Center for Advancing Translational Sciences [UL1TR004419] and the National Institute of Allergy and Infectious [U19AI136053]; ClinicalTrials.gov number, NCT03907397.).

Background: Little is known about the ontogeny of T cell immunity during infancy in farming and urban lifestyles due to the lack of immunophenotyping in such birth cohorts. Methods: Two birth cohorts (farming and urban) at differing risks and rates of allergic diseases were compared. Blood mononuclear cells were collected from infants at birth, and 6 and 12 months of age. Full spectrum flow cytometry, followed by traditional gating and the Scalable Weighted Iterative Flow‐clustering Technique (SWIFT) high‐dimensional analysis, were used to identify cell populations that differed between farming and urban infants. Additionally, single‐cell RNAseq and multiplex cytokine assays were used to assess the function of cell populations of interest. Results: Several regulatory T cell (Treg) subpopulations were elevated in farming lifestyles and in non‐atopic infants. A unique effector memory CD25 ⁺ CD127 ⁺ CD161 ⁻ CD49d ⁺ CCR4 ⁺ CRTH2 ⁺ Th2 population was elevated at 6 months in urban infants and in those who developed atopic dermatitis and/or food allergy and allergic sensitization. Although this population shared Th2 and IL‐9 skewing with Th2A cells, the population uniquely failed to express CD161, produced more IL‐2 and TNF‐α, and upregulated the differentially expressed genes (DEGs), FOXP3 and the cytokine inducible SH2‐containing protein gene ( CISH ) relative to Th2A cells. This population has been termed Th2B cells. Conclusion: We describe a unique effector memory Th2 population elevated in urban high‐risk infants, potentially implicated in the development of allergic disease.

Background: Among peanut‐allergic individuals, there is high variability in the amount of peanut that triggers reactions (i.e., reaction threshold) that is not predictable or well‐understood. We conducted this study to characterize relationships between the oral and gut microbiomes and systemic processes associated with reaction threshold in peanut allergy (PA).Methods: In a cohort of 120 children with suspected PA who underwent double‐blind, placebo‐controlled food challenges, we generated and analyzed parallel profiles of the oral microbiome, gut microbiome, peripheral blood transcriptome, peripheral blood cytometry, and serum antibody levels to identify threshold‐associated markers and their inter‐relationships.Results: The 120 participants included 23 children with no PA, 74 with high‐threshold PA (reacting to ≥ 443 mg cumulative peanut protein), and 23 with low‐threshold PA (reacting to < 443 mg cumulative peanut protein). Ten hub microbes were each identified in saliva and stool microbiome networks that were constructed, including the hub microbes Rothia aeria in saliva and Bacteroides sp. in stool that were associated with reaction threshold. These hub microbes were also associated with peripheral blood transcript levels for threshold‐associated key drivers of FcγR‐mediated phagocytosis and TLR signaling. Correlation network construction with additional data on threshold‐associated peripheral blood neutrophil abundance and peanut‐specific serum IgE and Ara h 2 antibody levels revealed central roles for saliva Rothia aeria and stool Bacteroides sp. in local‐systemic networks for IgE‐ and IgG‐mediated peanut allergy.Conclusions: This integrated study of oral and stool microbiomes, blood transcriptome, cellular profiles, and peanut‐specific serum antibodies revealed new relationships between local microbiota and systemic measures associated with reaction threshold in peanut allergy.

Summary: Food allergies occur due to a lack of tolerance to the proteins found in foods. While IgE‐ and non‐IgE‐mediated food allergies have different clinical manifestations, epidemiology, pathophysiology, and management, they share dysregulated T cell responses. Recent studies have shed light on the contributions of different T cell subsets to the development and persistence of different food allergic diseases. This review discusses the role of T cells in both IgE‐ and non‐IgE‐mediated food allergies and considers the potential future investigations in this context.

Regulatory T cells (Treg) exert a crucial role in the suppression of exacerbated T helper (Th) cell responses, including those of type 2 Th (Th2) cells, and in the maintenance of tolerance to environmental antigens and food allergens. The functional capacity of Tregs to suppress Th2 responses has been studied through activation and immunosuppression assays using cells from mice and humans. The immunosuppression assay is an essential in vitro tool that allows the evaluation of the Treg capacity to limit the proliferation and expansion of conventional T cells. This approach enables the determination of the suppressive ability of different Treg subsets. In this chapter, we describe a basic and well-established immunosuppression protocol for human and murine Treg that has been widely applied in food allergy research. Key words Conventional T cells Human Immunosuppression assay Mouse PBMCs Regulatory T cells Spleen