Ara h 2_105-124-Specific TH2A Cells Drive Peanut Allergy in DRB1*15:01 Individuals: A Detailed Epitope Analysis

The IgE-mediated CD4 T-cell response to peanut (Arachis hypogaea) is heterogeneous, yet TH2 cells remain central drivers of pathology. This study aimed to dissect this complexity at the epitope level by focusing on the HLA-DRB1*15:01-DRB5*01:01 haplotype. Specifically, we examined how distinct epitope-specific T-cell subsets shape the immunological landscape of peanut allergy in peanut-allergic (PA) versus non-peanut-allergic (NPA) individuals.

Using in vitro and ex vivo MHC-II tetramer approaches, the phenotype, frequency, function, and transcriptome of CD4 T-cell responses to novel Ara h epitopes were assessed. Bulk RNA sequencing further characterised these T cells, allowing identification of subsets associated with TH2 polarisation in PA individuals.

Eleven HLA-DRB1*15:01 and DRB5*01:01-restricted epitopes were identified in Ara h 1, 2, 3, 6, 7, and 8 using tetramer-guided epitope mapping on cell lines, followed by ex vivo validation in peripheral blood. T-cell phenotype was epitope-dependent, with a distinct TH2A population specific to the epitope Ara h 2_105-124 (Ara h 2 p14) detected only in PA donors. These TH2A cells were phenotypically and transcriptionally distinct, marked by high CRTH2/CD161, low CD27, IL-5 production, and gene enrichment in cytokine signalling and lipid metabolism. Other epitope-specific T-cell subsets displayed more heterogeneous gene profiles related to immune activation, differentiation, and antigen presentation, underscoring the complexity of peanut-specific responses even within a single HLA haplotype.

These findings reveal that the strong TH2 bias in DRB1*15:01-DRB5*01:01 PA individuals arises from a distinct subset of Ara h 2 p14-specific TH2A cells characterised by a specialised metabolic and cytokine signalling program. At the same time, the functional diversity observed in non-Ara h 2 p14 subsets highlights the potential for leveraging these populations in tolerance-promoting therapies. Understanding the epitope-level heterogeneity of peanut-specific T-cells provides insight into the epitope-specific mechanisms driving peanut allergy and has potential implications for therapeutic interventions.