Ara h 1-reactive T cells in individuals with peanut allergy

Background: Effective immunotherapy for peanut allergy is hampered by a lack of understanding of peanut-reactive CD4⁺ T cells. Objective: To identify, characterize, and track Ara h 1-reactive cells in subjects with peanut allergy by using Ara h 1-specific class II tetramers. Methods: Tetramer-guided epitope mapping was used to identify the antigenic peptides within the peanut allergen Ara h 1. Subsequently, HLA class II/Ara h 1-specific tetramers were used to determine the frequency and phenotype of Ara h 1-reactive T cells in subjects with peanut allergy. Cytokine profiles of Ara h 1-reactive T cells were also determined. Results: Multiple Ara h 1 epitopes with defined HLA restriction were identified. Ara h 1-specific CD4⁺ T cells were detected in all of the subjects with peanut allergy tested. Ara h 1-reactive T cells in subjects with allergy expressed CCR4 but did not express CRTH2. The percentage of Ara h1-reactive cells that expressed the β7 integrin was low compared with total CD4⁺ T cells. Ara h 1- reactive cells that secreted IFN-γ, IL-4, IL-5, IL-10, and IL-17 were detected. Conclusion: In individuals with peanut allergy, Ara h 1-reactive T cells occurred at moderate frequencies, were predominantly CCR4⁺ memory cells, and produced IL-4. Class II tetramers can be readily used to detect Ara h 1-reactive T cells in the peripheral blood of subjects with peanut allergy without in vitro expansion and would be effective for tracking peanut-reactive CD4⁺ T cells during immunotherapy.