Identification of Ara h 2 T-cell Epitopes for Use in a T cell-peptide Vaccine

Abstract

RATIONALE: T cell epitope-based peptide immunotherapy has been found effective in treating certain allergic diseases. Therefore we sought to identify the most immunodominant T cell epitopes of Ara h 2, as candidates for peptide immunotherapy, and define any HLA associations with these epitopes. METHODS: T cell proliferation assays were performed on 70 peanut allergic subjects. 1x106 PBMCs were cultured for 4 days with crude peanut extract, anti-CD3/CD28 beads or over-lapping 20-mer Ara h 2 peptides and then pulsed with tritiated thymidine (1μCi). Cell supernatants from a subset of peptide-stimulated cells were evaluated for cytokine production (IL-13, IL-5, IFNγ and TNFα). DNA was isolated for HLA-DRB1* and HLA-DQB1* typing. RESULTS: Three T-cell epitope regions were identified: aa # 27-56 (cluster A), #92-126 (B) and #122-141 (C). A dominant Th2 cytokine response was induced by these epitopes [(median (pg/mL), range) A: IL-5 (58.9, 3.06-950.32), IL-13 (35.1, 2.75-1119.15); B: IL-5 (21.7, 2.98-661.96), IL-13 (13.4, 2.82-442.47); C: IL-5 (12.5, 2.79-295.11), IL-13 (11.9, 2.82-230.33)] compared to baseline response. Preliminary data show a significant correlation between SI values and cytokine production (IL-5, IL-13; Spearman r≥0.5; p≤0.0007). For all three regions, HLA-DQ6 was one of the most frequent alleles identified, accompanied by DQ7 in clusters A and C, and by DQ8 in B. HLA-DRB1*1302 showed similar distribution for all clusters, whereas *0402 was more frequent in B and *0701 in C. CONCLUSIONS: Three T-cell epitope regions recognized by common HLA alleles are responsible for Th2 cytokine responses in peanut-allergic patients. They may provide good candidates for a T-cell peptide vaccine.