Identification and characterisation of HLA-DRB1*0101 restricted CD4+ T cell epitopes in the major grass pollen allergens Phl p 1 and Phl p 5

Abstract

Over 10 million people in the UK suffer from allergic rhinitis. The majority have symptoms caused by grass pollen exposure. Phl p 1 and Phl p 5 are the major grass pollen allergens in Timothy grass (Phleum pratense). Specific grass pollen immunotherapy using whole extract is an effective disease-modifying treatment, but it is associated with severe, life-threatening systemic IgE-mediated side-effects. One strategy to improve safety and clinical efficacy is to develop peptide immunotherapy for grass pollen allergy. The aim of this thesis was to identify HLA-DR1-restricted CD4+ T cell epitopes of Phl p 1 and Phl p 5 by complementary approaches of epitope mapping: in silico prediction, tetramer guided epitope mapping and human HLA-DR1 transgenics. I investigated recognition of HLA-DR1-restricted CD4+ T cell epitopes in allergic and non-allergic individuals and characterised epitope-specific CD4+ T cells, according to cell surface markers and cytokine production. HLA-DR1 transgenics were primed with either Phl p 1 or Phl p 5b protein and the T cell lines generated were screened using a panel of overlapping peptides in 3H-thymidine incorporation assays. HLA-DR1-tetramers loaded with Phl p 1 or Phl p 5b peptides were used in tetramer guided epitope mapping studies using PBMC from HLA-DR1+, grass-allergic, seasonal allergic rhinitis patients. Tetramer-positive populations were detectable in PBMC of >75% of patients studied. Epitope-specific CD4+ T cells were detectable immediately ex vivo in allergic and non-allergic individuals. Data suggest that epitope-specific CD4+ T cells from allergic individuals exhibit an effector memory, Th2-like phenotype. This study identified HLA-DR1-restricted CD4+ T cell epitopes for Phl p 1 and Phl p 5b and characterised epitope-specific CD4+ T cell responses. The epitopes identified may be used in peptide-based vaccines for grass pollen immunotherapy.