Grass‐specific CD 4 + T‐cells exhibit varying degrees of cross‐reactivity, implications for allergen‐specific immunotherapy

Summary Background Conceptually, allergic responses may involve cross‐reactivity by antibodies or T ‐cells. While I g E cross‐reactivity among grass‐pollen allergens has been observed, cross‐reactivity at the allergen‐specific T ‐cell level has been less documented. Identification of the patterns of cross‐reactivity may improve our understanding, allowing optimization of better immunotherapy strategies. Objectives We use P hleum pratense as model for the studying of cross‐reactivity at the allergen‐specific CD 4 + T cell level among DR 04:01 restricted P ooideae grass‐pollen T ‐cell epitopes. Methods After in vitro culture of blood mono‐nucleated cells from grass‐pollen‐allergic subjects with specific P ooideae antigenic epitopes, dual tetramer staining with APC ‐labelled DR 04:01/ P hleum pratense tetramers and PE ‐labelled DR 04:01/ P ooideae grass homolog tetramers was assessed to identify cross‐reactivity among allergen‐specific DR 04:01‐restricted T ‐cells in six subjects. Direct ex vivo staining enabled the comparison of frequency and phenotype of different P ooideae grass‐pollen reactive T ‐cells. Intracellular cytokine staining ( ICS ) assays were also used to examine phenotypes of these T ‐cells. Results T‐cells with various degrees of cross‐reactive profiles could be detected. P oa p 1 97–116 , L ol p 1 221–240 , L ol p 5a 199–218 , and P oa p 5a 199–218 were identified as minimally cross‐reactive T ‐cell epitopes that do not show cross‐reactivity to P hl p 1 and P hl p 5a epitopes. Ex vivo tetramer staining assays demonstrated T ‐cells that recognized these minimally cross‐reactive T ‐cell epitopes are present in G rass‐pollen‐allergic subjects. Conclusions Our results suggest that not all Pooideae grass epitopes with sequence homology are cross‐reactive. Non‐cross‐reactive T ‐cells with comparable frequency, phenotype and functionality to P hl p‐specific T ‐cells suggest that a multiple allergen system should be considered for immunotherapy instead of a mono‐allergen system.