Abstract Allergen-specic T cells play a key role in the patho-genesis of allergic diseases through provision of help for allergen-specic B cells and control of in-ammatory responses. Allergen immunotherapy using intact allergen proteins (given either sub-cutaneously or sublingually) is clinically eective and demonstrates enduring ecacy (i. e., disease modifying). However, the requirement for monthly injections or daily sublingual administration (both
for 3 years), combined with a high frequency of local and systemic adverse events, results in poor compli-ance. Targeting allergen-specic T cells with syn-thetic peptides representing dominant T  cell epi-topes markedly decreases treatment times (4–8 in-tradermal injections), reduces adverse events and provides ecacy for at least 2 years. We have devel-oped peptide immunotherapies for allergies trig-gered by cats, house dust mites, and grass pollen. Each of these consists of a mixture of seven peptides containing multiple dominant T cell epitopes and each have demonstrated statistically signicant improvements in rhinoconjunctivitis symptom scores in controlled allergen challenge facilities. ‰e mechanisms of action appear to involve in-creased IL-10 production, intra- and inter-molecu-lar suppression, and down-regulation of chemo-kine pathways. In contrast, treatment does not appear to be associated with deletion of aller-gen-specic T  cells, nor with the induction of allergen-specic IgG (as is seen with conventional whole allergen immunotherapy).