Abstract: Almost 25% of the population in industrialized countries and more than 130 million people worldwide are suffering from Type I hyperresponsiveness.Allergen-specific Immunotherapy（SIT） represents one of the few curative approaches toward type I hyperresponsiveness.However,there are three major problems with SIT.First,presently SIT is performed with natural allergen extracts,containing mixtures of allergens,nonallergenic and/or toxic proteins,and other macromolecules,which are hard to standardize.Second,systemic administration of allergen can cause severe 19B-mediated side effects during the treatment on patients,and third,therapeutically effective dose often cannot be achieved because of non-standardized extracts or side effects.Since pure and standardized recombinant allergens can be formulated to replace natural extracts,using genetic engineered allergens for SIT become a possible and promising method for immunotherapy.