Mimotopes for immunotherapy of allergic disease

Research project P 14339 Mimotopes for immunotherapy of allergic disease Erika JENSEN-JAROLIM 08.05.2000 Antibodies recognize preferentially conformational epitopes that often are composed of different discontinous sections of the amino acid sequence (1), only exceptionally continuous epitopes may be found (2). Based on the amino acid sequence, detailed epitope mapping of an allergen molecule may be restricted. Therefore, it is important to apply alternative methods for the characterization of IgE epitopes, like bippanning of phage display peptide libraries. By this method, high affmity peptide ligands mimicking natural antigens (mimotopes) can be selected and characterized. We have used this method for the first time for characterizing mimotopes of birch pollen major allergen Bet v 1 and the panallergen profilin. (3, 4). The goal of the present project is the characterization of IgE epitopes of important allergens, which can be used in immunization strategies to modify the, allergic immune response. From in vitro studies using the major birch pollen allergen Bet v 1 as a model, it is known that the IgE binding capacity of an allergen can he modified by IgG. IgG antibodies have contrasting biological effects and may enhance or inhibit IgE binding depending on the epitope specificity (5). It is very likely that the beneficia I type of IgG is directed towards IgE epitopes and can, thereby, interfere with the allergen/IgE interaction, in other words, can act as a blocking antibody. The use of phage display peptide libraries will allow us to define IgE mimotopes, which can be used for precise immunizations resulting in the formation of blocking IgG. In this respect, the choice of a suitable carrier material for the synthetic production of immunogenic mirnotope conjugates will be an aim ofthestudy. The studies delineated in this research proposal i) should provide valuable information on the nature of allergen IgE epitopes , ii) should greatly enhance our knowledge about immunization strategies with peptide mimotopes derived from biopannings, and iii) should result in the development of a new strategy to interfere therapeutically with an ongoing immune response of type I allergy.

In allergy IgE antibodies are formed by the patient, which attach to histamine-loaded cells of the skin and mucosal sites. In case the allergen re-enters the body, it may crosslink two neighbouring IgE molecules. Only if this critical event occurs, cells will be activated and do immediately and explosively release histamine into the surrounding tissues. Histamine is responsible for eliciting immediate symptoms, like conjunctivitis, hay fever of asthma. Due to the fact that cross linking is such a basic event in allergy, we analysed in great detail the molecular structures of important allergens from birch and grass pollen, which are abundant for IgE-binding, so called epitopes. These are surface exposed, three-dimensional structures, which could be revealed by mimotope technique. Thereby, small structural peptides are selected from bacteriophage libraries, which mimic natural epitopes especially well, so- called mimotopes. They are suited for localization of IgE epitopes and can, moreover, be applied for vaccinations. The latter achieves antibodies of a distinct class, IgG, which are able to recognize and trap the allergen, but cannot be fixed to effector cells as IgE can. Allergen immunotherapy has a similar effect and induces IgG antibodies. This form of therapy is conducted since 1911 in a more ore less unchanged fashion using natural extracts from allergen sources (grass pollen, birch pollen, etc.), even if it sometimes produces dangerous side effects, because contained allergens may crosslink existent IgE in the allergic patient. The aim of this study was, therefore, to produce a mimotope vaccine with the following advantages: 1) perfect mimic of a natural allergen epitope, but 2) not able to crosslink IgE. We selected ABP (Albumin-binding protein from Streptococcus) as a fusion partner for a mimotope of Bet v 1, the major birch pollen allergen. The Mimotop-ABP fusion protein was indeed capable of inducing IgG antibodies against the allergen when we immunized mice. When mice were sensitized to birch pollen allergen Bet v 1, skin tests with this fusion protein did not elicit allergic reactivity (wheal and flare reaction), whereas the allergen did have cross linking capability. ABP was demonstrated to be a carrier with excellent immunogenicity, similar as bacteriophages themselves. In ongoing experiments we investigate whether the quantity (titres) or quality (affinity) of induced IgG will be sufficient to hinder the interaction between allergen and IgE, which has an excellent affinity, but is formed in low amounts only.