Tolerance induction through molecular chimerism in allergy

Immunoglobulin E-mediated allergy (type I allergy) affects more than 25 % of the population in industrialized countries with increasing prevalence. Individuals suffering from type I allergy are reacting against specific environmental antigens (allergens) of different species. The disease manifests in immediate reactions like hay-fever and; more severely; acute anaphylaxis and asthma. The only causative therapy so far is immunotherapy, a vaccination strategy, where increasing doses of crude extracts are repeatedly administered. Several strategies for prevention of type I allergy have been investigated so far in experimental models, like the induction of mucosal tolerance, but these strategies are characterized by limited robustness and relatively short- time effects. Recently, we developed a novel strategy for prevention of type I allergy based on the concept of molecular chimerism. One single full length major grass pollen allergen was introduced into murine hematopoietic stem cells and these modified allergen-expressing cells (in a membrane-anchored fashion) were transplanted into preconditioned syngeneic mice. Co-existence of the allergen-expressing and the recipient hematopoietic cells leads to so-called molecular chimerism. We could demonstrate that these allergen-expressing cells remained stable through the whole follow up long term. Further tolerance towards the introduced allergen was induced at the B- cell, T-cell and effector-cell levels. To avoid the potential risks of anaphylaxis and sensitization by introduction of a full length, membrane-anchored allergen we will investigate mechanisms regarding induced tolerance by molecular chimerism in type I allergy in the proposed project. Central and peripheral T cell tolerance and B cell tolerance will be studied and the predominant mechanisms in tolerance maintenance will be clarified. If B cell tolerance is a consequence of T cell tolerance, the allergen will be expressed in the cytoplasm to induce T-cell tolerance by peptide presentation via MHC molecules. Dominant T cell epitopes will be expressed in a surface and cytoplasmic fashion and introduced into hematopoietic stem cells subsequently transplanted into syngeneic recipients. The proposed project will elucidate mechanisms of tolerance induced by molecular chimerism and identify allergen peptides responsible for tolerance induction. These peptides provide the basis for potential prevention towards several allergens of different sources.

Type I or IgE-mediated allergy is a common disease affecting about 25 % of the population in industrialized countries. To avoid allergy we developed a preventive cell-based approach. In a mouse model we modified autologous (or genetically identical) cells to express a protein, which is responsible for allergy (the model allergen Phl p 5 from pollen of timothy grass) on the surface of bone marrow cells. Subsequently those modified Phl p 5-bearing cells were transplanted into a recipient mouse. After treatment with Phl p 5 mice did not develop allergy anymore, they became tolerant. In this project we could ameliorate the recipient treatment (e.g. reduction and loss of toxic irradiation) and determine the mechanisms of tolerance. Therefore it was important to generate a mouse expressing Phl p 5 on the surface of all body cells. The cells of this mouse (as a donor) can further be used to substitute bone marrow cells to mature hematopoietic cells.