Prophylaxis and Therapy of Allergy by Mucosal Tolerance Induction with Recombinant Allergens or Allergen Constructs

The mucosal immune system, present along the respiratory, gastrointestinal and genitourinary tract, has to discriminate between harmful pathogens and innocuous antigens, such as food, airborne antigens or the commensal bacterial flora. Therefore the mucosal immune system has acquired two opposing immunological functions, i.e. the induction of immunity and defence of mucosal pathogens, and the induction and maintenance of tolerance to environmental antigens and bacterial flora. As described for autoimmunity a breakdown or failure of tolerance induction is believed to lead also to allergies and food enteropathies. Based on the physiological role to prevent hypersensitivity reactions, tolerance induction via the mucosa has been proposed as a treatment strategy against inflammatory diseases, such as allergies. The aim of our research is to develop mucosal allergy vaccines based on the induction of mucosal tolerance and/or the induction of counter-regulatory immune responses with or without the use of certain mucosal antigen delivery systems, such as lactic acid bacteria. The use of recombinant allergens instead of allergen extracts with varying allergen content and composition may be essential for improvement of the treatment efficacy. In the present review we give examples of different animal models of type I allergy/asthma. Using these models we demonstrate that recombinant allergens or hypoallergenic variants thereof can be successfully used to induce mucosal tolerance in a prophylactic as well as a therapeutic treatment regime. That the concept of mucosal tolerance induction/mucosal vaccine delivery may in principal also function in humans is supported by recent clinical trials with locally (sublingual) applied immunotherapy.