Antigen-specific tolerance in immunotherapy of Th2-associated allergic diseases

Allergic diseases are an increasing health concern, particularly in the developed world. The standard clinical approach to treatment of allergic disease focuses on allergen avoidance and symptom control but does little to address the underlying Th2 bias of disease. Specific immunotherapy (SIT) consisting of controlled administration of allergen, however, has been demonstrated to successfully induce desensitization and tolerance in an antigen-specific manner for a variety of Th2-mediated diseases. This review focuses on the mechanisms by which current SIT approaches induce tolerance as well as discussing attempts to modify the safety and efficacy of SIT. These refinements focus on three major aspects of SIT: the route of antigen administration, modification of the antigen to remove allergenic epitopes and reduce adverse events and choice of adjuvant used to induce tolerance and/or immune deviation from Th2 to Th1 and regulatory T-cell (Treg) phenotypes. Synthesis of these recent developments in SIT provides considerable promise for more robust therapies with improved safety profiles to improve resolution of allergic disease and its associated costs.