Allergen-specific immunotherapy for respiratory allergies: from meta-analysis to registration and beyond

Allergen-specific immunotherapy (SIT) is an etiology-based treatment for respiratory and Hymenoptera-allergic diseases. Although introduced a century ago, SIT was not widely accepted for many years until its efficacy in the treatment of both allergic rhinoconjunctivitis and allergic asthma was demonstrated in appropriate double-blind, placebo-controlled trials and its mechanism of action was better understood. The indications for allergen-specific immunotherapy have been specified in consensus reports. Allergen-specific immunotherapy is primarily targeted to benefit patients with Hymenoptera allergy or severe upper and mild to moderate lower allergic respiratory diseases that are poorly controlled by pharmacologic treatments or who are unable or unwilling to use the latter. Several recent developments have helped to reinforce the position of SIT in the overall therapeutic management of respiratory allergies: (1) improvement in the quality of allergen extracts as a result of standardization, (2) better understanding of SIT's mechanism of action, (3) the introduction of sublingual tablets and their rigorous registration as pharmaceutical therapies by regulatory agencies, and (4) rationalization of prescribing patterns. There is a requirement for additional well designed, well executed, randomized trials in adults and children with allergic rhinitis and asthma, with a special focus on optimal patient selection, dosage, and treatment duration. In this review, the authors put into perspective current international expert recommendations on the use of SIT (in relation to levels of clinical evidence) and analyze what is needed for the future.