Immunotherapy in asthma: an updated systematic review

Allergen-specific immunotherapy (hyposensitization or desensitization) has long been a controversial treatment for asthma. Although beneficial effects upon clinically relevant outcomes have been demonstrated in randomized controlled trials, there remains a risk of severe and sometimes fatal anaphylaxis. The recommendations of professional bodies have ranged from cautious acceptance (1) to outright dismissal (2). A recent WHO position paper, which has been endorsed by eight other intemational and national bodies, concluded that allergen immunotherapy was an effective treatment for patients with allergic asthma (3). We have previously conducted a meta-analysis of 20 randomized controlled trials of allergen immunotherapy for asthma published between 1954 and 1990 (4). We subsequently conducted a systematic review for the Cochrane Collaboration, including a further 34 trials published between 1957 and 1997 (5). Both reviews concluded that subjects randomized to immunotherapy reported significantly fewer asthma symptoms, required significantly less asthma medication, and demonstrated both reduced nonspecific and reduced allergen-specific bronchial hyperreactivity (BHR) compared to those randomized to placebo. During recent years, there has been increasing interest in new allergen vaccines and new methods of delivery including oral, sublingual, and inhaled immunotherapy. Recombinant peptides containing the relevant epitopes, but lacking the ability to cross-link IgE bound to mast cells, have been evaluated in clinical trials. Finally, the Cochrane Collaboration has standardized protocols for systematic reviews and improved the statistical software for performing meta-analysis. Thus, it was again opportune to update our systematic review of allergen-specific immunotherapy for asthma.