Clinical Evaluation of Allergen Immunotherapy for Allergic Asthma

Allergen immunotherapy (AIT) is the only available disease-modifying treatment for IgE-mediated allergic disease. Unlike conventional pharmacotherapy, AIT targets the underlying immune dysregulation driving allergic asthma (AA), with the potential to induce sustained off-treatment benefits. This narrative review examines the available evidence from both randomized controlled trials (RCTs) and real-world evidence to provide an updated and balanced overview of the clinical role of AIT in AA across different age groups. RCTs indicate that AIT can improve asthma symptom scores, reduce medication requirements and exacerbation risk, with additional steroid-sparing effects; however, findings are not consistent across trials. The strongest evidence is confined to house dust mite SLIT tablets, and the most recent Cochrane review judged the evidence insufficient for firm conclusions. Observational database studies enrolling up to 445,000 patients are consistent with these findings, reporting reductions in asthma events, medication use and treatment step-up, although their design precludes causal inference. Beyond symptomatic control, AIT has demonstrated a preventive role by interrupting the allergic trajectory, reducing the risk of new-onset asthma in patients with allergic rhinitis, and slowing progression to more severe asthma phenotypes. Long-term follow-up studies, mostly small and open in design, suggest that benefit may persist for up to 15 years after AIT discontinuation. Preliminary uncontrolled evidence also suggests that AIT may be feasible in selected patients with well-controlled severe asthma. In conclusion, AIT represents a uniquely positioned, disease-modifying strategy in the management of AA, with potential benefits spanning symptom control, prevention of disease onset and progression, and long-term benefits persisting after treatment discontinuation.