Allergen Immunotherapy: The Evidence Supporting the Efficacy and Safety of Subcutaneous Immunotherapy and Sublingual Forms of Immunotherapy for Allergic Rhinitis/Conjunctivitis and Asthma.

Allergen immunotherapy is a recognized key therapeutic modality for the treatment of allergic respiratory disease - definitive studies have provided evidence-based data to demonstrate its effectiveness in allergic rhinitis and asthma due to the inhalation of proteinaceous allergic substances from specific seasonal pollens, dust mites, animal allergens, and certain mold spores. Over the ensuing decades, laboratory investigations, have provided objective evidence to demonstrate immunologic changes, including production of protective IgG antibody, suppression of IgE antibody, upregulation of regulatory T-cells, and an induction of a state of immune tolerance to the offending allergen(s). Tangential to this work were carefully designed clinical studies that defined allergen dose and duration of treatment, established the importance of preparing extracts with standardized allergens (or well-defined extracts) based on major protein moieties, utilized allergen provocation models to demonstrate efficacy superior to placebo. In the U.S., the use of subcutaneous immunotherapy (SCIT) extracts for allergen immunotherapy (AIT) was grandfathered in by the FDA based on expert literature review. In contrast, sublingual tablet immunotherapy (SLIT-tablets) underwent formal clinical development programs (Phase I-III clinical trials) that provided the necessary clinical evidence for safety and efficacy that led to regulatory agency approvals for the treatment of allergic rhinitis in properly characterized allergic patients. The allergy specialist's treatment options currently include traditional subcutaneous allergen immunotherapy and specific sublingual tablets approved for grass, ragweed, house dust mites, trees belonging to the birch homologous group, and Japanese Cedar. Tangential to this are sublingual drops (SLIT-drops) that are increasingly being used off-label (albeit not FDA-approved) in the U.S. This article will review the evidence-based literature supporting the use of these forms of AIT, as well as focus on several current controversies and gaps in our knowledge base that have relevance for the appropriate selection of patients for treatment with specific AIT.