Evolution of subcutaneous allergen immunotherapy (part 1): from first developments to mechanism-driven therapy concepts

Background: Subcutaneous allergen immunotherapy (SCIT) is the classic causal treatment method for IgE-mediated allergic respiratory disease. A growing understanding of the fundamentals of immunological mechanisms sets the path for further clinical improvement of this treatment. Innovations in SCIT comprise both treatment schedules and new forms of allergen extracts applied. Nonmodified allergen preparations in the form of aqueous or physically coupled (semidepot) extracts, as well as chemically modified allergens (allergoids) are currently on the market for SCIT in Germany. However, to date the clinical documentation of SCIT products in clinical studies is heterogeneous. Methods: A selective literature search was conducted in PubMed and Medline, and recent publications in German-language journals not available in these literature databases were also analyzed. This literature search comprised original and review articles both in German and in English. Results: SCIT is a long-established and well-documented treatment method for inhalant and insect venom allergies, with its efficacy and safety demonstrated in both the adult as well as in the pediatric population. In line with the German Therapy Allergen Ordinance (TAV) several products for SCIT are currently being investigated in clinical trials. Treatment schedules are continuous year-round (perennial), preseasonal, and combined pre-/coseasonal. The initial up-dosing phase can be performed with standard, cluster or rush procedures. SCIT is particularly well established for frequently occurring inhalant allergens such as pollen from grasses, Betula sp. (birch, alder, hazel), house dust mites (Dermatophagoides sp.), and insect venoms (bee and wasp venoms). However, good data are also available for a number of other therapeutic allergens, e.g., weed pollen such as ragweed, mugwort, etc., molds, e.g., Alternaria, Cladosporium, etc., storage mites, and animal dander (e.g., cat). Moreover, further clinical investigations on new indications such as treatment effects on e.g., oral allergy syndrome or atopic dermatitis are currently underway. Conclusion: When adequately administered by physicians with allergological expertise, SCIT preparations are safe, well-tolerated, and clinically effective.