ALLERGEN-SPECIFIC IMMUNOTHERAPY: VACCINES FOR ALLERGIC DISEASES

Abstract

Allergen-specific immunotherapy (ASIT) is the most effective method of allergy treatment which consists of exposure to small doses of antigen responsible for development of allergic condition in the particular patient. Therefore, one may achieve desensitization to this antigen. The history of ASIT application lasts for more than 100 years, and, over this time, huge clinical evidence for the usage of the method has been accumulated. Use of ASIT causes reduction of allergy symptoms and treatment needs and, moreover, it has the potential for long-term clinical benefit, by preventing the development of allergy and its symptoms. The treatment affects basic immunological mechanisms responsible for the development of clinical symptoms. ASIT is an antiinflammatory, pathogenetic and prophylactic treatment of allergic airway disease. The review considers the results of major clinical trials of the ASIT applications for treatment of allergic diseases of the respiratory system (allergic rhinitis and bronchial asthma). Various schemes of ASIT are discussed including its different variants (injectable and sublingual ASIT), the issues of preparation choice for ASIT from those currently available on the pharmaceutical market, patient selection criteria, and the issues of modern molecular allergodiagnostic (allergic sensitization mapping of the patient at molecular level), in order to optimize them. Immunological mechanisms of ASIT are also considered, since appropriate views are rather contraversial. The ASIT effect is mediated through the following basic immunological mechanisms: the suppressed increase of the eosinophil concentrations, reduced duration of the delayed hypersensitivity phase, as well as initiation and maintenance of the Th2-to-Th1-like immune response transition. Regulatory T-cells play a major role in implementation of the immunological mechanism in ASIT, they have a significant impact on the Th2 response suppression. Such suppression may proceed via increased production of specific IgG antibodies, primarily of IgG4 subtype. The shift of balance between IgE and IgG4 towards IgG4 production is now considered a fundamental condition for successful ASIT. It has been proven that the allergen-specific IgG4 antibodies against IgE persist after discontinuation of the treatment and can provide long-term clinical tolerance. Modern prospectives for development of new forms and species of preparations for ASIT are also reviewed. Two groups of drugs for ASIT have been adopted for clinical practice until now, i.e., allergens and allergoids (allergens chemically modified by treatment with formaldehyde, in order to enhance their immunogenicity and to reduce the incidence of adverse allergic reactions associated with their application). Immunological mechanisms of SLIT (sublingual immunotherapy) are subjected to special consideration. So far, SLIT is the safest and most promising option of ASIT today, its usage is most expedient in pediatric practice.