House-Dust Mite Immunotherapy in Asthma: Uncertainties and Therapeutic Strategies

Purpose of reviewThe prevalence of house dust mites (HDM)-sensitization is high in allergic asthma (AA), especially in tropical/subtropical countries in Asia and South America. As HDM-sensitization can contribute to the subsequent development of HDM-driven asthma, poor asthma control and exacerbations, allergen immunotherapy (AIT) might reduce the growing global burden of allergic asthma.Recent findingsAIT builds immunotolerance via upregulation of T-regulatory (reg) cells, leading to increase secretion of IL-10 and TGF-beta which suppress the Th2 response to allergens. IL-10 also induces the class-switch to plasma cells that produce IgG4 that competes with Ig E's binding on mast cell. Encouragingly, 2 recent multicentre trials showed that HDM AIT could lead to improvements in clinically relevant health outcomes: reduction in asthma exacerbations and inhaled corticosteroid usage.The uptake of AIT remains low due to difficulties with long-term adherence and lack of robust cost-effectiveness studies. There is limited standardization of techniques to compare the efficacy between different AIT administration routes and formulation. In clinical practice, it is challenging to differentiate "asthma with HDM sensitization" from "HDM-driven asthma". Additionally, Blomia tropicalis (Blo.t) play an important allergenic role especially in tropics, in addition to the Dermatophagoides species but is not found in many AIT formulations. It is uncertain if Blo.t sensitised patients will respond equally to these HDM AIT.SummaryWe will summarise (a) global differences in HDM sensitization, (b) disease-modifying mechanisms behind HDM AIT (c) differences between the subcutaneous and sublingual route (d) therapeutic strategies in HDM-driven asthma to maximise cost-effectiveness.