Purpose of review: Allergen-specific immunotherapy (AIT) targets the IgE-mediated response to specific allergen(s). Accordingly, a monosensitized patient would be the ideal candidate for AIT. However, most patients are polysensitized; thus, two main problems emerge: first, whether AIT with a clinically relevant allergen is effective in polysensitized patients, and second, whether the use of a few allergens (European approach) or of mixtures containing all the possibly sensitizing allergens (USA approach) should be used. Of note, only in recent years has the so-called 'component resolved diagnosis' introduced new diagnostic opportunities. In the present article, the available experimental data concerning the controversial aspects of single versus multiallergen AIT are reviewed.
Recent findings: Some data are only available from isolated studies, which are often not controlled, and few trials on the argument have been recently conducted. Main findings are that AIT can be effective in both monosensitized and polysensitized patients, as shown by large trials with grass extracts.
Summary: The evidence for the efficacy of allergen mixes is still weak, but component-resolved diagnosis could represent a valuable help in selecting the allergen. As a matter of fact, comparative trials on multiple versus single allergen immunotherapy would be expensive and time-consuming: this justifies the paucity of data.
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