Several approaches to find a better adjuvant, focus immunomodulation, and reduce allergenicity are under investigation to improve the efficacy and safety of specific immunotherapy.

We performed an investigation of the in vitro and in vivo effects of a purified allergen chemically conjugated to a novel 8-OH modified adenine as an adjuvant.

Purified group 2 major allergen from house dust mite chemically conjugated to 4-(6-amino-9-benzyl-8-hydroxy-9H-purin-2-ylsulfanyl)-butyric acid succinimidyl ester was analyzed by using mass spectrometry. The adduct (nDer p 2–Conj) was assayed for Toll-like receptor activation on transfected HEK293 cells, stimulation of innate cells, and effects on the functional phenotype of specific T-cell lines and clones by means of flow cytometry, real-time PCR, and expression of T_H-related transcription factors. Lung cells and sera of nDer p 2–Conj–sensitized C57Bl/6 mice were studied by means of cytology, histology, real-time PCR, and ELISA.

nDer p 2–Conj stimulated IL-12 and IFN-α production from monocytes and plasmacytoid dendritic cells, respectively, retaining the ability to trigger Toll-like receptor 7 exclusively, and expanded human allergen-specific lymphocytes with reduced ability to produce T_H2-related cytokines and increased IFN-γ levels, as based on GATA-3/T-bet expression. In vivo adduct-sensitized mice exhibited reduced eosinophil infiltration and IL-13 expression in the airways, IFN-γ upregulation together with IgE downregulation, and an increase in allergen-specific IgG_2a levels in sera. The conjugate exhibited reduced ability to activate human FcεRI⁺ cells without inducing T_H17 cells or autoantibodies.

The codelivery of an allergen with a modified adenine as a conjugate inducing modulatory cytokines from innate cells redirects in vitro and in vivo pathogenic T_H2 responses without eliciting harmful effects.