Biomarkers for successful allergen immunotherapy: are we there yet?

Purpose of review Allergen immunotherapy (AIT) is the only established disease-modifying treatment for IgE-mediated allergic disease, yet treatment remains largely empirical at the individual-patient level. This review critically examines current and emerging biomarkers for successful AIT, distinguishing biomarkers of biological activity from those capable of predicting clinical response, monitoring treatment efficacy, or identifying sustained clinical benefit after treatment withdrawal. Recent findings AIT induces reproducible changes across humoral, cellular and effector pathways, including allergen-specific blocking antibodies, regulatory T-cell and B-cell responses, suppression of type 2 immunity, and reduced effector-cell responsiveness. Recent research has increasingly moved beyond isolated biomarkers towards combined immune signatures, component-resolved antibody profiles, local mucosal biomarkers and multiomics approaches. These studies suggest that treatment response may ultimately be predicted by integrated biological signatures rather than individual measurements. However, prospective external validation remains limited and no biomarker or biomarker signature is currently ready for routine clinical use. Summary The major challenge in AIT biomarker research is no longer demonstrating that treatment modifies the immune response, but identifying measurements that improve clinical decisions. No currently available biomarker reliably determines who should receive AIT, whether an individual patient is developing durable disease modification, or when treatment can safely be discontinued. The future will probably lie in composite signatures integrating clinical phenotype with selected molecular, cellular and functional measurements.