Co-delivery of targeted hypoallergens and resiquimod powders using silk fibroin microneedles for effective allergen-specific immunotherapy.

Rationale: The cutaneous route exploits the immunocompetence of the skin, making it a favourable route for allergen-specific immunotherapy (AIT), but there must be a balance between minimal skin disruption and precise allergen delivery. Thus, we propose the use of powder-laden microneedles (pMNs) for the sustained epidermal delivery of powdery hypoallergens and immunomodulators. Methods: In this study, targeted hypoallergenic derivatives, namely, mannan-ovalbumin (mOVA) conjugates, were synthesized in a single-step process. For minimally invasive self-administration into the skin, pMNs were constructed using highly biocompatible silk fibroin (SF) with a cavity in the basal portion of each needle, which was filled with lyophilized mOVA and resiquimod powders (mOVA/R848 pMN). The resulting mOVA/R848 pMN arrays were thoroughly examined for their physical morphology, mechanical property, accumulation ability, and immune profile. Results: The deposition of powdery mOVA and R848 improved uptake by skin dendritic cells (DCs) and stimulated the immune system more than 10 d after application. On the basis of these features, mOVA/R848 pMN arrays increased the induction of protective immune mechanisms to suppress Th2 immunity, including the Treg/Th1 bias, as well as the production of anti-inflammatory cytokines and neutralizing antibodies in an asthmatic mouse model. Compared with traditional subcutaneous immunotherapy (SCIT), a total dose of only 75 μg of OVA over three treatments was sufficient to restore immune balance and alleviate allergic symptoms during allergen exposure, highlighting the dose-sparing and frequency-sparing potential of mOVA/R848 pMN. Conclusion: Optimal mOVA/R848 pMN arrays represent a new therapeutic strategy for allergy treatment with convenient administration and satisfactory outcomes.