Induction of regulatory T cells by an aluminum-CpG combination adjuvant for therapeutic and preventive vaccination against pollen allergy.

Pollen allergy is a prevalent allergic disorder affecting a substantial proportion of the global population. Allergen-specific immunotherapy (ASIT) is the only disease-modifying treatment, acting by inducing regulatory T cells (Tregs) and Th1-based immunity. However, current ASIT approaches often elicit insufficient allergen-specific tolerance and fail to correct underlying immune dysregulation, thereby limiting clinical efficacy. Here, a combination adjuvant composed of aluminum oxyhydroxide and CpG oligodeoxynucleotides (Al-CpG) is developed and formulated with the T-cell epitope derived from the Artemisia allergen Art v 1 (rArt v 1). Al-CpG significantly enhances rArt v 1 uptake and presentation by bone marrow-derived dendritic cells (BMDCs) and promotes the secretion of IFN-γ and IL-10. In both therapeutic and prophylactic murine models of pollen allergy, Al-CpG vaccination significantly alleviated allergic symptoms, suppressed airway inflammation, and restored immune homeostasis. Mechanistically, Al-CpG induces a robust expansion of CD25+FoxP3+ Tregs in concert with IFN-γ-producing CD4+ T cells, indicative of coordinated regulatory and Th1 immune programming. Adoptive transfer of Al-CpG-conditioned BMDCs further demonstrates preferential expansion of stable, thymus-derived (Helios+FoxP3+) Tregs in draining lymph nodes and systemic immune reprogramming toward a regulated state in the spleen, as evidenced by increased Treg frequencies and CTLA-4 upregulation. Collectively, these findings identify Al-CpG as a safe and effective adjuvant platform that synergistically induces immune tolerance and immune deviation, highlighting its potential for next-generation pollen allergy vaccines and broader applications in the prevention and treatment of allergic diseases.