Novel adjuvant delivery system constructed by alum-emulsion hybrid nanoparticles with TLR9 agonists boosts vaccine immunity.

Vaccine Adjuvant Delivery Systems (VADSs) that integrate both delivery and adjuvancy constitute a vital strategy in modern vaccine research. Herein, we employed microfluidics to blend nanosized aluminum hydroxide (XA) and a nanoemulsion (XE) in varying proportions. A 2:3 (v/v) mixture produced nanoparticles (XAE) of approximately 220 nm with near-neutral zeta potential, which significantly enhanced antigen uptake in DC2.4 cells and displayed stronger adjuvant activity than XA or XE alone. By electrostatically adsorbing the TLR9 agonist CpG onto XAE, we constructed XAEC as an integrated delivery platform that co-delivers antigens and immune-stimulatory molecules, thereby improving CpG's bioavailability and biocompatibility. This XAEC platform generated an "immune-activated microenvironment" at the injection site, fostering antigen-presenting cell (APC) recruitment, augmenting antigen presentation, facilitating vaccine trafficking to immune organs, and eliciting a Th1-biased immune response. XAEC substantially boosted immunogenicity in prophylactic Respiratory Syncytial Virus (RSV) and Varicella-Zoster Virus (VZV) vaccines and induced potent antitumor responses in a Human Papillomavirus (HPV) tumor model. Hence, XAEC emerges as a promising next-generation vaccine adjuvant system.