Development and Preliminary Mechanistic Evaluation of a Novel Liposomal QS-21 and CpG ODNs Adjuvant System for...

Developing potent adjuvants is critical for enhancing vaccine efficacy, particularly for subunit antigens. Background/Objectives: This study evaluates a novel composite adjuvant system combining liposomal QS-21 and CpG ODNs to enhance vaccine-induced immunogenicity, particularly Th1-type cellular immunity. Methods: To mitigate QS-21's hemolytic toxicity and ensure precision delivery, a stable liposomal formulation was developed. Mice models were established using varicella-zoster virus (VZV) glycoprotein E (gE) or ovalbumin (OVA) as antigens to evaluate humoral and cellular immune responses. Results: Immunization with gE protein formulated with this novel adjuvant synergistically triggered robust immune responses, outperforming single adjuvants and the combination of QS-21/MPL. Across broad dose ranges, it induced higher Th1-type cellular immunity and comparable humoral immunity relative to AS01_B. Mechanistic studies revealed that the adjuvant significantly enhances the recruitment of dendritic cells (DCs), monocytes, and neutrophils to draining lymph nodes (dLNs) while upregulating co-stimulatory molecules CD40 and CD86 on DCs. Furthermore, the formulation triggered robust, transient increases in Th1-associated cytokines (IFN-γ, IL-12) and chemokines (CXCL9, CXCL10) across the injection site, serum, and dLNs. Conclusions: These findings indicate that the liposomal QS-21 and CpG ODNs system is a highly effective platform for promoting robust Th1-biased immunity, offering a promising adjuvant candidate and a solid experimental foundation for developing next-generation vaccines requiring potent cellular immunity.