Surface-Engineered Polygonatum Sibiricum Polysaccharide CaCO3 Microparticles as Novel Vaccine Adjuvants to Enhance Immune Response

Micro- and nanoparticles delivery systems have been widely studied as vaccine adjuvants to enhance immunogenicity and sustain long-term immune responses. Polygonatum sibiricum polysaccharide (PSP) has been widely studied as an immunoregulator in improving immune responses. In this study, we synthesized and characterized cationic modified calcium carbonate (CaCO₃) microparticles loaded with PSP (PEI-PSP-CaCO₃, CTAB-PSP-CaCO₃), studied the immune responses elicited by PEI-PSP-CaCO₃ and CTAB-PSP-CaCO₃ carrying ovalbumin (OVA). Our results demonstrated that PEI-PSP-CaCO₃ significantly enhanced the secretion of IgG and cytokines (IL-4, IL-6, IFN-γ, and TNF-α) in vaccinated mice. Additionally, PEI-PSP-CaCO₃ induced the activation of dendritic cells (DCs), T cells, and germinal center (GC) B cells in draining lymph nodes (dLNs). It also enhanced lymphocyte proliferation, increased the ratio of CD4⁺/CD8⁺ T cells, and elevated the frequency of CD3⁺ CD69⁺ T cells in spleen lymphocytes. Therefore, PEI-PSP-CaCO₃ microparticles induced a stronger cellular and humoral immune response and could be potentially useful as a vaccine delivery and adjuvant system.