A Ganoderma lucidum Polysaccharide-Modified Nanoadjuvant Elicits Potent Cellular Immunity for Hepatitis B Vaccine

Background: Aluminum-adjuvanted hepatitis B vaccines effectively prevent primary HBV infection but predominantly favor humoral immunity and have limited capacity to induce strong cellular responses. To improve immune-response quality, we developed a Ganoderma lucidum polysaccharide-modified hybrid nanoparticle adjuvant (GHNP) for hepatitis B surface antigen (HBsAg) vaccination. Methods: Cationic PEG-PCL/DOTAP hybrid nanoparticles (HNPs) were surface-modified with Ganoderma lucidum polysaccharide (GLP) at different mass ratios and characterized by particle size, polydispersity index, zeta potential, and transmission electron microscopy. Antigen uptake, RAW264.7 cell viability, MHC II expression, and TLR2/4-associated TNF-α secretion were evaluated in vitro. C57BL/6 mice were immunized intramuscularly with PBS, HBsAg, HBsAg + Aluminum, HBsAg@HNP, or HBsAg@GHNP6 on Days 0, 14, and 28. HBsAg-specific antibodies, splenocyte activation, proliferation, and cytokine secretion were assessed. Results: GHNP6 showed suitable physicochemical properties, acceptable cytocompatibility at concentrations up to 10 μg·mL−1, and efficient model-antigen uptake. GHNP increased MHC II expression in RAW264.7 cells, and TLR2/4 inhibition reduced nanoparticle-associated TNF-α secretion, supporting involvement of these pathways in immune activation. In vivo, HBsAg@GHNP6 induced robust HBsAg-specific IgG responses and a higher IgG2a/IgG1 ratio than HBsAg@HNP and HBsAg + Aluminum. It also produced the highest splenocyte proliferation after HBsAg restimulation, with lower IL-6 secretion than HBsAg + Aluminum and moderately increased IFN-γ compared with PBS and free HBsAg. Conclusions: GHNP integrates nanoparticle-assisted antigen delivery with GLP-mediated immunomodulation and represents a promising strategy for enhancing cellular immune responses while maintaining humoral immunity in HBsAg vaccination.