Immune enhancement of rhamnolipid/manganese calcium phosphate mineralized nanoparticle: A promising subunit antigen delivery system

The use of biomimetic mineralization strategy is promising to solve the problem of poor stability and immune effect of subunit antigens. However, non-specifically inducing protein mineralization is still a challenge. we hypothesized that rhamnolipids with both protein and metal binding capacity could be used to develop more functional and biocompatible calcium mineralized nanoparticle (RMCP). The results show that rhamnolipids synergistically enhanced the mineralization of protein with manganese ions and improved 21 % the loading antigens of RMCP compared to manganese calcium phosphate nanoparticles. Transmission electron microscopy (TEM) and Dynamic Light Scattering (DLS) showed particle size of RMCP is 260 ± 12.1 nm with spherical morphology. In vitro experiments have shown that RMCP effectively activate immune cells through the cGAS-STING and NLRP3 pathways and demonstrated a higher level of cytokines in RAW264.7 Macrophages. In vivo, RMCP triggered an increased IgG titer with 16.5-fold IgG2a/IgG1 ratio compared to the aluminum adjuvant which improved the recovery status after challenge in mice. We used biological surfactants for the first time to enhance the biomimetic mineralization process of subunit antigen, which provides a new approach for constructing calcium-based biocompatible antigen delivery vectors, helping to develop a new generation of stable, efficient, and safe subunit vaccines.