Mechanistic investigation of calcium phosphate mineralization potentiating the cellular immune response of foot-and-mouth disease virus-like particle vaccines

Virus-like particles (VLPs), composed of structural proteins, have emerged as a promising vaccine platform for preventing infectious diseases due to their outstanding advantages. Enhancing immune responses specific to VLPs, particularly cellular immunity, has emerged as a pivotal area of current immunological research. The nanovaccines for the foot-and-mouth disease virus (FMDV) composed of VLPs mineralized with calcium phosphate (VLPs-CaP), developed based on biomineralization principles, demonstrates superior immunogenicity. In this study, we elucidated the efficacy and mechanism of VLPs-CaP in eliciting cellular immune responses. The results demonstrated that VLPs-CaP were efficiently internalized by dendritic cells (DCs) via energy-dependent endocytosis mediated by actin, microtubules, and clathrin. Upon uptake, VLPs-CaP decomposed within lysosomes, leading to the release of Ca²⁺ ions and an increase in lysosomal permeability. This facilitates the escape of VLPs into the cytoplasm for cross-presentation. Furthermore, CaP mineralization enhanced the level of activation of DCs by FMDV VLPs, evidenced by elevated expression of CD40 and CD86, and the secretion of IL-2 and IL-12p70. Immunization studies in mice revealed that VLPs-CaP elicited higher levels of specific antibodies compared to unmineralized VLPs; notably, there was an increased IgG2a/IgG1 ratio along with a greater number of cytotoxic T lymphocytes (CTLs). This study elucidated the mechanism by which CaP-mineralized VLPs induce cellular immune responses, offering new insights and strategies aimed at enhancing the cellular immune efficacy of VLP-based vaccines that primarily elicit humoral immunity.