Influenza virus-like particles presenting <i>Toxoplasma gondii</i> dense granule protein 7 protect mice from lethal ME49 challenge

<i>Toxoplasma gondii</i> dense granule antigen 7 (GRA7) is a membrane-associated protein expressed across parasite life cycle and represents a promising vaccine target. This study aimed to develop a GRA7-based virus-like particle (VLP) vaccine and assess its protective efficacy. GRA7 VLPs were constructed using an influenza M1 scaffold via the baculovirus expression system. Female BALB/c mice were immunized intranasally three times and orally challenged with lethal <i>T. gondii</i> ME49 cysts. Humoral and cellular immune responses, brain inflammation, and parasite burden were evaluated at 40 days post-infection. Body weight reduction and survival rate were monitored after challenge. GRA7 VLPs induced robust <i>T. gondii</i>-specific IgG in serum after immunization. Following challenge with cysts, elevated antibody levels were detected in intestinal, fecal, and brain tissues, accompanied by enhanced activation of IgG-secreting cells, germinal center B cells, memory B cells, as well as CD4⁺ and CD8⁺ T cells in antigen-restimulated splenocytes of vaccinated mice. Notably, vaccinated mice exhibited 100% survival and sustained body weight, alongside a marked reduction in cerebral pro-inflammatory cytokines and parasite cyst burden. GRA7 VLPs confer strong systemic and mucosal immunity and significant protection against chronic toxoplasmosis, underscoring their potential as a promising vaccine platform.