Enhancing immune responses to a DNA vaccine encoding Toxoplasma gondii GRA14 by calcium phosphate nanoparticles as an adjuvant

•A novel DNA vaccine containing Toxoplasma gondii GRA14 gene was constructed.•We examined the immunological properties of calcium phosphate nanoparticles (CaPN) as nano-adjuvant.•Immunization with pcGRA14 coated by CaPN enhanced immune responses and decreased parasite load.

Several approaches have been used to improve the immunogenicity of DNA vaccines. In the current study, we constructed the plasmid encoding T. gondii dense granule 14 (GRA14) and investigated the immunological properties of calcium phosphate nanoparticles (CaPNs) as nano-adjuvant to enhance the protective efficacy of pcGRA14. BALB/c mice intramuscularly injected three times at two-week intervals and the immune responses were evaluated using lymphocyte proliferation assay, cytokine and antibody measurements, survival times, and parasite load of mice challenged with the virulent T. gondii RH strain. The results showed that the immune responses were induced in mice receiving pcGRA14 DNA vaccine. Interestingly, pcGRA14 coated with nanoparticles led to statistically significant enhancements of cellular and humoral immune responses against Toxoplasma infection (P < 0.05). After challenge with RH strain of T. gondii, immunized mice with pcGRA14 showed prolong survival time compared to control groups (P < 0.05). In addition, pcGRA14 coated with nano-adjuvant exhibited the lowest parasitic load in the infected mice tissues. For the first time, our data indicate that the pcGRA14 coated with CaPN was more effective for stimulation of immune responses and should be considered as an adjuvant in the design of vaccines against toxoplasmosis.

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