Comparative efficacy of a multi-epitope DNA vaccine via intranasal, peroral, and intramuscular delivery against lethal Toxoplasma gondii infection in mice

Background: Toxoplasmosis is an important zoonosis, being a cause of congenital disease and abortion in animals and humans. DNA vaccination as a promising vaccine remains a challenge for an improved delivery system. Methods: In this study, attenuated Salmonella typhimurium BRD509 was used to deliver a DNA vaccine encoding several epitopes, derived from the tachyzoite proteins SAG1, GRA1, ROP2, GRA4 and bradyzoite proteins SAG2C, SAG2X of Toxoplasma gondii and A(2)/B subunit of cholera toxin. The recombinant plasmids were electroporated into attenuated Salmonella typhimurium. Humoral and cellular immune responses were evaluated for BALB/c mice administered with this attenuated recombinant Salmonella vaccine via the oral and nasal route or by intramuscular injection with DNA plasmid directly. Results: High IgG levels were present in the mice immunized intramuscularly, while IgA levels were higher in the oral and nasal immunization groups. Furthermore, cellular immunity was activated in oral immunization groups with 60% survival rate following challenge with high virulent RH strain. Conclusions: The results from this study indicate that a DNA vaccine encoding multi-epitopes of T. gondii delivered by attenuated Salmonella is promising.