Comparison of two BCG adjuvants in enhancing the immunogenicity of a DNA vaccine encoding the Toxoplasma gondii ROP2 gene in BALB/c mice

The lack of a definitive treatment against toxoplasmosis and its high prevalence encouraged us to seek ways to expand DNA vaccines. The rhoptry protein 2 (ROP2) of Toxoplasma gondii is one of the most important antigens expressed in all three stages of the parasite's life cycle. BCG is an immune stimulator and can act as an important adjuvant for protection against infectious diseases. The recombinant pcROP2 plasmid was constructed, transfected into CHO cells, and protein expression was confirmed by western blotting. The recombinant plasmids (100 µg/100 µL) and two types of BCG adjuvants, namely intact BCG and BCG lysate, were injected into female BALB/c mice three times. Then, immunological factors (total IgG, IgG2a, and IgG1) and two cytokines, including IFN-γ and IL-4, were measured, and the survival rate of the mice after challenge with T. gondii tachyzoites was monitored. The group receiving pcROP2 +BCG lysate produced more IgG2a and total IgG than the other groups (p ≤ 0.05). Evaluation of spleen cytokines IFN-γ and IL-4 showed that IFN-γ levels were significantly higher in mice receiving the recombinant plasmid and BCG lysate compared to the other groups. In mice receiving pcROP2 +BCG lysate, the survival rate was higher than in the other groups, suggesting that pcROP2 +BCG lysate is more effective at inducing cellular immune responses and may be suitable for increasing the lifespan of mice with acute toxoplasmosis. • Intact BCG and BCG lysate enhance immune responses and survival rate of DNA vaccine encoding ROP2. • BCG lysate significantly enhanced IgG2a and total IgG responses compared to intact BCG. • The pcROP2 +BCG lysate formulation promoted strong Th1-type immunity via elevated IFN-γ levels. • Immunized mice exhibited prolonged survival after challenge with the highly virulent RH strain. • BCG lysate shows promise as an adjuvant to improve the efficacy of T. gondii DNA vaccines.