In this study, we generated a deletion mutant in the type 1 RH (RHΔ) strain and tested the protective efficacies of vaccination using RHΔ tachyzoites against acute, chronic, and congenital infections in Kunming mice. Mice vaccinated with RHΔ mounted a strong humoral and cellular response as shown by elevated levels of anti–specific IgG, IL-2, IL-12, IFN-γ, and IL-10. All RHΔ-vaccinated mice survived a lethal challenge with 1 × 10 tachyzoites of type 1 RH or ToxoDB#9 (PYS or TgC7) strain as well as 100 cysts or oocysts of Prugniuad strain. All mock-vaccinated plus infected mice have died. Vaccination also protected against cyst- or oocyst-caused chronic infection, reduced vertical transmission caused by oocysts, increased litter size, and maintained body weight of pups born to dams challenged with 10 oocysts on day 5 of gestation. In contrast, all mock-vaccinated plus oocysts-infected dams had aborted, and no fetus has survived. Vaccinated dams remained healthy postinfection, and their brain cyst burden was significantly reduced compared with mock-vaccinated dams infected with oocysts. In vivo depletion of CD4 T cells, CD8 T cells, and B cells revealed that CD8 T cells are involved in the protection of mice against infection. Additionally, adoptive transfer of CD8 T cells from RHΔ-vaccinated mice significantly enhanced the survival of naive mice infected with the pathogenic strain. Together, these data reaffirm the importance of CD8 T cell responses in future vaccine design for toxoplasmosis and present gene as a promising vaccine candidate.
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