Evaluation of protective efficacy of recombinant Toxoplasma gondii DDX39 protein vaccine against acute and chronic T. gondii infection in mice

Toxoplasma gondii, a pervasive parasite responsible for toxoplasmosis, poses significant health risks to humans and animals. In this study, we investigated the immunogenicity and protective efficacy of the recombinant T. gondii DDX39 protein formulated with ISA201 adjuvant (rTgDDX39) as a candidate vaccine against toxoplasmosis. The full-length of TgDDX39 gene was successfully amplified, cloned into the pET-30a vector, and expressed in BL21 (DE3) competent cells, which was purified and identified as a 57.1 kDa protein via sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Western blot analysis confirmed that rTgDDX39 was specifically recognized by serum from T. gondii-infected mice. Furthermore, immunization of rats with rTgDDX39 generated antiserum that could specifically recognize the native TgDDX39 protein in T. gondii tachyzoite lysates. Immunofluorescence assay revealed that TgDDX39 was primarily located in the nucleus and perinuclear region of tachyzoites. Our vaccination strategy significantly increased T cell proliferation, with CD4⁺ T cells rising by 21.9% and CD8⁺ T cells by 57.8% by the sixth week compared to the adjuvant control group. Additionally, high titers of anti-rTgDDX39 IgG antibodies were detected in vaccinated mice, with a notable induction of IgG1 and IgG2a isotypes, and IgG1/IgG2a > 1 suggests a Th2-biased immune response.

Furthermore, in vitro and in vivo assays demonstrated that polyclonal antibodies raised against rTgDDX39 could inhibit the proliferation of T. gondii RH tachyzoites, highlighting the potential of these antibodies to neutralize this parasite effectively. This study provides compelling evidence of the immunogenicity and protective efficacy of rTgDDX39, supporting its potential as a potential candidate vaccine against toxoplasmosis. The protective efficacy of the vaccine was evaluated in mice challenged with acute (RH) and chronic (PRU) strains of T. gondii, showing a survival time extended to 17 days in the acute model, compared to 13.5 and 14 days in the control groups, and a significant 34% reduction in cyst burden in the chronic model. Additionally, the survival rate in the PRU-infected mice increased from 15 to 20% in the control groups to 45% in the vaccinated group. In vitro and in vivo assays demonstrated that polyclonal antibodies raised against rTgDDX39 could inhibit the proliferation of T. gondii RH tachyzoites, highlighting the potential of these antibodies to neutralize the parasite effectively. This study provides compelling evidence of the immunogenicity and protective efficacy of rTgDDX39, supporting its potential as a candidate vaccine against toxoplasmosis.