Immunostimulatory efficacy and protective potential of putative TgERK7 protein in mice experimentally infected by Toxoplasma gondii

Live-attenuated PruΔgra72 strain of Toxoplasma gondii induces strong protective immunity against acute and chronic toxoplasmosis in mice

BACKGROUND

Toxoplasma gondii is an intracellular opportunistic pathogenic protozoan that poses serious threats, particularly in immunocompromised individuals. In the absence of a robust prophylactic measure, the mitigation and management of toxoplasmosis present formidable challenges to public health. We recently found that GRA72 plays an important role in parasitophorous vacuole (PV) morphology, growth and virulence of T. gondii. However, whether gra72-deficient strain can be used as a vaccine remains unknown.

METHODS

We first examined the attenuated virulence of gra72 gene knockout strain (PruΔgra72) and the parasite load in organs of the infected mice. Subsequently, we evaluated the immune-protective effects of the PruΔgra72 vaccination against challenge with various types of T. gondii tachyzoites and Pru cysts. Furthermore, levels of antibodies and cytokines induced by PruΔgra72 vaccination were examined. Statistical analysis was conducted by Student's t-test or Mantel-Cox log-rank test based on data obtained from three independent experiments with GraphPad Prism 8.0.

RESULTS

We found that PruΔgra72 strain exhibited a significantly attenuated virulence even at the highest dose of 5 × 107 tachyzoites in Kunming mice model. The significant decrease of brain cyst burden and parasite load in the organs of the PruΔgra72-infected mice suggested its potentiality as a live-attenuated vaccine. Hence, we explored the protective immunity of PruΔgra72 vaccination against toxoplasmosis. Results showed that vaccination with 5 × 106 PruΔgra72 tachyzoites triggered a strong and sustained Th1-biased immune response, marked by significantly increased levels of anti-T. gondii IgG antibodies, and significantly higher levels of Th1 type cytokines (IL-2, IL-12 and IFN-γ) compared to that of Th2 type (IL-4 and IL-10). Vaccination with 5 × 106 PruΔgra72 tachyzoites in mice conferred long-term protection against T. gondii infection by less virulent tachyzoites (ToxoDB#9 PYS and Pru strains) and Pru cysts, provided partial protection against acute infection by high virulent Type I RH tachyzoites and significantly decreased brain cyst burden of chronically infected mice.

CONCLUSIONS

The avirulent PruΔgra72 induced strong protective immunity against acute and chronic T. gondii infection and is a promising candidate for developing a safe and effective live-attenuated vaccine against T. gondii infection.

In Vitro Virulence Contrast of Seven Genetically Distinct Toxoplasma gondii Isolates After Rejuvenation In Vivo

BACKGROUND

In the past for more than 100 years at least 300 genotypes of Toxoplasma gondii were recorded and several traditional isolates such as RH, GT1, ME49, PRU and VEG were used repeatedly to clarify the pathogenic mechanisms and the epidemiological significance to human, but for if their virulence was mutative post-iterative passages it remains confused.

OBJECTIVE

Therefore, in the study, seven genetically distinct T. gondii including C7 and PYS previously discovered in China were reidentified by sequencing the head of hsp40 locus to distinguish their virulence in vitro post-rejuvenation in vivo.

RESULTS

Our data showed the nucleotides were different in 18 positions and 7 of them can be used to type T. gondii isolates. Total 634 plaques of T. gondii without two or more overlaps indicated that RH and GT1 tachyzoites possess stronger power than other five isolates in vitro (p < 0.001), followed by ME49, PRU, C7, PYS, and the weakest VEG. Based on the shapes of plaques, we found the ratio of their width/length was associated with the virulence of T. gondii, and speculated it could be used to judge T. gondii tachyzoites in vitro, whereas the data of simple linear regression analyses did not agree.

CONCLUSIONS

Together, virulence of seven genetically distinct T. gondii isolates that can be distinguished by seven mutative nucleotides in hsp40 was redefined in vitro post-rejuvenation in vivo, and it cannot be directly judged just according to the shapes of plaques formed in vitro.

Advances in Toxoplasma gondii Vaccines: Current Strategies and Challenges for Vaccine Development

Toxoplasmosis, caused by the apicomplexan parasite Toxoplasma gondii, is one of the most damaging parasite-borne zoonotic diseases of global importance. While approximately one-third of the entire world’s population is estimated to be infected with T. gondii, an effective vaccine for human use remains unavailable. Global efforts in pursuit of developing a T. gondii vaccine have been ongoing for decades, and novel innovative approaches have been introduced to aid this process. A wide array of vaccination strategies have been conducted to date including, but not limited to, nucleic acids, protein subunits, attenuated vaccines, and nanoparticles, which have been assessed in rodents with promising results. Yet, translation of these in vivo results into clinical studies remains a major obstacle that needs to be overcome. In this review, we will aim to summarize the current advances in T. gondii vaccine strategies and address the challenges hindering vaccine development.

Toxoplasma invasion delayed by TgERK7 eradication

Toxoplasma gondii causes serious clinical toxoplasmosis in humans mostly due to its asexual life cycles, which can be artificially divided into five tightly coterminous stages. Any radical or delay for the stage will result in tremendous changes immediately behind. We previously demonstrated that TgERK7 is associated with the intracellular proliferation of T. gondii, but during the process, other stages before were not meanwhile determined. To further clarify the function of ERK7 gene in T. gondii, the complemental strain of ΔTgERK7 tachyzoites created previously was engineered via electric transfection with the recombinant pUC/Tgerk7 plasmid, named pUC/TgERK7 strain in this study, and was used together with ΔTgERK7 and wild-type GT1 strains to retrospect the phenotypic changes including invasion and attachment. The results showed that TgERK7 protein can be re-expressed in the ΔTgERK7 tachyzoites and eradication of this protein leads to significantly lower invasion of T. gondii at 1 h and 2 h post-infection (P < 0.05), which is the key factor causing the following slow intracellular proliferation, in comparison with wild-type GT1 and pUC/TgERK7 parasites; noteworthily, at other early time points including 15 min for attachment assay was no statistical difference (P > 0.05). The data suggested that ERK7 protein in T. gondii is an important virulence factor that participates in the invasion of this parasite.