Immunization With a DNA Vaccine Encoding the Toxoplasma gondii’ s GRA39 Prolongs Survival and Reduce Brain Cyst Formation in a Murine Model

Abstract

Toxoplasma gondii, an obligate intracellular protozoan parasite, can cause infect almost all warm-blooded animals and humans. To evaluate the immunogenicity and protective efficacy of T. gondii GRA39 (TgGRA39) in mice by using DNA immunization, we constructed a recombinant eukaryotic plasmid pVAX-TgGRA39. The specific immune responses in immunized mice were analyzed by serum antibody and cytokine measurements, lymphocyte proliferation assays and flow cytometry of T lymphocyte subclasses. Also, protective efficacy against acute and chronic T. gondii infection was assessed by observing the survival time after challenge with the highly virulent T. gondii RH strain (Genotype I) and counting the number of cyst-forming in brain at 4 weeks post-infection with the cyst-forming PRU strain of T. gondii (Genotype II), respectively. Our results showed that DNA immunization with pVAX-GRA39 via intramuscular injection three times, at 2-week intervals could elicit humoral and cellular immune response, indicated by enhanced levels of IgG and IgG2a antibodies (a slightly elevated IgG2a to IgG1 ratio), and increased levels of cytokines IFN-γ, IL-2, IL-12, IL-17A, IL-17F, IL-22 and IL-23 and percentages of CD3+ CD4+ CD8- and CD3+ CD8+ CD4– T cells, in contrast to non-immunized mice. The significant increase in the expression levels of IL-6, TGF-β1, IL-1β, and the transcription factor factors RORγt, RORα, and STAT3 involved in the activation and pathway of Th17 and Tc17 cells, were also observed. However, no significant difference was detected in level of IL-4 and IL-10 (p > 0.05). These effective immune responses had mounted protective immunity against T. gondii infection, with a prolonged survival time (16.80 ± 3.50 days) and reduced cyst numbers (44.5%) in comparison to the control mice. Our data indicated that pVAX-TgGRA39 could induce effective humoral, and Th1-type, Th17, and Tc17 cellular immune responses, and may represent a promising vaccine candidate against both acute and chronic T. gondii infection.

A novel mRNA vaccine, TGGT1_278620 mRNA-LNP, prolongs the survival time in BALB/c mice with acute toxoplasmosis

“…Survival time is a direct and reliable indicator of the safety and efficacy of T. gondii candidate vaccines. Although the TG_620 mRNA-LNP vaccine did not induce complete protection against high virulence T. gondii infection, it did induce better partial protection than other T. gondii vaccines, such that the survival time of the mice in this study was longer than that in some previous studies ( 43 , 59 ) and even longer than that of the combined DNA vaccine ( 60 ). Mice immunized with TG_620 mRNA-LNP were able to elicit both humoral and cellular immune responses against T. gondii .…”

Comparison of the immune response and protection against the experimental Toxoplasma gondii infection elicited by immunization with the recombinant proteins BAG1, ROP8, and BAG1‐ROP8

“…IL-2 is another important Th1-biased cytokine that regulates the proliferation and activity of CD8+ T cells, which is important for resistance to toxoplasma infection. 32 The levels of IL-2 in rTgBAG1, rTgROP8, and rTgBAG1-rTgROP8 groups were all increased, and the rTgBAG1-rTgROP8 group produced the highest levels of IL-2. In summary, the rTgBAG1-rTgROP8 group showed a higher advantage, indicating that the immune response can be significantly enhanced by immunizing with proteins of multiple antigens.…”

“…Correspondingly, the rTgBAG1‐TgROP8 group survived the infection with TgCtwh3 for the longest time (12 days). IL‐2 is another important Th1‐biased cytokine that regulates the proliferation and activity of CD8+ T cells, which is important for resistance to toxoplasma infection 32 . The levels of IL‐2 in rTgBAG1, rTgROP8, and rTgBAG1‐rTgROP8 groups were all increased, and the rTgBAG1‐rTgROP8 group produced the highest levels of IL‐2.…”

Immunization of BALB/c Mice with Killed Tachyzoites of Toxoplasma gondii against Acute Toxoplasmosis

“…For preventing Toxoplasma infection, the vaccine in veterinary seems more progressive than medical as the S48 strain Toxovax® live vaccine has been developed originally for use in sheep, but by now there was no available vaccine for human ( 25 ), reflecting exploring safety vaccine is most important not only for animals but also for human beings. Towards this target, a range of veterinary vaccines in candidate were designed in the past few years to help control T. gondii acute and/or chronic infections through eliminating cysts in brain and muscle tissues ( 26 , 27 ), preventing congenital toxoplasmosis ( 28 ), and reducing oocysts shedding in cats ( 29 ), but for the protective efficacy all of them were not satisfactory.…”