Mic1-3 Knockout Toxoplasma gondii is a good candidate for a vaccine against T. gondii-induced abortion in sheep

This study assessed the effectiveness of a mutant strain of Toxoplasma gondii (RH strain) lacking the mic1 and mic3 genes (Mic1-3KO) against Toxoplasma abortion in sheep. Ewes were inoculated subcutaneously with 105 Mic1-3KO tachyzoïtes in three independent experiments. Following vaccination, Mic1-3KO induced a mild febrile response and serum IgG antibodies, which persisted throughout the experiments. Tissue cysts formed in the sheep, but were not, under our experimental conditions, infectious when given orally. Ewes were mated two months after vaccination and were orally challenged with the PRU strain of T. gondii at mid-gestation (400 oocysts in Experiments 1 and 2; 100 oocysts in Experiment 3). Challenge of vaccinated pregnant ewes resulted in a slight febrile response, whereas unvaccinated ewes developed a more severe, characteristic febrile response of longer duration. After challenge, all unvaccinated ewes aborted whereas 62%, 91% and 64% (Experiments 1, 2 and 3 respectively) of the lambs from vaccinated ewes were viable, with no clinical signs of infection. Mic1-3KO was as effective as S48, the strain used as a live vaccine for sheep (Toxovax®). A dose of 105 Mic1-3KO tachyzoites was sufficient to induce protection (versus a dose of 2 × 106). Both subcutaneous and intraperitoneal injections were effective. Moreover, preliminary results showed the potential of Mic1-3KO to reduce the development of tissue cysts in lambs born to vaccinated ewes. This study demonstrates that Mic1-3KO is a potent vaccine candidate

Vaccines against toxoplasma gondii : challenges and opportunities

Development of vaccines against Toxoplasma gondii infection in humans is of high priority, given the high burden of disease in some areas of the world like South America, and the lack of effective drugs with few adverse effects. Rodent models have been used in research on vaccines against T. gondii over the past decades. However, regardless of the vaccine construct, the vaccines have not been able to induce protective immunity when the organism is challenged with T. gondii, either directly or via a vector. Only a few live, attenuated T. gondii strains used for immunization have been able to confer protective immunity, which is measured by a lack of tissue cysts after challenge. Furthermore, challenge with low virulence strains, especially strains with genotype II, will probably be insufficient to provide protection against the more virulent T. gondii strains, such as those with genotypes I or II, or those genotypes from South America not belonging to genotype I, II or III. Future studies should use animal models besides rodents, and challenges should be performed with at least one genotype II T. gondii and one of the more virulent genotypes. Endpoints like maternal-foetal transmission and prevention of eye disease are important in addition to the traditional endpoint of survival or reduction in numbers of brain cysts after challenge

Immunization with Toxoplasma gondii GRA17 deletion mutant induces partial protection and survival in challenged mice

Toxoplasmosis remains a world-threatening disease largely because of the lack of a fully effective vaccine. Here, we created a ΔGRA17 mutant by disrupting the virulence factor GRA17 using CRISPR-Cas9 method. Then, we tested whether ΔGRA17 tachyzoites can be used as a live-attenuated vaccine against acute, chronic, and congenital Toxoplasma gondii infection in mice. Immune response evoked by ΔGRA17 immunization suggested a sequential Th1 and Th2 T cell response, indicated by high levels of Th1 and a mixed Th1/Th2 cytokines at 28 and 70 days after immunization, respectively. ΔGRA17-mediated immunity fully protected mice against lethal infection with wild-type (wt) RH strain, heterologous challenge with PYS, and TgC7 strains of the Chinese ToxoDB#9 genotype, and T. gondii Pru strain. Although parasite cysts were detected in 8 out of 10 immunized mice, cyst burden in the brain was significantly reduced (P < 0.05) in immunized mice (53 ± 15 cysts/brain) compared to non-immunized mice (4,296 ± 687 cysts/brain). In respect to congenital infection, the litter size, survival rate, and body weight (BW) of pups born to ΔGRA17-immunized dams were not different compared to pups born to naïve control dams (P = 0.24). However, a marked reduction in the litter size (P < 0.001), survival rate, and BW (P < 0.01) of pups born to non-immunized and infected dams was detected. Also, immunized dams infected with type II Pru strain had significantly (P < 0.001) less cyst burden in the brain compared with non-immunized and infected dams. These findings show that immunization with ΔGRA17 strain evokes cell-mediated and neutralizing antibody responses and confers some degree of protection against challenge with homologous and heterologous virulent T. gondii strains

Immunization with a DNA vaccine cocktail encoding TgPF, TgROP16, TgROP18, TgMIC6, and TgCDPK3 genes protects mice against chronic toxoplasmosis

Toxoplasmosis is a zoonotic disease caused by the intracellular protozoan Toxoplasma gondii; and a major source of infection in humans is via ingestion of T. gondii tissue cysts. Ultimately, the goal of anti-toxoplasmosis vaccines is to elicit a sustainable immune response, capable of preventing formation of the parasite tissue cysts—or, at least, to restrain its growth. In this study, we formulated a cocktail DNA vaccine and investigated its immunologic efficacy as a protection against the establishment of T. gondii cysts in the mouse brain. This multicomponent DNA vaccine, encoded the TgPF, TgROP16, TgROP18, TgMIC6, and TgCDPK3 genes, which play key roles in the pathogenesis of T. gondii infection. Results showed that mice immunized via intramuscular injection three times, at 2-week intervals with this multicomponent DNA vaccine, mounted a strong humoral and cellular immune response, indicated by significantly high levels of total IgG, CD4+ and CD8+ T lymphocytes, and antigen-specific lymphocyte proliferation when compared with non-immunized mice. Immunization also induced a mixed Th1/Th2 response, with a slightly elevated IgG2a to IgG1 ratio. The increased production of proinflammatory cytokines gamma-interferon, interleukin-2, and interleukin-12 (p 0.05). The number of brain cysts in immunized mice was significantly less than those in non-immunized mice (643.33 ± 89.63 versus 3,244.33 ± 96.42, p < 0.0001), resulting in an 80.22% reduction in the parasite cyst burden. These findings indicate that a multicomponent DNA vaccine, encoding TgPF, TgROP16, TgROP18, TgMIC6, and TgCDPK3 genes, shows promise as an immunization strategy against chronic toxoplasmosis in mice, and calls for a further evaluation in food-producing animals

Key Limitations and New Insights Into the Toxoplasma gondii Parasite Stage Switching for Future Vaccine Development in Human, Livestock, and Cats

International audienceToxoplasmosis is a parasitic disease affecting human, livestock and cat. Prophylactic strategies would be ideal to prevent infection. In a One Health vaccination approach, the objectives would be the prevention of congenital disease in both women and livestock, prevention/reduction of T. gondii tissue cysts in food-producing animals; and oocyst shedding in cats. Over the last few years, an explosion of strategies for vaccine development, especially due to the development of genetic-engineering technologies has emerged. The field of vaccinology has been exploring safer vaccines by the generation of recombinant immunogenic proteins, naked DNA vaccines, and viral/bacterial recombinants vectors. These strategies based on single- or few antigens, are less efficacious than recombinant live-attenuated, mostly tachyzoite T. gondii vaccine candidates. Reflections on the development of an anti-Toxoplasma vaccine must focus not only on the appropriate route of administration, capable of inducing efficient immune response, but also on the choice of the antigen (s) of interest and the associated delivery systems. To answer these questions, the choice of the animal model is essential. If mice helped in understanding the protection mechanisms, the data obtained cannot be directly transposed to humans, livestock and cats. Moreover, effectiveness vaccines should elicit strong and protective humoral and cellular immune responses at both local and systemic levels against the different stages of the parasite. Finally, challenge protocols should use the oral route, major natural route of infection, either by feeding tissue cysts or oocysts from different T. gondii strains. Effective Toxoplasma vaccines depend on our understanding of the (1) protective host immune response during T. gondii invasion and infection in the different hosts, (2) manipulation and modulation of host immune response to ensure survival of the parasites able to evade and subvert host immunity, (3) molecular mechanisms that define specific stage development. This review presents an overview of the key limitations for the development of an effective vaccine and highlights the contributions made by recent studies on the mechanisms behind stage switching to offer interesting perspectives for vaccine development

Prospects for a human Toxoplasma vaccine

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Induction of protective immunity against toxoplasmosis in mice by immunization with Toxoplasma gondii RNA

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Vaccins on mucosal surfaces

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Co-delivery of PLGA nanoparticles loaded with rSAG1 antigen and TLR ligands: An efficient vaccine against chronic toxoplasmosis

International audienceAlthough vaccination is a promising approach for the control of toxoplasmosis, there is currently no commercially available human vaccine. Adjuvants such as delivery vehicles and immunomodulators are critical components of vaccine formulations. In this study, Poly (D, l-lactide-co-glycolide) (PLGA) nanoparticles were applied to serve as delivery system for both surface antigen-1 (SAG1), a candidate vaccine against toxoplasmosis and two TLR ligands, monophosphoryl lipid A (MPL) and imiquimod (IMQ), respectively. Compared to rSAG1 alone, CBA/J mice immunized with rSAG1-PLGA produced higher anti-SAG1 IgG antibodies titers. This response was increased by the co-administration of IMQ-PLGA (p < 0.01). Compared to IMQ-PLGA co-administration, MPL-PLGA co-administration further increased the humoral response (p < 0.01) and potentiated the Th1 humoral response. Compared to rSAG1 alone, rSAG1-PLGA, or rSAG1-PLGA mixed with IMQ-PLGA or MPL-PLGA similarly enhanced the cellular response characterized by the production of IFN-γ, IL-2, TNF-α and low levels of IL-5, indicating a Th1-biased immunity. The induced immune responses, led to significant brain cyst reductions (p < 0.01) after oral challenge with T. gondii cysts in mice immunized with either rSAG1-PLGA, rSAG1-PLGA + IMQ-PLGA, rSAG1-PLGA + MPL-PLGA formulations. Taken together the results indicated that PLGA nanoparticles could serve as a platform for dual-delivery of antigens and immunomodulators to provide efficacious vaccines against toxoplasmosis

Protective Mucosal Th2 Immune Response against Toxoplasma gondii by Murine Mesenteric Lymph Node Dendritic Cells

Toxoplasma gondii, an obligate intracellular parasite pathogen which initially invades the intestinal epithelium before disseminating throughout the body, may cause severe sequelae in fetuses and life-threatening neuropathy in immunocompromised patients. Immune protection is usually thought to be performed through a systemic Th1 response; considering the route of parasite entry it is important to study and characterize the local mucosal immune response to T. gondii. Despite considerable effort, Toxoplasma-targeted vaccines have proven to be elusive using conventional strategies. We report the use of mesenteric lymph node dendritic cells (MLNDCs) pulsed ex vivo with T. gondii antigens (TAg) as a novel investigation approach to vaccination against T. gondii-driven pathogenic processes. Using a murine model, we demonstrate in two genetically distinct mouse strains (C57BL/6 and CBA/J) that adoptively transferred TAg-pulsed MLNDCs elicit a mucosal Toxoplasma-specific Th2-biased immune response in vivo and confer strong protection against infection. We also observe that MLNDCs mostly traffic to the intestine where they enhance resistance by reduction in the mortality and in the number of brain cysts. Thus, ex vivo TAg-pulsed MLNDCs represent a powerful tool for the study of protective immunity to T. gondii, delivered through its natural route of entry. These findings might impact the design of vaccine strategies against other invasive microorganisms known to be delivered through digestive tract