Induction of protective Th1 immune responses in mice by vaccination with recombinant Toxoplasma gondii nucleoside triphosphate hydrolase-II

Construction of Toxoplasma gondii SRS29C nucleic acid vaccine and comparative immunoprotective study of an SRS29C and SAG1 combination

Toxoplasma gondii is an intracellular protozoan parasite that infects all nucleated cells except the red blood cells. Currently, nucleic acid vaccines are being widely investigated in Toxoplasma gondii control, and several nucleic acid vaccine candidate antigens have shown good protection in various studies. The aim of this study was to construct a nucleic acid vaccine with Toxoplasma gondii SRS29C as the target gene. We explored the nucleic acid vaccine with Toxoplasma surface protein SRS29C and the combined gene of SRS29C and SAG1 and evaluated its immunoprotective effect against Toxoplasma gondii. To amplify the gene fragment and clone it to the expression vector, the recombinant plasmid pEGFP-SRS29C was constructed by PCR. Eukaryotic cells were transfected with the plasmid, and the expression of the target protein was assessed using the Western blot method. The level of serum IgG was determined via ELISA, and the splenic lymphocyte proliferation ability was detected using the CCK-8 method. The percentages of CD4+ and CD8+ T cells were measured by flow cytometry. Mice were immunised three times with single-gene nucleic acid vaccine and combination vaccine. Splenic lymphocytokine expression was determined using ELISA kits. The mice's survival time was monitored and recorded during an in vivo insect assault experiment, and the vaccine's protective power was assessed. The outcomes showed that PCR-amplification of an SRS29C gene fragment was successful. The 4,733-bp vector fragment and the 1,119-bp target segment were both recognised by double digestion. Additionally, after transfection of the recombinant plasmid pEGFP-SRS29C, Western blot examination of the extracted protein revealed the presence of a target protein strip at 66kDa. The test results demonstrated that the IgG content in the serum of the pEGFP-SRS29C group and the co-immunization group was significantly higher than that of the PBS group and the empty vector group. The IgG potency induced by the co-immunization group was higher than that of the pEGFP-SRS29C group and the pEGFP-SAG1 group, the number of splenic lymphocyte proliferation number was higher than that of the PBS group and the empty vector group. The CD4+/CD8+ T ratio was higher than that of the PBS group and the empty vector group. The expression of IFN-γ and TNF-α in the splenocytes of the pEGFP-SRS29C group and the combined immunisation group was significantly higher following antigen stimulation. In the worm attack experiments, mice in the PBS and empty vector groups perished within 9 days of the worm attack, whereas mice in the pEGFP-SRS29C group survived for 18 days, mice in the pEGFP-SAG1 group survived for 21 days, and mice in the co-immunization group survived for 24 days. This demonstrates that the constructed Toxoplasma gondii nucleic acid vaccine pEGFP-SRS29C and the combined gene vaccine can induce mice to develop certain humoral and cellular immune responses, and enhance their ability to resist Toxoplasma gondii infection.

Protective immunity induced by DNA vaccine containing TgGRA35, TgGRA42, and TgGRA43 against Toxoplasma gondii infection in Kunming mice

Background

Toxoplasma gondii can cause congenital infection and abortion in humans and warm-blooded animals. T. gondii dense granule proteins, GRA35, GRA42, and GRA43, play a critical role in the establishment of chronic infection. However, their potential to induce protective immunity against T. gondii infection remains unexplored.

Objective

This study aimed to test the efficacy of a DNA vaccine encompassing GRA35, GRA42, and GRA43 in inducing protective immunity against the highly virulent T. gondii RH strain (type I) and the brain cyst-forming PRU strain (type II).

Methods

The eukaryotic plasmids pVAX-GRA35, pVAX-GRA42, and pVAX-GRA43 were constructed and formulated into two- or three-gene cocktail DNA vaccines. The indirect immunofluorescence assay (IFA) was used to analyze their expression and immunogenicity. Mice were immunized with a single-gene, two-genes, or multicomponent eukaryotic plasmid, intramuscularly. We assessed antibody levels, cytotoxic T-cell (CTL) responses, cytokines, and lymphocyte surface markers by using flow cytometry. Additionally, mouse survival and cyst numbers in the brain of mice challenged 1 to 2 months postvaccination were determined.

Results

Specific humoral and cellular immune responses were elicited in mice immunized with single-, two-, or three-gene cocktail DNA vaccine, as indicated by significant increases in serum antibody concentrations of total IgG, IgG2a/IgG1 ratio, cytokine levels (IFN-γ, IL-2, IL-12, IL-4, and IL-10), lymphocyte proliferation, lymphocyte populations (CD4+ and CD8+ T lymphocytes), CTL activities, and survival, as well as decreased brain cysts, in comparison with control mice. Moreover, compared with pVAX-GRA35 + pVAX-GRA42, pVAX-GRA42 + pVAX-GRA43, or pVAX-GRA35 + pVAX-GRA43, multicomponent DNA vaccine with three genes (pVAX-GRA35 + pVAX-GRA42 + pVAX-GRA43) induced the higher humoral and cellular immune responses, including serum antibody concentrations, cytokine levels, lymphocyte proliferation, lymphocyte populations, CTL activities and survival, resulting in prolonged survival time and reduced brain cyst loads. Furthermore, mice immunized with pVAX-GRA35 + pVAX-GRA42, pVAX-GRA42 + pVAX-GRA43, or pVAX-GRA35 + pVAX-GRA43 showed greater Th1 immune responses and protective efficacy than the single-gene-vaccinated groups.

Conclusion

These results demonstrate that TgGRA35, TgGRA42, or TgGRA43 are vaccine candidates against T. gondii infection, and the three-gene DNA vaccine cocktail conferred the strongest protection against T. gondii infection.

Toxoplasma gondii infection in goats: serological, pathological, and clinical monitoring during gestation

This study aimed to evaluate Toxoplasma gondii infection in pregnant goats. The goats were divided into two groups: group one (G1) comprised of 31 pregnant goats naturally infected with T. gondii, and group two (G2) comprised of seven uninfected pregnant goats from a flock with a history of abortion due to toxoplasmosis. Serological investigation, ultrasonography, and clinical testing were performed on all goats during gestation. Serum samples from goats and their offspring (precolostral) were collected to evaluate the vertical transmission of T. gondii. Samples from placentas and aborted fetuses were also collected for molecular and histopathological analysis. Results showed that in G1, estrus recurrence occurred in 22.6% (7/31) of the goats, embryonic death in 3.3% (1/31), and abortion in 19.4% (6/31). An increase in anti-T. gondii antibodies was observed in G1 goats at day 150 of pregnancy. T. gondii DNA was detected in 42.8% (3/7) of aborted fetuses and was associated with histopathological lesions caused by this parasite. Moreover, toxoplasmosis in field conditions caused by genotype ToxoDB #1 in pregnant goats resulted in severe reproductive loss in the flock.

With Chitosan and PLGA as the Delivery Vehicle, Toxoplasma gondii Oxidoreductase-Based DNA Vaccines Decrease Parasite Burdens in Mice

Toxoplasma gondii (T. gondii) is an intracellular parasitic protozoan that can cause serious public health problems. However, there is no effectively preventive or therapeutic strategy available for human and animals. In the present study, we developed a DNA vaccine encoding T. gondii oxidoreductase from short-chain dehydrogenase/reductase family (TgSDRO-pVAX1) and then entrapped in chitosan and poly lactic-co-glycolic acid (PLGA) to improve the efficacy. When encapsulated in chitosan (TgSDRO-pVAX1/CS nanospheres) and PLGA (TgSDRO-pVAX1/PLGA nanospheres), adequate plasmids were loaded and released stably. Before animal immunizations, the DNA vaccine was transfected into HEK 293-T cells and examined by western blotting and laser confocal microscopy. Th1/Th2 cellular and humoral immunity was induced in immunized mice, accompanied by modulated secretion of antibodies and cytokines, promoted the maturation and MHC expression of dendritic cells, and enhanced the percentages of CD4+ and CD8+ T lymphocytes. Immunization with TgSDRO-pVAX1/CS and TgSDRO-pVAX1/PLGA nanospheres conferred significant immunity with lower parasite burden in the mice model of acute toxoplasmosis. Furthermore, our results also lent credit to the idea that TgSDRO-pVAX1/CS and TgSDRO-pVAX1/PLGA nanospheres are substitutes for each other. In general, the current study proposed that TgSDRO-pVAX1 with chitosan or PLGA as the delivery vehicle is a promising vaccine candidate against acute toxoplasmosis.

C57BL/6 mice immunized with synthetic peptides from Toxoplasma gondii surface and microneme immunodominant antigens are able to decrease parasite burden in the brain tissues

Toxoplasmosis is a disease caused by Toxoplasma gondii, an intracellular protozoan able to infect a wide range of hosts. The infection is particularly severe in immunocompromised patients or during pregnancy, circumstances in which the parasite could find a more favorable microenvironment to replicate and invade host tissues. The current treatment consists in toxic drugs for the patients, being not appropriate for the fetuses and immunodeficient patients. So far, there is a lack of available vaccine to prevent the disease. The present study aimed to evaluate the immune response induced by peptides derived from parasite immunodominant proteins from key components, as surface, rhoptry, microneme and dense granule antigens. A panel of eleven peptides was selected considering the highest scores for B cell epitope prediction by in silico analyses. The peptides were divided in groups, according to the parasite organelle locations, and used to immunize C57BL/6 mice. The animals were submitted to three doses of immunization and infected by 10 cysts of T. gondii ME49 strain. Blood samples were collected and used to measure the production of antibodies and cytokines, while the brains were collected to determine the parasite burden by quantitative polymerase chain reaction (qPCR). It was found that synthetic peptides from all targets were able to induce IgG synthesis in immunized mice, as well as to modulate the Th1/Th2 cytokine production, particularly the MIC and SRS groups, which presented the IFN-γ/IL-10 and TNF-α/IL-10 ratios 30 and 10 times higher, respectively, when compared with non-immunized group. Interestingly, the animals from MIC and SRS groups had significantly lower levels of T. gondii DNA in their brains. In summary, it can be concluded that peptides mainly from SRS and MIC parasite components constitute relevant targets to design vaccine candidates against parasite burden observed during chronic toxoplasmosis.

Leishmania infantum nucleoside triphosphate diphosphohydrolase 1 (NTPDase 1) B-domain: Antibody antiproliferative effect on the promastigotes and IgG subclass responses in canine visceral leishmaniasis

A nucleoside triphosphate diphosphohydrolase-1 (NTPDase 1) was identified on the surface, flagellum and kinetoplast from L. infantum promastigotes by immunocytochemistry and confocal laser scanning microscopy, using immune sera that recognized specifically the B domain of NTPDase 1 and produced against synthetic peptides (LbB1LJ and LbB2LJ) derived from this domain. The polyclonal antibodies had effective antileishmanial effect, reducing significantly in vitro promastigotes growth (21-25%), an antiproliferative effect also demonstrated by immune sera produced against recombinant r-pot B domain, and two other synthetic peptides (potB1LJ and potB2LJ). In addition, using these biomolecules in ELISA technique, IgG1 and IgG2 subclasses reactivities of either healthy dogs or infected by L. infantum and classified clinically as asymptomatic, oligosymptomatic and symptomatic were tested. Analysis of distinct IgG1 and IgG2 seropositivities patterns suggested antibody subclasses binding epitopes along B domain for protection against infection, indicating this domain as a new tool for prophylactic and immunotherapeutic investigations.

Could Araucaria heterophylla resin extract be used as a new treatment for toxoplasmosis?

Toxoplasmosis is a worldwide parasitic disease responsible for serious health problems to human. The currently available drugs used for toxoplasmosis treatment showed a limited efficacy and cause serious host toxicity. The in vitro screening for toxoplasmicidal activity of Araucaria heterophylla resin (AHR) extract and its major component 13-epi-cupressic acid (CUP) showed that both AHR (EC₅₀ = 3.90) and CUP (EC₅₀ = 3.69) have high toxoplasmicidal activity in comparison with standard cotrimoxazole (EC₅₀ = 4.28). The antiprotozoal effects of AHR and CUP were investigated against acute and chronic toxoplasmosis using mice models. Two groups of Swiss albino mice were infected by RH Toxoplasma strain intraperitoneally and by Me49 strain orally. Both groups were treated with AHR and CUP in different doses. Their effects were evaluated by survival rate, peritoneal, spleen and liver parasite burdens, brain cyst burden, NO serum level and histopathological lesions. The ultrastructural changes of tachyzoites of acutely infected mice were studied using scanning electron microscopy (SEM). There is an evidence of toxoplasmicidal activity of AHR and CUP in acute and chronic experimental toxoplasmosis. In the acute model, mice treated with AHR and CUP showed prolonged survival rates, a significant decrease in the parasite density in peritoneal lavage and pathological insult in both liver and spleen compared with that of untreated ones. SEM results denote evident morphological alterations of treated tachyzoites. In chronic experimental toxoplasmosis, AHR and CUP treated groups could significantly reduce brain cyst burden by 96.05% and 98.02% respectively. This study indicates that AHR and CUP showed potent toxoplasmicidal activities experimentally and could be used as a potential natural nontoxic agent for treatment of toxoplasmosis.

Propranolol efficacy as a novel adjuvant for immunization against Toxoplasma gondii tachyzoites

Severe or lethal damages, caused by Toxoplasma gondii infection in congenital cases and immunocompromised patients implies the necessity for development of a vaccine and an appropriate adjuvant would be needed to elicit a protective Th1 biased-immune response. The adjuvant activity of propranolol was surveyed and compared with alum by immunization of BALB/c mice with protein components of T. gondii tachyzoites. Five groups of BALB/c mice were immunized with phosphate buffered saline (negative control), Toxoplasma lysate antigen (TLA), alum plus TLA, Propranolol plus TLA, and alum, propranolol and TLA. Immunization efficacy was evaluated by lymphocyte proliferation and DTH tests, challenge with live tachyzoites, IFN-γ production by spleen cells, serum TNF-α concentration and anti- Toxoplasma total IgG, IgG1 and IgG2a measurements. Mice of the PRP-TLA group induced significantly more IFN-γ and TNF-α production and lymphocyte proliferation than other groups. This group of mice also showed more anti-T. gondii IgG2a and DTH responses and showed a significantly increased survival time after challenge. These findings indicate that propranolol as an adjuvant in combination with TLA, may enhance cellular immunity against T. gondii.

Resistance to Chronic Toxoplasma gondii Infection Induced by a DNA Vaccine Expressing GRA16

Toxoplasma gondii can infect all warm-blooded animals including human beings. T. gondii dense granule protein 16 (TgGRA16) as a crucial virulence factor could modulate the host gene expression. Here, a DNA vaccine expressing TgGRA16 was constructed to explore the protective efficacy against T. gondii infection in Kunming mice. The immune responses induced by pVAX-GRA16 were also evaluated. Mice immunized with pVAX-GRA16 could elicit higher levels of specific IgG antibody and strong cellular response compared to those in controls. The DNA vaccination significantly increased the levels of cytokines (IFN-γ, IL-2, IL-4, and IL-10) and the percentages of CD4+ and CD8+ T cells in mice. After lethal challenge, mice immunized with pVAX-GRA16 (8.4 ± 0.78 days) did not show a significant longer survival time than that in controls (7.1 ± 0.30 days) (p > 0.05). However, in chronic toxoplasmosis model (administration of 10 brain cysts of PRU strain orally), numbers of tissue cysts in mice immunized with pVAX-GRA16 were significantly reduced compared to those in controls (p < 0.05) and the rate of reduction could reach 43.89%. The results indicated that the TgGRA16 would be a promising vaccine candidate for further development of effective epitope-based vaccines against chronic T. gondii infection in mice.

Induction of Protective Immunity against Toxoplasma gondii in Mice by Nucleoside Triphosphate Hydrolase-II (NTPase-II) Self-amplifying RNA Vaccine Encapsulated in Lipid Nanoparticle (LNP)

RNA-based vaccine represents an irresistible and safe immunization strategy with decreasing theoretical risks of genomic integration and malignant cell transformation. To our knowledge, however, there is no report about development of RNA vaccine against Toxoplasma gondii infection. We have previously demonstrated that the recombinant T. gondii nucleoside triphosphate hydrolase-II (NTPase-II) protein is able to provide protective Th1 cell-mediated immunity against T. gondii. Herein, we evaluated the immunogenic potential of a self-amplifying RNA vaccine-encoding T. gondii NTPase-II gene, RREP-NTPase-II, delivered by a synthetic lipid nanoparticle (LNP). Immunization of mice with naked RREP-NTPase-II induced a strong cellular and humoral immune response with high-IgG antibody titers and IFN-γ production. The immunized mice displayed significantly prolonged survival time and reduction in brain parasite load (46.4%) compared with control group. Furthermore, mice vaccinated with RREP-NTPase-II-encapsulated LNP displayed significantly enhanced protection against acute infection as well as chronic infection with PRU cyst, which shows 62.1% reduction in brain cyst burden in comparison to control group. These results suggest that the combination of self-amplifying RNA and LNP ion would be beneficial to the development of a safe and long-acting vaccine against toxoplasmosis.

Protective immune response in mice induced by a suicidal DNA vaccine encoding NTPase-II gene of Toxoplasma gondii

DNA-based alphaviral RNA replicon vectors, also called suicidal DNA vectors, have been employed to alleviate biosafety concerns attribution to its ability to induce apoptotic cell death of the transfected cells. Toxoplasma gondii nucleoside triphosphate hydrolase-II (TgNTPase-II), which facilitates the parasite to salvage purines from the host cell for survival and replication, have been demonstrated to be a potential vaccine candidate for toxoplasmosis. Herein, we evaluated the immunogenic potential of a suicidal DNA vaccine encoding TgNTPase-II gene, pDREP-TgNTPase-II, delivered intramuscularly in combination with electroporation. Immunization of mice with pDREP-TgNTPase-II elicited specific humoral responses, with high IgG antibody titers and a mixed IgG1/IgG2a response. The cellular immune response was associated with high level production of IFN-γ, IL-2, IL-10 cytokines and low level IL-4 production as well as the increase of the percentage of CD8+ T cells, indicating that a Th1 predominant response was elicited. Furthermore, mice vaccinated with this suicidal DNA vaccine displayed partial protection against acute infection with the virulent RH strain as well as chronic infection with PRU cyst, which shows 77.7% and 71.4% reduction in brain cyst burden in comparison to PBS and pDREP-eGFP control group, respectively. Based on the cellular and antibody responses, the suicidal DNA vaccine elicited a Th1-predominant immune response against T. gondii challenge.

Vaccination with Toxoplasma gondii calcium-dependent protein kinase 6 and rhoptry protein 18 encapsulated in poly(lactide-co-glycolide) microspheres induces long-term protective immunity in mice

Background

Toxoplasmosis is a worldwide zoonosis caused by the intracellular parasite Toxoplasma gondii. However, no effective vaccine is yet available. Poly(lactide-co-glycolide) polymers can reduce protein degradation and sustain the release of antigens over a long period, which could generate a long-lasting immune response in vivo. Using a mouse model of toxoplasmosis, we evaluated the protective efficacy of vaccination with two recombinant proteins, which are formulated in biodegradable polymers.

Methods

Two recombinant proteins, rCDPK6 and rROP18, were encapsulated in poly(d,l-lactide-co-glycolide) (PLG), and then injected subcutaneously into Kunming mice. The mice immune responses were evaluated in terms of lympho-proliferation, cytokine expression, and antibodies. The survival of infected mice and brain cyst formation were also evaluated at 6 weeks after challenge with T. gondii RH strain (genotype I) or PRU strain (genotype II).

Results

Both protein vaccines induced Th1-biased immune responses, with increased specific antibodies and T cells, high levels of interferon-γ and interleukin 2, and strong lymphocyte proliferative responses. The mice immunized with the various protein vaccines survived slightly longer time than the control groups (P > 0.05) after injection with T. gondii RH strain. There were fewer brain cysts in the mice in all the immunized groups than that in the control groups, and the brain cysts were significantly reduced in mice immunized with proteins + 206, rCDPK6 + PLG and rCDPK6 + rROP18 + PLG (P < 0.05) compared controls. Further comparison of the immune responses to the proteins adjuvanted with PLG or Montanide™ ISA 206 VG 6 weeks after the last immunization revealed that antigens encapsulated in PLG conferred greater protective immunity against challenge.

Conclusions

These findings suggest that the two recombinant T. gondii proteins encapsulated in PLG conferred immunity to T. gondii for an extended period, providing the foundation for the further development of a commercial vaccine against toxoplasmosis.

Experimental ovine toxoplasmosis: influence of the gestational stage on the clinical course, lesion development and parasite distribution

The relation between gestational age and foetal death risk in ovine toxoplasmosis is already known, but the mechanisms involved are not yet clear. In order to study how the stage of gestation influences these mechanisms, pregnant sheep of the same age and genetic background were orally dosed with 50 oocysts of Toxoplasma gondii (M4 isolate) at days 40 (G1), 90 (G2) and 120 (G3) of gestation. In each group, four animals were culled on the second, third and fourth week post infection (pi) in order to evaluate parasite load and distribution, and lesions in target organs. Ewes from G1 showed a longer period of hyperthermia than the other groups. Abortions occurred in all groups. While in G2 they were more frequent during the acute phase of the disease, in G3 they mainly occurred after day 20 pi. After challenge, parasite and lesions in the placentas and foetuses were detected from day 19 pi in G3 while in G2 or G1 they were only detected at day 26 pi. However, after initial detection at day 19 pi, parasite burden, measured through RT-PCR, in placenta or foetus of G3 did not increase significantly and, at in the third week pi it was lower than that measured in foetal liver or placenta from G1 to G3 respectively. These results show that the period of gestation clearly influences the parasite multiplication and development of lesions in the placenta and foetus and, as a consequence, the clinical course in ovine toxoplasmosis.

Recombinant Toxoplasma gondii phosphoglycerate mutase 2 confers protective immunity against toxoplasmosis in BALB/c mice

Toxoplasmosis is one of the most widespread zoonoses worldwide. It has a high incidence and can result in severe disease in humans and livestock. Effective vaccines are needed to limit and prevent infection with Toxoplasma gondii. In this study, we evaluated the immuno-protective efficacy of a recombinant Toxoplasma gondii phosphoglycerate mutase 2 (rTgPGAM 2) against T. gondii infection in BALB/c mice. We report that the mice nasally immunised with rTgPGAM 2 displayed significantly higher levels of special IgG antibodies against rTgPGAM 2 (including IgG1, IgG2a and IgAs) and cytokines (including IFN-γ, IL-2 and IL-4) in their blood sera and supernatant of cultured spleen cells compared to those of control animals. In addition, an increased number of spleen lymphocytes and enhanced lymphocyte proliferative responses were observed in the rTgPGAM 2-immunised mice. After chronic infection and lethal challenge with the highly virulent T. gondii RH strain by oral gavage, the survival time of the rTgPGAM 2-immunised mice was longer (P < 0.01) and the survival rate (70%) was higher compared with the control mice (P < 0.01). The reduction rate of brain and liver tachyzoites in rTgPGAM 2-vaccinated mice reached approximately 57% and 69% compared with those of the control mice (P < 0.01). These results suggest that rTgPGAM 2 can generate protective immunity against T. gondii infection in BALB/c mice and may be a promising antigen in the further development of an effective vaccine against T. gondii infection.

Protective immunity against acute toxoplasmosis in BALB/c mice induced by a DNA vaccine encoding Toxoplasma gondii elongation factor 1-alpha

BACKGROUND

Toxoplasma gondii can infect almost all warm-blood animals including human beings. The high incidence and severe damage that can be caused by T. gondii infection clearly indicates the need for the development of a vaccine. T. gondii elongation factor 1-alpha (TgEF-1α) plays an important role in pathogenesis and host cell invasion for this parasite. The aim of this study was to evaluate the immune protective efficacy of a DNA vaccine encoding TgEF-1α gene against acute T. gondii infection in mice.

METHODS

A DNA vaccine (pVAX-EF-1α) encoding T. gondii EF-1a (TgEF-1α) gene was constructed and its immune response and protective efficacy against lethal challenge in BALB/c mice were evaluated.

RESULTS

Mice inoculated with the pVAX-EF-1α vaccine had a high level of specific anti-T. gondii antibodies and produced high levels of IFN-gamma, interleukin (IL)-4, and IL-17. The expression levels of MHC-I and MHC-II molecules as well as the percentages of both CD4(+) and CD8(+) T cells in mice vaccinated with pVAX-EF-1α were significantly increased (p < 0.05), compared with those in all the mice from control groups (blank control, PBS, and pVAXI). Immunization with pVAX-EF-1α significantly (p < 0.05) prolonged mouse survival time to 14.1 ± 1.7 days after challenge infection with the virulent T. gondii RH strain, compared with mice in the control groups which died within 8 days.

CONCLUSIONS

DNA vaccination with pVAX-EF-1α triggered strong humoral and cellular responses and induced effective protection in mice against acute T. gondii infection, indicating that TgEF-1α is a promising vaccine candidate against acute toxoplasmosis.

The effect of chitosan nanospheres on the immunogenicity of Toxoplasma lysate vaccine in mice

Toxoplasmosis, a zoonotic parasitic disease, is a huge challenge for which there is no effective vaccine up till now. In this study, chitosan nanospheres encapsulated with Toxoplasma lysate vaccine was evaluated for its ability to protect mice against both acute and chronic toxoplasmosis models of infection. Results showed that chitosan nanospheres were equally effective to Freund's incomplete adjuvant (FIA) in enhancing the efficacy of Toxoplasma lysate vaccine. The effectiveness was demonstrated by the delayed death of vaccinated mice following challenge either with virulent RH or avirulent Me49 strains, the significant decrease in parasite density in different organs, significant increase in the humoral and cellular immune response (IgG and IFN γ) with a marked reduction of pathological changes in the different organs. However chitosan nanospheres were superior to FIA due to their cost effective preparation and much less necrotic changes induced in the studied organs. The success of chitosan polymer as an alternative to commonly used adjuvants paves the way for the use of other newly developed polymers to be used in the field of vaccine development.

Intranasal immunisation of the recombinant Toxoplasma gondii receptor for activated C kinase 1 partly protects mice against T. gondii infection

Nasal vaccination is an effective therapeutic regimen for preventing certain infectious diseases. The mucosal immune response is important for resistance to Toxoplasma gondii infection. In this study, we evaluated the immune responses elicited in BALB/c mice by nasal immunisation with recombinant T. gondii receptor for activated C kinase 1 (rTgRACK1) and their protective efficacy against T. gondii RH strain during both chronic and lethal infections. Nasal vaccination with rTgRACK1 increased the level of secretory IgA in nasal, intestinal and vesical washes, and the level of IFN-γ and IL-2 in intestinal washes, indicating that rTgRACK1 vaccination promotes mucosal immune responses. The mice immunised with rTgRACK1 also displayed increased levels of rTgRACK1-specific IgA, total IgG, IgG1 and in particular IgG2a in their blood sera, increased production of IFN-γ, IL-2 and IL-4 but not IL-10 from their isolated spleen cells, and enhanced splenocyte proliferation in vitro. rTgRACK1-vaccinated mice were effectively protected against infection with T. gondii RH strain, showing over 50% reduction of tachyzoite burdens in their liver and brain tissues during a chronic infection, and also a 45% increase in their survivals during a lethal challenge. These results indicate that rTgRACK1 might represent an intriguing immunogen for developing a mucosal vaccine against toxoplasmosis.

Intranasal immunisation with recombinant Toxoplasma gondii actin partly protects mice against toxoplasmosis

Toxoplasma gondii is a ubiquitous protozoan intracellular parasite, the causative agent of toxoplasmosis, and a worldwide zoonosis for which an effective vaccine is needed. Actin is a highly conserved microfilament protein that plays an important role in the invasion of host cells by T. gondii. This study investigated the immune responses elicited by BALB/c mice after nasal immunisation with a recombinant T. gondii actin (rTgACT) and the subsequent protection against chronic and lethal T. gondii infections. We evaluated the systemic response by proliferation, cytokine and antibody measurements, and we assessed the mucosal response by examining the levels of TgACT-specific secretory IgA (SIgA) in nasal, vaginal and intestinal washes. Parasite load was assessed in the liver and brain, and the survival of mice challenged with a virulent strain was determined. The results showed that the mice immunised with rTgACT developed high levels of specific anti-rTgACT IgG titres and a mixed IgG1/IgG2a response with a predominance of IgG2a. The systemic immune response was associated with increased production of Th1 (IFN-γ and IL-2), Th2 (IL-4) and Treg (IL-10) cytokines, indicating that not only Th1-type response was induced, but also Th2- and Treg-types responses were induced, and the splenocyte stimulation index (SI) was increased in the mice immunised with rTgACT. Nasal immunisation with rTgACT led to strong mucosal immune responses, as seen by the increased secretion of SIgA in nasal, vaginal and intestinal washes. The vaccinated mice displayed significant protection against lethal infection with the virulent RH strain (survival increased by 50%), while the mice chronically infected with RH exhibited lower liver and brain parasite loads (60.05% and 49.75%, respectively) than the controls. Our data demonstrate, for the first time, that actin triggers a strong systemic and mucosal response against T. gondii. Therefore, actin may be a promising vaccine candidate against toxoplasmosis.

A comparative study between excretory/secretory and autoclaved vaccines against RH strain of Toxoplasma gondii in murine models

Toxoplasma gondii is an obligate intracellular protozoan that has a major importance in public health, in addition to veterinary medicine. Therefore, the development of an effective vaccine for controlling toxoplasmosis is an important goal. Excretory/secretory antigens (ESA), were previously identified as potential vaccine candidates, proved to play important roles in the pathogenesis and immune escape of the parasite. In addition, autoclaved Toxoplasma vaccine (ATV) is a special type of killed vaccine, recently characterized. The aim of the present work was, to compare between excretory/secretory and ATV against RH strain of T. gondii in mice based on; parasitological and histopathological levels. Tachyzoites were harvested from peritoneal exudates of infected mice and were used for challenge infection and vaccine preparation. BCG was used as an adjuvant. Mice were allocated equally into five groups; they were vaccinated intradermally over the sternum. The results of this study showed that the survival time after challenge, extended up to 16 days in ESA vaccinated group and up to 15 days in autoclaved Toxoplasma vaccinated group. ESA vaccinated group exhibited a profound decrease in parasite load following parasite challenge with a higher percentage of reduction in parasite count in all examined organs than the autoclaved Toxoplasma vaccinated group. The histopathological picture of the liver in both immunized groups, revealed marked reduction in the pathological changes observed as compared to controls, especially in ESA vaccinated group. It was concluded that vaccination with ESA showed more promising results versus ATV, as demonstrated by the survival rate of vaccinated mice, tachyzoites count and histopathological examination.

Protective immunity against Toxoplasma gondii induced by DNA immunization with the gene encoding a novel vaccine candidate: calcium-dependent protein kinase 3

Background

Toxoplasma gondii can infect almost all warm-blood animals including human beings. The plant-like calcium-dependent protein kinases (CDPKs) harbored by T. gondii are involved in gliding motility, cell invasion, egress and some other developmental processes, and so have been implicated as important virulence factors.

Methods

In the present study, we constructed a DNA vaccine expressing T. gondii CDPK3 (TgCDPK3) and evaluated its protective efficacy against T. gondii infection in Kunming mice. The gene sequence encoding TgCDPK3 was inserted into the eukaryotic expression vector pVAX I, and mice were immunized with pVAX-CDPK3 intramuscularly.

Results

The results showed that mice immunized with pVAX-CDPK3 developed a high level of specific antibodies and a strong lymphoproliferative response. The significantly increased levels of IFN-γ, IL-2, IL-12 (p70) and IL-23 and high ratio of IgG2a to IgG1 antibody titers indicated that a Th1 type response was elicited after immunization with pVAX-CDPK3. Furthermore, the percentage of CD4+ T cells in mice vaccinated with pVAX-CDPK3 was significantly increased. After lethal challenge with the tachyzoites of the virulent T. gondii RH strain, the mice immunized with pVAX-CDPK3 prolonged the survival time from 10 days to 24 days (13.5 ± 4.89) compared to untreated mice or those received PBS or pVAX I which died within 7 days (P < 0.05). In chronic infection model (10 cysts of the T. gondii PRU strain), the numbers of brain cysts of the mice immunized with pVAX-CDPK3 reduced significantly when compared with those in control groups (P < 0.05), and the rate of reduction could reach to about 50%.

Conclusions

TgCDPK3 can generate protective immunity against acute and chronic T. gondii infection in Kunming mice and is a promising vaccine candidate for further development of an effective vaccine against T. gondii.

DNA immunization with eukaryotic initiation factor-2α of Toxoplasma gondii induces protective immunity against acute and chronic toxoplasmosis in mice

Toxoplasma gondii infection is a serious health problem of humans and animals worldwide. T. gondii eukaryotic initiation factor-2α (TgIF2α) plays a crucial role in parasite viability and is an important virulence factor of T. gondii. To evaluate the vaccine potential of TgIF2α, we constructed a novel eukaryotic plasmid pVAX-IF2α expressing TgIF2α from the RH strain and validated expression and immunogenicity in vitro in the Marc145 cell expression system by indirect immunofluorescence (IFA). Administration of pVAX-IF2α intramuscularly induced specific humoral immune responses including high levels of specific TgIF2α IgG antibody and a mixed IgG1/IgG2a response with a predominance of IgG2a production. The cellular immune response was elicited, showing significant production of IFN-γ and IL-2 associated with Th1 type response, and thus strong cell-mediated cytotoxic activity with increased frequencies of IFN-γ parameters analyzed in both CD4(+) and CD8(+) T cell compartments (CD4(+) IFN-γ(+) T cells and CD8(+) IFN-γ(+) T cells). Immunization resulted in partial protection against acute and chronic toxoplamosis in outbred Kunming mice, demonstrated by a significantly prolonged survival time (15.9±4.6 days) after challenge with the virulent RH strain and significant reduction in brain cysts (44.1%) against chronic infection with PRU cyst in contrast to control mice. Our data suggested that pVAX-IF2α could be used as a DNA vaccine candidate against both acute and chronic T. gondii infection by the activation of effective humoral and cellular immune responses.

Vaccines against Toxoplasma gondii: new developments and perspectives

Toxoplasmosis caused by the protozoan Toxoplasma gondii is a major public health problem, infecting one-third of the world human beings, and leads to abortion in domestic animals. A vaccine strategy would be an ideal tool for improving disease control. Many efforts have been made to develop vaccines against T. gondii to reduce oocyst shedding in cats and tissue cyst formation in mammals over the last 20 years, but only a live-attenuated vaccine based on the S48 strain has been licensed for veterinary use. Here, the authors review the recent development of T. gondii vaccines in cats, food-producing animals and mice, and present its future perspectives. However, a single or only a few antigen candidates revealed by various experimental studies are limited by only eliciting partial protective immunity against T. gondii. Future studies of T. gondii vaccines should include as many CTL epitopes as the live attenuated vaccines.

Toxoplasma gondii protein disulfide isomerase (TgPDI) is a novel vaccine candidate against toxoplasmosis

Toxoplasma gondii is a ubiquitous protozoan parasite that can infect all warm-blooded animals, including both mammals and birds. Protein disulfide isomerase (PDI) localises to the surface of T. gondii tachyzoites and modulates the interactions between parasite and host cells. In this study, the protective efficacy of recombinant T. gondii PDI (rTgPDI) as a vaccine candidate against T. gondii infection in BALB/c mice was evaluated. rTgPDI was expressed and purified from Escherichia coli. Five groups of animals (10 animals/group) were immunised with 10, 20, 30, 40 μg of rTgPDI per mouse or with PBS as a control group. All immunisations were performed via the nasal route at 1, 14 and 21 days. Two weeks after the last immunisation, the immune responses were evaluated by lymphoproliferative assays and by cytokine and antibody measurements. The immunised mice were challenged with tachyzoites of the virulent T. gondii RH strain on the 14th day after the last immunisation. Following the challenge, the tachyzoite loads in tissues were assessed, and animal survival time was recorded. Our results showed that the group immunised with 30 μg rTgPDI showed significantly higher levels of specific antibodies against the recombinant protein, a strong lymphoproliferative response and significantly higher levels of IgG2a, IFN-gamma (IFN-γ), IL-2 and IL-4 production compared with other doses and control groups. While no changes in IL-10 levels were detected. After being challenged with T. gondii tachyzoites, the numbers of tachyzoites in brain and liver tissues from the rTgPDI group were significantly reduced compared with those of the control group, and the survival time of the mice in the rTgPDI group was longer than that of mice in the control group. Our results showed that immunisation with rTgPDI elicited a protective immune reaction and suggested that rTgPDI might represent a promising vaccine candidate for combating toxoplasmosis.

DNA vaccine encoding the Toxoplasma gondii bradyzoite-specific surface antigens SAG2CDX protect BALB/c mice against type II parasite infection

The surface antigens SAG2C, SAG2D, and SAG2X, which expressed specifically on bradyzoite stage of Toxoplasma gondii, have been demonstrated to be important for persistence of cyst in the brain. In this study, DNA vaccines expressing SAG2C, SAG2D, and SAG2X of T. gondii were constructed and their protective efficacy were evaluated in BALB/c mice. Mice vaccinated with pVAX1-SAG2C (pSAG2C), pVAX1-2D (pSAG2D) or pVAX1-2X (pSAG2C) showed higher levels of serum IgG antibodies and lymphocyte proliferation response compared to PBS and pVAX1 treated mice (p<0.05). The immune response was characterized by a strong Th1 response and increased cytokine production of IL-2 and IFN-γ. Vaccinated mice displayed significant protection against the challenge with the cyst of T. gondii genotype II strain of PRU (cyst-forming in mouse). A significant reduction in the brain cyst burden was detected in the mice immunized with pSAG2C (72%), pSAG2D (23%), pSAG2X (69%) alone and even more reduction rate, 77%, was achieved in the combination group compared to PBS treated mice. The results implied that immunization with DNA vaccines expressing SAG2C, SAG2D, and SAG2X, and, in particular, a combination of all three DNA plasmids, could effectively protect the mice against T. gondii chronic infection.

Evaluation of protective effect of multiantigenic DNA vaccine encoding MIC3 and ROP18 antigen segments of Toxoplasma gondii in mice

The high incidence and severe damage caused by Toxoplasma gondii infection clearly indicates the need for the development of a vaccine. In this study, we evaluated the immune responses and protection against toxoplasmosis by immunizing ICR mice with a multiantigenic DNA vaccine. To develop the multiantigenic vaccine, two T. gondii antigens, MIC3 and ROP18, selected on the basis of previous studies were chosen. ICR mice were immunized subcutaneously with PBS, empty pcDNA3.1 vector, pMIC3, pROP18, and pROP18-MIC3, respectively. The results of lymphocyte proliferation assay, cytokine, and antibody determinations showed that mice immunized with pROP18-MIC3 elicited stronger humoral and Th1-type cellular immune responses than those immunized with single-gene plasmids, empty plasmid, or phosphate-buffered saline. After a lethal challenge with the highly virulent T. gondii RH strain, a prolonged survival time in pROP18-MIC3-immunized mice was observed in comparison to control groups. Our study indicates that the introduction of multiantigenic DNA vaccine is more powerful and efficient than single-gene vaccine, and deserves further evaluation and development.

Protective immunity induced by a DNA vaccine expressing eIF4A of Toxoplasma gondii against acute toxoplasmosis in mice

Toxoplasma gondii is an obligate intracellular protozoan parasite infecting humans, mammals and birds. Eukaryotic translation initiation factor (eIF4A) is a newly identified protein associated with tachyzoite virulence. To evaluate the protective efficacy of T. gondii eIF4A, a DNA vaccine (pVAX-eIF4A) encoding T. gondii eIF4A (Tg-eIF4A) gene was constructed. The expression ability of this recombinant DNA plasmid was examined in Marc145 cells by IFA. Then, Kunming mice were intramuscularly immunized with pVAX-eIF4A and followed by challenge infection with the highly virulent T. gondii RH strain. The results showed that vaccination with pVAX-eIF4A elicited specific humoral responses, with high IgG antibody titers and specific lymphocyte proliferative responses. The cellular immune response was associated with significant production of IFN-γ, IL-2 in Kunming mice, and a mixed IgG1/IgG2a response with predominance of IgG2a production, indicating that a Th1 type response was elicited after immunization with pVAX-eIF4A. In addition, the increase of the percentage of CD8+ T cells in lymphoid in mice suggested the activation of MHC class I restricted antigen presentation pathways. After lethal challenge, the mice vaccinated with the pVAX-eIF4A showed a significantly prolonged survival time (23.0±5.5 days) compared with control mice which died within 7 days of challenge (P<0.05). These results demonstrate that pVAX-eIF4A could elicit strong humoral, Th1-type cellular immune responses and increase survival time of immunized mice, suggesting that eIF4A is a promising vaccine candidate against acute T. gondii infection in mice.

Multicomponent DNA vaccine-encoding Toxoplasma gondii GRA1 and SAG1 primes: anti-Toxoplasma immune response in mice

A multicomponent DNA vaccine, encoding Toxoplasma gondii GRA1 and SAG1, was constructed and tested for its ability to confer protection. BALB/c mice were challenged with tachyzoites of the virulent T. gondii RH strain at 4 weeks following the last immunization, and immune responses and survival times were observed. The results show that vaccination by the multicomponent vaccine prolonged survival of mice challenged with the T. gondii RH strain (from average 4.50 ± 0.22 to 7.60 ± 0.74 days); induced high levels of IgG antibody (from 0.252 ± 0.080 to 0.790 ± 0.083), IFN-gamma (from 598.74 ± 67.50 to 853.77 ± 66.74 pg/ml), and IL-2 (from 89.44 ± 10.66 to 192.24 ± 19.90 pg/ml); changed the CD4(+)/CD8(+) lymphocyte ratio (from 1.81 ± 0.14 to 1.09 ± 0.19); and stimulated NK cell-killing activity (from 46.81 ± 3.96 to 64.15 ± 7.71 %). These findings demonstrate that a multicomponent DNA vaccine, encoding GRA1 and SAG1, primes a strong humoral and cellular immune response and enhances protection against T. gondii challenge. The new, combined DNA vaccine provides another means to combat T. gondii infection.