DNA vaccination with genes encoding Toxoplasma gondii antigens ROP5 and GRA15 induces protective immunity against toxoplasmosis in Kunming mice

Innovative prevention and control of coccidiosis: targeting sporogony for new control agent development

Coccidiosis is one of the most significant diseases affecting the poultry industry, with recent estimates indicating that it causes annual losses exceeding £10 billion globally. Increasing concerns over drug residues and resistance have elevated the importance of safe and effective vaccines as the primary method for controlling coccidiosis and other animal diseases. However, current commercial live vaccines for coccidiosis can negatively impact the feed conversion rates of young broilers and induce subclinical symptoms of coccidiosis, limiting their widespread adoption. Eimeria species, the causative agents of coccidiosis, exhibit unique biological characteristics. Their life cycle involves 2 or more generations of schizogony and 1 generation of gametogony within the host, followed by sporogony in a suitable external environment. Sporogony is crucial for Eimeria oocysts to become infectious and propagate within the host. Focusing on the sporogony process of Eimeria presents a promising approach to overcoming technical challenges in the efficient control of coccidiosis, addressing the urgent need for sustainable and healthy farming practices. This paper systematically reviews existing control strategies for coccidiosis, identifies current challenges, and emphasizes the research progress and future directions in developing control agents targeting sporogony. The goal is to provide guidance for the formulation of scientific prevention and control measures for coccidiosis.

Protective efficacy of recombinant Toxoplasma gondii dense granule protein 15 against toxoplasmosis in C57BL/6 mice

Toxoplasma gondii is a pervasive protozoan parasite that is responsible for significant zoonoses. A wide array of vaccines using different effector molecules of T. gondii have been studied worldwide to control toxoplasmosis. None of the existing vaccines are sufficiently effective to confer protective immunity. Among the different Toxoplasma-derived effector molecules, T. gondii dense granule protein 15 from the type II strain (GRA15 (II)) was recently characterized as an immunomodulatory molecule that induced host immunity via NF-κB. Therefore, we assessed the immunostimulatory and protective efficacy of recombinant GRA15 (II) (rGRA15) against T. gondii infection in a C57BL/6 mouse model. We observed that rGRA15 treatment increased the production of IL-12p40 from mouse peritoneal macrophages in vitro. Immunization of mice with rGRA15 induced the production of anti-TgGRA15-specific IgG, IgG1 and IgG2c antibodies. The rGRA15-sensitized spleen cells from mice inoculated with the same antigen strongly promoted spleen cell proliferation and IFN-γ production. Immunization with rGRA15 significantly enhanced the survival rate of mice and dramatically decreased parasite burden in mice challenged with the Pru (type II) strain. These results suggested that rGRA15 triggered humoral and cellular immune responses to control infection. However, all of the immunized mice died when challenged with the GRA15-deficient Pru strain or the RH (type I) strain. These results suggest that GRA15 (II)-dependent immunity plays a crucial role in protection against challenge infection with the type II strain of T. gondii. This study is the first report to show GRA15 (II) as a recombinant vaccine antigen against Toxoplasma 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.

Screening of apical membrane antigen-1 (AMA1), dense granule protein-7 (GRA7) and rhoptry protein-16 (ROP16) antigens for a potential vaccine candidate against Toxoplasma gondii for chickens

Toxoplasmosis is a zoonotic disease caused by the protozoan parasite, Toxoplasma gondii known to infect almost all animals, including birds and humans globally. This disease has impacted the livestock industry and public health, where infection of domestic animals increases the zoonotic risk of transmission of infection to humans, threatening public health. Hence the need to discover novel and safe vaccines to fight against toxoplasmosis. In the current study, a novel multiepitope vaccine was designed using immunoinformatics techniques targeting T. gondii AMA1, GRA7 and ROP16 antigens, consisting of antigenic, immunogenic, non-allergenic and cytokine inducing T-cell (9 CD8⁺ and 15 CD4⁺) epitopes and four (4) B-cell epitopes fused together using AAY, KK and GPGPG linkers. The tertiary model of the proposed vaccine was predicted and validated to confirm the structural quality of the vaccine. The designed vaccine was highly antigenic (antigenicity = 0.6645), immunogenic (score = 2.89998), with molecular weight of 73.35 kDa, instability and aliphatic index of 28.70 and 64.10, respectively; and GRAVY of -0.363. The binding interaction, stability and flexibility were assessed with molecular docking and dynamics simulation, which revealed the proposed vaccine to have good structural interaction (binding affinity = -106.882 kcal/mol) and stability when docked with Toll like receptor-4 (TLR4). The results revealed that the Profilin-adjuvanted vaccine is promising, as it predicted induction of enhanced immune responses through the production of cytokines and antibodies critical in blocking host invasion.

Co-Immunization with DNA Vaccines Expressing SABP1 and SAG1 Proteins Effectively Enhanced Mice Resistance to Toxoplasma gondii Acute Infection

Toxoplasma gondii (T. gondii) has many intermediate hosts, obligately invades nucleated cells, and seriously threatens human and animal health due to a lack of effective drugs and vaccines. Sialic acid-binding protein 1 (SABP1) is a novel invasion-related protein that, like surface antigen 1 (SAG1), is found on the plasma membrane of T. gondii. To investigate the immunogenicity and protective efficacy of DNA vaccines expressing SABP1 and SAG1 proteins against T. gondii acute infection, the recombinant plasmids pVAX1-SABP1 and pVAX1-SAG1 were produced and administered intramuscularly in Balb/c mice. Serum antibody levels and subtypes, lymphocyte proliferation, and cytokines were used to assess immunized mice's humoral and cellular immune responses. Furthermore, the ability of DNA vaccines to protect mice against T. gondii RH tachyzoites was tested. Immunized mice exhibited substantially higher IgG levels, with IgG2a titers higher than IgG1. When the immune group mice's splenocytes were stimulated with T. gondii lysate antigen, Th1-type cytokines (IL-12p70, IFN-γ, and IL-2) and Th2-type cytokine (IL-4) increased significantly. The combined DNA vaccine significantly increased the immunized mouse survival compared to the control group, with an average death time extended by 4.33 ± 0.6 days (p < 0.0001). These findings show that DNA vaccines based on the SABP1 and SAG1 genes induced robust humoral and cellular immunity in mice, effectively protecting against acute toxoplasmosis and potentially serving as a viable option for vaccination to prevent T. gondii infection.

Protective efficacy of Toxoplasma gondii bivalent MAG1 and SAG1 DNA vaccine against acute toxoplasmosis in BALB/c mice

Toxoplasma gondii can infect a wide range of warm-blooded animals, causing a global toxoplasmosis zoonotic epidemic. Surface antigen 1 (SAG1) protein is expressed at the proliferative tachyzoite stage, whereas matrix antigen 1 (MAG1) is expressed at the bradyzoite and tachyzoite stages. These two proteins were found to perform protective roles in previous studies; however, their synergetic protective efficacy as a DNA vaccine against toxoplasmosis has not been clarified. In this study, we constructed recombinant pcDNA3.1( +)-TgMAG1 (pMAG1), pcDNA3.1( +)-TgSAG1 (pSAG1), and pcDNA3.1( +)-TgMAG1-TgSAG1 (pMAG1-SAG1) plasmids and administered them intramuscularly to immunize mice. The levels of anti-T. gondii IgG in serum and cytokines, such as Interleukin (IL)-4, IL-10, and Interferon (IFN)-γ, in splenocytes were measured using ELISA and the respective culture supernatants. Lethal doses of T. gondii (type I) RH strain tachyzoites were administered to immunized mice, and mortality was assessed. Conversely, mice infected with low doses of tachyzoites were monitored to determine their survival rates, and parasite burden analyses of the brains and livers were conducted. The bivalent TgMAG1 and TgSAG1 DNA vaccines exhibited excellent protective immunity against toxoplasmosis in mice, with higher serum IgG and splenocyte IFN-γ release levels, longer survival days, and reduced parasite burden in the brain and liver tissues (p < 0.05). These findings provide a new perspective for the development of T. gondii vaccines.

Toxoplasma gondii GRA15 DNA Vaccine with a Liposomal Nanocarrier Composed of an SS-Cleavable and pH-Activated Lipid-like Material Induces Protective Immunity against Toxoplasmosis in Mice

Toxoplasma gondii affects the health of humans and livestock and causes severe illness in the fetus and immunocompromised individuals. Because of the high incidence and severe consequences of T. gondii infection, a safe and suitable vaccine is needed. We found that lipid nanoparticles (LNPs) consisting of a series of functional materials prepared with vitamin E, such as SS-cleavable and pH-activated lipid-like materials (ssPalmE), were a safe and efficient way to develop next-generation DNA vaccines. In this study, we prepared ssPalmE-LNP to encapsulate pCpG-free-T. gondii dense granule protein 15 DNA (ssPalmE-LNP_TgGRA15). Following a challenge infection with avirulent PLK strain of T. gondii, the mice immunized with ssPalmE-LNP_TgGRA15 had a significantly higher survival rate and lower clinical scores compared with unimmunized and ssPalmE-LNP_non-coding-immunized mice. Immunization of mice with the ssPalmE-LNP_TgGRA15 led to a significantly higher production of specific IgG1 and IG2c antibodies compared with unimmunized and ssPalmE-LNP_non-coding-immunized mice, while there was no statistically significant difference in the concentration of serum interferon-gamma at the acute stage of the infection. These findings indicate that ssPalmE-LNP is an effective cargo for the transportation of DNA vaccines for protozoan infections. To explore the mechanism of protective immunity induced by ssPalmE-LNP_TgGRA15, further immunological study is needed in the future.

Protective Effect Against Toxoplasmosis in BALB/c Mice Vaccinated With Recombinant Toxoplasma gondii MIF, CDPK3, and 14-3-3 Protein Cocktail Vaccine

Toxoplasma gondii can infect almost all endotherm organisms including humans and cause life-threatening toxoplasmosis in immunocompromised individuals, which leads to serious public health problems. Developing an excellent vaccine against this disease is impending. In present study, we formulated a cocktail protein vaccine including the TgMIF, TgCDPK3, and Tg14-3-3 proteins, which play critical roles in T. gondii infection. The recombinant protein vaccines were constructed and assessed by vaccination in BALB/c mice. We organized the mice in various protein combination groups of vaccines, and all mice were immunized with corresponding proteins at 0, 2, and 4 weeks. The specific protective effects of the vaccines on mice against T. gondii were analyzed by the mensuration of cytokines, serum antibodies, splenocyte proliferation assay, survival time, and parasite cyst burden of mice after the challenge. The study indicated that mice immunized with all three multicomponent proteins vaccine triggered a strong immune response with highest levels of IFN-γ production and IgG antibody compared with the other two protein combinations and controls. Moreover, there was an increase in IL-4 production and antigen-specific lymphocyte proliferation. The parasite cysts were significantly reduced (resulting in an 82.7% reduction), and survival time was longer in immunized mice with three multicomponent proteins compared with the other groups of mice. The enhanced humoral and cell-mediated immunity indicated that the protein cocktail vaccine containing three antigens provided effective protection for mice. These results indicated that recombinant TgMIF, TgCDPK3, and Tg14-3-3 multicomponent proteins were potential candidates for vaccine against toxoplasmosis.

Protective Immunity Induced by TgMIC5 and TgMIC16 DNA Vaccines Against Toxoplasmosis

Toxoplasma gondii is an obligate intracellular parasite, which is responsible for a widely distributed zoonosis. Effective vaccines against toxoplasmosis are necessary to protect the public health. The aim of this study is to evaluate the immune efficacy of DNA vaccines encoding TgMIC5 and TgMIC16 genes against T. gondii infection. The recombinant plasmid pVAX-MIC5 and pVAX-MIC16 were constructed and injected intramuscularly in mice. The specific immune responses and protection against challenge with T. gondii RH tachyzoites were evaluated by measuring the cytokine levels, serum antibody concentrations, lymphocyte proliferation, lymphocyte populations, and the survival time. The protection against challenge with the T. gondii RH tchyzoites and PRU cysts was examined by evaluation of the reduction in the brain cyst burden. The results indicated that immunized mice showed significantly increased levels of IgG, IFN-γ, IL-2, IL-12p70, and IL-12p40 and percentages of CD4⁺ and CD8⁺ T cells. Additionally, vaccination prolonged the mouse survival time and reduced brain cysts compared with controls. Mouse groups immunized with a two-gene cocktail of pVAX-MIC5 + pVAX-MIC16 were more protected than mouse groups immunized with a single gene of pVAX-MIC5 or pVAX-MIC16. These results demonstrate that TgMIC5 and TgMIC16 induce effective immunity against toxoplasmosis and may serve as a good vaccine candidate against T. gondii infection.

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

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.

Genetic immunization against toxoplasmosis: A review article

Toxoplasma gondii is a protozoan coccidian parasite belonging to Phylum Apicomplexa and is the causative agent of toxoplasmosis as a zoonotic disease around the world. It is one of the most important protozoa which is transmitted via various routes and infects several warm-blooded animals. The seroprevalence of T. gondii infection is high worldwide and leads to clinical, psychological, and economic problems. At present, available drug therapy for toxoplasmosis has severe side effects, so the development of new anti-toxoplasma drugs or effective vaccines is mandatory. Therefore, different measures have been taken for the development of anti-toxoplasmosis vaccines, and various studies have shown that DNA vaccines could be one of the most successful approaches against the intracellular parasite, T. gondii. Many of these studies have evaluated the efficacy of immunogenicity and different aspects of the DNA vaccines for toxoplasmosis including single genes or multi-gene plasmids with or without adjuvants. Most of the literature confirms that DNA vaccines containing different antigens of the toxoplasma parasite can induce suitable immune response and protection in acute or chronic toxoplasmosis. Therefore, in this review article, we aimed to discuss the current status of DNA vaccines as a new immunization method against toxoplasmosis.

Efficient Immunization of BALB/c Mice against Pathogenic Brucella melitensis and B. ovis: Comparing Cell-Mediated and Protective Immune Responses Elicited by pCDNA3.1 and pVAX1 DNA Vaccines Coding for Omp31 of Brucella melitensis

Background

Brucella spp. are intracellular pathogens, therefore cell-mediated immunity is the main response to inhibit survival and growth of the bacteria in vertebrate host.

Objective

Many eukaryotic plasmid vectors are being used in setting up DNA vaccines which may show different efficiencies in same conditions. This is important in designing the vaccines and immunization strategies. We looked into the probable differences of immune responses induced by different eukaryotic DNA plasmid vectors (pcDNA3.1 and pVAX1) harboring the same Omp31 gene of B. melitensis.

Materials and Methods

Female BALB/c mice were immunized with pcDNA -omp31 and pVAX-omp31 and further boosted with recombinant Omp31. Subclasses of specific serum IgG against the rOmp31 were measured by ELISA. Cytokines responses to rOmp31 in Splenocyte cultures of the immunized mice were evaluated by measuring the production of IL-4, IL-10, IL-12 and IFN-γ. Protective responses of the immunized mice were evaluated by intraperitoneal challenge with pathogenic Brucella melitensis 16M and Brucella ovis PA76250.

Results

Both DNA vaccine candidates conferred potent Th1-type responses with higher levels of cytokines and immunoglobulins observed in mice immunized with pVAX-omp31. Although pcDNA-omp31 and pVAX-omp31 both elicited protective immunity, mice immunized with the latter showed a higher protection against both B. melitensis and B. ovis PA76250.

Conclusion

The results of this study highlight the significant differences between efficiency of diverse plasmid backbones in DNA vaccines which code for an identical antigen. Comparing various plasmid vectors should be considered as an essential part of the studies aiming construction of DNA vaccines for intracellular pathogens.

Adjuvantic cytokine IL-33 improves the protective immunity of cocktailed DNA vaccine of ROP5 and ROP18 against toxoplasma gondii infection in mice

Toxoplasma gondii is a threat for immunocompromized individuals, and no treatment is available for enhancing immunity against infection. Molecular adjuvants may improve the efficacy of DNA vaccine-induced T cell immunity. Here, we report that cocktailed DNA immunization with ROP5 and ROP18 boosted immune responses induced by a single DNA immunization with ROP5 or ROP18, but also that co-administration of molecular adjuvant IL-33 enhanced immune efficacy induced by this cocktailed DNA vaccination. These improved immune responses were characterized by higher Toxoplasma-specific IgG2a titers, Th1 responses associated with the production of IFN-γ, IL-2, IL-12, as well as cell-mediated activity with higher frequencies of CD8+ and CD4+ T cells. More importantly, this enhanced immunity has the ability to confer remarkable protection against a high dose lethal challenge of the T. gondii RH strain and thus against chronic infection with the T. gondii PRU strain. These data show that IL-33 is a promising immunoadjuvant to facilitate humoral as well as cellular immunity in a vaccine setting against T. gondii, and suggest that it should be evaluated in strategies against other apicomplexan parasites.

Evaluation of immune protection against Toxoplasma gondii infection in mice induced by a multi-antigenic DNA vaccine containing TgGRA24, TgGRA25 and TgMIC6

Toxoplasma gondii infection is prevalent in humans and animals worldwide. In this study, recombinant eukaryotic expression plasmids (pVAX-GRA24, pVAX-GRA25 and pVAX-MIC6) were constructed, and then injected into Kunming mice intramuscularly, as cocktailed plasmids or as single-gene plasmids. We evaluated immune protective responses by detecting the titer of antibodies and cytokine production of IFN-γ, IL-2, IL-4, IL-10, IL-12 and IL-23, the percentages of the subclasses of T lymphocytes, as well as the records of the survival time and cyst decrement in the brain of the mouse model after challenge with the T. gondii RH and Pru strains, respectively. Compared with the control groups, antibody and cytokine production were significantly increased, while the survival times of mice in all immunized groups were also prolonged, and the number of T. gondii cysts in their brains were decreased significantly (29.03% for pVAX-GRA24; 40.88% for pVAX-GRA25; 37.70% for pVAX-MIC6; 48.06% for pVAX-GRA24 + pVAX-GRA25; and 55.37% for pVAX-GRA24 + pVAX-GRA25 + pVAX-MIC6). The mouse group immunized with the three-gene cocktail (TgGRA24 + TgGRA25 + TgMIC6) had better performance in each detection index than the mouse groups immunized with the two-gene cocktail of TgGRA24 + TgGRA25, which was better than that in the group immunized with the single gene vaccine of TgGRA24, TgMIC6 or TgGRA25. In conclusion, TgGRA24 or TgGRA25 may be good vaccine candidates against T. gondii infection, but the three-gene cocktail of TgGRA24, TgMIC6 and TgGRA25 may induce the strongest protective immunity. Further studies of multi-antigenic DNA vaccines or cocktailed vaccines against T. gondii infection are necessary.

Live Attenuated Pru:Δcdpk2 Strain of Toxoplasma gondii Protects Against Acute, Chronic, and Congenital Toxoplasmosis

Background

The threat of Toxoplasma gondii infection in immunocompromised individuals and pregnant women necessitates the development of a safe and effective vaccine. Here, we examined the immune protection conferred by a live attenuated strain of T. gondii.

Methods

We tested the efficacy of intraperitoneal vaccination using 500 Ca2+-dependent protein kinase 2 (cdpk2)-deficient tachyzoites of T. gondii Pru strain against acute, chronic, and congenital toxoplasmosis in mice. The kinetics of antibody response, cytokines, and other quantifiable correlates of protection against T. gondii infection were determined.

Results

Vaccination with Pru:Δcdpk2 induced a high level of anti-T. gondii immunoglobulin G titer, type 1 T-helper (Th1) response at 28 days postvaccination, and a mixed Th1/type 2 T-helper response at 70 days postvaccination. All vaccinated mice survived a heterologous challenge with 1000 tachyzoites of RH or ToxoDB#9 (PYS or TgC7) strains. Also, vaccination protected against homologous infection with 20 T. gondii Pru cysts, and improved pregnancy outcome by reducing parasite cyst load in the brain, maintaining litter size and body weight of pups born to vaccinated dams challenged with 10 Pru cysts compared to pups born to unvaccinated dams.

Conclusions

The use of T. gondii Pru:Δcdpk2 mutant strain represents a promising approach to protection against acute, chronic, and congenital toxoplasmosis in mice.

A systematic review on the role of GRA proteins of Toxoplasma gondii in host immunization

Toxoplasma gondii is a widespread obligatory intracellular parasite infecting humans and most of all other warm-blooded animals. Currently there is no any accepted vaccine for prevention of T. gondii infection. Many studies are focused on using of various excretory secretory antigens (ESA); and among them dense granule antigens (GRAs) being involved in parasite survival, virulence and replication processes, are considered as one of the predominant vaccine candidates. The aim of this systematic review is to prepare more comprehensive understanding of these antigens to reduce T. gondii infection in humans and animals. English databases, including PubMed, Science Direct, Google Scholar, Scopus, ISI Web of Science were systematically searched and papers evaluating GRA antigens published until June 2019 were selected. Evaluation of selected publications revealed that GRA4 and GRA7 substantially increased survival time of the experimental animals. It is noticeable that the maximum reduction in cyst burden was observed in BALB/c mice vaccinated with combination of GRA3, GRA7 and M2AP antigens (93.5%). GRA6 and GRA10 have shown high immunogenicity and GRA1 and 2 are important for virulence and induction of immune responses. This review will be helpful for researchers to conduct more effective studies in the field of immunization against T. gondii infection.

Protective Effect Against Toxoplasmosis in BALB/c Mice Vaccinated With Toxoplasma gondii Macrophage Migration Inhibitory Factor

Toxoplasma gondii is an obligate intracellular parasite responsible for toxoplasmosis, which can cause severe disease in the fetus and immunocompromised individuals. Developing an effective vaccine is crucial to control this disease. Macrophage migration inhibitory factor (MIF) has gained substantial attention as a pivotal upstream cytokine to mediate innate and adaptive immune responses. Homologs of MIF have been discovered in many parasitic species, and one homolog of MIF has been isolated from the parasite Toxoplasma gondii. In this study, the recombinant Toxoplasma gondii MIF (rTgMIF) as a protein vaccine was expressed and evaluated by intramuscular injection in BALB/c mice. We divided the mice into different dose groups of vaccines, and all immunizations with purified rTgMIF protein were performed at 0, 2, and 4 weeks. The protective efficacy of vaccination was analyzed by antibody assays, cytokine measurements and lymphoproliferative assays, respectively. The results obtained indicated that the rTgMIF vaccine elicited strong humoral and cellular immune responses with high levels of IgG antibody and IFN-γ production compared to those of the controls, in addition to slight higher levels of IL-4 production. After vaccination, a stronger lymphoproliferative response was also noted. Additionally, the survival time of mice immunized with rTgMIF was longer than that of the mice in control groups after challenge infection with virulent T. gondii RH tachyzoites. Moreover, the number of brain tissue cysts in vaccinated mice was reduced by 62.26% compared with the control group. These findings demonstrated that recombinant TgMIF protein is a potential candidate for vaccine development against toxoplasmosis.

GRA24-Based DNA Vaccine Prolongs Survival in Mice Challenged With a Virulent Toxoplasma gondii Strain

Toxoplasma gondii causes infections in a wide range of intermediate hosts and remains a threatening disease worldwide because of the lack of effective drugs and vaccines. Dense granule protein 24 (GRA24) is a novel essential virulence factor that is transferred into the nucleus of host cells from the parasitophorous vacuole to regulate gene expression. In the present study, bioinformatic analysis showed that GRA24 had a high score for B-cell and T-cell epitopes compared with surface antigen 1 (SAG1), which has been studied as a promising vaccine candidate. As a DNA vaccine, pVAX1-GRA24 was injected intramuscularly into BALB/c mice and the induced immune response was evaluated. pVAX1-GRA24 induced high levels of a mixed Th1/Th2 cytokines at 6 weeks after immunization. Antibody determinations, cytokines [interferon gamma (IFN-γ), interleukin (IL)-12, IL-4, IL-10], antigen-specific lymphocyte proliferation, CD4+ and CD8+ T lymphocytes, and cytotoxic T lymphocyte activity showed that mice immunized with pVAX1-GRA24 produced specific humoral and cellular immune responses. The expression levels of interferon regulatory factor 8 (IRF8), nuclear factor kappa B (NF-κB), and T-Box 21 (T-bet) were significantly higher in the pVAX1-GRA24 immunization group than in the control groups. Survival times were prolonged significantly (24.6 ± 5.5 days) in the mice immunized with pVAX1-GRA24 compared with the mice in the control groups, which died within 7 days of T. gondii challenge (p < 0.05). The results of the present study showed that pVAX1-GRA24 induced a T. gondii-specific immune response and thus represents a promising candidate vaccine to treat toxoplasmosis.

Rhoptry antigens as Toxoplasma gondii vaccine target

Toxoplasmosis is a cosmopolitan zoonotic infection, caused by a unicellular protozoan parasite known as Toxoplasma gondii that belongs to the phylum Apicomplexa. It is estimated that over one-third of the world's population has been exposed and are latently infected with the parasite. In humans, toxoplasmosis is predominantly asymptomatic in immunocompetent persons, while among immunocompromised individuals may be cause severe and progressive complications with poor prognosis. Moreover, seronegative pregnant mothers are other risk groups for acquiring the infection. The life cycle of T. gondii is very complex, indicating the presence of a plurality of antigenic epitopes. Despite of great advances, recognize and construct novel vaccines for prevent and control of toxoplasmosis in both humans and animals is still remains a great challenge for researchers to select potential protein sequences as the ideal antigens. Notably, in several past years, constant efforts of researchers have made considerable advances to elucidate the different aspects of the cell and molecular biology of T. gondii mainly on microneme antigens, dense granule antigens, surface antigens, and rhoptry proteins (ROP). These attempts thereby provided great impetus to the present focus on vaccine development, according to the defined subcellular components of the parasite. Although, currently there is no commercial vaccine for use in humans. Among the main identified T. gondii antigens, ROPs appear as a putative vaccine candidate that are vital for invasion procedure as well as survival within host cells. Overall, it is estimated that they occupy about 1%–30% of the total parasite cell volume. In this review, we have summarized the recent progress of ROP-based vaccine development through various strategies from DNA vaccines, epitope or multi epitope-based vaccines, recombinant protein vaccines to vaccines based on live-attenuated vectors and prime-boost strategies in different mouse models.

Systematic review and meta-analysis of variation in Toxoplasma gondii cyst burden in the murine model

Toxoplasma gondii is an obligate intracellular protozoan parasite that infects approximately 30% of the population of the United States, with worldwide distribution. The chronic (latent) infection, mediated by the bradyzoite parasite life stage, has attracted attention due to possible links to host behavioral alteration and psychomotor effects. Mice are a common model organism for studying the chronic stage, as they are natural hosts of infection. Notably, published studies demonstrate vast ranges of measured cyst burden within the murine brain tissue. The inconsistency of measured cyst burden within and between experiments makes interpretation of statistical significance difficult, potentially confounding studies of experimental anti-parasitic approaches. This review analyzes variation in measured cyst burden in a wide array of experimental mouse infections across published literature. Factors such as parasite infection strain, mouse strain, mode of infection, and infectious dose were all examined. The lowest variation in measured cyst burden occurred with the commonly available Balb/c and CBA mice undergoing infection by the ME49 strain of T. gondii. A summary of cyst variation and average cyst counts in T. gondii mouse models is presented, which may be useful for designing future experiments.

Vaccination against Toxoplasma gondii using rhoptry antigens: a systematic review

Toxoplasma gondii is an obligate intracellular parasitic protozoan that infects a wide variety of vertebrates as intermediate hosts. The aim of the current systematic review study is to clarify the latest status of studies in the literature regarding rhoptry-associated recombinant proteins or rhoptry-associated recombinant DNAs as potential vaccines against toxoplasmosis. The search was performed systematically in 8 databases, four in English and four in Persian, up to February 2017. Overall, ROP2 was the most commonly used ROPs in DNA vaccines (27.27%) and protein vaccines (6.81%). Furthermore, regarding the type of adjuvants, route and dose of vaccination, animal models, challenge methods, and measurement of immune responses has been discussed in the text. It is hoped that this article help researchers to conduct more effective studies in the field of immunization against T. gondii.

A Gene-Based Positive Selection Detection Approach to Identify Vaccine Candidates Using Toxoplasma gondii as a Test Case Protozoan Pathogen

Over the last two decades, various in silico approaches have been developed and refined that attempt to identify protein and/or peptide vaccines candidates from informative signals encoded in protein sequences of a target pathogen. As to date, no signal has been identified that clearly indicates a protein will effectively contribute to a protective immune response in a host. The premise for this study is that proteins under positive selection from the immune system are more likely suitable vaccine candidates than proteins exposed to other selection pressures. Furthermore, our expectation is that protein sequence regions encoding major histocompatibility complexes (MHC) binding peptides will contain consecutive positive selection sites. Using freely available data and bioinformatic tools, we present a high-throughput approach through a pipeline that predicts positive selection sites, protein subcellular locations, and sequence locations of medium to high T-Cell MHC class I binding peptides. Positive selection sites are estimated from a sequence alignment by comparing rates of synonymous (dS) and non-synonymous (dN) substitutions among protein coding sequences of orthologous genes in a phylogeny. The main pipeline output is a list of protein vaccine candidates predicted to be naturally exposed to the immune system and containing sites under positive selection. Candidates are ranked with respect to the number of consecutive sites located on protein sequence regions encoding MHCI-binding peptides. Results are constrained by the reliability of prediction programs and quality of input data. Protein sequences from Toxoplasma gondii ME49 strain (TGME49) were used as a case study. Surface antigen (SAG), dense granules (GRA), microneme (MIC), and rhoptry (ROP) proteins are considered worthy T. gondii candidates. Given 8263 TGME49 protein sequences processed anonymously, the top 10 predicted candidates were all worthy candidates. In particular, the top ten included ROP5 and ROP18, which are T. gondii virulence determinants. The chance of randomly selecting a ROP protein was 0.2% given 8263 sequences. We conclude that the approach described is a valuable addition to other in silico approaches to identify vaccines candidates worthy of laboratory validation and could be adapted for other apicomplexan parasite species (with appropriate data).

Evaluation of Protective Immune Response Induced by a DNA Vaccine Encoding GRA8 against Acute Toxoplasmosis in a Murine Model

Toxoplasma gondii is an apicomplexan zoonotic protozoan parasite that infects most species of warm-blooded animals, including humans. The heavy incidence and severe or lethal damage caused by T. gondii infection clearly indicate a need for the development of an effective vaccine. T. gondii GRA8 is a member of the dense granules protein family and is used as a marker of acute infection. In the present study, we evaluated the protective immunity induced by DNA vaccination based on a recombinant eukaryotic plasmid, pDsRed2-GRA8, against acute toxoplasmosis in mice. BALB/c mice were intramuscularly immunized with the pDsRed2-GRA8 plasmid and then challenged by infection with the highly virulent GFP-RH strain of T. gondii. The specific immune responses and protective efficacy against T. gondii of this vaccine were analyzed by measuring cytokine and serum antibody titers, splenocyte proliferation assays, and the survival times of mice after challenge. Our results showed that mice immunized with pDsRed2-GRA8 demonstrated specific humoral and cellular responses, induced higher IgG antibody titers with predominant IgG2a production; increased levels of IL-10, IL-12 (p70), IFN-γ, TNF-α, and splenocyte proliferation; and prolonged survival times compared to those of control mice. The present study showed that DNA immunization with pDsRed2-GRA8 induced humoral and cellular immune responses, and all immunized mice showed greater Th1-type immune responses and longer survival times than those of control mice. These results indicated that T. gondii GRA8 DNA immunization induces a partial protective effect against acute toxoplasmosis.

Recent progress in microneme-based vaccines development against Toxoplasma gondii

Toxoplasmosis is a cosmopolitan zoonotic disease, which infect several warm-blooded mammals. More than one-third of the human population are seropositive worldwide. Due to the high seroprevalence of Toxoplasma gondii infection worldwide, the resulting clinical, mental, and economical complications, as well as incapability of current drugs in the elimination of parasites within tissue cysts, the development of a vaccine against T. gondii would be critical. In the past decades, valuable advances have been achieved in order to identification of vaccine candidates against T. gondii infection. Microneme proteins (MICs) secreted by the micronemes play a critical role in the initial stages of host cell invasion by parasites. In this review, we have summarized the recent progress for MIC-based vaccines development, such as DNA vaccines, recombinant protein vaccines, vaccines based on live-attenuated vectors, and prime-boost strategy in different mouse models. In conclusion, the use of live-attenuated vectors as vehicles to deliver and express the target gene and prime-boost regimens showed excellent outcomes in the development of vaccines against toxoplasmosis, which need more attention in the future studies.

Immuno-efficacy of DNA vaccines encoding PLP1 and ROP18 against experimental Toxoplasma gondii infection in mice

We constructed a new plasmid pIRESneo/ROP18/PLP1 that was injected intramuscularly into Kunming mice to evaluate its immune efficacy. The immunized mice exhibited significantly increased serum IgG2a levels, lymphocyte counts and Th1-type cytokine (IL-2, IL-12 and IFN-γ) levels. Moreover, the immunized mice exhibited longer survival times (44.7 ± 2.1 days for ROP18/PLP1 and 47.2 ± 2.9 days for ROP18/PLP1 + IL-18) and lower brain cyst burden (68.9% for ROP18/PLP1 and 72.4% for ROP18/PLP1 + IL-18) than control mice after T. gondii challenge. Our results demonstrate that the multiple-gene DNA vaccine including both ROP18 and PLP1 elicits greater protection against T. gondii challenge and stronger immunogenicity than single-gene vaccines.

Moving towards improved vaccines for Toxoplasma gondii

INTRODUCTION

Toxoplasma gondii is an intracellular parasitic protozoan that infects almost all warm-blooded animals and humans, resulting in threats to public health and economic losses. Despite continuous research efforts, there are still very few effective strategies against toxoplasmosis. In the past few years, numerous vaccination experiments have been performed to control T. gondii infection.

AREAS COVERED

In this review, the authors summarize the development of T. gondii vaccines with proper adjuvants, ranging from live or live-attenuated vaccines to protein vaccines, DNA vaccines, epitope vaccines and novel vaccines. They also highlight the challenges involved in the development of T. gondii vaccines, including specific impediments and shortcomings.

EXPERT OPINION

Moving towards the development of effective vaccines against T. gondii is not only a tedious mission but also a difficult challenge. Future studies should consider new approaches and strategies for vaccine development, particularly novel vaccines and genetic adjuvants, as well as optimizing immunization protocols and evaluation criteria.

Vaccination with a DNA vaccine encoding Toxoplasma gondii ROP54 induces protective immunity against toxoplasmosis in mice

Toxoplasma gondii is an obligatory intracellular protozoan, which infects most of the warm-blooded animals, causing serious public health problems and enormous economic losses worldwide. The rhoptry effector protein 54 (ROP54) has been indicated as a virulence factor that promotes Toxoplasma infection by modulating GBP2 loading onto parasite-containing vacuoles, which can modulate some aspects of the host immune response. In order to evaluate the immuno-protective value of ROP54, we constructed a eukaryotic recombinant plasmid expressing T. gondii ROP54 and intramuscularly immunized Kunming mice with this recombinant plasmid against acute and chronic toxoplasmosis. All mice immunized with pVAX-ROP54 elicited a high level of specific antibody responses, a significant increase of lymphocyte proliferation, and a significant level of Th1-type cytokines (IFN-γ, IL-2 and IL-12p70), in addition to an increased production of Th2-type cytokines (IL-4 and IL-10). These results demonstrated that pVAX-ROP54 induced significant cellular and humoral (Th1/Th2) immune responses, which extended the survival time (13.0±1.15days for pVAX-ROP54 vs 6.7±0.48days for pVAX I, 6.8±0.42days for PBS and 6.5±0.53 for blank control) and significantly reduced cyst burden (35.9% for pVAX-ROP54, 1% for pVAX I and 2% for PBS, compared with blank control) of immunized mice. These results indicate that the recombinant ROP54 plasmid can provide partial protection and might be a potential vaccine candidate against acute and chronic toxoplasmosis.

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.

Co-administration of interleukins 7 and 15 with DNA vaccine improves protective immunity against Toxoplasma gondii

Toxoplasma gondii is an obligatory intracellular parasite, which can infect all warm-blooded animals including humans. Cytokines, including IL-15 and IL-7, play a critical role in the regulation of the homeostasis of naive and memory T cells. Co-administration the DNA vaccine with cytokines may improve its efficacy. IL-7 and IL-15 from splenic tissues of Kunming mice were cloned, and eukaryotic plasmid pVAX-IL-7-IL-15 was constructed. Kunming mice were administrated with DNA vaccine expressing T. gondii calcium-dependent protein kinase 1 (TgCDPK1), pVAX-CDPK1, in the presence or absence of IL-7 and IL-15 plasmids (pVAX-IL-7-IL-15), immune responses were analyzed including lymphoproliferative assay, cytokine and serum antibody measurements, flow cytometric surface markers on lymphocytes, and thus protective immunity against acute and chronic T. gondii infection was estimated. Mice injected with pVAX-CDPK1 supplemented with pVAX-IL-7-IL-15 showed higher Toxoplasma-specific IgG2a titers, Th1 responses associated with the production of IFN-γ, IL-2 as well as cell-mediated cytotoxic activity where stronger frequencies of IFN-γ secreting CD8+ and CD4+ T cells (CD8+/CD4+ IFN-γ+ T cells) compared to controls. Co-administration of pVAX-IL-7-IL-15 and pVAX-CDPK1 significantly (P < 0.05) increased survival time (18.07 ± 5.43 days) compared with pVAX-CDPK1 (14.13 ± 3.85 days) or pVAX-IL-7-IL-15 (11.73 ± 1.83 days) alone, and pVAX-IL-7-IL-15 + pVAX-CDPK1 significantly reduced the number of brain cysts (73.5%) in contrast to pVAX-CDPK1 (46.0%) or pVAX-IL-7-IL-15 alone (45.0%). Our results indicate that supplementation of DNA vaccine with IL-7 and IL-15 would facilitate specific humoral and cellular immune responses elicited by DNA vaccine against acute and chronic T. gondii infection in mice.

Recent advances in developing vaccines against Toxoplasma gondii: an update

Toxoplasma gondii, a significant public health risk, is able to infect almost all warm-blooded animals including humans, and it results in economic losses in production animals. In the last three years, a large number of vaccination experiments have been performed to control T. gondii infection, with the target of limiting the acute infection and reducing or eliminating tissue cysts in the intermediate hosts. In this paper, we summarize the latest results of the veterinary vaccines against T. gondii infection since 2013. Immunization with live-attenuated whole organisms of non-reverting mutants has been shown to induce remarkably potent immune responses associated with control of acute and chronic toxoplasmosis. The non-cyst-forming mutants are promising new tools for the development of veterinary vaccines against T. gondii infection.

Towards vaccine against toxoplasmosis: evaluation of the immunogenic and protective activity of recombinant ROP5 and ROP18 Toxoplasma gondii proteins

Toxoplasmosis is one of the most common parasitic infections worldwide. An effective vaccine against human and animal toxoplasmosis is still needed to control this parasitosis. The polymorphic rhoptry proteins, ROP5 and ROP18, secreted by Toxoplasma gondii during the invasion of the host cell have been recently considered as promising vaccine antigens, as they appear to be the major determinants of T. gondii virulence in mice. The goal of this study was to evaluate their immunogenic and immunoprotective activity after their administration (separately or both recombinant proteins together) with the poly I:C as an adjuvant. Immunization of BALB/c and C3H/HeOuJ mice generated both cellular and humoral specific immune responses with some predominance of IgG1 antibodies. The spleen cells derived from vaccinated animals reacted to the parasite's native antigens. Furthermore, the immunization led to a partial protection against acute and chronic toxoplasmosis. These findings confirm the previous assumptions about ROP5 and ROP18 antigens as valuable components of a subunit vaccine against toxoplasmosis.

Protective efficacy of two novel DNA vaccines expressing Toxoplasma gondii rhomboid 4 and rhomboid 5 proteins against acute and chronic toxoplasmosis in mice

OBJECTIVES

To evaluate the protective efficacy of two novel DNA vaccines expressing Toxoplasma gondii rhomboid 4 (ROM4) and rhomboid 5 (ROM5) proteins against acute and chronic toxoplasmosis.

METHODS

DNA vaccines (pVAX-TgROM5 and pVAX-TgROM4) were constructed and their immunogenicity evaluated in Kunming mice.

RESULTS

Mice vaccinated with pVAX-TgROM5 or pVAX-TgROM4 elicited strong Th1-type humoral and cellular responses, with higher level of IgG antibody titers (the predominance of IgG2a production), and increased levels of CD4(+) and CD8(+) T cells and cytokines IFN-γ, IL-2, IL-12 (p70) and IL-23. Mice vaccinated with pVAX-TgROM5 (11 days) showed a significantly longer survival time compared with controls (8 days) (p < 0.05) after lethal challenge. Brain cyst numbers of mice vaccinated with pVAX-TgROM5 and pVAX-TgROM4 reduced significantly (p < 0.05) (72.04 and 44.08%, respectively) compared with control groups after chronic challenge.

CONCLUSION

The pVAX-TgROM5 showed a better protective efficacy against acute and chronic toxoplasmosis compared to pVAX-TgROM4.