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

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

Download Full-text

A Combined Adjuvant TF–Al Consisting of TFPR1 and Aluminum Hydroxide Augments Strong Humoral and Cellular Immune Responses in Both C57BL/6 and BALB/c Mice

Vaccines ◽

10.3390/vaccines9121408 ◽

2021 ◽

Vol 9 (12) ◽

pp. 1408

Author(s):

Qiao Li ◽

Zhihua Liu ◽

Yi Liu ◽

Chen Liang ◽

Jiayi Shu ◽

...

Keyword(s):

Immune Responses ◽

Vaccine Development ◽

Inbred Mouse ◽

Effective Vaccine ◽

Mouse Strains ◽

Cellular Immune Responses ◽

Recombinant Hbsag ◽

Cellular Immune

TFPR1 is a novel adjuvant for protein and peptide antigens, which has been demonstrated in BALB/c mice in our previous studies; however, its adjuvanticity in mice with different genetic backgrounds remains unknown, and its adjuvanticity needs to be improved to fit the requirements for various vaccines. In this study, we first compared the adjuvanticity of TFPR1 in two commonly used inbred mouse strains, BALB/c and C57BL/6 mice, in vitro and in vivo, and demonstrated that TFPR1 activated TLR2 to exert its immune activity in vivo. Next, to prove the feasibility of TFPR1 acting as a major component of combined adjuvants, we prepared a combined adjuvant, TF–Al, by formulating TFPR1 and alum at a certain ratio and compared its adjuvanticity with that of TFPR1 and alum alone using OVA and recombinant HBsAg as model antigens in both BALB/c and C57BL/6 mice. Results showed that TFPR1 acts as an effective vaccine adjuvant in both BALB/c mice and C57BL/6 mice, and further demonstrated the role of TLR2 in the adjuvanticity of TFPR1 in vivo. In addition, we obtained a novel combined adjuvant, TF–Al, based on TFPR1, which can augment antibody and cellular immune responses in mice with different genetic backgrounds, suggesting its promise for vaccine development in the future.

Download Full-text

Resolution ofStaphylococcus aureusBiofilm Infection Using Vaccination and Antibiotic Treatment

Infection and Immunity ◽

10.1128/iai.00451-10 ◽

2011 ◽

Vol 79 (4) ◽

pp. 1797-1803 ◽

Cited By ~ 86

Author(s):

Rebecca A. Brady ◽

Graeme A. O'May ◽

Jeff G. Leid ◽

Megan L. Prior ◽

J. William Costerton ◽

...

Keyword(s):

Antibiotic Treatment ◽

Vaccine Development ◽

Hypothetical Protein ◽

Quadrivalent Vaccine ◽

Effective Vaccine ◽

Vast Number ◽

Protective Antigens ◽

Biofilm Model

ABSTRACTStaphylococcus aureusinfections, particularly those from methicillin-resistant strains (i.e., MRSA), are reaching epidemic proportions, with no effective vaccine available. The vast number and transient expression of virulence factors in the infectious course of this pathogen have made the discovery of protective antigens particularly difficult. In addition, the divergent planktonic and biofilm modes of growth with their accompanying proteomic changes also demonstrate significant hindrances to vaccine development. In this study, a multicomponent vaccine was evaluated for its ability to clear a staphylococcal biofilm infection. Antigens (glucosaminidase, an ABC transporter lipoprotein, a conserved hypothetical protein, and a conserved lipoprotein) were chosen since they were found in previous studies to have upregulated and sustained expression in a biofilm, bothin vitroandin vivo. Antibodies against these antigens were first used in microscopy studies to localize their expression inin vitrobiofilms. Each of the four antigens showed heterogeneous production in various locations within the complex biofilm community in the biofilm. Based upon these studies, the four antigens were delivered simultaneously as a quadrivalent vaccine in order to compensate for this varied production. In addition, antibiotic treatment was also administered to clear the remaining nonattached planktonic cells since the vaccine antigens may have been biofilm specific. The results demonstrated that when vaccination was coupled with vancomycin treatment in a biofilm model of chronic osteomyelitis in rabbits, clinical and radiographic signs of infection significantly reduced by 67 and 82%, respectively, compared to infected animals that were either treated with vancomycin or left untreated. In contrast, vaccination alone resulted in a modest, and nonsignificant, decrease in clinical (34% reduction) and radiographic signs (9% reduction) of infection, compared to nonvaccinated animal groups untreated or treated with vancomycin. Lastly, MRSA biofilm infections were significantly cleared in 87.5% of vaccinated and antibiotic-treated animals, while antibiotics or vaccine alone could not significantly clear infection compared to controls (55.6, 22.2, and 33.3% clearance rates, respectively). This approach to vaccine development may lead to the generation of vaccines against other pathogenic biofilm bacteria.

Download Full-text

1,25(OH)2D3 inhibits in vitro and in vivo intracellular growth of apicomplexan parasite Toxoplasma gondii

The Journal of Steroid Biochemistry and Molecular Biology ◽

10.1016/j.jsbmb.2006.12.058 ◽

2007 ◽

Vol 103 (3-5) ◽

pp. 811-814 ◽

Cited By ~ 11

Author(s):

Rohan Rajapakse ◽

Béatrice Uring-Lambert ◽

Kumari L. Andarawewa ◽

R.P. Rajapakse ◽

Ahmed Abou-Bacar ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Apicomplexan Parasite ◽

Intracellular Growth

Download Full-text

Nano DNA Vaccine Encoding Toxoplasma gondii Histone Deacetylase SIR2 Enhanced Protective Immunity in Mice

Pharmaceutics ◽

10.3390/pharmaceutics13101582 ◽

2021 ◽

Vol 13 (10) ◽

pp. 1582

Author(s):

Zhengqing Yu ◽

Yujia Lu ◽

Wandi Cao ◽

Muhammad Tahir Aleem ◽

Junlong Liu ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Histone Deacetylase ◽

Dna Vaccine ◽

Laser Scanning ◽

Lethal Dose ◽

Parasite Burden ◽

Effective Vaccine ◽

Th2 Immune Response ◽

Plga Nanospheres

The pathogen of toxoplasmosis, Toxoplasma gondii (T. gondii), is a zoonotic protozoon that can affect the health of warm-blooded animals including humans. Up to now, an effective vaccine with completely protection is still inaccessible. In this study, the DNA vaccine encoding T. gondii histone deacetylase SIR2 (pVAX1-SIR2) was constructed. To enhance the efficacy, chitosan and poly (d, l-lactic-co-glycolic)-acid (PLGA) were employed to design nanospheres loaded with the DNA vaccine, denoted as pVAX1-SIR2/CS and pVAX1-SIR2/PLGA nanospheres. The pVAX1-SIR2 plasmids were transfected into HEK 293-T cells, and the expression was evaluated by a laser scanning confocal microscopy. Then, the immune protections of pVAX1-SIR2 plasmid, pVAX1-SIR2/CS nanospheres, and pVAX1-SIR2/PLGA nanospheres were evaluated in a laboratory animal model. The in vivo findings indicated that pVAX1-SIR2/CS and pVAX1-SIR2/PLGA nanospheres could generate a mixed Th1/Th2 immune response, as indicated by the regulated production of antibodies and cytokines, the enhanced maturation and major histocompatibility complex (MHC) expression of dendritic cells (DCs), the induced splenocyte proliferation, and the increased percentages of CD4+ and CD8+ T lymphocytes. Furthermore, this enhanced immunity could obviously reduce the parasite burden in immunized animals through a lethal dose of T. gondii RH strain challenge. All these results propose that pVAX1-SIR2 plasmids entrapped in chitosan or PLGA nanospheres could be the promising vaccines against acute T. gondii infections and deserve further investigations.

Download Full-text

Defining levels of dengue virus serotype-specific neutralizing antibodies induced by a live attenuated tetravalent dengue vaccine (TAK-003)

10.1101/2020.09.23.308817 ◽

2020 ◽

Author(s):

Laura J. White ◽

Ellen Young ◽

Mark Stoops ◽

Sandra Henein ◽

Ralph S. Baric ◽

...

Keyword(s):

Dengue Virus ◽

Neutralizing Antibodies ◽

Vaccine Development ◽

Severe Disease ◽

Effective Vaccine ◽

Dengue Vaccine ◽

Unique Type ◽

Vaccine Component ◽

Virus Serotype

AbstractThe four dengue virus serotypes (DENV1-4) infect several hundred million people each year living in tropical and sub-tropical regions. Clinical development of DENV vaccines is difficult because immunity to a single serotype increases risk of severe disease during a second infection with a new serotype. Leading vaccines are based on tetravalent formulations to induce simultaneous and balanced protective immunity to all 4 serotypes. TAK-003 is a tetravalent live attenuated dengue vaccine candidate developed by Takeda Vaccines Inc, which is currently being evaluated in phase 3 efficacy trials. Here, we use antibody depletion methods and chimeric, epitope transplant DENVs to characterize the specificity of neutralizing antibodies in dengue-naïve adults and non-human primates immunized with TAK-003. Our results demonstrate that TAK-003 induced high levels of DENV2 neutralizing antibodies that recognized unique (type-specific) epitopes on DENV2. In contrast, most vaccinated subjects developed lower levels of DENV1, DENV3 and DENV4 neutralizing antibodies that mainly targeted epitopes that were conserved (cross-reactive) between serotypes. We conclude that the DENV2 component in the vaccine is immunodominant because of the high levels of serum neutralizing antibodies targeting type-specific epitopes. We also conclude that DENV1, 3 and 4 vaccine components are less immunogenic because most study subjects did not develop type-specific serum neutralizing antibodies to these serotypes. While DENV vaccine development has been guided by the presence of neutralizing antibodies to each serotype as a benchmark, our results indicate that the presence of neutralizing antibodies alone are not a reliable indicator of the immunogenicity of each vaccine component.Author summaryThe development of tetravalent dengue vaccines has been guided by neutralizing antibodies to each serotype as a correlate of safe and effective vaccine induced immunity. However, the absolute levels of neutralizing antibodies to each serotype has proven to be an unreliable correlate of protection. Levels of antibodies to epitopes that are unique to each serotype, which are measures of immunity independently stimulated by each vaccine component, rather than total quantity of neutralizing antibodies, are likely to be better correlates of protection. Here, we mapped the specificity of antibodies induced by the Takeda tetravalent dengue vaccine TAK-003 in monkeys and humans with no prior immunity to dengue. The TAK-003 vaccine induces high levels of serotype 2 specific neutralizing antibodies that map to known protective epitopes. In contrast, the serotype 1, 3 and 4 neutralizing antibody responses are lower and mainly consist of cross-reactive antibodies binding to epitopes conserved between serotypes. These heterotypic antibodies, which are most likely derived from the serotype 2 component, may not provide long term protection in vivo.

Download Full-text

Anticytomegalovirus Peptides Point to New Insights for CMV Entry Mechanisms and the Limitations ofIn VitroScreenings

mSphere ◽

10.1128/msphere.00586-18 ◽

2019 ◽

Vol 4 (1) ◽

Cited By ~ 3

Author(s):

Joseph W. Jackson ◽

Trevor J. Hancock ◽

Pranay Dogra ◽

Ravi Patel ◽

Ravit Arav-Boger ◽

...

Keyword(s):

Heparan Sulfate ◽

Vaccine Development ◽

Murine Cytomegalovirus ◽

Effective Vaccine ◽

Antiviral Peptides ◽

Highly Effective ◽

Binding Peptides ◽

Cell Spread

ABSTRACTHuman cytomegalovirus (HCMV) is a ubiquitous betaherpesvirus that can cause severe disease followingin uteroexposure, during primary infection, or latent virus reactivation in immunocompromised populations. These complications lead to a 1- to 2-billion-dollar economic burden, making vaccine development and/or alternative treatments a high priority. Current treatments for HCMV include nucleoside analogues such as ganciclovir (GCV), foscarnet, and cidofovir. Recently, letermovir, a terminase complex inhibitor, was approved for prophylaxis after stem cell transplantation. These treatments have unwanted side effects, and HCMV is becoming resistant to them. Therefore, we sought to develop an alternative treatment that targets a different stage in viral infection. Currently, small antiviral peptides are being investigated as anti-influenza and anti-HIV treatments. We have developed heparan sulfate-binding peptides as tools for preventing CMV infections. These peptides are highly effective at stopping infection of fibroblasts within vitro-derived HCMV and murine cytomegalovirus (MCMV). However, they do not prevent MCMV infectionin vivo. Interestingly, these peptides inhibit infectivity ofin vivo-derived CMVs, albeit not as well as tissue culture-grown CMVs. We further demonstrate that this class of heparan sulfate-binding peptides is incapable of inhibiting MCMV cell-to-cell spread, which is independent of heparan sulfate usage. These data indicate that inhibition of CMV infection can be achieved using synthetic polybasic peptides, but cell-to-cell spread andin vivo-grown CMVs require further investigation to design appropriate anti-CMV peptides.IMPORTANCEIn the absence of an effective vaccine to prevent HCMV infections, alternative interventions must be developed. Prevention of viral entry into susceptible cells is an attractive alternative strategy. Here we report that heparan sulfate-binding peptides effectively inhibit entry into fibroblasts ofin vitro-derived CMVs and partially inhibitin vivo-derived CMVs. This includes the inhibition of urine-derived HCMV (uCMV), which is highly resistant to antibody neutralization. While these antiviral peptides are highly effective at inhibiting cell-free virus, they do not inhibit MCMV cell-to-cell spread. This underscores the need to understand the mechanism of cell-to-cell spread and differences betweenin vivo-derived versusin vitro-derived CMV entry to effectively prevent CMV’s spread.

Download Full-text

Synthetic Peptides Elicit Strong Cellular Immunity in Visceral Leishmaniasis Natural Reservoir and Contribute to Long-Lasting Polyfunctional T-Cells in BALB/c Mice

Vaccines ◽

10.3390/vaccines7040162 ◽

2019 ◽

Vol 7 (4) ◽

pp. 162 ◽

Cited By ~ 5

Author(s):

Rory Cristiane Fortes De Brito ◽

Jamille Mirelle de Oliveira Cardoso ◽

Levi Eduardo Soares Reis ◽

Fernando Augusto Siqueira Mathias ◽

Rodrigo Dian de Oliveira Aguiar-Soares ◽

...

Keyword(s):

T Cells ◽

Visceral Leishmaniasis ◽

In Silico ◽

Vaccine Development ◽

Subcellular Location ◽

Effector Memory ◽

Effective Vaccine ◽

Polyfunctional T Cells

Reverse vaccinology or immunoinformatics is a computational methodology which integrates data from in silico epitope prediction, associated to other important information as, for example, the predicted subcellular location of the proteins used in the design of the context of vaccine development. This approach has the potential to search for new targets for vaccine development in the predicted proteome of pathogenic organisms. To date, there is no effective vaccine employed in vaccination campaigns against visceral leishmaniasis (VL). For the first time, herein, an in silico, in vitro, and in vivo peptide screening was performed, and immunogenic peptides were selected to constitute VL peptide-based vaccines. Firstly, the screening of in silico potential peptides using dogs naturally infected by L. infantum was conducted and the peptides with the best performance were selected. The mentioned peptides were used to compose Cockt-1 (cocktail 1) and Cockt-2 (cocktail 2) in combination with saponin as the adjuvant. Therefore, tests for immunogenicity, polyfunctional T-cells, and the ability to induce central and effector memory in T-lymphocytes capacity in reducing the parasite load on the spleen for Cockt-1 and Cockt-2 were performed. Among the vaccines under study, Cockt-1 showed the best results, eliciting CD4+ and CD8+ polyfunctional T-cells, with a reduction in spleen parasitism that correlates to the generation of T CD4+ central memory and T CD8+ effector memory cells. In this way, our findings corroborate the use of immunoinformatics as a tool for the development of future vaccines against VL.

Download Full-text

Development of an Oral Salmonella-Based Vaccine Platform against SARS-CoV-2

Vaccines ◽

10.3390/vaccines10010067 ◽

2022 ◽

Vol 10 (1) ◽

pp. 67

Author(s):

Wonsuck Yoon ◽

Yongsung Park ◽

Seunghyun Kim ◽

Iel Soo Bang

Keyword(s):

Large Scale ◽

Vaccine Development ◽

Oral Vaccine ◽

Oral Bacteria ◽

Expression Vectors ◽

Effective Vaccine ◽

Vaccine Platform ◽

In Vivo Experiments

Effective vaccine development for global outbreaks, such as the coronavirus disease 2019 (COVID-19), has been successful in the short run. However, the currently available vaccines have been associated with a higher frequency of adverse effects compared with other general vaccines. In this study, the possibility of an oral bacteria-based vaccine that can be safely used as a platform for large-scale, long-term immunization was evaluated. A well-known Salmonella strain that was previously considered as a vaccine delivery candidate was used. Recombinant Salmonella cells expressing engineered viral proteins related with COVID-19 pathogenesis were engineered, and the formulation of the oral vaccine candidate strain was evaluated by in vitro and in vivo experiments. First, engineered S proteins were synthesized and cloned into expression vectors, which were than transformed into Salmonella cells. In addition, when orally administrated to mice, the vaccine promoted antigen-specific antibody production and cellular immunity was induced with no significant toxicity effects. These results suggest that Salmonella strains may represent a valuable platform for the development of an oral vaccine for COVID-19 as an alternative to tackle the outbreak of various mutated coronavirus strains and new infectious diseases in the future.

Download Full-text

A capsular polysaccharide-expressing live vaccine suppresses streptococcal toxic shock-like syndrome and provides sequence type-independent protection during Streptococcus suis infection

10.1101/335349 ◽

2018 ◽

Author(s):

Zhiwei Li ◽

Peixi Chang ◽

Jiali Xu ◽

Chen Tan ◽

Xiaohong Wang ◽

...

Keyword(s):

Gene Deletion ◽

Capsular Polysaccharide ◽

Vaccine Development ◽

Streptococcus Suis ◽

Sequence Type ◽

Effective Vaccine ◽

Toxic Shock ◽

Proinflammatory Responses

AbstractStreptococcus suis (S. suis) is an encapsulated zoonotic pathogen, which is responsible for bacterial meningitis and streptococcal toxic shock-like syndrome (STSLS). Despite many attempts to develop an effective vaccine, none is currently available. Here, a capsular polysaccharide (CPS)-expressing attenuated mutant 2015033 was constructed by deleting five virulence-associated factors (sly, scpA, ssnA, fhb, and ssads) in an outbreak S. suis strain SC19. Genes mentioned above are associated with either innate immunity-evading or tissue barrier-invading. Deletion of these genes did not impact the growth ability and CPS generation of 2015033, and the mutant exhibited no hemolytic activity to erythrocytes and no cytotoxicity to different epithelial or endothelial cells. In addition, 2015033 was more easily eliminated by whole human blood in vitro and by mouse blood in vivo. In addition, 2015033 showed a diminished invasive ability in different mouse organs (brain, lung, and liver) and avirulent properties in mice associated with weak inflammation-inducing ability. Immunization with 2015033 triggered T cell-dependent immunity and this immunity suppressed STSLS during SC19 infection by inhibiting excessive proinflammatory responses. In addition, immunization with 2015033 successfully conferred sequence type (STs)-independent protection to mice during heterogeneous infections (ST1, ST7, and ST658). This study presents the feasibility of the strategy of multi-gene deletion for the development of promising live vaccines against invasive encapsulated pathogens.IMPORTANCES. suis is a traditional zoonotic agent causing human meningitis and STSLS, which is also a neglected emerging food-borne pathogen. Increasing antimicrobial resistance invokes reduction of preventative use of antibiotics in livestock creating an urgent need for effective vaccines. Given the expression of CPS is the basis for promising vaccines against encapsulated pathogens, and in order to find an effective and economical strategy for CPS-based vaccine development, multi-gene deletion was introduced into the design of a S. suis vaccine for the first time. From our results, CPS-expressing attenuated mutant 2015033 exhibited diminished evasive ability against the innate immune system and reduced invasive properties against different host barriers. To our knowledge, 2015033 is the first STSLS-suppressing S. suis vaccine to provide STs-independent protection during heterogeneous infections.

Download Full-text

Substrate-mediated regulation of the arginine transporter of Toxoplasma gondii

PLoS Pathogens ◽

10.1371/journal.ppat.1009816 ◽

2021 ◽

Vol 17 (8) ◽

pp. e1009816

Author(s):

Esther Rajendran ◽

Morgan Clark ◽

Cibelly Goulart ◽

Birte Steinhöfel ◽

Erick T. Tjhin ◽

...

Keyword(s):

Amino Acid ◽

Toxoplasma Gondii ◽

Apicomplexan Parasite ◽

Upstream Open Reading Frame ◽

Amino Acid Transporters ◽

Reading Frame ◽

Intracellular Parasites ◽

Biosensor Strain ◽

Sense And Respond

Intracellular parasites, such as the apicomplexan Toxoplasma gondii, are adept at scavenging nutrients from their host. However, there is little understanding of how parasites sense and respond to the changing nutrient environments they encounter during an infection. TgApiAT1, a member of the apicomplexan ApiAT family of amino acid transporters, is the major uptake route for the essential amino acid L-arginine (Arg) in T. gondii. Here, we show that the abundance of TgApiAT1, and hence the rate of uptake of Arg, is regulated by the availability of Arg in the parasite’s external environment, increasing in response to decreased [Arg]. Using a luciferase-based ‘biosensor’ strain of T. gondii, we demonstrate that the expression of TgApiAT1 varies between different organs within the host, indicating that parasites are able to modulate TgApiAT1-dependent uptake of Arg as they encounter different nutrient environments in vivo. Finally, we show that Arg-dependent regulation of TgApiAT1 expression is post-transcriptional, mediated by an upstream open reading frame (uORF) in the TgApiAT1 transcript, and we provide evidence that the peptide encoded by this uORF is critical for mediating regulation. Together, our data reveal the mechanism by which an apicomplexan parasite responds to changes in the availability of a key nutrient.

Download Full-text