CD8+-T-cell-dependent control of Trypanosoma cruzi infection in a highly susceptible mouse strain after immunization with recombinant proteins based on amastigote surface protein 2

Fighting Strategies Against Chagas' Disease: A Review

Chagas disease, caused by Trypanosoma cruzi, remains a significant public health challenge, particularly in Latin America, where it is one of the most neglected diseases and is primarily transmitted by triatomine insects. The disease exhibits complexity due to its diverse transmission routes, including vectorial and non-vectorial mechanisms such as blood transfusions and congenital transmission. Effective monitoring and control strategies are critical to mitigating its impact. This review focuses on current monitoring and control efforts, emphasizing the importance of enhanced surveillance systems, improved risk assessments, and integrated vector control programs. Surveillance plays a pivotal role in early detection and timely intervention, particularly in endemic regions, while vector control remains central to reducing transmission. Moreover, the development of novel diagnostic tools, treatments, and vaccines is a crucial step in advancing control efforts. This review also highlights the involvement of local governments, international organizations, and civil society in executing these strategies, stressing the need for sustained political commitment to ensure the success of public health programs. By addressing key challenges in monitoring, control, and prevention, this review aims to provide insights and recommendations to further global efforts in reducing the burden of Chagas disease.

Treatments and the Perspectives of Developing a Vaccine for Chagas Disease

Chagas disease (CD) treatment and vaccine development are critical due to the significant health burden caused by the disease, especially in Latin America. Current treatments include benznidazole and nifurtimox, which are most effective in the acute phase of the disease but less so in the chronic phase, often with significant side effects. Here, using the available literature, we summarize the progress in vaccine development and new treatments that promise to reduce CD incidence and improve the quality of life for those at risk, particularly in endemic regions. New treatment options, such as posaconazole and fexinidazole, are being explored to improve efficacy and reduce adverse effects. Vaccine development for CD remains a high priority. The complex life stages and genetic diversity of Trypanosoma cruzi present challenges, but several promising vaccine candidates are under investigation. These efforts focus on stimulating a protective immune response through various innovative approaches.

Harnessing RNA Technology to Advance Therapeutic Vaccine Antigens against Chagas Disease

Chagas disease (CD) (American trypanosomiasis caused by Trypanosoma cruzi) is a parasitic disease endemic in 21 countries in South America, with increasing global spread. When administered late in the infection, the current antiparasitic drugs do not prevent the onset of cardiac illness leading to chronic Chagasic cardiomyopathy. Therefore, new therapeutic vaccines or immunotherapies are under development using multiple platforms. In this study, we assessed the feasibility of developing an mRNA-based therapeutic CD vaccine targeting two known T. cruzi vaccine antigens (Tc24─a flagellar antigen and ASP-2─an amastigote antigen). We present the mRNA engineering steps, preparation, and stability of the lipid nanoparticles and evaluation of their uptake by dendritic cells, as well as their biodistribution in c57BL/J mice. Furthermore, we assessed the immunogenicity and efficacy of two mRNA-based candidates as monovalent and bivalent vaccine strategies using an in vivo chronic mouse model of CD. Our results show several therapeutic benefits, including reductions in parasite burdens and cardiac inflammation, with each mRNA antigen, especially with the mRNA encoding Tc24, and Tc24 in combination with ASP-2. Therefore, our findings demonstrate the potential of mRNA-based vaccines as a therapeutic option for CD and highlight the opportunities for developing multivalent vaccines using this approach.

ASP-2/Trans-sialidase chimeric protein induces robust protective immunity in experimental models of Chagas' disease

Immunization with the Amastigote Surface Protein-2 (ASP-2) and Trans-sialidase (TS) antigens either in the form of recombinant protein, encoded in plasmids or human adenovirus 5 (hAd5) confers robust protection against various lineages of Trypanosoma cruzi. Herein we generated a chimeric protein containing the most immunogenic regions for T and B cells from TS and ASP-2 (TRASP) and evaluated its immunogenicity in comparison with our standard protocol of heterologous prime-boost using plasmids and hAd5. Mice immunized with TRASP protein associated to Poly-ICLC (Hiltonol) were highly resistant to challenge with T. cruzi, showing a large decrease in tissue parasitism, parasitemia and no lethality. This protection lasted for at least 3 months after the last boost of immunization, being equivalent to the protection induced by DNA/hAd5 protocol. TRASP induced high levels of T. cruzi-specific antibodies and IFNγ-producing T cells and protection was primarily mediated by CD8⁺ T cells and IFN-γ. We also evaluated the toxicity, immunogenicity, and efficacy of TRASP and DNA/hAd5 formulations in dogs. Mild collateral effects were detected at the site of vaccine inoculation. While the chimeric protein associated with Poly-ICLC induced high levels of antibodies and CD4⁺ T cell responses, the DNA/hAd5 induced no antibodies, but a strong CD8⁺ T cell response. Immunization with either vaccine protected dogs against challenge with T. cruzi. Despite the similar efficacy, we conclude that moving ahead with TRASP together with Hiltonol is advantageous over the DNA/hAd5 vaccine due to pre-existing immunity to the adenovirus vector, as well as the cost-benefit for development and large-scale production.

Immunization with a Trypanosoma cruzi cyclophilin-19 deletion mutant protects against acute Chagas disease in mice

Human infection with the protozoan parasite Trypanosoma cruzi causes Chagas disease for which there are no prophylactic vaccines. Cyclophilin 19 is a secreted cis-trans peptidyl isomerase expressed in all life stages of Trypanosoma cruzi. This protein in the insect stage leads to the inactivation of insect anti-parasitic peptides and parasite transformation whereas in the intracellular amastigotes it participates in generating ROS promoting the growth of parasites. We have generated a parasite mutant with depleted expression of Cyp19 by removal of 2 of 3 genes encoding this protein using double allelic homologous recombination. The mutant parasite line failed to replicate when inoculated into host cells in vitro or in mice indicating that Cyp19 is critical for infectivity. The mutant parasite line also fails to replicate in or cause clinical disease in immuno-deficient mice further validating their lack of virulence. Repeated inoculation of mutant parasites into immuno-competent mice elicits parasite-specific trypanolytic antibodies and a Th-1 biased immune response and challenge of mutant immunized mice with virulent wild-type parasites is 100% effective at preventing death from acute disease. These results suggest that parasite Cyp19 may be candidate for small molecule drug targeting and that the mutant parasite line may warrant further immunization studies for prevention of Chagas disease.

Sec22b-dependent antigen cross-presentation is a significant contributor of T cell priming during infection with the parasite Trypanosoma cruzi

Antigen cross-presentation is a vital mechanism of dendritic cells and other antigen presenting cells to orchestrate the priming of cytotoxic responses towards killing of infected or cancer cells. In this process, exogenous antigens are internalized by dendritic cells, processed, loaded onto MHC class I molecules and presented to CD8⁺ T cells to activate them. Sec22b is an ER-Golgi Intermediate Compartment resident SNARE protein that, in partnership with sintaxin4, coordinates the recruitment of the transporter associated with antigen processing protein and the peptide loading complex to phagosomes, where antigenic peptides that have been proteolyzed in the cytosol are loaded in MHC class I molecules and transported to the cell membrane. The silencing of Sec22b in dendritic cells primary cultures and conditionally in dendritic cells of C57BL/6 mice, critically impairs antigen cross-presentation, but neither affects other antigen presentation routes nor cytokine production and secretion. Mice with Sec22b conditionally silenced in dendritic cells (Sec22b^-/-) show deficient priming of CD8⁺ T lymphocytes, fail to control tumor growth, and are resistant to anti-checkpoint immunotherapy. In this work, we show that Sec22b^-/- mice elicit a deficient specific CD8⁺ T cell response when challenged with sublethal doses of Trypanosoma cruzi trypomastigotes that is associated with increased blood parasitemia and diminished survival.

Vaccine Design against Chagas Disease Focused on the Use of Nucleic Acids

Chagas disease is caused by the protozoan Trypanosoma cruzi and is endemic to Central and South America. However, it has spread around the world and affects several million people. Treatment with currently available drugs cause several side effects and require long treatment times to eliminate the parasite, however, this does not improve the chronic effects of the disease such as cardiomyopathy. A therapeutic vaccine for Chagas disease may be able to prevent the disease and improve the chronic effects such as cardiomyopathy. This vaccine would be beneficial for both infected people and those which are at risk in endemic and non-endemic areas. In this article, we will review the surface antigens of T. cruzi, in order to choose those that are most antigenic and least variable, to design effective vaccines against the etiological agent of Chagas disease. Also, we discuss aspects of the design of nucleic acid-based vaccines, which have been developed and proven to be effective against the SARS-CoV-2 virus. The role of co-adjuvants and delivery carriers is also discussed. We present an example of a chimeric trivalent vaccine, based on experimental work, which can be used to design a vaccine against Chagas disease.

Nano-Medicines a Hope for Chagas Disease!

Chagas disease, is a vector-mediated tropical disease whose causative agent is a parasitic protozoan named Trypanosoma cruzi. It is a very severe health issue in South America and Mexico infecting millions of people every year. Protozoan T. cruzi gets transmitted to human through Triatominae, a subfamily of the Reduviidae, and do not have any effective treatment or preventative available. The lack of economic gains from this tropical parasitic infection, has always been the reason behind its negligence by researchers and drug manufacturers for many decades. Hence there is an enormous requirement for more efficient and novel strategies to reduce the fatality associated with these diseases. Even, available diagnosis protocols are outdated and inefficient and there is an urgent need for rapid high throughput diagnostics as well as management protocol. The current advancement of nanotechnology in the field of healthcare has generated hope for better management of many tropical diseases including Chagas disease. Nanoparticulate systems for drug delivery like poloxamer coated nanosuspension of benzimidazole have shown promising results in reducing toxicity, elevating efficacy and bioavailability of the active compound against the pathogen, by prolonging release, thereby increasing the therapeutic index. Moreover, nanoparticle-based drug delivery has shown promising results in inducing the host’s immune response against the pathogen with very few side effects. Besides, advances in diagnostic assays, such as nanosensors, aided in the accurate detection of the parasite. In this review, we provide an insight into the life cycle stages of the pathogen in both vertebrate host and the insect vector, along with an overview of the current therapy for Chagas disease and its limitations; nano carrier-based delivery systems for antichagasic agents, we also address the advancement of nano vaccines and nano-diagnostic techniques, for treatment of Chagas disease, majorly focusing on the novel perspectives in combating the disease.

The Trypanosoma cruzi TcTASV-C protein subfamily administrated with U-Omp19 promotes a protective response against a lethal challenge in mice

The development of a Chagaś disease vaccine has yet the need for the identification of novel combinations of antigens and adjuvants. Here, the performance of TcTASV-C proteins that are virulence factors of trypomastigotes and belong to a novel surface protein family specific for T. cruzi, have been evaluated as antigens for a prophylactic vaccine. Several immunization schemes in which TcTASV-C was combined with aluminum hydroxide, saponin and/or U-Omp19 were assayed. Aluminum hydroxide and saponin were assayed together to trigger different pathways of the immune response simultaneously. U-Omp19 is a promising novel adjuvant able to promote a Th1 immune response with IFNg production, thus an interesting molecule to be tested as adjuvant for the control of T. cruzi infection. Therefore, U-Omp19 was added to the aluminum hydroxide-saponin formulation as well as assayed individually with TcTASV-C. The immunization with TcTASV-C and U-Omp19 had the best performance as a prophylactic vaccine. Mice presented the lowest parasitemias and improved survival by 40% after being challenged with a highly virulent T. cruzi strain, which promoted 100% mortality in all other immunized groups. Immunization with TcTASV-C and U-Omp19 triggered cellular responses with IFN-γ and IL-17 production and with lytic antibodies that could explain the protection achieved by this vaccination scheme. To our knowledge, this is the first time that U-Omp19 is tested with a defined T. cruzi antigen in a vaccine formulation.

Chagas disease vaccine design: the search for an efficient Trypanosoma cruzi immune-mediated control

Chagas disease is currently endemic to 21 Latin-American countries and has also become a global concern because of globalization and mass migration of chronically infected individuals. Prophylactic and therapeutic vaccination might contribute to control the infection and the pathology, as complement of other strategies such as vector control and chemotherapy. Ideal prophylactic vaccine would produce sterilizing immunity; however, a reduction of the parasite burden would prevent progression from Trypanosoma cruzi infection to Chagas disease. A therapeutic vaccine for Chagas disease may improve or even replace the treatment with current drugs which have several side effects and require long term treatment that frequently leads to therapeutic withdrawal. Here, we will review some aspects about sub-unit vaccines, the rationale behind the selection of the immunogen, the role of adjuvants, the advantages and limitations of DNA-based vaccines and the idea of therapeutic vaccines. One of the main limitations to advance vaccine development against Chagas disease is the high number of variables that must be considered and the lack of uniform criteria among research laboratories. To make possible comparisons, much of this review will be focused on experiments that kept many variables constant including antigen mass/doses, type of eukaryotic plasmid, DNA-delivery system, mice strain and sex, lethal and sublethal model of infection, and similar immunogenicity and efficacy assessments.

Advances in nanocarriers as drug delivery systems in Chagas disease

Chagas disease is one of the most important public health problems in Latin America due to its high mortality and morbidity levels. There is no effective treatment for this disease since drugs are usually toxic with low bioavailability. Serious efforts to achieve disease control and eventual eradication have been unsuccessful to date, emphasizing the need for rapid diagnosis, drug development, and a reliable vaccine. Novel systems for drug and vaccine administration based on nanocarriers represent a promising avenue for Chagas disease treatment. Nanoparticulate systems can reduce toxicity, and increase the efficacy and bioavailability of active compounds by prolonging release, and therefore improve the therapeutic index. Moreover, nanoparticles are able to interact with the host's immune system, modulating the immune response to favour the elimination of pathogenic microorganisms. In addition, new advances in diagnostic assays, such as nanobiosensors, are beneficial in that they enable precise identification of the pathogen. In this review, we provide an overview of the strategies and nanocarrier-based delivery systems for antichagasic agents, such as liposomes, micelles, nanoemulsions, polymeric and non-polymeric nanoparticles. We address recent progress, with a particular focus on the advances of nanovaccines and nanodiagnostics, exploring new perspectives on Chagas disease treatment.

Epitope Capsid-Incorporation: New Effective Approach for Vaccine Development for Chagas Disease

Background:

Previously we reported that a hexon-modified adenovirus (Ad) vector containing the invasive neutralizing epitope of Trypanosoma cruzi (T. cruzi) trypomastigote gp83 (Ad5-gp83) provided immunoprotection against T. cruzi infection. The purpose of this work was to design an improved vaccine for T. cruzi using a novel epitope capsid incorporation strategy. Thus, we evaluated the immunoprotection raised by co-immunization with Ad5-gp83 and an Ad vector containing an epitope (ASP-M) of the T. cruzi amastigote surface protein 2.

Methods:

Protein IX (pIX)-modified Ad vector (Ad5-pIX-ASP-M) was generated, characterized, and validated. C3H/He mice were immunized with Ad5-pIX-ASP-M and Ad5-gp83 and the cell-mediated responses were evaluated by enzyme-linked immunospot (ELISPOT) assay and intracellular staining. Immunized mice were challenged with T. cruzi to evaluate the vaccine efficacy.

Results:

Our findings indicate that Ad5-pIX-ASP-M was viable. Specific CD8⁺ T-cell mediated responses prior to the challenge show an increase in IFNγ and TNFα production. A single immunization with Ad5-pIX-ASP-M provided protection from T. cruzi infection, but co-immunizations with Ad5-pIX-ASP-M and Ad5-gp83 provided a higher immunoprotection and increased survival rate of mice.

Conclusions:

Overall, these results suggest that the combination of gp83 and ASP-M specific epitopes onto the capsid-incorporated adenoviruses would provide superior protection against Chagas disease as compared with Ad5-gp83 alone.

Antigen targeting to dendritic cells allows the identification of a CD4 T-cell epitope within an immunodominant Trypanosoma cruzi antigen

Targeting antigens to dendritic cells (DCs) by using hybrid monoclonal antibodies (mAbs) directed against DC receptors is known to improve activation and support long-lasting T cell responses. In the present work, we used the mAb αDEC205 fused to the Trypanosoma cruzi amastigote surface protein 2 (ASP-2) to identify a region of this protein recognized by specific T cells. The hybrid αDEC-ASP2 mAb was successfully generated and preserved its ability to bind the DEC205 receptor. Immunization of BALB/c mice with the recombinant mAb in the presence of polyriboinosinic: polyribocytidylic acid (poly (I:C)) specifically enhanced the number of IFN-γ producing cells and CD4+ T cell proliferation when compared to mice immunized with a mAb without receptor affinity or with the non-targeted ASP-2 protein. The strong immune response induced in mice immunized with the hybrid αDEC-ASP2 mAb allowed us to identify an ASP-2-specific CD4+ T cell epitope recognized by the BALB/c MHCII haplotype. We conclude that targeting parasite antigens to DCs is a useful strategy to enhance T cell mediated immune responses facilitating the identification of new T-cell epitopes.

Gene-deleted live-attenuated Trypanosoma cruzi parasites as vaccines to protect against Chagas disease

Chagas disease is a neglected tropical disease caused by the protozoan parasite Trypanosoma cruzi. This illness is now becoming global, mainly due to congenital transmission, and so far, there are no prophylactic or therapeutic vaccines available to either prevent or treat Chagas disease. Therefore, different approaches aimed at identifying new protective immunogens are urgently needed. Live vaccines are likely to be more efficient in inducing protection, but safety issues linked with their use have been raised. The development of improved protozoan genetic manipulation tools and genomic and biological information has helped to increase the safety of live vaccines. These advances have generated a renewed interest in the use of genetically attenuated parasites as vaccines against Chagas disease. This review discusses the protective capacity of genetically attenuated parasite vaccines and the challenges and perspectives for the development of an effective whole-parasite Chagas disease vaccine.

Tc52 amino-terminal-domain DNA carried by attenuated Salmonella enterica serovar Typhimurium induces protection against a Trypanosoma cruzi lethal challenge

In this work we immunized mice with DNA encoding full-length Tc52 or its amino- or carboxy-terminal (N- and C-term, respectively) domain carried by attenuated Salmonella as a DNA delivery system. As expected, Salmonella-mediated DNA delivery resulted in low antibody titers and a predominantly Th1 response, as shown by the ratio of IgG2a/IgG1-specific antibodies. Despite modest expression of Tc52 in trypomastigotes, the antibodies elicited by vaccination were able to mediate lysis of the trypomastigotes in the presence of complement and inhibit their invasion of mammal cells in vitro. The strongest functional activity was observed with sera from mice immunized with Salmonella carrying the N-term domain (SN-term), followed by Tc52 (STc52), and the C-term domain (SC-term). All immunized groups developed strong cellular responses, with predominant activation of Th1 cells. However, mice immunized with SN-term showed higher levels of interleukin-10 (IL-10), counterbalancing the inflammatory reaction, and also strong activation of Tc52-specific gamma interferon-positive (IFN-γ(+)) CD8(+) T cells. In agreement with this, although all prototypes conferred protection against infection, immunization with SN-term promoted greater protection than that with SC-term for all parameters tested and slightly better protection than that with STc52, especially in the acute stage of infection. We conclude that the N-terminal domain of Tc52 is the section of the protein that confers maximal protection against infection and propose it as a promising candidate for vaccine development.

CD8(+) T cell-mediated immunity during Trypanosoma cruzi infection: a path for vaccine development?

MHC-restricted CD8⁺ T cells are important during infection with the intracellular protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. Experimental studies performed in the past 25 years have elucidated a number of features related to the immune response mediated by these T cells, which are important for establishing the parasite/host equilibrium leading to chronic infection. CD8⁺ T cells are specific for highly immunodominant antigens expressed by members of the trans-sialidase family. After infection, their activation is delayed, and the cells display a high proliferative activity associated with high apoptotic rates. Although they participate in parasite control and elimination, they are unable to clear the infection due to their low fitness, allowing the parasite to establish the chronic phase when these cells then play an active role in the induction of heart immunopathology. Vaccination with a number of subunit recombinant vaccines aimed at eliciting specific CD8⁺ T cells can reverse this path, thereby generating a productive immune response that will lead to the control of infection, reduction of symptoms, and reduction of disease transmission. Due to these attributes, activation of CD8⁺ T lymphocytes may constitute a path for the development of a veterinarian or human vaccine.

Time course study of the antigen-specific immune response to a PLGA microparticle vaccine formulation

Microparticle-based vaccine delivery systems are known to promote enhanced immune responses to protein antigens and can elicit TH1-biased responses when used in combination with Toll-like receptor (TLR) agonists. It is important to understand the kinetics of the immune responses to microparticle-based protein vaccines in order to predict the duration of protective immunity and to optimize prime-boost vaccination regimens. We carried out a 10-week time course study to investigate the magnitude and kinetics of the antibody and cellular immune responses to poly(lactic-co-glycolic acid) (PLGA) microparticles containing 40 μg ovalbumin (OVA) protein and 16 μg CpG-ODN adjuvant (MP/OVA/CpG) in comparison to OVA-containing microparticles, soluble OVA plus CpG, or OVA formulated with Alhydrogel(®) aluminum adjuvant. Mice vaccinated with MP/OVA/CpG developed the highest TH1-associated IgG2b and IgG2c antibody titers, while also eliciting TH2-associated IgG1 antibody titers on par with Alhydrogel(®)-formulated OVA, with all IgG subtype titers peaking at day 56. The MP/OVA/CpG vaccine also induced the highest antigen-specific splenocyte IFN-γ responses, with high levels of IFN-γ responses persisting until day 42. Thus the MP/OVA/CpG formulation produced a sustained and heightened humoral and cellular immune response, with an overall TH1 bias, while maintaining high levels of IgG1 antibody equivalent to that seen with Alhydrogel(®) adjuvant. The time course kinetics study provides a useful baseline for designing vaccination regimens for microparticle-based protein vaccines.

Vaccination using recombinants influenza and adenoviruses encoding amastigote surface protein-2 are highly effective on protection against Trypanosoma cruzi infection

In the present study we evaluated the protection raised by immunization with recombinant influenza viruses carrying sequences coding for polypeptides corresponding to medial and carboxi-terminal moieties of Trypanosoma cruzi ´s amastigote surface protein 2 (ASP2). Those viruses were used in sequential immunization with recombinant adenovirus (heterologous prime-boost immunization protocol) encoding the complete sequence of ASP2 (Ad-ASP2) in two mouse strains (C57BL/6 and C3H/He). The CD8 effector response elicited by this protocol was comparable to that observed in mice immunized twice with Ad-ASP2 and more robust than that observed in mice that were immunized once with Ad-ASP2. Whereas a single immunization with Ad-ASP2 sufficed to completely protect C57BL/6 mice, a higher survival rate was observed in C3H/He mice that were primed with recombinant influenza virus and boosted with Ad-ASP2 after being challenged with T. cruzi. Analyzing the phenotype of CD8+ T cells obtained from spleen of vaccinated C3H/He mice we observed that heterologous prime-boost immunization protocol elicited more CD8+ T cells specific for the immunodominant epitope as well as a higher number of CD8+ T cells producing TNF-α and IFN-γ and a higher mobilization of surface marker CD107a. Taken together, our results suggest that immunodominant subpopulations of CD8+ T elicited after immunization could be directly related to degree of protection achieved by different immunization protocols using different viral vectors. Overall, these results demonstrated the usefulness of recombinant influenza viruses in immunization protocols against Chagas Disease.

Recombinant yellow fever viruses elicit CD8+ T cell responses and protective immunity against Trypanosoma cruzi

Chagas’ disease is a major public health problem affecting nearly 10 million in Latin America. Despite several experimental vaccines have shown to be immunogenic and protective in mouse models, there is not a current vaccine being licensed for humans or in clinical trial against T. cruzi infection. Towards this goal, we used the backbone of Yellow Fever (YF) 17D virus, one of the most effective and well-established human vaccines, to express an immunogenic fragment derived from T. cruzi Amastigote Surface Protein 2 (ASP-2). The cDNA sequence of an ASP-2 fragment was inserted between E and NS1 genes of YF 17D virus through the construction of a recombinant heterologous cassette. The replication ability and genetic stability of recombinant YF virus (YF17D/ENS1/Tc) was confirmed for at least six passages in Vero cells. Immunogenicity studies showed that YF17D/ENS1/Tc virus elicited neutralizing antibodies and gamma interferon (IFN-γ) producing-cells against the YF virus. Also, it was able to prime a CD8⁺ T cell directed against the transgenic T. cruzi epitope (TEWETGQI) which expanded significantly as measured by T cell-specific production of IFN-γ before and after T. cruzi challenge. However, most important for the purposes of vaccine development was the fact that a more efficient protective response could be seen in mice challenged after vaccination with the YF viral formulation consisting of YF17D/ENS1/Tc and a YF17D recombinant virus expressing the TEWETGQI epitope at the NS2B-3 junction. The superior protective immunity observed might be due to an earlier priming of epitope-specific IFN-γ-producing T CD8⁺ cells induced by vaccination with this viral formulation. Our results suggest that the use of viral formulations consisting of a mixture of recombinant YF 17D viruses may be a promising strategy to elicit protective immune responses against pathogens, in general.

Re-circulation of lymphocytes mediated by sphingosine-1-phosphate receptor-1 contributes to resistance against experimental infection with the protozoan parasite Trypanosoma cruzi

T-cell mediated immune responses are critical for acquired immunity against infection by the intracellular protozoan parasite Trypanosoma cruzi. Despite its importance, it is currently unknown where protective T cells are primed and whether they need to re-circulate in order to exert their anti-parasitic effector functions. Here, we show that after subcutaneous challenge, CD11c(+)-dependent specific CD8(+) T-cell immune response to immunodominant parasite epitopes arises almost simultaneously in the draining lymph node (LN) and the spleen. However, until day 10 after infection, we observed a clear upregulation of activation markers only on the surface of CD11C(+)PDCA1(+) cells present in the LN and not in the spleen. Therefore, we hypothesized that CD8(+) T cells re-circulated rapidly from the LN to the spleen. We investigated this phenomenon by administering FTY720 to T. cruzi-infected mice to prevent egress of T cells from the LN by interfering specifically with signalling through sphingosine-1-phosphate receptor-1. In T. cruzi-infected mice receiving FTY720, CD8 T-cell immune responses were higher in the draining LN and significantly reduced in their spleen. Most importantly, FTY720 increased susceptibility to infection, as indicated by elevated parasitemia and accelerated mortality. Similarly, administration of FTY720 to mice genetically vaccinated with an immunodominant parasite antigen significantly reduced their protective immunity, as observed by the parasitemia and survival of vaccinated mice. We concluded that re-circulation of lymphocytes mediated by sphingosine-1-phosphate receptor-1 greatly contributes to acquired and vaccine-induced protective immunity against experimental infection with a human protozoan parasite.

The Immune Response to Trypanosoma cruzi: Role of Toll-Like Receptors and Perspectives for Vaccine Development

In the past ten years, studies have shown the recognition of Trypanosoma cruzi-associated molecular patterns by members of the Toll-like receptor (TLR) family and demonstrated the crucial participation of different TLRs during the experimental infection with this parasite. In the present review, we will focus on the role of TLR-activated pathways in the modulation of both innate and acquired immune responses to T. cruzi infection, as well as discuss the state of the art of vaccine research and development against the causative agent of Chagas disease (or American trypanosomiasis).

Vaccine development against Trypanosoma cruzi and Chagas disease

The pathology of Chagas disease presents a complicated and diverse picture in humans. The major complications and destructive evolutionary outcomes of chronic infection by Trypanosoma cruzi in humans include ventricular fibrillation, thromboembolism and congestive heart failure. Studies in animal models and human patients have revealed the pathogenic mechanisms during disease progression, pathology of disease and features of protective immunity. Accordingly, several antigens, antigen-delivery vehicles and adjuvants have been tested to elicit immune protection to T. cruzi in experimental animals. This review summarizes the research efforts in vaccine development against Chagas disease during the past decade.

Advances and challenges towards a vaccine against Chagas disease

Chagas disease is major public health problem, affecting nearly 10 million people, characterized by cardiac alterations leading to congestive heart failure and death of 20-40% of the patients infected with Trypanosoma cruzi, the protozoan parasite responsible for the disease. A vaccine would be key to improve disease control and we review here the recent advances and challenges of a T. cruzi vaccine. There is a growing consensus that a protective immune response requires the activation of a Th1 immune profile, with the stimulation of CD8 (+) T cells. Several vacines types, including recombinant proteins, DNA and viral vectors, as well as heterologous prime-boost combinations, have been found immunogenic and protective in mouse models, providing proof-of-concept data on the feasibility of a preventive or therapeutic vaccine to control a T. cruzi infection. However, several challenges such as better end-points, safety issues and trial design need to be addressed for further vaccine development to proceed.

A DNA vaccine encoding for TcSSP4 induces protection against acute and chronic infection in experimental Chagas disease

Immunization of mice with plasmids containing genes of Trypanosoma cruzi induces protective immunity in the murine model of Chagas disease. A cDNA clone that codes for an amastigote-specific surface protein (TcSSP4) was used as a candidate to develop a DNA vaccine. Mice were immunized with the recombinant protein rTcSSP4 and with cDNA for TcSSP4, and challenged with bloodstream trypomastigotes. Immunization with rTcSSP4 protein makes mice more susceptible to trypomastigote infection, with high mortality rates, whereas mice immunized with a eukaryotic expression plasmid containing the TcSSP4 cDNA were able to control the acute phase of infection. Heart tissue of gene-vaccinated animals did not show myocarditis and tissue damage at 365 days following infection, as compared with control animals. INF-γ was detected in sera of DNA vaccinated mice shortly after immunization, suggesting the development of a Th1 response. The TcSSP4 gene is a promising candidate for the development of an anti-T. cruzi DNA vaccine.

Requirement of UNC93B1 reveals a critical role for TLR7 in host resistance to primary infection with Trypanosoma cruzi

UNC93B1 associates with TLR3, 7, and 9, mediating their translocation from the endoplasmic reticulum to the endolysosome, thus allowing proper activation by microbial nucleic acids. We found that the triple-deficient 3d mice, which lack functional UNC93B1 as well as functional endosomal TLRs, are highly susceptible to infection with Trypanosoma cruzi. The enhanced parasitemia and mortality in 3d animals were associated with impaired proinflammatory response, including reduced levels of IL-12p40 and IFN-γ. Importantly, the phenotype of 3d mice was intermediary between MyD88(-/-) (highly susceptible) and TLR9(-/-) (moderately susceptible), indicating the involvement of an additional UN93B1-dependent TLR(s) on host resistance to T. cruzi. Hence, our experiments also revealed that TLR7 is a critical innate immune receptor involved in recognition of parasite RNA, induction of IL-12p40 by dendritic cells, and consequent IFN-γ by T lymphocytes. Furthermore, we show that upon T. cruzi infection, triple TLR3/7/9(-/-) mice had similar phenotype than 3d mice. These data imply that the nucleic acid-sensing TLRs are critical determinants of host resistance to primary infection with T. cruzi.

Subdominant/cryptic CD8 T cell epitopes contribute to resistance against experimental infection with a human protozoan parasite

During adaptive immune response, pathogen-specific CD8⁺ T cells recognize preferentially a small number of epitopes, a phenomenon known as immunodominance. Its biological implications during natural or vaccine-induced immune responses are still unclear. Earlier, we have shown that during experimental infection, the human intracellular pathogen Trypanosoma cruzi restricts the repertoire of CD8⁺ T cells generating strong immunodominance. We hypothesized that this phenomenon could be a mechanism used by the parasite to reduce the breath and magnitude of the immune response, favoring parasitism, and thus that artificially broadening the T cell repertoire could favor the host. Here, we confirmed our previous observation by showing that CD8⁺ T cells of H-2^a infected mice recognized a single epitope of an immunodominant antigen of the trans-sialidase super-family. In sharp contrast, CD8⁺ T cells from mice immunized with recombinant genetic vaccines (plasmid DNA and adenovirus) expressing this same T. cruzi antigen recognized, in addition to the immunodominant epitope, two other subdominant epitopes. This unexpected observation allowed us to test the protective role of the immune response to subdominant epitopes. This was accomplished by genetic vaccination of mice with mutated genes that did not express a functional immunodominant epitope. We found that these mice developed immune responses directed solely to the subdominant/cryptic CD8 T cell epitopes and a significant degree of protective immunity against infection mediated by CD8⁺ T cells. We concluded that artificially broadening the T cell repertoire contributes to host resistance against infection, a finding that has implications for the host-parasite relationship and vaccine development.

Biological and immunological characterization of recombinant Yellow Fever 17D viruses expressing a Trypanosoma cruzi Amastigote Surface Protein-2 CD8+ T cell epitope at two distinct regions of the genome

BACKGROUND

The attenuated Yellow fever (YF) 17D vaccine virus is one of the safest and most effective viral vaccines administered to humans, in which it elicits a polyvalent immune response. Herein, we used the YF 17D backbone to express a Trypanosoma cruzi CD8+ T cell epitope from the Amastigote Surface Protein 2 (ASP-2) to provide further evidence for the potential of this virus to express foreign epitopes. The TEWETGQI CD8+ T cell epitope was cloned and expressed based on two different genomic insertion sites: in the fg loop of the viral Envelope protein and the protease cleavage site between the NS2B and NS3. We investigated whether the site of expression had any influence on immunogenicity of this model epitope.

RESULTS

Recombinant viruses replicated similarly to vaccine virus YF 17D in cell culture and remained genetically stable after several serial passages in Vero cells. Immunogenicity studies revealed that both recombinant viruses elicited neutralizing antibodies to the YF virus as well as generated an antigen-specific gamma interferon mediated T-cell response in immunized mice. The recombinant viruses displayed a more attenuated phenotype than the YF 17DD vaccine counterpart in mice. Vaccination of a mouse lineage highly susceptible to infection by T. cruzi with a homologous prime-boost regimen of recombinant YF viruses elicited TEWETGQI specific CD8+ T cells which might be correlated with a delay in mouse mortality after a challenge with a lethal dose of T. cruzi.

CONCLUSIONS

We conclude that the YF 17D platform is useful to express T. cruzi (Protozoan) antigens at different functional regions of its genome with minimal reduction of vector fitness. In addition, the model T. cruzi epitope expressed at different regions of the YF 17D genome elicited a similar T cell-based immune response, suggesting that both expression sites are useful. However, the epitope as such is not protective and it remains to be seen whether expression of larger domains of ASP-2, which include the TEWETGQI epitope, will elicit better T-CD8+ responses to the latter. It is likely that additional antigens and recombinant virus formulations will be necessary to generate a protective response.

Co-administration of a plasmid DNA encoding IL-15 improves long-term protection of a genetic vaccine against Trypanosoma cruzi

Background

Immunization of mice with the Trypanosoma cruzi trans-sialidase (TS) gene using plasmid DNA, adenoviral vector, and CpG-adjuvanted protein delivery has proven highly immunogenic and provides protection against acute lethal challenge. However, long-term protection induced by TS DNA vaccines has not been reported. The goal of the present work was to test whether the co-administration of a plasmid encoding IL-15 (pIL-15) could improve the duration of protection achieved through genetic vaccination with plasmid encoding TS (pTS) alone.

Methodology

We immunized BALB/c mice with pTS in the presence or absence of pIL-15 and studied immune responses [with TS-specific IFN-γ ELISPOT, serum IgG ELISAs, intracellular cytokine staining (IFN-γ, TNF-α, and IL-2), tetramer staining, and CFSE dilution assays] and protection against lethal systemic challenge at 1 to 6 months post vaccination. Mice receiving pTS alone developed robust TS-specific IFN-γ responses and survived a lethal challenge given within the first 3 months following immunization. The addition of pIL-15 to pTS vaccination did not significantly alter T cell responses or protection during this early post-vaccination period. However, mice vaccinated with both pTS and pIL-15 challenged 6 months post-vaccination were significantly more protected against lethal T. cruzi challenges than mice vaccinated with pTS alone (P<0.05). Improved protection correlated with significantly higher numbers of TS-specific IFN-γ producing total and CD8⁺ T cells detected>6 months post immunization. Also, these TS-specific T cells were better able to expand after in vitro re-stimulation.

Conclusion

Addition of pIL-15 during genetic vaccination greatly improved long-term T cell survival, memory T cell expansion, and long-term protection against the important human parasite, T. cruzi.

Effect of a combination DNA vaccine for the prevention and therapy of Trypanosoma cruzi infection in mice: role of CD4+ and CD8+ T cells

Chagas disease is a major public health problem, with about 10 million infected people, and DNA vaccines are a promising alternative for the control of Trypanosoma cruzi, the causing agent of the disease. We tested here a new DNA vaccine encoding a combination of two leading parasite antigens, TSA-1 and Tc24, for the prevention and therapy of T. cruzi infection. Immunized Balb/c mice challenged by T. cruzi presented a significantly lower parasitemia and inflammatory cell density in the heart compared to control mice. Similarly, the therapeutic administration of the DNA vaccine was able to significantly reduce the parasitemia and inflammatory reaction in acutely infected Balb/c and C57BL/6 mice, and reduced cardiac tissue inflammation in chronically infected ICR mice. Therapeutic vaccination induced a marked increase in parasite-specific IFNγ producing CD4(+) and CD8(+) T cells in the spleen as well as an increase in CD4(+) and CD8(+) T cells in the infected cardiac tissue. In addition, some effect of the DNA vaccine could still be observed in CD4-knockout C57BL/6 mice, which presented a lower parasitemia and inflammatory cell density, but not in CD8-deficient mice, in which the vaccine had no effect. These results indicate that the activation of CD8(+) T cells plays a major role in the control of the infection by the therapeutic DNA vaccine, and to a somewhat lesser extent CD4(+) T cells. This observation opens interesting perspectives for the potentiation of this DNA vaccine candidate by including additional CD8(+) T cell antigens/epitopes in future vaccine formulations.

The endless race between Trypanosoma cruzi and host immunity: lessons for and beyond Chagas disease

Infection with the protozoan parasite Trypanosoma cruzi, the agent of Chagas disease, is characterised by a variable clinical course - from symptomless cases to severe chronic disease with cardiac and/or gastrointestinal involvement. The variability in disease outcome has been attributed to host responses as well as parasite heterogeneity. In this article, we review studies indicating the importance of immune responses as key determinants of host resistance to T. cruzi infection and the pathogenesis of Chagas disease. Particular attention is given to recent studies defining the role of cognate innate immune receptors and immunodominant CD8+ T cells that recognise parasite components - both crucial for host-parasite interaction and disease outcome. In light of these studies we speculate about parasite strategies that induce a strong and long-lasting T-cell-mediated immunity but at the same time allow persistence of the parasite in the vertebrate host. We also discuss what we have learned from these studies for increasing our understanding of Chagas pathogenesis and for the design of new strategies to prevent the development of Chagas disease. Finally, we highlight recent studies employing a genetically engineered attenuated T. cruzi strain as a vaccine shuttle that elicits potent T cell responses specific to a tumour antigen and protective immunity against a syngeneic melanoma cell line.

Immune responses to gp82 provide protection against mucosal Trypanosoma cruzi infection

The potential use of the Trypanosoma cruzi metacyclic trypomastigote (MT) stage-specific molecule glycoprotein-82 (gp82) as a vaccine target has not been fully explored. We show that the opsonization of T. cruzi MT with gp82-specific antibody prior to mucosal challenge significantly reduces parasite infectivity. In addition, we investigated the immune responses as well as the systemic and mucosal protective immunity induced by intranasal CpG-adjuvanted gp82 vaccination. Spleen cells from mice immunized with CpG-gp82 proliferated and secreted IFN-γ in a dose-dependent manner in response to in vitro stimulation with gp82 and parasite lysate. More importantly, these CpG-gp82-immunized mice were significantly protected from a biologically relevant oral parasite challenge.

CD8+ T cells specific for immunodominant trans-sialidase epitopes contribute to control of Trypanosoma cruzi infection but are not required for resistance

CD8(+) T cells are essential for controlling Trypanosoma cruzi infection. During Brazil strain infection, C57BL/6 mice expand parasite-specific CD8(+) T cells recognizing the dominant TSKB20 (ANYKFTLV) and subdominant TSKB74 (VNYDFTLV) trans-sialidase gene (TS)-encoded epitopes with up to 40% of all CD8(+) T cells specific for these epitopes. Although this is one of the largest immunodominant T cell responses described for any infection, most mice fail to clear T. cruzi and subsequently develop chronic disease. To determine if immunodominant TS-specific CD8(+) T cells are necessary for resistance to infection, we epitope-tolerized mice by high-dose i.v. injections of TSKB20 or TSKB74 peptides. Tolerance induction led to deletion of TS-specific CD8(+) T cells but did not prevent the expansion of other effector CD8(+) T cell populations. Mice tolerized against either TSKB20 or TSKB74, or both epitopes simultaneously, exhibited transient increases in parasite loads, although ultimately they controlled the acute infection. Furthermore, BALB/c mice tolerized against the TSKD14 peptide effectively controlled acute T. cruzi infection. These data are consistent with the hypothesis that development of high-frequency CD8(+) T cell populations focused on TS-derived epitopes contributes to optimal control of acute infection but is not required for the development of immune resistance.

Transcriptomic analyses of the avirulent protozoan parasite Trypanosoma rangeli

Two species of the genus Trypanosoma infective to humans have been extensively studied at a cell and molecular level, but study of the third, Trypanosoma rangeli, remains in relative infancy. T. rangeli is non-pathogenic, but is frequently mistaken for the related Chagas disease agent Trypanosoma cruzi with which it shares vectors, hosts, significant antigenicity and a sympatric distribution over a wide geographical area. In this study, we present the T. rangeli gene expression profile as determined by the generation of ESTs (Expressed Sequence Tags) and ORESTES (Open Reading Frame ESTs). A total of 4208 unique high quality sequences were analyzed, composed from epimastigote and trypomastigote forms of SC-58 and Choachí strains, representing the two major phylogenetic lineages of this species. Comparative analyses with T. cruzi and other parasitic kinetoplastid species allowed the assignment of putative biological functions to most of the sequences generated and the establishment of an annotated T. rangeli gene expression database. Even though T. rangeli is apathogenic to mammals, genes associated with virulence in other pathogenic kinetoplastids were found. Transposable elements and genes associated mitochondrial gene expression, specifically RNA editing components, are also described for the first time. Our studies confirm the close phylogenetic relationship between T. cruzi and T. rangeli and enable us to make an estimate for the size of the T. rangeli genome repertoire ( approximately 8500 genes).

Trypanosoma brucei: immunisation with plasmid DNA encoding invariant surface glycoprotein gene is able to induce partial protection in experimental African trypanosomiasis

Trypanosoma brucei is the etiological agent responsible for African trypanosomiasis, an infectious pathology which represents a serious problem of public health and economic losses in Sub-Saharan Africa. As one of the foremost neglected illnesses, few resources have been available for the development of vaccines or new drugs, in spite of the current therapeutical drugs showing little efficiency and high toxicity. Hence, it is obviously important to widen effective therapeutics and preventive strategies against African trypanosomiasis. In this work, we use the DNA vaccine model to evaluate immunisation effectiveness in mice challenged with Trypanosoma brucei brucei. We demonstrate that Balb/C mice immunised intramuscularly with a single dose of a DNA plasmid encoding a bloodstream-stage specific invariant surface glycoprotein (ISG) are partially protected from a lethal dose of T. b. brucei. Interestingly, the surviving animals show high levels of IgG2a anti-trypanosoma antibodies, suggesting that the Th1 response profile seems important for the induced mechanisms of immune protection.

Cross-priming in health and disease

Cross-priming is an important mechanism to activate cytotoxic T lymphocytes (CTLs) for immune defence against viruses and tumours. Although it was discovered more than 25 years ago, we have only recently gained insight into the underlying cellular and molecular mechanisms, and we are just beginning to understand its physiological importance in health and disease. Here we summarize current concepts on the cross-talk between the immune cells involved in CTL cross-priming and on its role in antimicrobial and antitumour defence, as well as in immune-mediated diseases.

Vaccine development against Trypanosoma cruzi and Leishmania species in the post-genomic era

Trypanosoma cruzi and the genus Leishmania are protozoan parasites causing diseases of major public health importance, and the recent completion of the sequencing of their genomes has opened new opportunities to further our understanding of the mechanisms required for protection and the development of vaccines. For example, trans-sialidases, one of the largest protein families from T. cruzi, contain dominant CD8+ T cell epitopes, and their use as preventive or therapeutic vaccines in different animal models has provided encouraging results. A much wider range of antigens and vaccine formulations have been tested against Leishmania, and new correlates for protection are being defined, such as the induction of multifunctional Th1 effector cells capable of producing a complex set of cytokines. Also, while a large number of these vaccine candidates have been rather successful in mouse models, their usefulness in more relevant animal models is still poor, in spite of significant immunogenicity. Novel proteomics and genomics approaches are being used for antigen discovery and the identification of new vaccine candidates, some of which have shown promise for the control of infection. These studies cast little doubt that T. cruzi and Leishmania genomes represent major resources for understanding key aspects of the mechanisms of immune protection against these parasites, and the increasing use of these tools will greatly impact vaccine development.

Chagas' disease: an update on immune mechanisms and therapeutic strategies

The final decade of the 20th century was marked by an alarming resurgence in infectious diseases caused by tropical parasites belonging to the kinetoplastid protozoan order. Among the pathogenic trypanosomatids, some species are of particular interest due to their medical importance. These species include the agent responsible for Chagas’ disease, Trypanosoma cruzi. Approximately 8 to 10 million people are infected in the Americas, and approximately 40 million are at risk. In the present review, we discuss in detail the immune mechanisms elicited during infection by T. cruzi and the effects of chemotherapy in controlling parasite proliferation and on the host immune system.

Trans-sialidase from Trypanosoma brucei as a potential target for DNA vaccine development against African trypanosomiasis

African trypanosomiasis (AT), also known as sleeping sickness in humans and Nagana in animals, is a disease caused by the protozoan parasite Trypanosoma brucei. AT is an extremely debilitating disease in human, cattle, and wild animals, and the treatment is difficult with frequent relapses. This work shows that BALB-c mice immunized intramuscularly with a single dose (100 microg) of a plasmid DNA encoding the 5'-terminal region of the trans-sialidase (nTSA) gene of T. brucei brucei are able to produce IgG antibodies that bind to the bloodstream form of T. brucei-protein extract and recognize the recombinant nTSA protein, expressed in Escherichia coli. Furthermore, this DNA vaccination process was able to protect 60% of mice submitted to a challenge assay with the infective form of T. brucei brucei parasites. These results demonstrate that a DNA vaccine coding for trans-sialidase from T. brucei is potentially useful in the prophylaxis of AT.

Perforin and gamma interferon expression are required for CD4+ and CD8+ T-cell-dependent protective immunity against a human parasite, Trypanosoma cruzi, elicited by heterologous plasmid DNA prime-recombinant adenovirus 5 boost vaccination

A heterologous prime-boost strategy using plasmid DNA, followed by replication-defective recombinant adenovirus 5, is being proposed as a powerful way to elicit CD4(+) and CD8(+) T-cell-mediated protective immunity against intracellular pathogens. We confirmed this concept and furthered existing research by providing evidence that the heterologous prime-boost regimen using the gene encoding amastigote surface protein 2 elicited CD4(+) and CD8(+) T-cell-mediated protective immunity (reduction of acute parasitemia and prolonged survival) against experimental infection with Trypanosoma cruzi. Protective immunity correlated with the presence of in vivo antigen-specific cytotoxic activity prior to challenge. Based on this, our second goal was to determine the outcome of infection after heterologous prime-boost immunization of perforin-deficient mice. These mice were highly susceptible to infection. A detailed analysis of the cell-mediated immune responses in immunized perforin-deficient mice showed an impaired gamma interferon (IFN-gamma) secretion by immune spleen cells upon restimulation in vitro with soluble recombinant antigen. In spite of a normal numeric expansion, specific CD8(+) T cells presented several functional defects detected in vivo (cytotoxicity) and in vitro (simultaneous expression of CD107a/IFN-gamma or IFN-gamma/tumor necrosis factor alpha) paralleled by a decreased expression of CD44 and KLRG-1. Our final goal was to determine the importance of IFN-gamma in the presence of highly cytotoxic T cells. Vaccinated IFN-gamma-deficient mice developed highly cytotoxic cells but failed to develop any protective immunity. Our study thus demonstrated a role for perforin and IFN-gamma in a number of T-cell-mediated effector functions and in the antiparasitic immunity generated by a heterologous plasmid DNA prime-adenovirus boost vaccination strategy.

Identification of novel vaccine candidates for Chagas' disease by immunization with sequential fractions of a trypomastigote cDNA expression library

The protozoan Trypanosoma cruzi is the etiological agent of Chagas' disease, a major chronic infection in Latin America. Currently, there are neither effective drugs nor vaccines for the treatment or prevention of the disease. Several T. cruzi surface antigens are being tested as vaccines but none of them proved to be completely protective, probably because they represent only a limited repertoire of all the possible T. cruzi target molecules. Taking into account that the trypomastigote stage of the parasite must express genes that allow the parasite to disseminate into the tissues and invade cells, we reasoned that genes preferentially expressed in trypomastigotes represent potential targets for immunization. Here we screened an epimastigote-subtracted trypomastigote cDNA expression library by genetic immunization, in order to find new vaccine candidates for Chagas' disease. After two rounds of immunization and challenge with trypomastigotes, this approach led to the identification of a pool of 28 gene fragments that improved in vivo protection. Sequence analysis of these putative candidates revealed that 19 out of 28 (67.85%) of the genes were hypothetical proteins or unannotated T. cruzi open reading frames, which certainly would not have been identified by other methods of vaccine discovery.

Novel protective antigens expressed by Trypanosoma cruzi amastigotes provide immunity to mice highly susceptible to Chagas' disease

Earlier studies have demonstrated in A/Sn mice highly susceptible to Chagas' disease protective immunity against lethal Trypanosoma cruzi infection elicited by vaccination with an open reading frame (ORF) expressed by amastigotes. In our experiments, we used this mouse model to search for other amastigote-expressed ORFs with a similar property. Fourteen ORFs previously determined to be expressed in this developmental stage were individually inserted into a eukaryotic expression vector containing a nucleotide sequence that encoded a mammalian secretory signal peptide. Immunization with 13 of the 14 ORFs induced specific antibodies which recognized the amastigotes. Three of those immune sera also reacted with trypomastigotes and epimastigotes. After a lethal challenge with Y strain trypomastigotes, the vast majority of plasmid-injected mice succumbed to infection. In some cases, a significant delay in mortality was observed. Only two of these ORFs provided protective immunity against the otherwise lethal infection caused by trypomastigotes of the Y or Colombia strain. These ORFs encode members of the trans-sialidase family of surface antigens related to the previously described protective antigen amastigote surface protein 2 (ASP-2). Nevertheless, at the level of antibody recognition, no cross-reactivity was observed between the ORFs and the previously described ASP-2 from the Y strain. In immunofluorescence analyses, we observed the presence of epitopes related to both proteins expressed by amastigotes of seven different strains. In conclusion, our approach allowed us to successfully identify two novel protective ORFs which we consider interesting for future studies on the immune response to Chagas' disease.

Infection with Trypanosoma cruzi restricts the repertoire of parasite-specific CD8+ T cells leading to immunodominance

Interference or competition between CD8(+) T cells restricted by distinct MHC-I molecules can be a powerful means to establish an immunodominant response. However, its importance during infections is still questionable. In this study, we describe that following infection of mice with the human pathogen Trypanosoma cruzi, an immunodominant CD8(+) T cell immune response is developed directed to an H-2K(b)-restricted epitope expressed by members of the trans-sialidase family of surface proteins. To determine whether this immunodominance was exerted over other non-H-2K(b)-restricted epitopes, we measured during infection of heterozygote mice, immune responses to three distinct epitopes, all expressed by members of the trans-sialidase family, recognized by H-2K(b)-, H-2K(k)-, or H-2K(d)-restricted CD8(+) T cells. Infected heterozygote or homozygote mice displayed comparably strong immune responses to the H-2K(b)-restricted immunodominant epitope. In contrast, H-2K(k)- or H-2K(d)-restricted immune responses were significantly impaired in heterozygote infected mice when compared with homozygote ones. This interference was not dependent on the dose of parasite or the timing of infection. Also, it was not seen in heterozygote mice immunized with recombinant adenoviruses expressing T. cruzi Ags. Finally, we observed that the immunodominance was circumvented by concomitant infection with two T. cruzi strains containing distinct immunodominant epitopes, suggesting that the operating mechanism most likely involves competition of T cells for limiting APCs. This type of interference never described during infection with a human parasite may represent a sophisticated strategy to restrict priming of CD8(+) T cells of distinct specificities, avoiding complete pathogen elimination by host effector cells, and thus favoring host parasitism.

Use of proteoliposome as a vaccine against Trypanosoma cruzi in mice

We have generated proteoliposomes carrying proteins of Trypanosoma cruzi for use as immunogens in BALB/c mice. T. cruzi trypomastigote and amastigote forms were sonicated and mixed with SDS, with 94% recovery of soluble proteins. To prepare proteoliposomes, we have used a protocol in which dipalmitoylphosphatidylcholine, dipalmitoyl-phosphatidylserine and cholesterol were incubated with the parasite proteins. BALB/c mice immunized with 20microg were able to generate antibodies which, in Western blotting, reacted with the proteins of T. cruzi. We further investigated the ability of peritoneal cells from immunized mice to arrest the intracellular replication of trypomastigotes, in vitro. After 72h of culture, the number of intracellular parasites in immunized macrophages decreased significantly, as compared to controls. Despite the fact that exposure of mice to T. cruzi proteins incorporated into proteoliposomes generate antibodies and activate macrophages, the immunized mice were not protected against T. cruzi intraperitoneal challenge.