Comparative evaluation of therapeutic DNA vaccines against Trypanosoma cruzi in mice

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.

Chagas Disease: A Silent Threat for Dogs and Humans

Chagas disease (CD) is a vector-borne Neglected Zoonotic Disease (NZD) caused by a flagellate protozoan, Trypanosoma cruzi, that affects various mammalian species across America, including humans and domestic animals. However, due to an increase in population movements and new routes of transmission, T. cruzi infection is presently considered a worldwide health concern, no longer restricted to endemic countries. Dogs play a major role in the domestic cycle by acting very efficiently as reservoirs and allowing the perpetuation of parasite transmission in endemic areas. Despite the significant progress made in recent years, still there is no vaccine against human and animal disease, there are few drugs available for the treatment of human CD, and there is no standard protocol for the treatment of canine CD. In this review, we highlight human and canine Chagas Disease in its different dimensions and interconnections. Dogs, which are considered to be the most important peridomestic reservoir and sentinel for the transmission of T. cruzi infection in a community, develop CD that is clinically similar to human CD. Therefore, an integrative approach, based on the One Health concept, bringing together the advances in genomics, immunology, and epidemiology can lead to the effective development of vaccines, new treatments, and innovative control strategies to tackle CD.

The high identity of the Trypanosoma cruzi Group-I of trans-sialidases points them as promising vaccine immunogens

Trans-sialidase (TS) superfamily of proteins comprises eight subgroups, being the proteins of Group-I (TS-GI) promising immunogens in vaccine approaches against Trypanosoma cruzi. Strikingly, TS-GI antigenic variability among parasite lineages and their influence on vaccine development has not been previously analyzed. Here, a search in GenBank detects 49 TS-GI indexed sequences, whereas the main infecting human different parasite discrete typing units (DTU) are represented. In silico comparison among these sequences indicate that they share an identity above 92%. Moreover, the antigenic regions (T-cell and B-cell epitopes) are conserved in most sequences or present amino acid substitutions that scarcely may alter the antigenicity. Additionally, since the generic term TS is usually used to refer to different immunogens of this broad family, a further in silico analysis of the TS-GI-derived fragments tested in preclinical vaccines was done to determine the coverage and identity among them, showing that overall amino acid identity of vaccine immunogens is high, but the segment coverage varies widely. Accordingly, strong H-2K, H-2I, and B-cell epitopes are dissimilarly represented among vaccine TS-derived fragments depending on the extension of the TG-GI sequence used. Moreover, bioinformatic analysis detected a set of 150 T-cell strong epitopes among the DTU-indexed sequences that strongly bind human HLA-I supertypes. In all currently reported experimental vaccines based on TS-GI fragments, mapping these 150 epitopes showed that they are moderately represented. However, despite vaccine epitopes do not present all the substitutions observed in the DTUs, these regions of the proteins are equally recognized by the same HLAs.  Interestingly, the predictions regarding global and South American population coverage estimated in these 150 epitopes are similar to the estimations in experimental vaccines when the complete sequence of TS-GI is used as an antigen. In silico prediction also shows that a number of these MHC-I restricted T-cell strong epitopes could be also cross-recognized by HLA-I supertypes and H-2Kb or H-2Kd backgrounds, indicating that these mice may be used to improve and facilitate the development of new TS-based vaccines and suggesting an immunogenic and protective potential in humans. Further molecular docking analyses were performed to strengthen these results. Taken together, different strategies that would cover more or eventually fully of these T-cell and also B-cell epitopes to reach a high level of coverage are considered.

Chagas Heart Disease: Beyond a Single Complication, from Asymptomatic Disease to Heart Failure

Chagas cardiomyopathy (CC), caused by the protozoan Trypanosoma cruzi, is an important cause of cardiovascular morbidity and mortality in developing countries. It is estimated that 6 to 7 million people worldwide are infected, and it is predicted that it will be responsible for 200,000 deaths by 2025. The World Health Organization (WHO) considers Chagas disease (CD) as a Neglected Tropical Disease (NTD), which must be acknowledged and detected in time, as it remains a clinical and diagnostic challenge in both endemic and non-endemic regions and at different levels of care. The literature on CC was analyzed by searching different databases (Medline, Cochrane Central, EMBASE, PubMed, Google Scholar, EBSCO) from 1968 until October 2022. Multicenter and bioinformatics trials, systematic and bibliographic reviews, international guidelines, and clinical cases were included. The reference lists of the included papers were checked. No linguistic restrictions or study designs were applied. This review is intended to address the current incidence and prevalence of CD and to identify the main pathogenic mechanisms, clinical presentation, and diagnosis of CC.

Comparing in vivo bioluminescence imaging and the Multi-Cruzi immunoassay platform to develop improved Chagas disease diagnostic procedures and biomarkers for monitoring parasitological cure

BACKGROUND

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi and is a serious public health problem throughout Latin America. With 6 million people infected, there is a major international effort to develop new drugs. In the chronic phase of the disease, the parasite burden is extremely low, infections are highly focal at a tissue/organ level, and bloodstream parasites are only intermittently detectable. As a result, clinical trials are constrained by difficulties associated with determining parasitological cure. Even highly sensitive PCR methodologies can be unreliable, with a tendency to produce "false-cure" readouts. Improved diagnostic techniques and biomarkers for cure are therefore an important medical need.

METHODOLOGY/PRINCIPAL FINDINGS

Using an experimental mouse model, we have combined a multiplex assay system and highly sensitive bioluminescence imaging to evaluate serological procedures for diagnosis of T. cruzi infections and confirmation of parasitological cure. We identified a set of three antigens that in the context of the multiplex serology system, provide a rapid, reactive and highly accurate read-out of both acute and chronic T. cruzi infection. In addition, we describe specific antibody responses where down-regulation can be correlated with benznidazole-mediated parasite reduction and others where upregulation is associated with persistent infection. One specific antibody (IBAG39) highly correlated with the bioluminescence flux and represents a promising therapy monitoring biomarker in mice.

CONCLUSIONS/SIGNIFICANCE

Robust, high-throughput methodologies for monitoring the efficacy of anti-T. cruzi drug treatment are urgently required. Using our experimental systems, we have identified markers of infection or parasite reduction that merit assessing in a clinical setting for the longitudinal monitoring of drug-treated patients.

Vaccine-linked chemotherapy with a low dose of benznidazole plus a bivalent recombinant protein vaccine prevents the development of cardiac fibrosis caused by Trypanosoma cruzi in chronically-infected BALB/c mice

Background

Chagas disease (CD) is caused by Trypanosoma cruzi and affects 6–7 million people worldwide. Approximately 30% of chronic patients develop chronic chagasic cardiomyopathy (CCC) after decades. Benznidazole (BNZ), one of the first-line chemotherapy used for CD, induces toxicity and fails to halt the progression of CCC in chronic patients. The recombinant parasite-derived antigens, including Tc24, Tc24-C4, TSA-1, and TSA-1-C4 with Toll-like receptor 4 (TLR-4) agonist-adjuvants reduce cardiac parasite burdens, heart inflammation, and fibrosis, leading us to envision their use as immunotherapy together with BNZ. Given genetic immunization (DNA vaccines) encoding Tc24 and TSA-1 induce protective immunity in mice and dogs, we propose that immunization with the corresponding recombinant proteins offers an alternative and feasible strategy to develop these antigens as a bivalent human vaccine. We hypothesized that a low dose of BNZ in combination with a therapeutic vaccine (TSA-1-C4 and Tc24-C4 antigens formulated with a synthetic TLR-4 agonist-adjuvant, E6020-SE) given during early chronic infection, could prevent cardiac disease progression and provide antigen-specific T cell immunity.

Methodology/ Principal findings

We evaluated the therapeutic vaccine candidate plus BNZ (25 mg/kg/day/7 days) given on days 72 and 79 post-infection (p.i) (early chronic phase). Fibrosis, inflammation, and parasite burden were quantified in heart tissue at day 200 p.i. (late chronic phase). Further, spleen cells were collected to evaluate antigen-specific CD4⁺ and CD8⁺ T cell immune response, using flow cytometry. We found that vaccine-linked BNZ treated mice had lower cardiac fibrosis compared to the infected untreated control group. Moreover, cells from mice that received the immunotherapy had higher stimulation index of antigen-specific CD8⁺Perforin⁺ T cells as well as antigen-specific central memory T cells compared to the infected untreated control.

Conclusions

Our results suggest that the bivalent immunotherapy together with BNZ treatment given during early chronic infection protects BALB/c mice against cardiac fibrosis progression and activates a strong CD8⁺ T cell response by in vitro restimulation, evidencing the induction of a long-lasting T. cruzi-immunity.

Chagas disease (CD) is a neglected tropical disease caused by the parasite Trypanosoma cruzi, transmitted through contact with infected feces of vectors bugs. CD can induce cardiac abnormalities including the development of fibrosis and eventually death. Benznidazole (BNZ) is the first-line drug approved against CD, however, its toxicity and lack of efficacy in the chronic phase have limited its use. Previous studies have demonstrated the feasibility of reducing doses of BNZ given in combination with therapeutic vaccines during the acute phase of CD, which increases its tolerability and reduces adverse side effects. Considering that patients are often diagnosed until more advanced stages of the disease, its necessary to evaluate therapies given in the chronic phase of CD. In this study, we evaluated a vaccine formulated with the recombinant T. cruzi-antigens TSA-1-C4 and Tc24-C4 and the adjuvant E6020-SE in combination with a low dose of BNZ given during the chronic phase of T. cruzi-infection using a murine model. The authors found that the combination therapy protects mice against cardiac fibrosis progression, allows the activation of a CD8⁺ T cell response, and induces a prolonged memory response against T. cruzi. This study supports the development of the vaccine-linked chemotherapy approach to prevent T. cruzi chronic infection.

Oxidative stress implications for therapeutic vaccine development against Chagas disease

INTRODUCTION

Pathogenesis of Chagas disease (CD) caused by the protozoan parasite Trypanosoma cruzi (T. cruzi) involves chronic oxidative and inflammatory stress. In this review, we discuss the research efforts in therapeutic vaccine development to date and the potential challenges imposed by oxidative stress in achieving an efficient therapeutic vaccine against CD.

AREAS COVERED

This review covers the immune and nonimmune mechanisms of reactive oxygen species production and immune response patterns during T. cruzi infection in CD. A discussion on immunotherapy development efforts, the efficacy of antigen-based immune therapies against T. cruzi, and the role of antioxidants as adjuvants is discussed to provide promising insights to developing future treatment strategies against CD.

EXPERT OPINION

Administration of therapeutic vaccines can be a good option to confront persistent parasitemia in CD by achieving a rapid, short-lived stimulation of type 1 cell-mediated immunity. At the same time, adjunct therapies could play a critical role in the preservation of mitochondrial metabolism and cardiac muscle contractility in CD. We propose combined therapy with antigen-based vaccine and small molecules to control the pathological oxidative insult would be effective in the conservation of cardiac structure and function in CD.

Vaccine-linked chemotherapy induces IL-17 production and reduces cardiac pathology during acute Trypanosoma cruzi infection

Chagas disease resulting from Trypanosoma cruzi infection leads to a silent, long-lasting chronic neglected tropical disease affecting the poorest and underserved populations around the world. Antiparasitic treatment with benznidazole does not prevent disease progression or death in patients with established cardiac disease. Our consortium is developing a therapeutic vaccine based on the T. cruzi flagellar—derived antigen Tc24-C4 formulated with a Toll-like receptor 4 agonist adjuvant, to complement existing chemotherapy and improve treatment efficacy. Here we demonstrate that therapeutic treatment of acutely infected mice with a reduced dose of benznidazole concurrently with vaccine treatment – also known as “vaccine-linked chemotherapy”—induced a T_H17 like immune response, with significantly increased production of antigen specific IL-17A, IL-23 and IL-22, and CD8 + T lymphocytes, as well as significantly increased T. cruzi specific IFNγ-producing CD4 + T lymphocytes. Significantly reduced cardiac inflammation, fibrosis, and parasite burdens and improved survival were achieved by vaccine-linked chemotherapy and individual treatments. Importantly, low dose treatments were comparably efficacious to high dose treatments, demonstrating potential dose sparing effects. We conclude that through induction of T_H17 immune responses vaccine-linked chemotherapeutic strategies could bridge the tolerability and efficacy gaps of current drug treatment in Chagasic patients.

Extent of polymorphism and selection pressure on the Trypanosoma cruzi vaccine candidate antigen Tc24

INTRODUCTION

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, is a major public health problem in the Americas, and existing drugs have severe limitations. In this context, a vaccine would be an attractive alternative for disease control. One of the difficulties in developing an effective vaccine lies in the high genetic diversity of T. cruzi. In this study, we evaluated the level of sequence diversity of the leading vaccine candidate Tc24 in multiple parasite strains.

METHODS AND RESULTS

We quantified its level of polymorphism within and between T. cruzi discrete typing units (DTUs) and how this potential polymorphism is structured by different selective pressures. We observed a low level of polymorphism of Tc24 protein, weakly associated with parasite DTUs, but not with the geographic origin of the strains. In particular, Tc24 was under strong purifying selection pressure and predicted CD8+ T-cell epitopes were mostly conserved. Tc24 strong conservation may be associated with structural/functional constrains to preserve EF hand domains and their calcium-binding loops, and Tc24 is likely important for the parasite fitness.

DISCUSSION

Together, these results show that a vaccine based on Tc24 is likely to be effective against a wide diversity of parasite strains across the American continent, and further development of this vaccine candidate should be a high priority.

DNA Vaccine Treatment in Dogs Experimentally Infected with Trypanosoma cruzi

Chagas disease is a chronic and potentially lethal disorder caused by the parasite Trypanosoma cruzi, and an effective treatment has not been developed for chronic Chagas disease. The objective of this study was to determine the effectiveness of a therapeutic DNA vaccine containing T. cruzi genes in dogs with experimentally induced Chagas disease through clinical, pathological, and immunological analyses. Infection of Beagle dogs with the H8 T. cruzi strain was performed intraperitoneally with 3500 metacyclic trypomastigotes/kg body weight. Two weeks after infection, plasmid DNA immunotherapy was administered thrice at 15-day intervals. The clinical (physical and cabinet studies), immunological (antibody and cytokine profiles and lymphoproliferation), and macro- and microscopic pathological findings were described. A significant increase in IgG and cell proliferation was recorded after immunotherapy, and the highest stimulation index (3.02) was observed in dogs treated with the pBCSSP4 plasmid. The second treatment with both plasmids induced an increase in IL-1, and the third treatment with the pBCSSP4 plasmid induced an increase in IL-6. The pBCSP plasmid had a good Th1 response regulated by high levels of IFN-gamma and TNF-alpha, whereas the combination of the two plasmids did not have a synergistic effect. Electrocardiographic studies registered lower abnormalities and the lowest number of individuals with abnormalities in each group treated with the therapeutic vaccine. Echocardiograms showed that the pBCSSP4 plasmid immunotherapy preserved cardiac structure and function to a greater extent and prevented cardiomegaly. The two plasmids alone controlled the infection moderately by a reduction in the inflammatory infiltrates in heart tissue. The immunotherapy was able to reduce the magnitude of cardiac lesions and modulate the cellular immune response; the pBCSP treatment showed a clear Th1 response; and pBCSSP4 induced a balanced Th1/Th2 immune response that prevented severe cardiac involvement. The pBCSSP4 plasmid had a better effect on most of the parameters evaluated in this study; therefore, this plasmid can be considered an optional treatment against Chagas disease in naturally infected dogs.

Epidemiology and pathogenesis of maternal-fetal transmission of Trypanosoma cruzi and a case for vaccine development against congenital Chagas disease

Trypanos o ma cruzi (T. cruzi or Tc) is the causative agent of Chagas disease (CD). It is common for patients to suffer from non-specific symptoms or be clinically asymptomatic with acute and chronic conditions acquired through various routes of transmission. The expecting women and their fetuses are vulnerable to congenital transmission of Tc. Pregnant women face formidable health challenges because the frontline antiparasitic drugs, benznidazole and nifurtimox, are contraindicated during pregnancy. However, it is worthwhile to highlight that newborns can be cured if they are diagnosed and given treatment in a timely manner. In this review, we discuss the pathogenesis of maternal-fetal transmission of Tc and provide a justification for the investment in the development of vaccines against congenital CD.

Antigen-Based Nano-Immunotherapy Controls Parasite Persistence, Inflammatory and Oxidative Stress, and Cardiac Fibrosis, the Hallmarks of Chronic Chagas Cardiomyopathy, in A Mouse Model of Trypanosoma cruzi Infection

Chagas cardiomyopathy is caused by Trypanosoma cruzi (Tc). We identified two candidate antigens (TcG2 and TcG4) that elicit antibodies and T cell responses in naturally infected diverse hosts. In this study, we cloned TcG2 and TcG4 in a nanovector and evaluated whether nano-immunotherapy (referred as nano2/4) offers resistance to chronic Chagas disease. For this, C57BL/6 mice were infected with Tc and given nano2/4 at 21 and 42 days post-infection (pi). Non-infected, infected, and infected mice treated with pcDNA3.1 expression plasmid encoding TcG2/TcG4 (referred as p2/4) were used as controls. All mice responded to Tc infection with expansion and functional activation of splenic lymphocytes. Flow cytometry showed that frequency of splenic, poly-functional CD4⁺ and CD8⁺ T cells expressing interferon-γ, perforin, and granzyme B were increased by immunotherapy (Tc.nano2/4 > Tc.p2/4) and associated with 88%–99.7% decline in cardiac and skeletal (SK) tissue levels of parasite burden (Tc.nano2/4 > Tc.p2/4) in Chagas mice. Subsequently, Tc.nano2/4 mice exhibited a significant decline in peripheral and tissues levels of oxidative stress (e.g., 4-hydroxynonenal, protein carbonyls) and inflammatory infiltrate that otherwise were pronounced in Chagas mice. Further, nano2/4 therapy was effective in controlling the tissue infiltration of pro-fibrotic macrophages and established a balanced environment controlling the expression of collagens, metalloproteinases, and other markers of cardiomyopathy and improving the expression of Myh7 (encodes β myosin heavy chain) and Gsk3b (encodes glycogen synthase kinase 3) required for maintaining cardiac contractility in Chagas heart. We conclude that nano2/4 enhances the systemic T cell immunity that improves the host’s ability to control chronic parasite persistence and Chagas cardiomyopathy.

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.

Immunity and vaccine development efforts against Trypanosoma cruzi

Trypanosoma cruzi (T. cruzi) is the causative agent for Chagas disease (CD). There is a critical lack of methods for prevention of infection or treatment of acute infection and chronic disease. Studies in experimental models have suggested that the protective immunity against T. cruzi infection requires the elicitation of Th1 cytokines, lytic antibodies and the concerted activities of macrophages, T helper cells, and cytotoxic T lymphocytes (CTLs). In this review, we summarize the research efforts in vaccine development to date and the challenges faced in achieving an efficient prophylactic or therapeutic vaccine against human CD.

A therapeutic vaccine prototype induces protective immunity and reduces cardiac fibrosis in a mouse model of chronic Trypanosoma cruzi infection

Chagas disease, caused by the parasite Trypanosoma cruzi, develops into chronic Chagas’ cardiomyopathy in ~30% of infected individuals, characterized by conduction disorders, arrhythmias, heart failure, and even sudden cardiac death. Current anti-parasitic treatments are plagued by significant side effects and poor efficacy in the chronic phase of disease; thus, there is a pressing need for new treatment options. A therapeutic vaccine could bolster the protective T_H1-mediated immune response, thereby slowing or halting the progression of chronic Chagas’ cardiomyopathy. Prior work in mice has demonstrated therapeutic efficacy of a Tc24 recombinant protein vaccine in the acute phase of Chagas disease. However, it is anticipated that humans will be vaccinated therapeutically when in the chronic phase of disease. This study investigates the therapeutic efficacy of a vaccine prototype containing recombinant protein Tc24, formulated with an emulsion containing the Toll-like receptor 4 agonist E6020 as an immunomodulatory adjuvant in a mouse model of chronic T. cruzi infection. Among outbred ICR mice vaccinated during chronic T. cruzi infection, there is a significant increase in the number of animals with undetectable systemic parasitemia (60% of vaccinated mice compared to 0% in the sham vaccine control group), and a two-fold reduction in cardiac fibrosis over the control group. The vaccinated mice produce a robust protective T_H1-biased immune response to the vaccine, as demonstrated by a significant increase in antigen-specific IFNγ-production, the number of antigen-specific IFNγ-producing cells, and IgG2a antibody titers. Importantly, therapeutic vaccination significantly reduced cardiac fibrosis in chronically infected mice. This is a first study demonstrating therapeutic efficacy of the prototype Tc24 recombinant protein and E6020 stable emulsion vaccine against cardiac fibrosis in a mouse model of chronic T. cruzi infection.

Chagas disease is a parasitic infection that can cause severe heart disease. Current treatments do not work well and have significant side effects. Because of this, the authors created a new vaccine prototype with the goal that it could be given to infected people to prevent Chagas-associated heart disease. The vaccine contains a manufactured protein identical to a protein in the parasite (called Tc24) as well as a component to help the body produce a protective immune response (a vaccine adjuvant called E6020). The vaccine would boost the body’s natural immune response to the parasite infection, reducing the number of parasites in the body, and protecting the heart. Frequently, people are not diagnosed until later in the infection, because the early (or acute) stage of disease can be mistaken for a common cold. Because of this, it is important to test the vaccine when given in the later (or chronic) stage of infection. The authors tested the vaccine in a mouse model of chronic T. cruzi infection and found that the vaccinated mice had lower levels of parasites in their body and less damage to their hearts. This research shows promising value of a therapeutic vaccine to prevent Chagas-associated heart disease in a mouse model, with the hope that the same effect could be found in humans one day.

Production of recombinant TSA-1 and evaluation of its potential for the immuno-therapeutic control of Trypanosoma cruzi infection in mice

A therapeutic vaccine for human Chagas disease (American trypanosomiasis caused by Trypanosoma cruzi) is under development based on the success of vaccinating mice with DNA constructs expressing the antigens Tc24 and Tc-TSA-1. However, because DNA and nucleic acid vaccines produce less than optimal responses in humans, our strategy relies on administering a recombinant protein-based vaccine, together with adjuvants that promote Th1-type immunity. Here we describe a process for the purification and refolding of recombinant TSA-1 expressed in Escherichia coli. The overall yield (20–25%) and endotoxin level of the purified recombinant TSA-1 (rTSA-1) is suitable for pilot scale production of the antigen for use in phase 1 clinical trials. Mice infected with T. cruzi were treated with rTSA-1, either alone or with Toll-like receptor 4 (TLR-4) agonist adjuvants including monophosphoryl lipid A (MPLA), glucopyranosyl lipid A (GLA, IDRI), and E6020 (EISEI, Inc). TSA-1 with the TLR-4 agonists was effective at reducing parasitemia relative to rTSA-1 alone, although it was difficult to discern a therapeutic effect compared to treatment with TLR-4 agonists alone. However, rTSA-1 with a 10 ug dose of MPLA optimized reductions in cardiac tissue inflammation, which were significantly reduced compared to MPLA alone. It also elicited the lowest parasite burden and the highest levels of TSA-1-specific IFN-gamma levels and IFN-gamma/IL-4 ratios. These results warrant the further evaluation of rTSA-1 in combination with rTc24 in order to maximize the therapeutic effect of vaccine-linked chemotherapy in both mice and non-human primates before advancing to clinical development.

Vaccine-Linked Chemotherapy Improves Benznidazole Efficacy for Acute Chagas Disease

Chagas disease affects 6 to 7 million people worldwide, resulting in significant disease burdens and health care costs in countries of endemicity. Chemotherapeutic treatment is restricted to two parasiticidal drugs, benznidazole and nifurtimox. Both drugs are highly effective during acute disease but are only minimally effective during chronic disease and fraught with significant adverse clinical effects. In experimental models, vaccines can be used to induce parasite-specific balanced T_H1/T_H2 immune responses that effectively reduce parasite burdens and associated inflammation while minimizing adverse effects. The objective of this study was to determine the feasibility of vaccine-linked chemotherapy for reducing the amount of benznidazole required to significantly reduce blood and tissue parasite burdens. In this study, we were able to achieve a 4-fold reduction in the amount of benznidazole required to significantly reduce blood and tissue parasite burdens by combining the low-dose benznidazole with a recombinant vaccine candidate, Tc24 C4, formulated with a synthetic Toll-like 4 receptor agonist, E6020, in a squalene oil-in-water emulsion. Additionally, vaccination induced a robust parasite-specific balanced T_H1/T_H2 immune response. We concluded that vaccine-linked chemotherapy is a feasible option for advancement to clinical use for improving the tolerability and efficacy of benznidazole.

Trypanosoma cruzi vaccine candidate antigens Tc24 and TSA-1 recall memory immune response associated with HLA-A and -B supertypes in Chagasic chronic patients from Mexico

Trypanosoma cruzi antigens TSA-1 and Tc24 have shown promise as vaccine candidates in animal studies. We evaluated here the recall immune response these antigens induce in Chagasic patients, as a first step to test their immunogenicity in humans. We evaluated the in vitro cellular immune response after stimulation with recombinant TSA-1 (rTSA-1) or recombinant Tc24 (rTc24) in mononuclear cells of asymptomatic Chagasic chronic patients (n = 20) compared to healthy volunteers (n = 19) from Yucatan, Mexico. Proliferation assays, intracellular cytokine staining, cytometric bead arrays, and memory T cell immunophenotyping were performed by flow cytometry. Peripheral blood mononuclear cells (PBMC) from Chagasic patients showed significant proliferation after stimulation with rTc24 and presented a phenotype of T effector memory cells (CD45RA-CCR7-). These cells also produced IFN-γ and, to a lesser extent IL10, after stimulation with rTSA-1 and rTc24 proteins. Overall, both antigens recalled a broad immune response in some Chagasic patients, confirming that their immune system had been primed against these antigens during natural infection. Analysis of HLA-A and HLA-B allele diversity by PCR-sequencing indicated that HLA-A03 and HLA-B07 were the most frequent supertypes in this Mexican population. Also, there was a significant difference in the frequency of HLA-A01 and HLA-A02 supertypes between Chagasic patients and controls, while the other alleles were evenly distributed. Some aspects of the immune response, such as antigen-induced IFN-γ production by CD4+ and CD8+ T cells and CD8+ proliferation, showed significant association with specific HLA-A supertypes, depending on the antigen considered. In conclusion, our results confirm the ability of both TSA-1 and Tc24 recombinant proteins to recall an immune response induced by the native antigens during natural infection in at least some patients. Our data support the further development of these antigens as therapeutic vaccine against Chagas disease.

Characterization and Stability of Trypanosoma cruzi 24-C4 (Tc24-C4), a Candidate Antigen for a Therapeutic Vaccine Against Chagas Disease

Chagas disease due to chronic infection with Trypanosoma cruzi is a neglected cause of heart disease, affecting approximately 6-10 million individuals in Latin America and elsewhere. T. cruzi Tc24, a calcium-binding protein in the flagellar pocket of the parasite, is a candidate antigen for an injectable therapeutic vaccine as an alternative or a complement to chemotherapy. Previously, we reported that a genetically engineered construct from which all cysteine residues had been eliminated (Tc24-C4) yields a recombinant protein with reduced aggregation and improved analytical purity in comparison to the wild-type form, without compromising antigenicity and immunogenicity. We now report that the established process for producing Escherichia coli-expressed Tc24-C4 protein is robust and reproducibly yields protein lots with consistent analytical characteristics, freeze-thaw, accelerated, and long-term stability profiles. The data indicate that, like most proteins, Tc24-C4 should be stable at -80°C, but also at 4°C and room temperature for at least 30 days, and up to 7-15 days at 37°C. Thus, the production process for recombinant Tc24-C4 is suitable for Current Good Manufacturing Practice production and clinical testing, based on process robustness, analytical characteristics, and stability profile.

Genetic Adjuvantation of a Cell-Based Therapeutic Vaccine for Amelioration of Chagasic Cardiomyopathy

Chagas disease, caused by infection with the protozoan parasite Trypanosoma cruzi, is a leading cause of heart disease ("chagasic cardiomyopathy") in Latin America, disproportionately affecting people in resource-poor areas. The efficacy of currently approved pharmaceutical treatments is limited mainly to acute infection, and there are no effective treatments for the chronic phase of the disease. Preclinical models of Chagas disease have demonstrated that antigen-specific CD8⁺ gamma interferon (IFN-γ)-positive T-cell responses are essential for reducing parasite burdens, increasing survival, and decreasing cardiac pathology in both the acute and chronic phases of Chagas disease. In the present study, we developed a genetically adjuvanted, dendritic cell-based immunotherapeutic for acute Chagas disease in an attempt to delay or prevent the cardiac complications that eventually result from chronic T. cruzi infection. Dendritic cells transduced with the adjuvant, an adenoviral vector encoding a dominant negative isoform of Src homology region 2 domain-containing tyrosine phosphatase 1 (SHP-1) along with the T. cruzi Tc24 antigen and trans-sialidase antigen 1 (TSA1), induced significant numbers of antigen-specific CD8⁺ IFN-γ-positive cells following injection into BALB/c mice. A vaccine platform transduced with the adenoviral vector and loaded in tandem with the recombinant protein reduced parasite burdens by 76% to >99% in comparison to a variety of different controls and significantly reduced cardiac pathology in a BALB/c mouse model of live Chagas disease. Although no statistical differences in overall survival rates among cohorts were observed, the data suggest that immunotherapeutic strategies for the treatment of acute Chagas disease are feasible and that this approach may warrant further study.

Immunization with Tc52 or its amino terminal domain adjuvanted with c-di-AMP induces Th17+Th1 specific immune responses and confers protection against Trypanosoma cruzi

The development of new adjuvants enables fine modulation of the elicited immune responses. Ideally, the use of one or more adjuvants should result in the induction of a protective immune response against the specific pathogen. We have evaluated the immune response and protection against Trypanosoma cruzi infection in mice vaccinated with recombinant Tc52 or its N- and C-terminal domains (NTc52 and CTc52) adjuvanted either with the STING (Stimulator of Interferon Genes) agonist cyclic di-AMP (c-di-AMP), a pegylated derivative of α-galactosylceramide (αGC-PEG), or oligodeoxynucleotides containing unmethylated CpG motifs (ODN-CpG). All groups immunized with the recombinant proteins plus adjuvant: Tc52+c-di-AMP, NTc52+c-di-AMP, CTc52+c-di-AMP, NTc52+c-di-AMP+αGC-PEG, NTc52+CpG, developed significantly higher anti-Tc52 IgG titers than controls. Groups immunized with c-di-AMP and Tc52, NTc52 or CTc52 showed the highest Tc52-specific IgA titers in nasal lavages. All groups immunized with the recombinant proteins plus adjuvant developed a strong specific cellular immune response in splenocytes and lymph node cells with significant differences for groups immunized with c-di-AMP and Tc52, NTc52 or CTc52. These groups also showed high levels of Tc52-specific IL-17 and IFN-γ producing cells, while NTc52+CpG group only showed significant difference with control in IFN-γ producing cells. Groups immunized with c-di-AMP and Tc52, NTc52 or CTc52 developed predominantly a Th17 and Th1immune response, whereas for NTc52+CpG it was a dominant Th1 response. It was previously described that αGC-PEG inhibits Th17 differentiation by activating NKT cells. Thus, in this work we have also included a group immunized with both adjuvants (NTc52+c-di-AMP+αGC-PEG) with the aim to modulate the Th17 response induced by c-di-AMP. This group showed a significant reduction in the number of Tc52-specific IL-17 producing splenocytes, as compared to the group NTc52+c-di-AMP, which has in turn correlated with a reduction in protection against infection. These results suggest that the Th17 immune response developed after immunizing with NTc52+c-di-AMP could have a protective role against T. cruzi infection. Groups NTc52+c-di-AMP, Tc52+c-di-AMP and NTc52PB, were the ones that showed better protection against infection with lower parasitemia and weight loss, and higher survival.

Chagas disease is a parasitic disease caused by a protozoan parasite (Trypanosoma cruzi) which has a complex life cycle including insect vector and mammalians. In Latin America, 7–10 million people are infected, 100 million people are at risk of infection, and about 56,000 new infection cases and 12,000 deaths are registered annually. Migration spread the geographic distribution of the disease to North America and Europe. The infection in humans has an initial acute stage followed by a chronic stage where up to 30% of patients develop cardiac alterations and 10% develop digestive, neurological or mixed alterations. The acute infection is hardly detected and there is not drug to treat the chronic infection. Thus, there is an urgent need for prophylactic and therapeutic vaccines development. Several attempts to find a vaccine antigen has been made and the protein Tc52 is a good candidate. In a vaccine composition, as important as the antigen is the adjuvants, which are substances able to increase, improve or modified the immune response. This research provides information about the immune response and protection against Trypanosoma cruzi infection elicited by Tc52 or portions of this molecule using different adjuvants.

Cysteine mutagenesis improves the production without abrogating antigenicity of a recombinant protein vaccine candidate for human chagas disease

A therapeutic vaccine for human Chagas disease is under development by the Sabin Vaccine Institute Product Development Partnership. The aim of the vaccine is to significantly reduce the parasite burden of Trypanosoma cruzi in humans, either as a standalone product or in combination with conventional chemotherapy. Vaccination of mice with Tc24 formulated with monophosphoryl-lipid A (MPLA) adjuvant results in a Th1 skewed immune response with elevated IgG2a and IFNγ levels and a statistically significant decrease in parasitemia following T. cruzi challenge. Tc24 was therefore selected for scale-up and further evaluation. During scale up and downstream process development, significant protein aggregation was observed due to intermolecular disulfide bond formation. To prevent protein aggregation, cysteine codons were replaced with serine codons which resulted in the production of a non-aggregated and soluble recombinant protein, Tc24-C4. No changes to the secondary structure of the modified molecule were detected by circular dichroism. Immunization of mice with wild-type Tc24 or Tc24-C4, formulated with E6020 (TLR4 agonist analog to MPLA) emulsified in a squalene-oil-in-water emulsion, resulted in IgG2a and antigen specific IFNγ production levels from splenocytes that were not significantly different, indicating that eliminating putative intermolecular disulfide bonds had no significant impact on the immunogenicity of the molecule. In addition, vaccination with either formulated wild type Tc24 or Tc24-C4 antigen also significantly increased survival and reduced cardiac parasite burden in mice. Investigations are now underway to examine the efficacy of Tc24-C4 formulated with other adjuvants to reduce parasite burden and increase survival in pre-clinical studies.

A prime-boost immunization with Tc52 N-terminal domain DNA and the recombinant protein expressed in Pichia pastoris protects against Trypanosoma cruzi infection

We have previously reported that the N-terminal domain of the antigen Tc52 (NTc52) is the section of the protein that confers the strongest protection against Trypanosoma cruzi infection. To improve vaccine efficacy, we conducted here a prime-boost strategy (NTc52PB) by inoculating two doses of pcDNA3.1 encoding the NTc52 DNA carried by attenuated Salmonella (SNTc52), followed by two doses of recombinant NTc52 expressed in Picchia pastoris plus ODN-CpG as adjuvant. This strategy was comparatively analyzed with the following protocols: (1) two doses of NTc52+ODN-CpG by intranasal route followed by two doses of NTc52+ODN-CpG by intradermal route (NTc52CpG); (2) four doses of SNTc52; and (3) a control group with four doses of Salmonella carrying the empty plasmid. All immunized groups developed a predominant Th1 cellular immune response but with important differences in antibody development and protection against infection. Thus, immunization with just SNTc52 induces a strong specific cellular response, a specific systemic antibody response that is weak yet functional (considering lysis of trypomastigotes and inhibition of cell invasion), and IgA mucosal immunity, protecting in both the acute and chronic stages of infection. The group that received only recombinant protein (NTc52CpG) developed a strong antibody immune response but weaker cellular immunity than the other groups, and the protection against infection was clear in the acute phase of infection but not in chronicity. The prime-boost strategy, which combines DNA and protein vaccine and both mucosal and systemic immunizations routes, was the best assayed protocol, inducing strong cellular and humoral responses as well as specific mucosal IgA, thus conferring better protection in the acute and chronic stages of infection.

A therapeutic nanoparticle vaccine against Trypanosoma cruzi in a BALB/c mouse model of Chagas disease

Chagas disease, caused by Trypanosoma cruzi, results in an acute febrile illness that progresses to chronic chagasic cardiomyopathy in 30% of patients. Current treatments have significant side effects and poor efficacy during the chronic phase; therefore, there is an urgent need for new treatment modalities. A robust TH1-mediated immune response correlates with favorable clinical outcomes. A therapeutic vaccine administered to infected individuals could bolster the immune response, thereby slowing or stopping the progression of chagasic cardiomyopathy. Prior work in mice has identified an efficacious T. cruzi DNA vaccine encoding Tc24. To elicit a similar protective cell-mediated immune response to a Tc24 recombinant protein, we utilized a poly(lactic-co-glycolic acid) nanoparticle delivery system in conjunction with CpG motif-containing oligodeoxynucleotides as an immunomodulatory adjuvant. In a BALB/c mouse model, the vaccine produced a TH1-biased immune response, as demonstrated by a significant increase in antigen-specific IFNγ-producing splenocytes, IgG2a titers, and proliferative capacity of CD8(+) T cells. When tested for therapeutic efficacy, significantly reduced systemic parasitemia was seen during peak parasitemia. Additionally, there was a significant reduction in cardiac parasite burden and inflammatory cell infiltrate. This is the first study demonstrating immunogenicity and efficacy of a therapeutic Chagas vaccine using a nanoparticle delivery system.

Expression, purification, immunogenicity, and protective efficacy of a recombinant Tc24 antigen as a vaccine against Trypanosoma cruzi infection in mice

The Tc24 calcium binding protein from the flagellar pocket of Trypanosoma cruzi is under evaluation as a candidate vaccine antigen against Chagas disease. Previously, a DNA vaccine encoding Tc24 was shown to be an effective vaccine (both as a preventive and therapeutic intervention) in mice and dogs, as evidenced by reductions in T. cruzi parasitemia and cardiac amastigotes, as well as reduced cardiac inflammation and increased host survival. Here we developed a suitable platform for the large scale production of recombinant Tc24 (rTc24) and show that when rTc24 is combined with a monophosphoryl-lipid A (MPLA) adjuvant, the formulated vaccine induces a Th1-biased immune response in mice, comprised of elevated IgG2a antibody levels and interferon-gamma levels from splenocytes, compared to controls. These immune responses also resulted in statistically significant decreased T. cruzi parasitemia and cardiac amastigotes, as well as increased survival following T. cruzi challenge infections, compared to controls. Partial protective efficacy was shown regardless of whether the antigen was expressed in Escherichia coli or in yeast (Pichia pastoris). While mouse vaccinations will require further modifications in order to optimize protective efficacy, such studies provide a basis for further evaluations of vaccines comprised of rTc24, together with alternative adjuvants and additional recombinant antigens.

Prophylactic and therapeutic DNA vaccines against Chagas disease

Chagas disease is a zoonosis caused by Trypanosoma cruzi in which the most affected organ is the heart. Conventional chemotherapy has a very low effectiveness; despite recent efforts, there is currently no better or more effective treatment available. DNA vaccines provide a new alternative for both prevention and treatment of a variety of infectious disorders, including Chagas disease. Recombinant DNA technology has allowed some vaccines to be developed using recombinant proteins or virus-like particles capable of inducing both a humoral and cellular specific immune response. This type of immunization has been successfully used in preclinical studies and there are diverse models for viral, bacterial and/or parasitic diseases, allergies, tumors and other diseases. Therefore, several research groups have been given the task of designing a DNA vaccine against experimental infection with T. cruzi. In this review we explain what DNA vaccines are and the most recent studies that have been done to develop them with prophylactic or therapeutic purposes against Chagas disease.

Oral multicomponent DNA vaccine delivered by attenuated Salmonella elicited immunoprotection against American trypanosomiasis

We have reported that attenuated Salmonella (S) carrying plasmids encoding the cysteine protease cruzipain (Cz) protects against Trypanosoma cruzi infection. Here, we determined whether immunoprotection could be improved by the oral coadministration of 3 Salmonella carrying the plasmids that encode the antigens Cz, Tc52, and Tc24. SCz+STc52+STc24-immunized mice presented an increased antibody response against each antigen compared with those in the single antigen-immunized groups, as well as higher trypomastigotes antibody-mediated lyses and cell invasion inhibition compared with controls. SCz+STc52+STc24-immunized and -challenged mice rendered lower parasitemia. Weight loss after infection was detected in all mice except those in the SCz+STc52+STc24 group. Moreover, cardiomyopathy-associated enzyme activity was significantly lower in SCz+STc24+STc52-immunized mice compared with controls. Few or no abnormalities were found in muscle tissues of SCz+STc24+STc52-immunized mice, whereas controls presented with inflammatory foci, necrosis, and amastigote nests. We conclude that a multicomponent approach that targets several invasion and metabolic mechanisms improves protection compared with single-component vaccines.

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.

From genome screening to creation of vaccine against Trypanosoma cruzi by use of immunoinformatics

Chagas disease is caused by the protozoan parasite Trypanosoma cruzi, and activation of CD8(+) T cells is crucial for a protective immune response. Therefore, the identification of antigens with major histocompatibility complex class I epitopes is a crucial step for vaccine development against T. cruzi. Our aim was to identify novel antigens and epitopes by immunoinformatics analysis of the parasite proteome (12 969 proteins) and to validate their immunotherapeutic potential in infected mice. We identified 172 predicted epitopes, using NetMHC and RANKPEP. The corresponding protein sequences were reanalyzed to generate a consensus prediction, and 26 epitopes were selected for in vivo validation. The interferon γ (IFN-γ) recall response of splenocytes from T. cruzi-infected mice confirmed that 10 of 26 epitopes (38%) induced IFN-γ production. The immunotherapeutic potential of a mixture of all 10 peptides was evaluated in infected mice. The therapeutic vaccine was able to control T. cruzi infection, as evidenced by reduced parasitemia, cardiac tissue inflammation, and parasite burden and increased survival. These findings illustrate the benefits of this approach for the rapid development of a vaccine against pathogens with large genomes. The identified peptides and the proteins from which they are derived are excellent candidates for the development of a vaccine against T. cruzi.

In vitro trypanocidal activity of solamargine and extracts from Solanum palinacanthum and Solanum lycocarpum of Brazilian cerrado

The present investigation was to evaluate the potential trypanocidal activity of crude ethanolic extract of the fruits of Solanum palinacanthum, Solanum lycocarpum and the glycoalcaloid, solamargine. S. palinacanthum and S. lycocarpum fruit powders were submitted to exhaustively extraction with 96% ethanol and solamargine were isolated from the extract of S. palinacanthum. Both extracts and solamargine were analysed for trypanocidal activity by using MTT colorimetric assay. Extracts of S. palinacanthum showed to be more active (IC50 = 175.9 µg.ml-1) than S. lycocarpum (IC50 = 194.7 µg.ml-1). Solamargine presented a strong activity (IC50 = 15.3 µg.ml-1), which can explain the better activity of the both extracts. Benznidazol (IC50 = 9.0 µg.ml-1) is the only drug used to treat Chagas' disease. These findings demonstrate for the first time that ethanol extracts obtained from both fruits of S. palinacanthum and S. lycocarpum and also solamargine have a potential anti-trypanosomal activity.

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.

Innovation for the 'bottom 100 million': eliminating neglected tropical diseases in the Americas

An estimated 100 million people in the Latin American and Caribbean (LAC) region live on less than US$2 per day, while another 46 million people in the US live below that nation's poverty line. Almost all of the 'bottom 100 million' people suffer from at least one neglected tropical disease (NTD), including one-half of the poorest people in the region infected with hookworms, 10% with Chagas disease, and up to 1-2% with dengue, schistosomiasis, and/or leishmaniasis. In the US, NTDs such as Chagas disease, cysticercosis, toxocariasis, and trichomoniasis are also common among poor populations. These NTDs trap the poorest people in the region in poverty, because of their impact on maternal and child health, and occupational productivity. Through mass drug administration (MDA), several NTDs are on the verge of elimination in the Americas, including lymphatic filariasis, onchocerciasis, trachoma, and possibly leprosy. In addition, schistosomiasis may soon be eliminated in the Caribbean. However, for other NTDs including hookworm infection, Chagas disease, dengue, schistosomiasis, and leishmaniasis, a new generation of 'anti-poverty vaccines' will be required. Several vaccines for dengue are under development by multinational pharmaceutical companies, whereas others are being pursued through non-profit product development partnerships (PDPs), in collaboration with developing country manufacturers in Brazil and Mexico. The Sabin Vaccine Institute PDP is developing a primarily preventive bivalent recombinant human hookworm vaccine, which is about to enter phase 1 clinical testing in Brazil, as well as a new therapeutic Chagas disease vaccine in collaboration with several Mexican institutions. The Chagas disease vaccine would be administered to seropositive patients to delay or prevent the onset of Chagasic cardiomyopathy (secondary prevention). Together, MDA and the development of new anti-poverty vaccines afford an opportunity to implement effective control and elimination strategies for the major NTDs in the Americas.

Challenge of chronically infected mice with homologous trypanosoma cruzi parasites enhances the immune response but does not modify cardiopathy: implications for the design of a therapeutic vaccine

Chagas disease is a Trypanosoma cruzi-induced zoonosis that has no natural cure. Local damage induced by the parasite and the immune response causes chronic heart and digestive lesions. Efforts to develop a therapeutic vaccine that boosts the immune response to completely clear the parasite are needed because there is no effective treatment for chronically infected patients. In an attempt to modify the host-parasite equilibrium to increase parasite destruction, we analyzed cardiopathy and the immune response in chronically infected mice that were challenged with live homologous parasites. Challenge with a single dose of parasite increased CD4(+) and CD8(+) T cell populations, gamma interferon (IFN-γ) production, and serum-specific IgG levels. However, subpatent parasitemias and cardiac tissue were not affected. Because of the short duration of the immune boost after a single challenge, we next evaluated the impact of four parasite doses, administered 3 weeks apart. At 1 to 2 months after the last dose, the numbers of CD4(+) T cells and IFN-γ-producing CD4(+) memory cells and the CD4(+) T cell proliferative response to T. cruzi antigen were increased in the spleen. The frequency of IFN-γ-producing CD8(+) memory cells in the blood was also increased. However, the sustained challenge did not favor TH1 development; rather, it induced an increase in serum-specific IgG1 levels and mixed TH1/TH2 cytokine production. Moreover, there were no significant changes in cardiac lesions and subpatent parasitemias. In conclusion, we believe that this study may help in elucidating the necessary elements for a successful therapeutic vaccine which may reduce cardiomyopathy in chronically infected human patients.

Accelerating the development of a therapeutic vaccine for human Chagas disease: rationale and prospects

Chagas disease is a leading cause of heart disease affecting approximately 10 million people in Latin America and elsewhere worldwide. The two major drugs available for the treatment of Chagas disease have limited efficacy in Trypanosoma cruzi-infected adults with indeterminate (patients who have seroconverted but do not yet show signs or symptoms) and determinate (patients who have both seroconverted and have clinical disease) status; they require prolonged treatment courses and are poorly tolerated and expensive. As an alternative to chemotherapy, an injectable therapeutic Chagas disease vaccine is under development to prevent or delay Chagasic cardiomyopathy in patients with indeterminate or determinate status. The bivalent vaccine will be comprised of two recombinant T. cruzi antigens, Tc24 and TSA-1, formulated on alum together with the Toll-like receptor 4 agonist, E6020. Proof-of-concept for the efficacy of these antigens was obtained in preclinical testing at the Autonomous University of Yucatan. Here the authors discuss the potential for a therapeutic Chagas vaccine as well as the progress made towards such a vaccine, and the authors articulate a roadmap for the development of the vaccine as planned by the nonprofit Sabin Vaccine Institute Product Development Partnership and Texas Children's Hospital Center for Vaccine Development in collaboration with an international consortium of academic and industrial partners in Mexico, Germany, Japan, and the USA.

Modeling the economic value of a Chagas' disease therapeutic vaccine

The health burden of Chagas' disease (resulting from Trypanosoma cruzi infection) in Latin America (estimated to outweigh that of malaria by 5-fold and affect 2-6 million people in Mexico alone) has motivated development of therapeutic vaccines to prevent infection progression to severe disease. Our economic model for a Chagas' therapeutic vaccine in Mexico suggests that a vaccine would be highly cost-effective and in many cases economically dominant (providing both cost savings and health benefits) throughout a range of protection durations, severe adverse event risk, and dosing regimens and would be most likely to provide a positive return on investment if the vaccine prevented (rather than delayed) the onset of cardiomyopathy.

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.

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.

Perspectives of vaccination in Chagas disease revisited

The perspectives for a Chagas Disease vaccine 30 years ago and today are compared. Antigens and adjuvants have improved, but logistic problems remain the same. Sterilizing vaccines have not been produced and animal models for chronic Chagas have not been developed. Vector control has been successful and Chagas incidence has come to a halt. We do not have a population candidate to vaccination now in Brazil. And if we had, we would not know how to evaluate the success of vaccination in a short time period. A vaccine may not seem important at the moment. However, scientific reasons and incertitudes about the future recommend that a search for a vaccine be continued.

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.

Therapeutic DNA vaccine against Trypanosoma cruzi infection in dogs

Chagas' disease is an important health problem in most Latin American countries, and a concern in dog populations, which act as a reservoir. We showed in previous studies that a therapeutic DNA vaccine could partially control the pathology after Trypanosoma cruzi infection in mice, and this vaccine may represent an alternative treatment for Chagas' disease. Here we evaluated the therapeutic efficacy of this vaccine in experimentally infected dogs for up to 2 months after infection. Our results suggest that DNA vaccine treatment may affect the immune response and delay Chagas' disease progression in T. cruzi-infected dogs, and confirm the potential of this novel treatment.

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.