Protective efficacy of the oral vaccine Tc24:Co1 produced in Schizochytrium sp. against Trypanosoma cruzi infection in a mouse model.

Trypanosoma cruzi parasite - causal Chagas disease agent - affects about 7 million people; no vaccine is available, and current medications have not been entirely effective. Multidisciplinary efforts are necessary for developing clinical vaccine prototypes. Thus, this research study aims to assess the expressed and whole-cell administration protection of the oral vaccine prototype Tc24:Co1 using Schizochytrium sp. microalga. High recombinant protein expression yields (675 µg/L) of algal culture were obtained. Additionally, Schizochytrium sp.-Tc24:Co1 resulted stable at 4 °C for up to six months and at 25 °C for three months. After receiving four oral doses of the vaccine, the mice showed a significant humoral immune response and a parasitemia reduction associated with a lack of heart inflammatory damage compared with the unvaccinated controls. The Schizochytrium sp.-Tc24:Co1 vaccine demonstrates to be promising as a prototype for further development showing protective effects against a T. cruzi challenge in a mouse model.

A short-term method to evaluate anti-leishmania drugs by inhibition of stage differentiation in Leishmania mexicana using flow cytometry.

Leishmaniasis is a vector-borne neglected tropical disease caused by the Leishmania spp. Parasite. The disease is transmitted to humans and animals by the bite of infected female sandflies during the ingestion of bloodmeal. Because current drug treatments induce toxicity and parasite resistance, there is an urgent need to evaluate new drugs. Most therapeutics target the differentiation of promastigotes to amastigotes, which is necessary to maintain Leishmania infection. However, in vitro assays are laborious, time-consuming, and depend on the experience of the technician. In this study, we aimed to establish a short-term method to assess the differentiation status of Leishmania mexicana (L. mexicana) using flow cytometry. Here, we showed that flow cytometry provides a rapid means to quantify parasite differentiation in cell culture as reliably as light microscopy. Interestingly, we found using flow cytometry that miltefosine reduced promastigote-to-amastigote differentiation of L. mexicana. We conclude that flow cytometry provides a means to rapidly assay the efficacy of small molecules or natural compounds as potential anti-leishmanials.

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 TH1/TH2 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 TH1/TH2 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.

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.

Molecular Testing of Environmental Samples as a Potential Source to Estimate Parasite Infection.

We discuss the potential usefulness of molecular testing of soil, dust, and water samples to detect medically important parasites, and where such testing could be used to supplement stool sampling in humans. A wide variety of parasites including protozoa and helminths, many of which are zoonotic, have an important infection reservoir in the environment. In some cases, this environmental period is essential for further parasite development. We describe the progress in implementing methods for the molecular detection of these parasites in soil across eight collaborating centers in Latin America and represent a variety of potential applications in improving our understanding of parasite epidemiology and mapping, surveillance, and control of these parasites. This methodology offers new opportunities for improving our understanding of a wide variety of parasites of public health importance and novel tools for their control.

Signature of cardiac alterations in early and late chronic infections with Trypanosoma cruzi in mice.

Chagas disease by Trypanosoma cruzi (T. cruzi) infection is a leading cause of myocarditis worldwide. Chagas cardiomyopathy is presented with a wide variety of conduction abnormalities including arrhythmias, first- and second-degree atrioventricular blockade, left ventricular systolic dysfunction and some cases heart failure leading to the death. Currently, there are no effective treatments available against advanced Chagas disease. With the advance in the development of novel therapies, it is important to utilize an animal model that can effectively replicate the diverse stages of Chagas disease, including chronic asymptomatic and symptomatic infection, that are akin to those observed in humans. Therefore, to characterize the cardiac alterations during the evolution of the infection, we evaluated the progression of cardiomyopathy caused by T. cruzi H1 infection in both BALB/c and ICR mouse models by performing electrocardiogram (ECG) studies in unanesthetized mice every month until 210 days post-infection (dpi). In the late chronic phase of infection, we also performed echocardiogram (ECHO) studies to further assess cardiac function. In conclusion, we demonstrated that ICR mice were more susceptible to cardiac alterations compared to BALB/c mice and both mouse strains are suitable experimental models to study chronic T. cruzi infection and novel treatments.

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.

A novel multi-epitope recombinant protein elicits an antigen-specific CD8+ T cells response in Trypanosoma cruzi-infected mice.

About 6.5 million people worldwide are afflicted by Chagas disease, which is caused by the protozoan parasite Trypanosoma cruzi. The development of a therapeutic vaccine to prevent the progression of Chagasic cardiomyopathy has been proposed as an alternative for antiparasitic chemotherapy. Bioinformatics tools can predict MHC class I CD8 + epitopes for inclusion in a single recombinant protein with the goal to develop a multivalent vaccine. We expressed a novel recombinant protein Tc24-C4.10E harboring ten nonameric CD8 + epitopes and using Tc24-C4 protein as scaffold to evaluate the therapeutic effect in acute T. cruzi infection. T. cruzi-infected mice were immunized with Tc24-C4.10E or Tc24-C4 in a 50-day model of acute infection. Tc24-C4.10E-treated mice showed a decreased parasitemia compared to the Tc24-C4 (non-adjuvant) immunized mice or control group. Moreover, Tc24-C4.10E induced a higher stimulation index of CD8 + T cells producing IFNγ and IL-4 cytokines. These results suggest that the addition of the MHC Class I epitopes to Tc24-C4 can synergize the antigen-specific cellular immune responses, providing proof-of-concept that this approach could lead to the development of a promising vaccine candidate for Chagas disease.

Immunopathology of natural infection with Trypanosoma cruzi in dogs.

Chagas disease is caused by Trypanosoma cruzi and dogs are an important reservoir of the parasite as well as a good model for the study of the pathogenesis of the disease. We aimed here at characterizing the immunopathology of naturally infected dogs in Merida, Yucatan, Mexico. Following an initial screening for T. cruzi seropositive stray dogs, we examined 9 seropositive and 10 seronegative animals. High lymphocytes and low monocytes counts were observed in peripheral blood from seropositives dogs. Three of nine seropositive dogs presented electrocardiographic alterations including right bundle branch block, sinusal block and QRS complex alterations and some right ventricle enlargement was noted. Histopathologic analysis of cardiac walls revealed significant inflammation with a clear tropism for the right ventricle, although most walls were affected. Seropositive dogs presented low IgG1 and high IgG2 levels. Higher IgG1 levels were associated with increased cardiac index and myocarditis, suggesting that a Th2 immune response leads to susceptibility and increased disease severity. These observations shed some light on the mechanisms of pathogenesis of Chagas disease in dogs, and provide a good framework for the evaluation of novel drugs and vaccines in this animal model.

A canine model of experimental infection with Leishmania (L.) mexicana.

BACKGROUND: Cutaneous leishmaniasis is a tropical disease affecting over one million patients annually and Leishmania (L.) mexicana is one of the major etiological agents in the Americas. Here we established the first experimental infection of L. (L.) mexicana in canids. METHODS: Beagle dogs were infected intradermally with culture-derived L. (L.) mexicana. We followed skin ulcer development, histopathological signs, parasite burden and the immune status of the infected dogs. RESULTS: All infected dogs developed uniform oval-craterform ulcers similar to those observed in humans, associated with mixed T helper 1/T helper 2 immune responses. Parasites were detected in the healed lesions 15 weeks post-infection. Higher anti-Leishmania IgG levels correlated with larger lesions and high IgG1/IgG2 ratio was associated with some level of splenomegaly. CONCLUSIONS: The canine model described in this work will be of use for further understanding of L. (L.) mexicana immunopathogenensis, and for drug and vaccine development.

Malaria vaccine efficacy: overcoming the helminth hurdle.

Several studies have documented that helminth infections can interfere with the development of the immune response of vaccines against different diseases, although some results have been contradictory. The mechanisms involved in the inhibition of the immune response to vaccination by helminth are still unclear, and murine models of helminth-malaria coinfections have proven helpful in investigating some aspects of the interactions involved. The study evaluated here focuses on the effect of helminth infection in mice on the immunogenicity and protective efficacy of two distinct malaria vaccine candidates, a transmission-blocking DNA vaccine based on Pfs25 antigen and a pre-erythrocytic vaccine based on irradiated sporozoites. Interestingly, the authors found that helminth infection dramatically reduced DNA vaccine immunogenicity, while immunization with irradiated sporozoites was able to induce a high level of antibodies and protection, independently of helminth infection. Immune suppression by helminth infection affected all IgG isotypes, suggesting no particular polarization of the immune response, but the generation of memory B cells was not affected. It will be of key interest to understand the mechanisms underlying the efficacy of the sporozoite vaccine, and its ability to overcome helminth immunosuppression, as this may help in the design of more effective vaccines.

Dirofilaria immitis and Trypanosoma cruzi natural co-infection in dogs.

Dirofilariasis (Dirofilaria immitis) and American trypanosomiasis (Trypanosoma cruzi) are zoonotic parasitic diseases affecting the hearts of a variety of mammalian host species, including dogs. In this study, some of the immunopathological characteristics of natural co-infection by these two parasites were compared with T. cruzi infection in dogs from Mexico. Antibody analysis in serum indicated significantly lower anti-T. cruzi IgG levels in co-infected dogs (n = 4) compared to those with T. cruzi infection alone (n = 9), together with a somewhat lower IgG2/IgG1 ratio. Cardiac tissue inflammation was limited and focal in co-infected animals whereas T. cruzi infected dogs had extensive and diffuse tissue inflammation. Three out of nine T. cruzi infected dogs and 1/4 of T. cruzi and D. immitis co-infected dogs showed cardiac alterations. The results showed that co-infections may interfere with host responses, and their significant prevalence (4/13 T. cruzi infected dogs) suggests that they should be taken into account by researchers and clinicians.