Distribution of alpha-galactosyl-containing epitopes on Trypanosoma cruzi trypomastigote and amastigote forms from infected Vero cells detected by Chagasic antibodies

New chemotherapy regimens and biomarkers for Chagas disease: the rationale and design of the TESEO study, an open-label, randomised, prospective, phase-2 clinical trial in the Plurinational State of Bolivia

INTRODUCTION

Chagas disease (CD) affects ~7 million people worldwide. Benznidazole (BZN) and nifurtimox (NFX) are the only approved drugs for CD chemotherapy. Although both drugs are highly effective in acute and paediatric infections, their efficacy in adults with chronic CD (CCD) is lower and variable. Moreover, the high incidence of adverse events (AEs) with both drugs has hampered their widespread use. Trials in CCD adults showed that quantitative PCR (qPCR) assays remain negative for 12 months after standard-of-care (SoC) BZN treatment in ~80% patients. BZN pharmacokinetic data and the nonsynchronous nature of the proliferative mammal-dwelling parasite stage suggested that a lower BZN/NFX dosing frequency, combined with standard or extended treatment duration, might have the same or better efficacy than either drug SoC, with fewer AEs.

METHODS AND ANALYSIS

New ThErapies and Biomarkers for ChagaS infEctiOn (TESEO) is an open-label, randomised, prospective, phase-2 clinical trial, with six treatment arms (75 patients/arm, 450 patients). Primary objectives are to compare the safety and efficacy of two new proposed chemotherapy regimens of BZN and NFX in adults with CCD with the current SoC for BZN and NFX, evaluated by qPCR and biomarkers for 36 months posttreatment and correlated with CD conventional serology. Recruitment of patients was initiated on 18 December 2019 and on 20 May 2021, 450 patients (study goal) were randomised among the six treatment arms. The treatment phase was finalised on 18 August 2021. Secondary objectives include evaluation of population pharmacokinetics of both drugs in all treatment arms, the incidence of AEs, and parasite genotyping.

ETHICS AND DISSEMINATION

The TESEO study was approved by the National Institutes of Health (NIH), U.S. Food and Drug Administration (FDA), federal regulatory agency of the Plurinational State of Bolivia and the Ethics Committees of the participating institutions. The results will be disseminated via publications in peer-reviewed journals, conferences and reports to the NIH, FDA and participating institutions.

TRIAL REGISTRATION NUMBER

NCT03981523.

Anti α1-3Gal antibodies and Gal content in gut microbiota in immune disorders and multiple sclerosis

Recent observations suggest that Gal antigen content in gut microbiota and anti-Gal antibody response may influence inflammation in immune related disorders. In this review we summarized the current knowledge on antibody response to the Gal epitope in various immune disorders. We discuss the origin of Gal antigen associated to gut microbiota. In multiple sclerosis, the possible mechanisms by which the altered microbiota and/or circulating anti-Gal level could affect the immune response in this disease are presented.

TcNST2encodes a Golgi-localized UDP-galactose transporter inTrypanosoma cruzi

Survival and infectivity of trypanosomatids rely on cell-surface and secreted glycoconjugates, many of which contain a variable number of galactose residues. Incorporation of galactose to proteins and lipids occurs along the secretory pathway from UDP-galactose (UDP-Gal). Before being used in glycosylation reactions, however, this activated sugar donor must first be transported across the endoplasmic reticulum and Golgi membranes by a specific nucleotide sugar transporter (NST). In this study, we identified an UDP-Gal transporter (named TcNST2 and encoded by the TcCLB.504085.60 gene) fromTrypanosoma cruzi, the etiological agent of Chagas disease. TcNST2 was identified by heterologous expression of selected putative nucleotide sugar transporters in a mutant Chinese Hamster Ovary cell line.TcNST2mRNA levels were detected in allT. cruzilife-cycle forms, with an increase in expression in axenic amastigotes. Confocal microscope analysis indicated that the transporter is specifically localized to the Golgi apparatus. A three-dimensional model of TcNST2 suggested an overall structural conservation as compared with members of the metabolite transporter superfamily and also suggested specific features that could be related to its activity. The identification of this transporter is an important step toward a better understanding of glycoconjugate biosynthesis and the role NSTs play in this process in trypanosomatids.

Synthesis and characterization of α-d-Galp-(1 → 3)-β-d-Galp epitope-containing neoglycoconjugates for chagas disease serodiagnosis

The immunodominant epitope α-d-Galp-(1 → 3)-β-d-Galp-(1 → 4)-d-GlcNAc, expressed in the mucins of the infective trypomastigote stage of Trypanosoma cruzi has been proposed for multiple clinical applications, from serodiagnosis of protozoan caused diseases to xenotransplantation or cancer vaccinology. It was previously shown that the analogue trisaccharide, with glucose in the reducing end instead of GlcNAc, was as efficient as the natural trisaccharide for recognition of chagasic antibodies. Here we describe the synthesis of α-d-Galp-(1 → 3)-β-d-Galp-(1 → 4)-d-Glcp functionalized as the 6-aminohexyl glycoside and its conjugation to BSA using the squarate method. The conjugate of 6-aminohexyl α-d-Galp-(1 → 3)-β-d-Galp was also prepared. Both neoglycoconjugates were recognized by serum samples of Trypanosoma cruzi-infected individuals and thus, are promising tools for the improvement of Chagas disease diagnostic applications.

The Trypanosoma cruzi Surface, a Nanoscale Patchwork Quilt

The Trypanosoma cruzi trypomastigote membrane provides a major protective role against mammalian host-derived defense mechanisms while allowing the parasite to interact with different cell types and trigger pathogenesis. This surface has been historically appreciated as a rather unstructured 'coat', mainly consisting of a continuous layer of glycolipids and heavily O-glycosylated mucins, occasionally intercalated with different developmentally regulated molecules displaying adhesive and/or enzymatic properties. Recent findings, however, indicate that the trypomastigote membrane is made up of multiple, densely packed and discrete 10-150nm lipid-driven domains bearing different protein composition; hence resembling a highly organized 'patchwork quilt' design. Here, we discuss different aspects underlying the biogenesis, assembly, and dynamics of this cutting-edge fashion outfit, as well as its functional implications.

Microbiota Control of Malaria Transmission

Stable mutualistic interactions between multicellular organisms and microbes are an evolutionarily conserved process with a major impact on host physiology and fitness. Humans establish such interactions with a consortium of microorganisms known as the microbiota. Despite the mutualistic nature of these interactions, some bacterial components of the human microbiota express immunogenic glycans that elicit glycan-specific antibody (Ab) responses. The ensuing circulating Abs are protective against infections by pathogens that express those glycans, as demonstrated for Plasmodium, the causative agent of malaria. Presumably, a similar protective Ab response acts against other vector-borne diseases.

Anti-Gal: an abundant human natural antibody of multiple pathogeneses and clinical benefits

Anti-Gal is the most abundant natural antibody in humans, constituting ~ 1% of immunoglobulins. Anti-Gal is naturally produced also in apes and Old World monkeys. The ligand of anti-Gal is a carbohydrate antigen called the 'α-gal epitope' with the structure Galα1-3Galβ1-4GlcNAc-R. The α-gal epitope is present as a major carbohydrate antigen in non-primate mammals, prosimians and New World monkeys. Anti-Gal can contributes to several immunological pathogeneses. Anti-Gal IgE produced in some individuals causes allergies to meat and to the therapeutic monoclonal antibody cetuximab, all presenting α-gal epitopes. Aberrant expression of the α-gal epitope or of antigens mimicking it in humans may result in autoimmune processes, as in Graves' disease. α-Gal epitopes produced by Trypanosoma cruzi interact with anti-Gal and induce 'autoimmune like' inflammatory reactions in Chagas' disease. Anti-Gal IgM and IgG further mediate rejection of xenografts expressing α-gal epitopes. Because of its abundance, anti-Gal may be exploited for various clinical uses. It increases immunogenicity of microbial vaccines (e.g. influenza vaccine) presenting α-gal epitopes by targeting them for effective uptake by antigen-presenting cells. Tumour lesions are converted into vaccines against autologous tumour-associated antigens by intra-tumoral injection of α-gal glycolipids, which insert into tumour cell membranes. Anti-Gal binding to α-gal epitopes on tumour cells targets them for uptake by antigen-presenting cells. Accelerated wound healing is achieved by application of α-gal nanoparticles, which bind anti-Gal, activate complement, and recruit and activate macrophages that induce tissue regeneration. This therapy may be of further significance in regeneration of internally injured tissues such as ischaemic myocardium and injured nerves.

Enzyme-linked immunosorbent assay with Trypanosoma cruzi excreted-secreted antigens (TESA-ELISA) for serodiagnosis of acute and chronic Chagas' disease

In the present report we describe the use of Trypomastigote Excreted-Secreted Antigens (TESA) as antigen in ELISA for Chagas' disease serodiagnosis. The study was carried out on 284 patients, 164 of whom were nonchagasic subjects including individuals with leishmaniasis or other pathologies, and 120 chagasic patients, being 53 in the acute (with positive IgA and IgM antibodies to T. cruzi) and 67 in the chronic phase. TESA-ELISA showed 100% positivity in the survey of IgG antibodies in chagasic patients (acute and chronic) and 100% positivity for IgM antibodies in acute phase sera. TESA preparation does not require biochemical purification procedures and does not present the cross-reactivity of leishmaniasis sera observed when ELISA with epimastigote alkaline extract (EAE) is performed. ELISA competition assays showed that anti-T. cruzi antibodies of sera from chagasic patients that react with TESA are different from those that react with EAE. Besides, partial characterization of TESA showed that several epitopes present in this fraction are absent in EAE.

Mucin-like molecules form a negatively charged coat that protects Trypanosoma cruzi trypomastigotes from killing by human anti-alpha-galactosyl antibodies

In the presence of sialic acid donors Trypanosoma cruzi acquires up to 10(7) sialic acid residues on its surface, in a reaction catalyzed by its unique trans-sialidase. Most of these sialic acid residues are incorporated into mucin-like glycoproteins. To further understand the biological role of parasite sialylation, we have measured the amount of mucin in this parasite. We found that both epimastigote and trypomastigote forms have the same number of mucin molecules per surface area, although trypomastigotes have less than 10% of the amount of glycoinositol phospholipids, the other major surface glycoconjugate of T. cruzi. Based on the estimated surface area of each mucin, we calculated that these molecules form a coat covering the entire trypomastigote cell. The presence of the surface coat is shown by transmission electron microscopy of Ruthenium Red-stained parasites. The coat was revealed by binding of antibodies isolated from Chagasic patients that react with high affinity to alpha-galactosyl epitopes present in the mucin molecule. When added to the trypomastigote, these antibodies cause an extensive structural perturbation of the parasite coat with formation of large blebs, ultimately leading to parasite lysis. Interestingly, lysis is decreased if the mucin coat is heavily sialylated. Furthermore, addition of MgCl2 reverses the protective effect of sialylation, suggesting that the sialic acid negative charges stabilize the surface coat. Inhibition of sialylation by anti-trans-sialidase antibodies, found in immunized animals, or human Chagasic sera, also increase killing by anti-alpha-galactosyl antibodies. Therefore, the large amounts of sialylated mucins, forming a surface coat on infective trypomastigote forms, have an important structural and protective role.

Cross-reactivity of anti-galactocerebroside autoantibodies with a Trypanosoma brucei proteolipidic epitope

Pathogenic mechanisms of the demyelinating encephalopathy featuring the nervous phase of human African trypanosomiasis (HAT) are largely unknown. They might include autoimmune disorders. A variety of autoantibodies is detected during the disease and we have previously evidenced anti-galactocerebroside (GalC) antibodies in the serum and cerebrospinal fluid (CSF) from patients in the nervous stage (stage II) of HAT. We now show that anti-GalC antibodies recognize an antigen located on the parasite membrane and common to different strains of trypanosomes. By using affinity chromatography with a rabbit anti-GalC antiserum, a 52-kD proteolipid was isolated from the membrane of Trypanosoma brucei (T. b.) brucei AnTat 1.9, AnTat 1. 1E, and T. b. rhodesiense Etat 1.2/R and Etat 1.2/S. Antibodies directed against this antigen were found in the CSF from patients with nervous stage HAT. These CSF also contained anti-GalC antibodies and adsorption with the proteolipid decreased anti-GalC reactivity. Immunization of mice with this antigen induced the production of antibodies which cross-reacted with GalC but no protection from experimental infection with T. b. brucei. These data support the hypothesis that anti-GalC antibodies detected in the CSF from HAT patients might be induced by molecular mimicry with a parasite antigen.

Lytic anti-alpha-galactosyl antibodies from patients with chronic Chagas' disease recognize novel O-linked oligosaccharides on mucin-like glycosyl-phosphatidylinositol-anchored glycoproteins of Trypanosoma cruzi

Sera of patients with chronic Chagas' disease (American trypanosomiasis) contain elevated levels of anti-alpha-galactosyl antibodies that are lytic to Trypanosoma cruzi. The T. cruzi trypomastigote F2/3 antigen complex recognized by these antibodies runs as a broad smear on SDS/PAGE [Almeida, Krautz, Krettli and Travassos (1993) J. Clin. Lab. Anal. 7, 307-316]. Treatment of T. cruzi trypomastigote cells with bacterial phosphatidylinositol-specific phospholipase C (PI-PLC) abolished most of their reactivity to chronic Chagas'-disease ((Chagasic, Ch) anti-alpha-galactosyl antibodies (anti-Gal). The F2/3 antigen complex, purified by solvent extraction and hydrophobic-interaction chromatography, contained 60% carbohydrate by weight and substantial amounts of Thr, Ser, Glx, Asx, Gly, Ala and Pro, but relatively few hydrophobic amino acids. The presence of myoinositol, ethanolamine and 1-O-hexadecylglycerol suggested the presence of glycosyl-phosphatidylinositol membrane anchors. This was confirmed by PI-PLC treatment, which rendered the F2/3 molecules hydrophilic and reactive to anti-(cross-reacting determinant) antibodies. The majority of the GlcNAc content of the F2/3 antigens was found at the reducing termini of oligosaccharides in O-glycosidic linkage to Thr residues. These O-linked oligosaccharides could be released by beta-elimination and by mild hydrazinolysis. The smallest released oligosaccharitol that was reactive with the Ch anti-Gal was Gal alpha 1-3Gal beta 1-4GlcNAcol (where GlcNAcol is N-acetyl-glucosaminitol). Several other Gal-containing oligosaccharitols were observed, most of which were branched and contained 4,6-di-O-substituted GlcNAcol at their reducing termini. About half of the total released oligosaccharitols could bind to immobilized Ch anti-Gal, but none of them bound to the anti-Gal isolated from normal human sera. These data suggest that the specificities of the Ch anti-Gal are quite different from the natural anti-Gal isolated from normal human sera. Therefore, these novel T. cruzi O-linked oligosaccharides are highly immunogenic under the conditions of natural infection and are the targets for lytic Ch anti-Gal.

Chemiluminescent immunoassays: discrimination between the reactivities of natural and human patient antibodies with antigens from eukaryotic pathogens, Trypanosoma cruzi and Paracoccidioides brasiliensis

Quantitative chemiluminescent enzyme-linked immunosorbent assay (ELISA) and dot-blotting procedures were developed to evaluate the reactivity of human antibodies with crude antigens and purified molecules of parasites and fungi, mainly Trypanosoma cruzi and Paracoccidioides brasiliensis. Reproducible, highly sensitive, and strictly dose-responding results were obtained, with the specificity depending on the kind of antigen used. Mixed antigens (epimastigote membrane and HIV-1 heptapeptide) applied in dots could be independently recognized by specific sera. Purified antigens (T. cruzi F2/3 and P. brasiliensis gp43) at very small concentrations gave specific reactions with patients' sera diluted > or = 1:1,000 and were very poorly reactive or unreactive with natural antibodies using the chemiluminescent immunoassays. P. brasiliensis crude antigen Fava Netto polysaccharide antigen (FNPA) contained peptide epitopes recognized by natural antibodies and carbohydrate epitopes reactive with sera from histoplasmosis patients. It is very important that sensitive chemiluminescence immunoassays be used with purified antigenic molecules to ensure specificity for the diagnosis and follow-up of parasitic and fungal infections.