Vaccine strategies against schistosomiasis

Distribution of Peripheral Memory T Follicular Helper Cells in Patients with Schistosomiasis Japonica

BACKGROUND

Schistosomiasis is a helminthic disease that affects more than 200 million people. An effective vaccine would be a major step towards eliminating the disease. Studies suggest that T follicular helper (Tfh) cells provide help to B cells to generate the long-term humoral immunity, which would be a crucial component of successful vaccines. Thus, understanding the biological characteristics of Tfh cells in patients with schistosomiasis, which has never been explored, is essential for vaccine design.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we investigated the biological characteristics of peripheral memory Tfh cells in schistosomiasis patients by flow cytometry. Our data showed that the frequencies of total and activated peripheral memory Tfh cells in patients were significantly increased during Schistosoma japonicum infection. Moreover, Tfh2 cells, which were reported to be a specific subpopulation to facilitate the generation of protective antibodies, were increased more greatly than other subpopulations of total peripheral memory Tfh cells in patients with schistosomiasis japonica. More importantly, our result showed significant correlations of the percentage of Tfh2 cells with both the frequency of plasma cells and the level of IgG antibody. In addition, our results showed that the percentage of T follicular regulatory (Tfr) cells was also increased in patients with schistosomiasis.

CONCLUSIONS/SIGNIFICANCE

Our report is the first characterization of peripheral memory Tfh cells in schistosomasis patients, which not only provides potential targets to improve immune response to vaccination, but also is important for the development of vaccination strategies to control schistosomiasis.

Biochemical analysis of a recombinant glutathione transferase from the cestode Echinococcus granulosus

Glutathione transferases (GSTs) are believed to be a major detoxification system in helminths. We describe the expression and functional analysis of EgGST, a cytosolic GST from Echinococcus granulosus, related to the Mu-class of mammalian enzymes. EgGST was produced as an enzymatically active dimeric protein (rEgGST), with highest specific activity towards the standard substrate 1-chloro-2,4-dinitrobenzene (CDNB; 2.5 micromol min(-1)mg(-1)), followed by ethacrynic acid. Interestingly, rEgGST displayed glutathione peroxidase activity (towards cumene hydroperoxide), and conjugated reactive carbonyls (trans-2-nonenal and trans,trans-2,4-decadienal), indicating that it may intercept damaging products of lipid peroxidation. In addition, classical GST inhibitors (cybacron blue, triphenylthin chloride and ellagic acid) and a number of anthelmintic drugs (mainly, hexachlorophene and rafoxanide) were found to interfere with glutathione-conjugation to CDNB; suggesting that they may bind to EgGST. Considered globally, the functional properties of rEgGST are similar to those of putative orthologs from Echinococcus multilcularis and Taenia solium, the other medically important cestodes. Interestingly, our results also indicate that differences exist between these closely related cestode GSTs, which probably reflect specific biological functions of the molecules in each parasitic organism.

Implementation of Human Schistosomiasis Control: Challenges and Prospects

Schistosomiasis is a major disease of public health importance in humans occurring in over 70 countries of the tropics and sub-tropics. In this chapter, the history of the control of schistosomiasis is briefly discussed and current methods of control of schistosomiasis are reviewed; including mollusciciding, biological control of the intermediate snail hosts, the development of drugs to kill the adult worms, provision of clean water and health education, with a focus on the African situation. Since an effective vaccine against schistosomiasis is lacking, the emphasis today is placed on the drug praziquantel (PZQ). The marked reduction in the cost of PZQ together with the support of the Bill and Melinda Gates Foundation has enabled the drug to be used more widely in sub-Saharan Africa. Nevertheless, with the possibility of resistance to praziquantel emerging, the potential role of other drugs, such as artemether, in the control of schistosomiasis is examined. The World Health Organization (WHO) anticipates that at least 75% of all schoolchildren at risk of morbidity from schistosomiasis will be treated by 2010, with the aim of reversing morbidity. The importance of recent international initiatives such as the Schistosomiasis Control Initiative (SCI) working in Mali, Niger, Burkina Faso, Zambia, Tanzania and Uganda is recognised. There are benefits to integrating the control of schistosomiasis with other disease control programmes, such as gastrointestinal helminths and/or lymphatic filariasis (LF), since this markedly reduces the cost of delivery of the treatment. Countries that are situated on the perimeter of the distribution of schistosomiasis have either achieved or have made progress towards the elimination of the disease. For control programmes to be successful in areas such as sub-Saharan Africa, it is absolutely essential that these programmes are sustainable. Thus, it will be vital for Ministries of Health and Education to budget for the control of diseases of poverty in addition to school health, and to utilise funds from a range of sources, such as, government funds, pooled donor contributions, or bilateral and international agencies.

Research on calpain of Schistosoma japonicum as a vaccine candidate

Vaccine development by the use of calpain of Schistosoma japonicum has been tried in our laboratory. We cloned cDNA encoding the heavy chain of S. japonicum calpain, and prepared recombinant molecule of a possible vaccine region of the heavy chain. When BALB/c mice were immunized with our recombinant calpain of S. japonicum with Freund's complete adjuvant, we observed significant reduction in worm burden (41.2% reduction, P<0.05), and also significant anti-fecundity effects. In this sense, calpain of S. japonicum seems to have infection control as well as anti-disease effects. Mechanisms of vaccine effects of calpain remain to be clarified, however, several effector mechanisms are suspected. In immunized mice, raised level of iNos expression was observed, while adhesion of peritoneal exudates cells were also observed in the presence of calpain-immunized sera, suggesting the possibilities of both cellular and humoral protective mechanisms. We examined tissue distribution of calpain in various developmental stages of S. japonicum. Strong signal was observed around excretory grand of cercariae, and they secreted calpain during their migratory movement tested in vitro. Together with the findings, calpain seems to induce larvicidal effects in the immunized mice. We observed time-course kinetics of antibody production against vaccine candidates in experimental S. japonicum infection in pigs. Although significant levels of antibody production were observed for paramyosin and GST, no significant antibody production was observed for calpain. This suggests that calpain is less immunogenic, and route of immunization and/or choice of adjuvant are important in future trials of calpain vaccine.

Vaccination with calpain induces a Th1-biased protective immune response against Schistosoma japonicum

A large subunit of calpain, a calcium-activated neutral proteinase, from Schistosoma japonicum was cloned and expressed in Escherichia coli. When BALB/c mice were immunized with purified recombinant calpain (r-calpain) emulsified in complete Freund's adjuvant, a significant reduction in the number of recovered worms and also in egg production per female worm was observed (P<0.01). Spleen cells of the immunized mice showed enhanced production of gamma interferon (IFN-gamma) by activated CD4(+) T cells. Considering our observation of elevated expression of inducible nitric oxide synthase mRNA in immunized mice, r-calpain-induced IFN-gamma seemed to upregulate the production of nitric oxide by macrophages and subsequently mediated the killing of schistosomulae in the lung. On the other hand, spleen cells of immunized mice showed only faint interleukin-4 production in response to r-calpain in vitro, suggesting that immunization with r-calpain alters the Th1-Th2 balance in murine hosts even during a Th2-promoting S. japonicum infection. Furthermore, histopathological study of the livers of immunized mice showed that granulomas formed around eggs were diminished in both size and number. Egg production by female worms was clearly decreased in immunized mice, suggesting that r-calpain also has antifecundity effects. Taken together, these results point to S. japonicum calpain as a potential vaccine candidate for both worm killing and disease prevention, possibly through the induction of a strong Th1-dominant environment in immunized mice.

Partial purification and characterization of Gastrothylax crumenifer somatic antigens

The soluble extracts of Gastrothylax crumenifer isolated from the rumen of buffalo (Bubalus bubalis) were fractionated on a Sephadex G-200 column. A total of eight major fractions (F1, F2, F3, F4, F5, F6, F7, and F8) were separated from the whole homogenate of G. crumenifer, and each of these fractions was tested for their antigenicity by ELISA against rabbit hyperimmune sera. It was observed that F1, F2, F3 and F4 were highly antigenic, F6 and F7 were moderately antigenic and F5 and F8 were poorly antigenic. The individual fractions analysed after SDS-PAGE and Western blotting indicated that the antigenic fractions of G. crumenifer are of low molecular weight, in the range of <14-50kDa, and predominant antigenic components which were evident in most of the Sephadex profiles were of Mr 15, 18, 19, 23-24 and 28-32kDa.

Local transient induction of inflammatory cytokines after intranasal administration of recombinant Bordetella pertussis

Inflammatory cytokines have been described to play a critical role in the orientation and amplification of the IgA immune response. In this study, we show that the intranasal administration of a Bordetella pertussis strain expressing the protective antigen glutathione-S-transferase of Schistosoma mansoni (Sm28GST) induced an inflammatory response in the lungs of mice, characterized by the production of inflammatory cytokines, such as Tumor Necrosis Factor alpha, Interleukin-6 and Transforming-Growth Factor beta. The production and the secretion of these cytokines in lung tissues were early and transient. Their presence was observed only during the first week after administration despite the persistence of the bacteria for 1 month. Two weeks after inoculation, Interleukin-10 secretion was detected in the lungs, which could explain the decrease in the production of inflammatory cytokines. These inflammation-regulating cytokines, induced in the lungs by the presence of the bacterial vector, could be part of the process generating the local immune response, in particular the anti-Sm28GST IgA response.

Cloning of Schistosoma mansoni transcription factor NF-YA subunit: phylogenic conservation of the HAP-2 homology domain

The CCAAT-binding factor NF-Y (CBF/CP1) is a heteromeric transcription factor involved in the regulation of a variety of eukaryotic genes. We identified NF-Y as the CCAAT activity binding to the promoter region of the gene coding for the 28-kDa glutathione S-transferase of the human parasite Schistosoma mansoni (Sm28GST). We isolated the NF-YA cDNA from S. mansoni (SmNF-YA): the complete 268 amino acid sequence harbors a region in its C-terminal part that shows homology with the subunit interaction and DNA-binding domains of the mammalian NF-YA; the N-terminal region has an amino acid composition reminiscent of the mammalian and echinoderm counterparts, rich in glutamine and hydrophobic residues, but shows no sequence similarity at the primary level. In vitro synthesized SMNF-YA is able to associate with mammalian NF-YB/C subunits in the absence of DNA and to bind to the Sm28GST CCAAT box. Surprisingly, a monoclonal antibody directed against the non-conserved Q-rich activation domain of mammalian NF-YA supershifts and immunoprecipitates SMNF-YA, strongly suggesting structure conservation in the activation domain between divergent species.

Schistosoma mansoni in the baboon: modulation of pathology after vaccination with polyclonal anti-idiotypic antibodies

Vaccination of five baboons with an anti-idiotypic vaccine to irradiated Schistosoma mansoni cercariae resulted in nearly 19% protection compared to 39% protection conferred to five baboons vaccinated with an irradiated vaccine. Vaccination with the anti-idiotypic antibodies resulted in a significant reduction of pathology and granuloma size following challenge with live unattenuated cercariae. Results presented in this work are considered highly significant because the anti-idiotypic vaccine markedly influenced schistosomiasis morbidity which is the main consideration in this disease.

Tissue expression of the Schistosoma mansoni 28 kDa glutathione S-transferase

The expression of the Schistosoma mansoni 28 kDa glutathione S-transferase (Sm28) was studied using molecular (PCR, in situ hybridization), and immunocytochemical techniques. The presence of Sm28 was demonstrated in all developmental stages of the parasite except the intra-uterine immature egg. In the parenchyma of male and female adult worms the distribution of Sm28 was limited to a subpopulation of parenchymal cells and to the dorsal tubercles of the male. The tegument, the muscles, the digestive tract, the neural mass, the vitelline glands, and mature gametes were not immunoreactive. Immature germinal cells in both sexes, and the ootype in the female genital system, were found to express Sm28. Deposits of immunoreactive material on host skin following cercarial penetration, exfoliation from the male tubercles, and especially emission of Sm28 from eggs in hepatic granulomas are suspected to be a source of antigen during the parasite infection. The reduction in worm fecundity previously observed in immunization experiments may result from an antibody response directed against Sm28 present in the ootype. There was no cross-reactivity observed, under the experimental conditions used, between the anti-Sm28 sera and either vertebrate or invertebrate host tissue.

Isolation and biochemical characterisation of a glutathione S-transferase from Echinococcus granulosus protoscoleces

A protein fraction migrating as a M(r) 24 kDa band on SDS-PAGE was isolated by affinity chromatography on glutathione-agarose from a soluble extract of E. granulosus proto-scoleces from sheep(UK). This fraction had glutathione S-transferase activity of 0.4 mumol min-1 mg-1 when measured using a standard synthetic substrate and its determined N-terminal amino acid sequence most closely resembled Mu class glutathione S-transferases. In addition, protoscoleces from the distinct sheep and horse E. granulosus strains showed a different pattern of glutathione-binding proteins: the M(r) 24 kDa species was obtained in both cases whereas an additional band of slightly faster electrophoretic mobility was isolated from horse(UK) protoscoleces.

Vaccination against animal parasites

A decade of molecular parasitology is beginning to bear fruit, with the appearance of several new, highly effective, practical vaccines against parasitic diseases. Recombinant antigen vaccines have been developed against cestode, nematode, trematode, protozoan and arthropod parasites. Greatest progress has been made with veterinary vaccines, where the ability to test numerous vaccine formulations in challenge trials has allowed more rapid identification of host-protective antigens than is possible with many medically important parasites. Several quite different approaches to vaccine development have been successful. The traditional approach using live, attenuated parasites continues to provide effective vaccines against several protozoan and nematode parasites. Recombinant DNA technology, monoclonal antibody technology, protein chemistry and immunochemistry have played critical roles in the outstanding success which has been achieved over the last 5 years in the development of defined-antigen vaccines. Two approaches have been successful in research towards defined antigen vaccines against parasites: (1) the 'natural antigen' approach where immune responses are stimulated to parasite molecules which are normally antigenic, and possibly host-protective, in infected hosts; (2) the 'naive antigen' approach where parasite molecules which are not antigenic, or of very low antigenicity, in infected hosts are used to raise immune responses capable of killing the parasite. This review examines the successful approaches taken towards the development of effective anti-parasite vaccines and the vaccines which have been produced to date.

Molecular characterisation and localisation of an Onchocerca volvulus pi-class glutathione S-transferase

Glutathione S-transferases (GSTs) constitute a major detoxification mechanism in helminth organisms and are regarded vaccine candidates against helminth infections. Onchocerca volvulus glutathione-binding proteins were purified from the aqueous soluble fraction of homogenised adult females by affinity chromatography on glutathione-agarose. The eluted proteins had a specific GST activity of 1.6 mumol min-1 mg-1. Immunohistochemical studies localised these antigens in the hypodermis, the wall of the seminal receptacle and spermatozoa of adult worms. A lambda gt11 clone was isolated from an expression library of O. volvulus by immunoscreening. Sequence analysis revealed that it encoded a pi-class GST with 60% identity with Caenorhabditis elegans and up to 45% identity with mammalian pi-class GSTs. Antibodies affinity selected with recombinant GST demonstrated cross-reactivity between Litomosoides sigmodontis and O. volvulus GSTs.

Effect of cholera toxin on vaccine-induced immunity and infection in murine schistosomiasis mansoni

Intradermal vaccination of mice with soluble adult worm antigen (SWAP) in combination with Mycobacterium bovis BCG (Swedish strain) induced significant protection against subsequent infection with Schistosoma mansoni cercariae. When cholera toxin (CT) was used as an adjuvant in combination with SWAP or fraction A, no significant protection was observed. However, intradermal vaccination in combination with CT triggered a strong anti-SWAP antibody response and induced a strong delayed-type hypersensitivity response to schistosome antigens (SWAP or fraction A), one significantly higher than that in the SWAP-BCG group. In addition, vaccinating mice intranasally with SWAP or cercarial antigen together with CT as adjuvant failed to induce any significant protection. Surprisingly, mice given CT alone intranasally revealed a significantly enhanced worm burden. These findings suggest that mucosal application of CT may modulate the host-parasite relationship in favor of parasite survival.

Immune-dependent chemotherapy of schistosomiasis

Host immune responses have been shown to enhance the efficacy of several schistosomicidal drugs. The evidence derives mainly from experiments on Schistosoma mansoni infections in the mouse with their immune status variously modulated; this review emphasises praziquantel (PZQ), which is now the main drug used for treatment of human schistosomiasis. Electron microscopy and indirect immunofluorescence indicate that PZQ disrupts the integrity of the surface membranes of S. mansoni, particularly those covering the dorsal tubercles of adult male worms, and this causes antigens which are the targets of antibody attack to be revealed. We review the evidence that two S. mansoni antigens in particular are implicated in the immune-dependent action of PZQ: a 200 kDa glycoprotein and a 27 kDa antigen with non-specific esterase activity. Consistent with the involvement of the latter antigen, increased non-specific esterase activity was demonstrated histochemically on the surface of intact PZQ-treated male worms, and we describe a chromogenic substrate assay for quantifying the amount of esterase activity that is exposed after drug treatment. The potential relevance of these observations for enhancing the efficacy of drugs currently used to treat human schistosomiasis, and for devising novel therapeutic strategies, is discussed.