Gene cloning and complete nucleotide sequence of philippine Schistosoma japonicum paramyosin

Development of Paramyosin as a Vaccine Candidate for Schistosomiasis

Schistosomiasis, caused by three principal species of diecious trematodes (flatworms), currently afflicts over 250 million individuals, results in an estimated 2–15% chronic disability, and contributes to poor health and economic stagnation in endemic areas. Although schistosomiasis is effectively treated with praziquantel, rapid reinfection with rebound morbidity precludes effective control based on chemotherapy alone and justifies current efforts to develop vaccines for these parasites. Paramyosin (Pmy), an invertebrate muscle-associated protein, has emerged as a promising vaccine candidate for both Schistosoma mansoni and Schistosoma japonicum. Herein, we discuss the discovery of Pmy, its development as a vaccine candidate in rodents and bovines, as well as studies of naturally occurring immune responses to Pmy in prospective, observational human studies. We conclude with a proposed developmental plan to move Pmy toward Phase I clinical trials.

The nature and combination of subunits used in epitope-based Schistosoma japonicum vaccine formulations affect their efficacy

Background

Schistosomiasis remains a major public health problem in endemic countries and is caused by infections with any one of three primary schistosome species. Although there are no vaccines available to date, this strategy appears feasible since natural immunity develops in individuals suffering from repeated infection during a lifetime. Since vaccinations resulting in both Th1- and Th2-type responses have been shown to contribute to protective immunity, a vaccine formulation with the capacity for stimulating multiple arms of the immune response will likely be the most effective. Previously we developed partially protective, single Th- and B cell-epitope-based peptide-DNA dual vaccines (PDDV) (T3-PDDV and B3-PDDV, respectively) capable of eliciting immune responses against the Schistosoma japonicum 22.6 kDa tegument antigen (Sj22.6) and a 62 kDa fragment of myosin (Sj62), respectively.

Results

In this study, we developed PDDV cocktails containing multiple epitopes of S. japonicum from Sj22.6, Sj62 and Sj97 antigens by predicting cytotoxic, helper, and B-cell epitopes, and evaluated vaccine potential in vivo. Results showed that mice immunized with a single-epitope PDDV elicited either Tc, Th, or B cell responses, respectively, and mice immunized with either the T3- or B3- single-epitope PDDV formulation were partially protected against infection. However, mice immunized with a multicomponent (3 PDDV components) formulation elicited variable immune responses that were less immunoprotective than single-epitope PDDV formulations.

Conclusions

Our data show that combining these different antigens did not result in a more effective vaccine formulation when compared to each component administered individually, and further suggest that immune interference resulting from immunizations with antigenically distinct vaccine targets may be an important consideration in the development of multicomponent vaccine preparations.

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Update on paramyosin in parasitic worms

Paramyosin was first identified as a structural component of invertebrate muscle. Analysis of crude, native, adult schistosome worm preparations identified a highly immunogenic protein which was later identified as paramyosin. Early vaccination/challenge studies with native paramyosin produced encouraging levels of protective efficacy against schistosomes, which led to the question as to how a sub-tegumental (muscular) protein could provide a target for vaccine-mediated immunological attack. Immunolocalisation studies of schistosomes confirmed the presence of paramyosin within the post-acetabular glands of cercariae and on the tegumental surface of lung schistosomula. Here we present an update on the more recent research on paramyosin in parasitic worms that has focused primarily in two directions: (i) further testing of the vaccine potency of paramyosin against schistosomes and other parasitic worms; and (ii) characterisation of the protein at the molecular and biochemical levels.

Observations on the musculature and isolated muscle fibres of the liver fluke, Fasciola hepatica

The liver fluke, Fasciola hepatica relies on a well-developed muscular system, not only for attachment, but for many aspects of its biology. Despite this, little is known about the system beyond the gross organization of the main somatic muscle layers. In the present study, a range of techniques have been applied to F. hepatica in order to understand more about various aspects of muscle organization, biochemistry (in terms of muscle proteins) and identity of isolated muscle fibres. Scanning electron microscopy has provided a direct visualization in situ of the somatic muscle layers and the organization of the muscle fibres within the ventral sucker. The muscle bundles contributing to the main somatic muscle layers are made up of up to 10 individual muscle fibres. Phalloidin staining for actin, in conjunction with confocal microscopy, confirmed the presence of 2 main somatic muscle layers (outer circular, inner longitudinal), beneath which lies a third layer of oblique muscle fibres. The use of propidium iodide in combination with phalloidin staining for actin demonstrated that the cell bodies associated with the 2 main somatic muscle layers are situated beneath the longitudinal muscle layer and are connected to their respective muscle fibres by short cytoplasmic processes. Myosin immunoreactivity was demonstrated in the somatic muscle layers and in the muscle layers surrounding various organ systems within the fluke. Double labelling for actin and myosin confirmed the co-localization of the 2 muscle proteins in the muscle fibres of the ventral sucker. Muscle fibres from the somatic muscle layers and the ventral sucker have been isolated and images obtained with phase-contrast microscopy and scanning electron microscopy. The muscle fibres contain actin and myosin, but lack a nucleus, the connection with the cell body having been broken during the isolation procedure.

Inhibition of the complement membrane attack complex by Schistosoma mansoni paramyosin

Larvae and adults of the parasitic blood fluke Schistosoma mansoni are resistant to killing by human complement. An earlier search by Parizade et al. for a schistosome complement inhibitor identified a 94-kDa surface protein which was named SCIP-1 (M. Parizade, R. Arnon, P. J. Lachmann, and Z. Fishelson, J. Exp. Med. 179:1625-1636, 1994). Following partial purification and analysis by mass spectrometry, we have determined SCIP-1 to be a surface-exposed form of the muscle protein paramyosin. As shown by immunofluorescence, anti-paramyosin antibodies label the surface of live schistosomula and adult worms. Like SCIP-1, purified native paramyosin reacts with a polyclonal rabbit anti-human CD59 antiserum, as shown by Western blot analysis. Also, the human complement components C8 and C9 bind to recombinant and native paramyosin. Analysis of paramyosin binding to fragments of C9 generated by thrombin or trypsin has demonstrated that paramyosin binds to C9 at a position located between Gly245 and Arg391. Paramyosin inhibited Zn(2+)-induced C9 polymerization and poly-C9 deposition onto rabbit erythrocytes (E(R)). In addition, paramyosin inhibited lysis of E(R) and of sensitized sheep erythrocytes by human complement. Finally, anti-paramyosin antibodies enhanced in vitro killing of schistosomula by normal and C4-depleted human complement. Taken together, these findings suggest that an exogenous form of S. mansoni paramyosin inhibits activation of the terminal pathway of complement and thus has an important immunomodulatory role in schistosomiasis.

Immune correlate study on human Schistosoma japonicum in a well-defined population in Leyte, Philippines: II. Cellular immune responses to S. japonicum recombinant and native antigens

Cellular immune responses to specific Schistosoma japonicum recombinant and native antigens were investigated in a defined study population of 155 individuals in the Philippines, where data collected from a 3-year observation of exposure, infection and reinfection pattern were used to categorically classify putative 'resistant' and 'susceptible' individuals. Using peripheral blood mononuclear cells (PBMC) of individuals enrolled in the study, in vitro lymphocyte proliferation and cytokine (IFN-gamma, IL-5 and IL-10) production in response to defined recombinant antigens (97 kDa paramyosin, 22 kDa tegumental antigen, 37 kDa glyceraldehyde-3-phosphate dehydrogenase, 14 kDa fatty acid binding protein and 28 kDa gluthathione-S-tranferase) and native antigen soluble worm antigen preparation (SWAP) were measured. Cellular responses to the recombinant and SWAP antigens suggest that Th1 type of response appear to be important in predicting resistance in this population. Of the five recombinant antigens tested, rPMY induced significant levels of IFN-gamma. The production of IL-10, a Th2-type cytokine was strongly implicated in immune regulation. Of importance was the evidence found for SWAP and rPMY induced IFN-gamma responses in predicting 'resistance'. It was noted that these associations were significant even after the effect of age and sex were accounted for in a multivariate analysis.

Recombinant paramyosin (rec-Sj-97) tested for immunogenicity and vaccine efficacy against Schistosoma japonicum in mice and water buffaloes

A primary vaccine candidate antigen against schistosomiasis is paramyosin (pmy), a myofibrillar protein found exclusively in invertebrates. Here we report the results of vaccine trials against the Asian schistosome undertaken on inbred and outbred mice and water buffaloes using a bacterially expressed and purified form of Schistosoma japonicum pmy (rec-Sj-97). Vaccination of the mice resulted in high levels of specific anti-pmy IgG antibodies when compared with adjuvant controls and significant reduction in worm burdens and in liver eggs. Furthermore, a significant reduction in liver eggs was recorded in two of the three water buffalo vaccine trials undertaken and, in all three trials, high levels of specific anti-pmy IgG antibodies were generated. There was no evidence of any toxic effects and the vaccine preparations and Quil A adjuvant were clearly well tolerated. The development of a vaccine intended for livestock animals such as bovines would be beneficial in two ways; directly by blocking transmission of schistosomiasis to humans and economically by contributing to healthier livestock. We are encouraged by the consistent efficacy in the mouse and the buffalo vaccine trials that resulted in a significant decrease in liver eggs. Indeed, predictions from mathematical models indicate that an egg reduction effect of 42-45% in buffaloes would be sufficient when combined with human treatment to control schistosomiasis japonica in the marshes and lakes along the middle and upper reaches of the Yangtze River, the most highly endemic areas for the disease in China.

Multi-epitope schistosome vaccine candidates tested for protective immunogenicity in mice

The major challenge in the development of anti-schistosome vaccines is to use defined antigens to stimulate an appropriate immune response that leads to resistance. Several promising candidate vaccine antigens including the glycolytic enzyme triose-phosphate isomerase (SmTPI), a 28 kDa glutathione-S-transferase (Sm28), the myofibrilar protein paramyosin (Sm97), an integral membrane protein (Sm23) and calpain (Smcalpain) have been characterised and their primary sequences derived for Schistosoma mansoni. Furthermore, sequences are available for synthetic peptides mimicking epitopes on these molecules capable of inducing schistosome-specific T- and B-cell responses. These schistosome vaccine candidates have generally been tested with varying degrees of success as single components, with only one report of the use of a multivalent antigen or multi-epitope approach. We describe the assembly of multiple defined and different epitopes of S. mansoni into a variety of single covalent structures; these included a DNA vaccine encoding different epitopes in tandem, the polyprotein itself that is encoded by this DNA and branched synthetic peptide epitope-based polymers in which the individual epitopes are pendant from an inert backbone. Each of the vaccine constructs examined, with the exception of the DNA vaccine, generated antibodies that were capable of binding to a tandem sequence of the epitopes. Although these results were encouraging, none of the constructs protected animals from subsequent challenge infection, indicating that the immune responses elicited were inadequate or inappropriate for parasite killing in vivo.

A vaccine against Asian schistosomiasis: the story unfolds

The development of an effective vaccine against the Asian schistosome is at a critical stage. Despite the fact that progress has been relatively slow, the successful use in animals of attenuated vaccines combined with recent encouraging results using defined native and recombinantly derived Schistosoma japonicum antigens, suggests that development of a safe and effective vaccine is feasible. This review examines current progress aimed at achieving this objective, and a summary is provided of recent results obtained with the most encouraging vaccine antigens. When available for wide-scale use, it is envisaged that the vaccine would be applied in the first instance, at least in China, in the veterinary context (to impact on human transmission) and then, perhaps, if required, clinically (to prevent or reduce disease). The search for the final product is likely to be demanding, and funding issues pertaining to Good Manufacturing Practice-scale-up of the vaccine for the required extensive veterinary coverage, and to support any future human trials, will need to be resolved. As such, we may still have to wait some time before the ultimate vaccine, possibly comprising a cocktail of several molecules, is available. Even then, the vaccine would probably be used optimally as one component of an integrated programme of schistosomiasis control that would include effective and well-tested approaches, such as health education and targeted chemotherapy.

Paramyosin is a major target of the human IgA response against Schistosoma japonicum

Human resistance and susceptibility to schistosomiasis is associated with age and specific antibody isotype responses against worm (SWAP) and egg (SEA) antigens. In a cross-sectional study of 176 individuals infected with Schistosoma japonicum in the Philippines, strikingly similar isotype response patterns against SWAP and SEA was observed when compared to other endemic areas. Interestingly, IgA titres to SWAP correlated with older age among S. japonicum-infected individuals (n = 176, P < 0.01), suggesting a role for this isotype in protective immunity. To identify the molecular targets of human IgA, 17 high-IgA/SWAP responders were identified from the said population. IgA antibodies from the majority (14/17) of these individuals recognized a band of 97 kDa (Sj97), comigrating in immunoblots with the myofibrillar protein paramyosin. The antigen was confirmed as paramyosin by expressed sequence tag (EST)-analysis of four clones obtained by screening an adult S. japonicum cDNA library with pooled IgA antisera and mouse antiparamyosin polyclonal antibodies. The identification of paramyosin as a major target of human IgA raises its potential as a vaccine candidate that targets mucosal immune responses. Since this antigen is exposed on the parasite surface only during the lung stages, we propose that human IgA contributes to parasite attrition during schistosome migration in the lungs.

The search for a vaccine against schistosomiasis--a difficult path but an achievable goal

The search for an effective vaccine against schistosomiasis, a parasitic disease currently affecting over 200 million people, remains a desirable but as yet challenging and elusive goal. Progress in the area has been relatively slow but research demonstrating the ability of humans to acquire natural immunity to schistosome infection, together with the successful use in animals of attenuated vaccines, supplemented with encouraging results obtained with defined antigens, suggests that development of a vaccine is achievable. Noteworthy also are recent immune correlate findings which shed light on the complex, putatively protective immune responses in humans, which have improved the prospects of success. With the first human clinical trial having been completed with a schistosome vaccine candidate, this review examines current progress aimed at achieving the objective of a safe and effective vaccine for widespread use against schistosomiasis. The review emphasises work undertaken in the author's laboratory and those of his chief collaborators in the search for a vaccine against schistosomiasis japonica, a disease of major public health significance in The People's Republic of China and The Philippines. Schistosomiasis vaccines should not be considered as the panacea for schistosomiasis control as, when available, it is generally envisaged that they would be used as one component of an integrated strategy complementing currently available and effective tools such as chemotherapy, improvements to sanitation, piped water supply, effective sewage draining and health education.

Generation, identification, and evaluation of expressed sequence tags from different developmental stages of the Asian blood fluke Schistosoma japonicum

Here we report 658 expressed sequence tags (ESTs) generated from the 5'-termini of clones randomly selected from directional cDNA libraries constructed from mRNAs from three developmental stages of Schistosoma japonicum. Putative identifications were assigned to 46. 2% of the ESTs; 6.4% were previously known from S. japonicum, 5.6% were previously known from S. mansoni, 34.2% were known from other organisms, and the remaining 53.8% may represent S. japonicum-specific genes. These 658 ESTs appeared to be derived from 457 unique genes, which together represent 2 to 3% of the 15,000 to 20,000 genes predicted to occur in the schistosome genome.

The vaccine efficacy of native paramyosin (Sj-97) against Chinese Schistosoma japonicum

One of the promising anti-schistosome vaccine candidates currently under investigation is paramyosin, a 97-kDa myofibrillar protein located in the muscles and tegument of schistosome worms. Here we describe the results of two vaccination/challenge experiments undertaken in mice using native paramyosin isolated from adult worms of a Chinese strain of Schistosoma japonicum. In both sets of experiments, a relatively low but consistent and significant reduction in worm burden was evident in mice vaccinated subcutaneously with S. japonicum paramyosin and Freund's adjuvant. In contrast, intraperitoneal vaccination of mice with Chinese strain S. japonicum paramyosin without adjuvant did not result in any reduction in worm numbers when compared with a saline control group. These data contrast with the impressive protection figures reported by another group who used a similar intraperitoneal vaccination protocol with native paramyosin extracted from Philippine strain S. japonicum.

The Role of Microscopy in the Investigation of Paramyosin as a Vaccine Candidate against Schistosoma japonicum

There has been growing interest in paramyosin as a vaccine component to combat schistosomiasis. Immunological and molecular techniques have been used in the past to investigate the effectiveness of a paramyosin vaccine as an anti-schistosomal treatment. However, recent localization studies at ultrastructural and morphological levels have highlighted a number of questions concerning the role of paramyosin within schistosome parasites. Debates about how a non-surface protein such as paramyosin might provide protection against schistosome infections have recently been addressed by microscopy results. Immunolocalization studies have indicated multiple functions of paramyosin within the parasite and provided insights into how a vaccine may target the parasite, as discussed here by Geoffrey Gobert.

A vaccine against the Asian schistosome, Schistosoma japonicum: an update on paramyosin as a target of protective immunity

Paramyosin from parasitic worms of the genus Schistosoma has shown promise as a vaccine target and it is one of the candidates selected by WHO for the development of a vaccine against schistosomiasis. Here we discuss the literature of the past decade and report on different recombinant paramyosin constructs we are using in our laboratory to develop a vaccine against the Asian schistosoma, Schistosoma japonicum.

Oral vaccination of mice with recombinant Schistosoma japonicum proteins induces specific anti-parasite antibodies and damage to adult worms after a challenge infection

Mucosal immunisation by the oral route represents a cheap and simple method for delivering protective antigens to a host against gastrointestinal and respiratory pathogens. In the case of schistosome (bloodfluke) worms, 2 life-cycle stages may be exposed to the host's mucosa; the larval schistosomulum is exposed to the respiratory mucosa and, depending on the species, the egg may come into contact with the intestinal or urinogenital mucosa. Both IgA and some Isotypes of IgG have been implicated in protective immunity against schistosomiasis in humans and in experimental animal models. We have used a novel approach to determine whether schistosome-specific antibodies and protective immunity could be generated in mice by oral administration of bacterial lysates containing recombinant Schistosoma japonicum proteins. The mice produced specific antibodies to paramyosin and GST26, 2 important vaccine candidates for schistosomiasis, but there was no significant reduction in worm burdens in groups of mice immunised with either protein. Significantly, however, transmission electron microscopy revealed damage to the teguments of adult female and male S. japonicum worms obtained from mice vaccinated with recombinant paramyosin; there was also extensive damage to the tegument of male worms recovered from mice vaccinated with recombinant GST26. Our observations that oral vaccination with bacterial lysates containing recombinant proteins induced particular classes and subclasses of circulating antibodies with resultant damage to the surface of adult worms may have important implications for the future development of oral vaccines against a systemic infection such as schistosomiasis.

Engineering and expression of a full length cDNA encoding Schistosoma japonicum paramyosin. Purification of the recombinant protein and its recognition by infected patient sera

A cDNA encoding the complete open reading frame of the Schistosoma japonicum paramyosin has been constructed and cloned. The 2600 bp cDNA was engineered by PCR using a N-terminally truncated paramyosin clone (pmy25) as template and a 57-mer primer that introduced the eight missing amino acids and matched the 5' sequence of pmy25 in conjunction with a pmy specific reverse primer. After cloning and expression, the recombinant protein was purified by affinity chromatography under non-denaturing conditions and was shown to have a molecular mass of 99 kDa which is equivalent to the expected size of the full length recombinant fusion protein, comprising the 97 kDa paramyosin plus an additional 2 kDa for the N-terminal fusion peptide incorporating the six histidine residues required for purification. In Western blot assays it reacted specifically with anti-paramyosin antibodies in sera from vaccinated animals and patients with Asian schistosomiasis. The engineering of the full-length cDNA encoding Schistosoma japonicum paramyosin, its bacterial expression and purification will facilitate future studies aimed at determining its efficacy as an anti-schistosomiasis vaccine.

Schistosomiasis vaccine development--the current picture

Development of a vaccine for schistosomiasis, a parasitic disease currently affecting over 200 million people worldwide, has been targeted as a priority by the World Health Organisation. Research demonstrating the ability of humans to acquire natural immunity to schistosome infection, together with the successful use of attenuated vaccines in animals both under laboratory and field conditions, suggest that development of a human vaccine is feasible. Attenuated vaccines for schistosomiasis are considered neither safe nor practicable for human use, however, and therefore other approaches must be considered. This review examines progress currently being undertaken in a number of different areas towards achieving the goal of a safe and effective human vaccine for schistosomiasis.