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

Investigation of recombinant Schistosoma japonicum paramyosin fragments for immunogenicity and vaccine efficacy in mice

Schistosoma japonicum paramyosin, a 97 kDa myofibrillar protein, is a recognized vaccine candidate against schistosomiasis. To improve its expression and to identify protective epitopic regions on paramyosin, the published Chinese Schistosoma japonicum paramyosin cDNA sequence was redesigned using Pichia codon usage and divided into four overlapping fragments (fragments 1, 2, 3, 4) of 747, 651, 669 and 678 bp, respectively. These gene fragments were synthesized and expressed in Pichia pastoris (fragments 2 and 3) or E. coli (fragments 1 and 4). The recombinant proteins were produced at high level and purified using a two-step process involving Ni-NTA affinity chromatography and gel filtration. BALB/c mice were immunized subcutaneously three times at 2-week-intervals with the purified proteins formulated in adjuvant Quil A. The protein fragments were highly immunogenic, inducing high, though variable, ELISA antibody titres, and each was shown to resemble native paramyosin in terms of its recognition by the anti-fragment antibodies in Western blotting. The immunized mice were subjected to cercarial challenge 2 weeks after the final injection and promising protective efficacy in terms of significant reductions in worm burdens, worm-pair numbers and liver eggs in the vaccinated mice resulted. There was no apparent correlation between the antibody titres generated and protective efficacy, as all fragments produced effective but similar levels of protection.

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.

Purification, characterization, and immunolocalization of paramyosin from the adult stage of Fasciola hepatica

Paramyosin, a vaccine candidate in different helminthiases, was purified from the adult liver fluke Fasciola hepatica using two different procedures. The first started with a crude extraction of paramyosin in high-salt buffer followed by gel filtration chromatography and two precipitation-solubilization cycles; in the second, anion exchange chromatography replaced the gel filtration step. In both cases, the apparent molecular weight of the purified protein determined by sodium dodecyl sulfate gel electrophoresis under reducing and non-reducing conditions was 97 kDa and 200 kDa, respectively. The molecular weights were consistent with the presence of a dimeric protein linked by disulfide bridges. Western blot analysis showed that the dimeric and monomeric forms were both recognized by an antiserum raised against the F. hepatica 97 kDa band (alpha-FhPmy), and by an anti- Schistosoma mansoni paramyosin immune serum. Immunohistochemistry using alpha-FhPmy demonstrated the localization of paramyosin within the subtegumental muscle and in muscle cells surrounding the gut of adult parasites. We also observed labeling of extramuscular structures like testes, surface lamellae of the gut and the tegument of adult flukes.

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.

Receptor for Fc on the surfaces of schistosomes

Schistosoma mansoni masks its surface with adsorbed host proteins including erythrocyte antigens, immunoglobulins, major histocompatibility complex class I, and beta(2)-microglobulin (beta(2)m), presumably as a means of avoiding host immune responses. How this is accomplished has not been explained. To identify surface receptors for host proteins, we biotinylated the tegument of live S. mansoni adults and mechanically transformed schistosomula and then removed the parasite surface with detergent. Incubation of biotinylated schistosome surface extracts with human immunoglobulin G (IgG) Fc-Sepharose resulted in purification of a 97-kDa protein that was subsequently identified as paramyosin (Pmy), using antiserum specific for recombinant Pmy. Fc also bound recombinant S. mansoni Pmy and native S. japonicum Pmy. Antiserum to Pmy decreased the binding of Pmy to Fc-Sepharose, and no proteins bound after removal of Pmy from extracts. Fluoresceinated human Fc bound to the surface, vestigial penetration glands, and nascent oral cavity of mechanically transformed schistosomula, and rabbit anti-Pmy Fab fragments ablated the binding of Fc to the schistosome surface. Pmy coprecipitated with host IgG from parasite surface extracts, indicating that complexes formed on the parasite surface as well as in vitro. Binding of Pmy to Fc was not inhibited by soluble protein A, suggesting that Pmy does not bind to the region between the CH2 and CH3 domains used by many other Fc-binding proteins. beta(2)m did not bind to the schistosome Fc receptor (Pmy), a finding that contradicts reports from earlier workers but did bind to a heteromultimer of labeled schistosomula surface proteins. This is the first report of the molecular identity of a schistosome Fc receptor; moreover it demonstrates an additional aspect of the unusual and multifunctional properties of Pmy from schistosomes and other parasitic flatworms.

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.

Protective immunity induced by the full-length cDNA encoding paramyosin of Chinese Schistosoma japonicum

The full-length cDNA encoding paramyosin of Chinese S. japonicum (Sjc97) has been cloned and sequenced for the first time. The homology of the nucleotide sequence of paramyosin and the deduced amino acid sequence between Chinese, Philippine, Japanese strains and S. mansoni (Sm97) were 99.7, 99.8 and 96% at amino acid level, respectively; 99.4, 99.2 and 91% at nucleotide level, respectively. The immunogenicity and protective efficacy of a DNA vaccine encoding Sjc97 was evaluated in C57BL/6 mice. Mice immunized intramuscularly with pCMV-Sjc97 resulted in predominantly IgG2a and IgG2b immune responses, and immune sera were able to mediate antibody-dependent macrophage mediated cytotoxicity in vitro. Cytokine profiles in immunized C57BL/6 mice demonstrated Th1 bias, with IFN-gamma and IL-2 production and lack of IL-4 and IL-5. Immunization with pCMV-Sjc97 conferred a significant level of protection against cercariae in C57BL/6 mice. These results demonstrate that the nucleic acid encoding Sjc97 was able to induce a Th1 type immune response and confer protective efficacy in C57BL/6 mice when administrated via the intramuscular route.

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.

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.

Production of interleukin-10 by peripheral blood mononuclear cells from residents of a marshland area in China endemic for Schistosoma japonicum

Interleukin-10 (IL-10) cytokine production was assessed using peripheral blood mononuclear cells (PBMC) from 67 individuals living in an area endemic for schistosomiasis japonica in China (Dongting Lake, Hunan Province), and 11 control subjects from a non-endemic part of the same Province. Production of IL-10 was measured following in vitro stimulation of PBMC using whole parasite extract (SWAP) or a panel of recombinant Schistosoma japonicum antigens (22-kDa tegumental membrane-associated antigen, glyceraldehyde-3-phosphate dehydrogenase, paramyosin, 14-kDa fatty acid-binding protein and 28-kDa glutathione S-transferase) which are of recognized interest in the development of protective immunity to schistosomiasis. Significantly, PBMC isolated from the exposed population compared with the non-exposed population produced higher levels of IL-10. There was a trend towards higher mean levels of IL-10 release in putatively resistant (insusceptible) (consistently egg negative but highly exposed) individuals compared with susceptible (egg-positive) subjects from the exposed population. Analysis of individual exposure (the duration of water contact and the percent body surface area in contact with water, expressed as m2 h/day) vs. IL-10 production indicated a weak but consistent and statistically significant inverse correlation, with lower levels of exposure being associated with higher levels of IL-10. These results suggest an association between IL-10 production and resistance to S. japonicum in subjects from this Chinese population exposed to infection.

Antibody isotype responses, infection and re-infection for Schistosoma japonicum in a marshland area of China

Antibody isotype responses to adult worm antigen (AWA) of Schistosoma japonicum and two recombinant proteins (paramyosin (PMY) and a 22 kDa tegumental membrane-associated antigen (TEG)) were analyzed in 137 individuals from an area moderately endemic for schistosomiasis in the Dongting Lake region, Hunan Province, China. The prevalence and geometric mean (GM) intensity of infection before the implementation of curative chemotherapy were 28.5% and 234.4 epg, respectively, but 9 months after treatment the prevalence (6.6%) and intensity (38.3 epg) had decreased. There was no significant difference in either the prevalence or intensity of infection between males and females. Specific IgG (total), IgG4, IgG2, IgA and IgE responses to AWA, PMY and TEG were measured by ELISA. Males produced significantly (P < 0.05) more anti-AWA total IgG, IgE, IgA, IgG4 and IgG2 antibodies, and anti-TEG IgG2 antibody than their female counterparts. The OD450 levels of anti-AWA, PMY and TEG antibody isotypes did not present clear age-dependent trends except for peak levels of anti-AWA IgG4 antibodies evident among subjects 20-29 years of age. The total IgG and IgG4 antibody profiles against AWA correlated well with current S. japonicum infections while anti-AWA IgG2, IgA and IgE antibodies did not show such an association. Anti-AWA-specific IgE antibody levels were positively correlated (r = 0.55) with anti-AWA specific IgG4 antibody levels. In addition, the overall percentage of responders (using a cut-off value obtained from normal controls) to all isotypes to AWA were higher than those observed for both the recombinant antigens. Only 18.2%, 16.8% and 7.3% of the study population were IgE responders to AWA, PMY and TEG. A longer follow-up period is required before we can more fully understand the role of IgE, if any, in protective immunity against schistosomiasis japonica.

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.

Differential antigen-stimulated proliferation of human mononuclear cells by recombinant Schistosoma japonicum antigens in a Chinese population

Peripheral blood mononuclear cells (PBMC) from 117 individuals living on two islands in an area (Dongting Lake) endemic for schistosomiasis japonica in China, and 15 control individuals from a non-endemic area of China, were assessed for antigen-stimulated proliferation against five recombinant Schistosoma japonicum antigens of recognized interest in the development of immunity to schistosomiasis. Two recombinant antigens, paramyosin and 28-kD glutathione-S-transferase, stimulated cellular proliferation (stimulation index > or = 3.0) in 38.5% and 42.5% of subjects, respectively, a level similar to that induced by a soluble whole parasite extract (51.3%). In contrast, three other recombinant antigens tested--a fatty acid binding protein, 22-kD tegumental membrane-associated antigen, and glyceraldehyde-3-phosphate dehydrogenase--stimulated PBMC proliferation in only 3-8% of subjects. Moreover, we also identified a positive association between the degree of exposure, and cellular proliferation following stimulation with recombinant paramyosin or whole parasite extract. Highly significant differences in antigen-stimulated proliferation were also observed between the two islands, Niangashan and Qingshan. The whole parasite extract stimulated proliferation in 90% of subjects from Niangashan island compared with only 42.1% of subjects from Qingshan island (chi2 = 16.88, P = 0.00004), while glutathione-S-transferase stimulated proliferation in 77.3% of subjects from Niangashan island compared with only 34.7% of subjects from Qingshan island (chi2 = 13.09, P = 0.003). A similar, but not significant, trend was observed for paramyosin and the fatty-acid binding protein. The identification of differential cellular proliferative responses to specific schistosome antigens within an infected human population may have important practical implications for vaccine development against schistosomiasis japonica.

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.