Abstract:
The present invention relates to helminthic derived antigenic material capable of inducing effective and long lasting protection against parasites, in particular to antigens that mediate protective immunity against helminths.

Description:
This is a continuation of application Ser. No. 08/178,555, filed on Jan. 6, 1994, which was abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to helminthic derived antigenic material capable of inducing effective and long lasting protection against parasites, in particular to antigens that mediate protective immunity against helminths. 
     Among the helminths, the digenetic trematodes or flukes, comprise over 100 families. The majority are comparatively harmless parasites living in the intestine and other organs of vertebrates and accordingly have received scant attention from applied parasitologists. Those trematodes which cause serious disease in man are the blood flukes or schistosomes and the liver flukes and lung flukes which are very important parasites that infect animals. 
     Fasciola the most important of the liver flukes is principally parasitic in domestic ruminants and is responsible for serious economic loss throughout the world (cattle, sheep and goats). 
     The main characteristic of the disease and one, which is responsible for pathology, morbidity and mortality of the mentioned animals, is the destruction of the host&#39;s liver tissue and damage to the bile ducts. Morbity is higher in young animals that are especially affected and become emaciated and die. Fasciola can also parasitize man, when given the opportunity and it is more frequent in Cuba and Latin America countries. Nevertheless, the true human liver fluke is another parasite, namely the Clonorchis sinensis, which is widespreach in China, Japan, Korea, Vietnam and India. Pathology is basically caused by thickening of bile duct walls and in severe cases cirrhosis of the liver and death. 
     Both Fasciola and Clonorchis gain entry passively as metacercariae ingested with food (herbage and raw fish for Fasciola and Clonorchis respectively) but their route of migration in the vertebrate&#39;s host body to the bile ducts differs. 
     While Clonorchis arrises in the bilary tree from the intestine through the ampulla of Vater, Fasciola migrates across the abdominal cavity, penetrating successively the intestine wall and liver parenchryma, causing more serious damage to host tissues. 
     As regards Fasciolosis in domestic animals, there are conflicting results and poor evidence to suggest that sheep or goats acquire immunity against Fasciola hepatica (Sinclair, 1967) after immunization with crude extracts. 
     There are also evidences to show that infection can persist for at least 11 years in experimentally infected sheep. (Durbin, 1952). It is also reported that very little or no reaction of the host against the parasite occurs; thus the survival of the sheep will depend entirely upon the number of metacercariae ingested (Boray, 1969). Cattle are considered to be more resistant: F. hepatica generally lives in this host from 9-12 months but it is the young calves that present the more severe clinical fasciolosis. 
     Several attempts have been made to identify immunoprophylatic antigens that could provide good basis for developing efficient vaccine against Fasciolosis. Basically two independent experimental strategies have ben pursed by several scientists based on: 1) immunity induced by irradiated live vaccines and 2) immunity induced by non-living vaccines. 
     Nevertheless, few attempts have been published on acquired resistance to Fasciola hepatica in calves using somatic fluke extracts (Ross. 1967; Hall and Lang, 1978, Hillyer, 1979) and they reported conflicting data. 
     Immunity induced by irradiated live vaccines has also showed frustrating results in experiments performed in mice, rabbits or sheep (Campbell et al., 1978, Hughes 1963); since there is no evidence of immunity developing in these animals following administration of irradiated metacercariae. 
     In addition, experiments with different extracts or excretory/secretory products from adult bile stage flukes were not immunogenic, providing that vaccinated animals presented low protection and pathological lesions in the liver parenchryma. 
     As reflected in the previous state of the art, it is expected that cattle would respond better to vaccination with non-living vaccines, but it was doubtful whether similar predictions could be made for sheep, on the basis of only mediocre protection induced by a number of different antigens in experimental animals. 
     The induction of protective immunity against F. hepatica by means of heterologous immunity has also been envisaged. Campbell et al (1977) showed that infection of sheep with Cysticercus tenuicollis, that is the metacestode stage of the dog tapeworn Taenia hydatigena, produced partial protection against F. hepatica, but Hughes et al. (1978), however, could not confirm this result. Other experiments were also unable to induce protection against Fasciola hepatica in experimental animals with this tapeworn. 
     Mice infected with bisexual adults of S. mansoni developed statistically significant resistance to F. hepatica and simultaneous infections with both parasites resulted in a reduced number of established schistosomes and reduced schistosome egg production per worm (Christensen et al. 1978). Calves infected with S. bovis also showed some resistance to F. hepatica and less pronounced liver tissue damage (Sirag et al. 1981). 
     Pelley and Hillyer, 1978, Hillyer and de Atica 1980, reported common antigens between F. hepatica and Schistosoma mansoni found in the Schistosoma egg. Another finding that indicates cross reactive immunity is the occurrence of false positive reactions in areas were both parasites are endemic. Hillyer, 1985 and Hillyer et al 1987, demonstrated also that a mixture of antigens derived from Fasciola hepatica can confer protection against subsequent infection with both F. hepatica and Schistosoma mansoni. 
     Schistosomisasis or Bilharzia is an ancient water-borne disease recorded by the Egyptians 4000 years ago and is today a world-wide public health problem estimated to afflict more than 200 million people in urban and peri-urban areas of the Third World. The three principal schistosomes infecting man are transmitted by freshwater snails and the free-swimming larvae, called cercariae, which are shed into the water and are able to penetrate host skin directly. After migration from the dermis through the lungs to the hepatic portal system, the schistosomes come to live in the small mesenteric or pelvic veins, where each female lays upwards of 100 eggs per day into the bloodstream. The host&#39;s immune reaction to those eggs which become lodged in the tissues is largely responsible for the chronic debilitating and often fatal disease. The extension of irrigation schemes, the construction of dams and the concentration of human populations are today contributing to the increase in the distribution and intensity of schistosome infection. Snail control and chemotherapy are the principal, but by no means satisfactory methods of control. An efficient vaccine would be the ultimate goal to aid considerably in the attempts to eradicate the disease. 
     A variety of host species can develop partial resistance to Schistosopma mansoni following prior infection or immunization with radiation attenuated cercariae (Smithers &amp; Doenhoff, 1982). The prior status of remission regarding the possibility to experimentally immunizing against S. mansoni infection (Clegg &amp; Smith, 1978) has been replaced by the current enthusiasm for the possibility of producing a defined and effective vaccine against this parasite with dead vaccines (Tendler, 1987). Nevertheless the major limitation remains the incomplete degree of protection achieved in animals in most experiments with purified and chemically defined parasite antigens. As described by several authors and reviewed by Smithers, 1982 there was a general consensus on the need to increase the level of protection induced by experimental immunoprophylaxis. However, the establishment of a good animal model for the development of an efficient vaccine against schistosomiasis, has been very hard to achieve. Progress is dependent on the identification and purification of highly effective antigenic molecules that would mediate protective immunity. (Schistosoma mansoni: Protective Antigens, M. Tendler--Mem. Inst. Oswaldo Cruz. Rio de Janeiro, Vol. 82, Suppl. IV: 125-128, 1987). 
     In previous studies on the search of antigens that mediate protective immunity against schistosomes, we reported on the use of a &#34;cocktail&#34; of schistosome components (called SE) early released during incubation of live and freshly perfused S. mansoni adult worm in phosphate buffered saline (Tendler &amp; Scapin, 1979; Kohn et al, 1979). Focusing on attempts to achieve protection against cercarial infection using as a vaccine, an experimental model was designed, in two different outbred animal hosts, the SW mouse and NZ rabbits, known to be fully susceptible and partially resistant to S. mansoni infection respectively. 
     In the New Zeland rabbit S. mansoni model, it was possible to establish a reliable pattern of percutaneous infections, with rather homogeneous adult worm loads, in terms of number and size of parasites and male/female ratios, for a long period after infection (Tendler, 1982, 1985, 1986). Recent evidence suggests that the use of the rabbit as an experimental host for S. mansoni may represent a new model of immunity for the disease (Almeida et al., 1987). 
     Immunization experiments performed in rabbits, with the SE mixture, resulted in very high levels of protection upon challenge (Scapin et al., 1980; Tendler, 1980; Tendler et al., 1982) (90% mean worm burden reduction in immunized animals compared to sex and age matched normal controls, when challenged simultaneously with the same number and pool of active cercariae from the --LE strain of S. mansoni). SW mice immunized with SE, have also shown to be significantly protected against challenge with normal cercariae and fully resistant to lethal infection (Tendler, 1986). To measure resistance, vaccinated and challenged animals, and the controls in parallel are submitted to hepatic and mesenteric perfusion for determination of adult parasite loads. The degree of protection is calculated by the difference in number of parasites recovered from control versus vaccinated animals (Tendler et al., 1982). 
     In the light of in vitro evidences that antibodies formed against different developmental stages of the parasite are effective in eosinophil or complement dependent cytotoxicity assays (Grzych et al., 1982; Smith et al., 1982), the characterization of antigens recognized by sera from demonstrably immune hosts, is used to identify antigenic molecules concerned with protective immunity (Bickle et al., 1986; Horowitz &amp; Arnon, 1985). Western blot experiments were undertaken to analyse the antibody response of SE vaccinated rabbits. Probing SE antigens with a panel of anti-sera derived from rabbits immunized by the same scheme (SE-FCA), the authors were able to demonstrate in immunoblots, two distinct patterns of recognition of SE antigens in these individuals. Interestingly, some SE antigens were restrictedly recognized only by anti-sera from almost fully protected rabbits. This finding enabled the authors to identify two subsets of antigens in SE; one common to all individual rabbit antisera, and a second subset restricted to highly protected animals. Those two patterns were respectively named Low and High protection patterns and used as &#34;differential&#34; antibodies. Taking advantage of these two patterns of recognition of SE components by polyclonal antibodies from rabbits that responded &#34;differentially&#34; to the same immunization scheme, (probably on account of individual variation, expected to occur in outbred populations), the strategy of screening cDNA libraries with those sera was applied. With the constraint of the incomplete understanding of critical mechanisms of protective response in both experimental and human schistosomiasis, screening procedures adopted by others frequently involved the use of infected human sera (&#34;putative&#34; immune or &#34;susceptible&#34; individuals of endemic areas  Carter &amp; Colley, 1986! or selected monoclonal or polyclonal sera from immunized animals  Lanar et al., 1986; Balloul et al., 1987!), that are directed against several non-characterized antigens. 
     In initial attempts towards the molecular cloning of potentially protective SE components, two cDNA libraries from whole adult worms of S. mansoni and S. japonicum constructed by Drs. Klinkert, University of Heidelberg and Donnelson/Henkle, Iowa University, respectively, were screened, with duplicate filters by differential screening. A parallel could be drawn with the results of immunoblots in that of two different sets of clones were detected, which presumably corresponds to the different in recognition by susceptible and resistant rabbit anti-SE sera. In additional experiments aiming at the identification of SE components, we compared in immunoblots, rabbit polyclonal anti-SE sera (High and Low protection) with a rabbit antiserum to purified schistosome paramyosin (kindly provided by Dr. A. Sher. NIH). This protein is a recently defined molecule, partially protective against S. mansoni challenge infection in inbred mice (Lanar et al., 1986), of Mr (x10 -3 )97, shown to be sensitive to proteolytic degradation to two major breakdown products of Mr (x10 -3 ) 95 and 78 (Pearce et al., 1986). 
     The 97/95/78 kD complex was recognized by both High and Low protection anti-SE sera and monospecific anti-paramyosin sera. The &#34;high&#34; protection anti-SE sera recognized in addition to paramyosin, other polypeptides which remained to be well characterized and assessed in terms of their protective activity and immunological role. The finding of paramyosin as a component of SE, reinforces previous indirect immunofluorescence studies performed on sections of adult schistosomes with rabbit anti SE sera, that reacted with eggs on the parasite surface and in between the muscle layers (Mendonca et al., 1987), in a similar fashion as demonstrated for paramyosin (Pearce et al., 1986). This finding, also paralleled results of immunoscreening of cDNA libraries performed, as mentioned above. Again, common paramyosin clones were isolated with both anti-paramyosin and anti-SE sera, with extra clones being recognized only by the latter rabbit sera (High protection). Among the other SE components of lower molecular weight, the 31/32 KD doublet, described as potential candidates for diagnosis of schistosomiasis (Klinkert et al., 1987) and recently identified as proteases located in the schistosome gut were also identified (Klinkert et al., 1988). These antigens and others which were identified in the saline extract showed a very low protection when tested. 
     The incubation of freshly perfused schistosomes in a chemically defined media (PBS) was aimed at the extraction of early released antigens from live adult worms (specially excretory/secretory products and tegumental components). This strategy was adopted in view of former frustrating attempts to induce consistent resistance against schistosomotic infection with different crude extracts of S. mansoni, that theoretically could be depleted of relevant function antigens. This premise was mainly influenced by the extraction procedures commonly adopted, that derived from the use of dead parasites. In fact, using SE emulsified in FCA (as preferential adjuvant) and administered by the subcutaneous/intradermal route, we achieve a high and long term duration protection in two experimental animals hosts against S. mansoni infection. The rational for the use of the rabbit model, unusual for protection trials, was to achieve &#34;tracking&#34; potentially protective and discrete antigens in a partially resistant host (to be further tested in susceptible hosts) that could therefore &#34;amplify&#34; the immune response and effector mechanisms of parasite killing since rabbits are a known potent antibody producer, they were envisaged as an important tool in this respect. 
     Studies on the induced immune response in vaccinated animals aiming at the identification of the functional relevant SE protective components, site and mechanisms of parasite death and protection markers, were the focus of our efforts in recent years, but less information on the molecular composition of SE, as well as on the identification and isolation of its protective components was available until recently. 
     The U.S. Pat. No. 4,396,600 issued on Aug. 2, 1983 in the name of Luigi Messineo &amp; Mauro Scarpin (according to Reexamination Certificate 461st B1 U.S. Pat. No. 4,396,000 issued on Feb. 11, 1986 it was cancelled) described an extract of adult Schistosome mansoni worms obtained by incubation in 0.15M sodium chloride-sodium phosphate buffer (pH 5.8) contains protein carboxydrates, and nucleic acid and or by-products of the latter component and resolves into four major fractions by gel chromatography in G-100 and G-200 Sephadex columns. Immunodiffusions tests with rabbit anti-total extract serum reveal three precipitation lines corresponding to fractions I and II and one with III or IV. Rabbits immunized with this total extract are found to be totally or partially (at least 77%) resistant to a challenge infection. The saline extract antigenic material is an effective vaccine for the treatment and immunization of schistosomiasis and other schistosome infection. 
     The official action mentioned above was based principally on two articles of the inventions and were used here as the principle of the present invention. Among the bulk of data that correspond to the background of present invention the most recent data were the cloning and sequencing of a SE derived component, identified as SM-14. 
     The most recent published study is &#34;A 14-KDa Schistosoma mansoni Polypeptide is Homologous to a gene family of fatty Acid Binding Proteins--The Journal of Biological Chemistry--vol. 266, No. 13, Issue of May 5, pp. 8447-8454, 1991; D. Moser, M. Tendler, G. Griffiths, and Mo-Quen Klinkert&#34;. This study describes the sequencing of the gene and the demonstration of the functional activity of the Sm-14 as a protein which binds lipids to the Sm-14 structure. 
     SUMMARY OF THE INVENTION 
     This invention relates to an antigen to confer protective immunity against helminthic infections of humans and animals and the process of vaccination for immunoprophylaxis of helminthological diseases of veterinarian and human medical interest. 
     The object of the present invention is a vaccine against the infection caused by Fasciola hepatica in cattle, goats and sheep. 
     Another object of the present invention is a vaccine against infection caused by Schistosome mansoni and all others species of Schistosoma which are responsible for infections and disease in humans and animals. 
     Still another object of the invention is a vaccine against infection caused by all species of helminths of medical and veterinary interest. 
     Further object of the present invention is the use of the rSm 14 in the diagnostic of Schistosomiasis and Fasciolosis. 
     An additional objective is a method for developing a vaccine against the human Schistosoma by using the same vaccinating antigen in the immunoprophylaxis of diseases caused by different parasite species which affect humans and various animals. 
     A further objective is the Sm-14 molecule which has a tri-dimensional structure defined according to the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawings will be provided by the Patent and Trademark Office upon request and payment of the necessary fee. 
     FIG. 1 shows a gel of the final antigen preparation (rSm 14 purification) in comparison with SE. 
     FIG. 2 shows the three dimensional structure of rSm 14 predicted by computer modelling. 
     FIGS. 3A, 3B, 3C and 3D show the evaluation of the level of protection of the rSm 14 according to experiment 1. 
     FIGS. 4A, 4B, 4C and 4D show the evaluation of the level of protection of the rSm 14 according to experiment 2. 
     FIGS. 5A, 5B, 5C and 5D show the evaluation of the level of protection of the rSm 14 according to experiment 3. 
     FIGS. 6A, 6B, and 6C show the evaluation of the level of protection of the rSm 14 according to experiment 4. 
     FIGS. 7A and 7B show the pooled results of experiments 1, 2, 3 and 4. 
     FIGS. 8A and 8B show the vaccination of Swiss mice with rSm 14 against infection with Fasciola hepatica. 
     FIG. 9 shows the liver of a non-vaccinated animal which was infected with Fasciola hepatica. 
     FIG. 10 also shows the liver of a non-vaccinated animal which was infected with Fasciola hepatica. 
     FIG. 11 shows the liver of a vaccinated animal which was infected with Fasciola hepatica. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The method for developing a vaccine against the human Schistosoma species by using the same vaccinating antigen in the immunoprophylaxis of diseases caused by different parasite species which affect humans and various animals can be described through the following steps: 
     achieving the isolation of a common cross reactive antigen (which according to the preferred embodiment of the present invention is the Sm-14) which is highly protective against both a disease of animals and humans; 
     testing this antigen as a vaccine for the immunoprophylaxis of the disease of animals in experimental and definite hosts for the parasite which causes the infection and/or the disease; 
     analysing the information derived from vaccination of the animal host, namely domestic ruminants, focusing all related questions and prerequisites for the final development of a vaccine against given human disease such as toxicology and pathology. 
     Using the method according to the present invention it is possible to find an antigen which is simultaneously highly effective as a vaccine against two parasitic diseases, of both domestic animals and humans. According to the preferred embodiment of the present invention the parasitic diseases of both domestic animals and humans are Fasciolosis and Schistosomiasis respectively, as well as other helminthic diseases which affect specifically humans as different animal species. 
     One of the antigens in the complex SE mixture, Sm-14, has been cloned and exhibits a significant homology with fatty acid binding proteins and also with Fh 15, a Fasciola hepatica antigen. This cross reactive antigen namely Sm-14, in its recombinant form--r Sm 14 confers protective immunity against both Schistosomiasis and Fasciolosis. 
     We will demonstrate here the ability of a recombinant form of Sm-14 to confer a high protection against Fasciola hepatica, Schistosoma mansoni, as well as all other species of Schistosoma and Echeinococcus and putatively other helminths that are pathogenic to humans and animals. The levels of protection achieved from experimental vaccination of hundreds of animals, have shown that Sm-14 is a major protective molecule derived from SE and is the candidate for both an anti-schistosome vaccine and anti-Fasciola vaccine. 
     The present invention will now be described in terms of, but not limited to, the examples. 
     EXAMPLE 1 
     The procedure for obtaining, characterizing and purifying the recombinant Sm-14 is described below: 
     Phase 1: 
     The transition from the protective saline extract (SE) to the molecular vaccine was achieved as follows: 
     a) A LE strain λgt 11 cDNA library (prepared from the adult worms of the LE endemic strain of Schistosoma mansoni) was screened with immune serum anti-SE derived from fully protected individuals (namely rabbits and rabbit &#34;High Protection&#34; serum as previously described in this document). 
     b) one species of cDNA clone recognized by rabbit anti--SE high protection serum that provide highly intense signals, was selected among others. 
     c) the sequence and characterization revealed the protein of 14 KDa named Sm 14 (the nucleotide and deduced amino acid sequence is the already published work of Moser, Tendler et al.). 
     A practical example of how to conduct the production of the cDNA clone is described in the state of the art. 
     Phase 2: 
     Expression of Sm 14 in an efficient vector system 
     The method to conduct this up to PDS-14 is described in the state of the art (A 14-KDa Schistosoma mansoni Polypeptide Is Homologous to a gene Family of Fatty Acid Binding Proteins, The Journal of Biological Chemistry, Vol. 266, No. 13, Issue of May 5, pp. 8447-8454, 1991.) as well as the identification and results of cloned cDNA sequence and it is incorporated here for reference. The cDNA encodes a polypeptide having the amino acid sequence of SEQ ID NO: 1. 
     Antiserum produced in rabbits immunized with the schistosome extract was used to screen the adult S. mansoni cDNA library (previously described). A clone designated Sm-14 was plaque-purified after three rounds of immunoscreening. The recombinant phage was lysogenized in E. coli Y1089 and induced to express a beta-galactosidase-Sm 14 fusion protein of 122 KDa. The protein was purified by preparation SDS-polyacrilamide gel electrophoresis, and antibodies to the fusion protein were raised in a rabbit. 
     The subcloning of Sm-14 and its expression in the present vector in which the trials of vaccination against Schistosoma and Fasciola were made are described below: 
     Excising the entire open reading frame encoding for Sm-14 from the original construct pDS--Sm-14 by cleavage with Bam HI and Himd III. 
     The obtained fragment was ligated into pGEMEX-1 (Promega) cleaved with the same enzymes. 
     Phase 3: 
     The resulting construct which in turn, resulted in the gene being in frame for expression as a fusion protein with the T7 gene 10 protein, under the control of a T7 RNA polymerase promoter, was used to transform E. coli strain BL 21 (DE 3) which contains the gene for T7 RNA polymerase under control of lacUV. The E. coli strain BL21 (DE3) was used for expression of recombinant protein. Other strains of E. coli may be alternatively employed for the same purpose, as well as other systems of expression, e.g. PDS-14 as already in the state of the art. 
     Phase 4: 
     Colonies containing the recombinant plasmid were grown overnight, and the expression of T7 RNA polymerase induced by the addition of IPTG during subsequent log phase growth. 
     This procedure resulted in the expression of a fusion protein with predicted molecular weight of 40 KDA (14 KDa from Sm-14 and 26 KDa from the gene 10 protein). 
     Phase 5: 
     The bacterial cells were collected by centrifugation (5000 rpm/10 min) and resuspended in a lysis buffer (50 mM Tris-HCl, pH 7.5, 2 mM EDTA, 1 mM DTT, 2 mg/ml lysozyme) and incubate on ice for 15 minutes. The lysates were then sonicated for two 30 second cycles and recentrifuged. The pellet was resuspended in a washing buffer (50 mM Tris-HCl, pH 7.5, 10 mM EDTA, 1 mM DTT, 0,5% Triton x-100) and centrifuged. 
     Phase 6: 
     Following a further round of resuspension and centrifugation the final pellet was resuspended in water. A SDS-PAGE was then run, the antigen purified by electroelution and stored at temperatures ranging from -70° C. to -200° C. until use. 
     FIG. 1 shows the degree of purity of rSM 14 and the high efficiency of the expression. 
     Analysis of polyacrylamide gel electrophoresis of total S. mansoni SE antigens and purified Sm-14 transferred to nitrocellulose paper. Lanes 1-3, SE and Sm-14 resolved in 10 and 15% SDS-PAGE respectively stained with C. blue. Lanes 2 and 4 immunoblot. Lane 2 was probed with polyclonal antiserum from a rabbit immunized with SE. Lane 4, rabbit anti-Sm-14 fusion protein antiserum. Standard molecular low markers are show in both side of the figure. 
     A following reference to FIG. 2 shows the three dimensional structure of Sm 14. 
     The computer modelling of the structure of Sm-14 according to the present invention is held on the basis of the known high homology of Sm-14 with proteins for which the crystal structure has been already determined. This gives a detailed and reliable three-dimensional structure of Sm-14 to be modelled by computer modelling. 
     The three-dimensional structure teaches that: (1) Sm-14 is a barrel shaped protein; (2) the fatty acid binds within the barrel; (3) the barrel is formed by ten beta pleated sheets; (4) the sheets are joined by shorts loops; (5) the loops exhibit divergence between members of the family of fatty acid binding proteins and is responsible for the antigenicity of Sm-14. 
     EXAMPLE 2 
     Example 2 includes experiments 1 to 4. The protocols of experiments 1 to 4 were carried out as described below, and they show the protective activity of SE and Sm-14 in Swiss mice. 
     The immunization protocols with SE (300 ug/ml per dose/animal) and Sm 14 fusion protein (10 ug/ml/dose) were performed with the following immunization protocol which consists of two doses of the antigen, with or without Freund&#39;s adjuvant, given to naive mice at intervals of seven days by subcutaneous injection followed by a booster dose 21 days after the second dose. The intervals between the application of the vaccinating doses can be varied. After an intervals of 60 days (which also can be varied, for example 45 days) the animals were challenged with 100 cercariae. 
     The overall protection for each group of animals (immunized challenged animals and respective controls) was calculated as follows: 
     
         C-V/C×100 
    
     where C=parasites recovered from controls; and, V=parasites recovered from vaccinated animals. 
     The results are shown in Table I. 
     Different control groups characterized by sex and age matched SW mice, simultaneously challenged with the same number and pool of S. mansoni cercariae, were used as infection controls for each individual experiment. These animals received only parallel injections of PBS (Phosphate Buffered Saline). Additional control groups for the fusion protein (gene 10) and the adjuvant (Freund&#39;s complete adjuvant) were also included. 
     In experiment 1, protective activity of rSm-14 with or without adjuvant (FCA) was analyzed in parallel to the activity of gene 10 protein, as can be observed in Table II. Mean worm burdens recovered from mice vaccinated with purified gene 10 protein, with or without FCA, were virtually the same as worm burden harvested from animals of PBS control group. 
     In experiment 2 the protective activity induced by rSm-14 and rSm-14 with FCA was assayed in comparison to vaccination with SE (with or without FCA). 
     Experiment 3 and 4 were designed to test the activity of the FCA alone and the reproductibility of protective activity induced by vaccination with rSm-14. 
     In all experiments the high capacity of rSm-14 to induce significantly high levels of immuno protection against further challenged infection of mice with S. mansoni is conclusively demonstrated. 
     Statistical analysis of presented data shows that worm burden recovered from the vaccinated groups is significantly lower (p&lt;0.05) than mean number of parasites harboured from non-vaccinated--infected animal. 
     EXAMPLE 3 
     This example shows a protective activity of SE and rSm-14 in rabbits. 
     The immunization protocols are the same as those used in Swiss mice in Example 2. The amounts of dose/animal are indicated in Table II. The rabbits were challenged with 1000 cercariae (instead of 100 as in Example 2). 
     Table II shows the capacity of rSm-14 to induce significantly high levels of immune protection against challenge infection of rabbits with S. mansoni. 
     Furthermore, this example makes clear the activity of rSm 14 as an isolated antigen in comparison with the SE mixture. 
     The results are shown in Table II. 
     EXAMPLE 4 
     This example demonstrates experiments 1 to 4 of Example 2 (which means that the same immunization protocols were used) but with a different methodology to evaluate protection. 
     This methodology is based on the establishment of vaccine-induced resistance, by means of a populational analysis of worm burdens frequencies through the distribution of worm burdens in a series of parasite ranges. 
     The results are shown in Table III. 
     According to Table III purified recombinant Sm-14 stimulated a level of protection that was not significantly different from that of intact SE as judged by mean levels of worm burden (Table 1). The levels of protection achieved with SE are consistent with previously published results. Of particular interest is the fact that a similar level of protection is achieved with or without adjuvant which bodies well for the use of the antigen in humans. In addition, the fact that we successfully protected groups of outbred Swiss mice with the antigen shows that genetic restriction of the immune system does not result in gross variations of the protective response. 
     As can be seen in Table III, completely different patterns of worm burden distribution were observed in the vaccinated versus non-vaccinated groups. Particularly striking is the difference in the number of mice in the group with 0-10 worms. Following a challenge infection of 100 cercariae/mouse none of the non-vaccinated mice had levels of infection in this range and peak of frequency (60%) for infected (non-vaccinated) animals was in the range of 21-30 worms. In contrast, the peak of frequency (64.5%) for mice vaccinated with either SE or Sm-14 fell within the range of 0-10 worms/mouse. 
     As can be seen, according to the present invention, it is of particular interest that essentially the whole of the protective effect of the complex SE mixture can be reproduced with this single antigen. Trials with other defined antigens derived from SE (glutathione-S-transferase and paramyosin) did not result in the same high level of protection. As mentioned above Sm-14 also has a significant level of homology with various fatty acid binding proteins. 
     The results shown in Table III of experiments 1 to 4 are demonstrated graphically in FIGS. 3 (3A, 3B, 3C and 3d) 6 (6A, 6B and 6C). 
     FIGS. 3 (3A, 3B, 3C and 3d) to 6 (6A, 6B and 6C) correspond to experiments 1 to 4. In these figures it is possible to evaluate the protection through the analysis of the population profiles of the worm burden of vaccinated versus non-vaccinated groups. 
     FIGS. 7A and 7B show pooled results. 
     EXAMPLE 5 
     In this Example vaccinated mice were challenged with 500 and 1000 cer./animal or challenged 2 or 3 times (100 cerc./animal/infection) with one week interval between each. As can be noted size and number of challenge infections is varied. 
     The protection induced by three 10 ug doses of protein (rSm 14) injected, remains higher than 50% against a 500 or 1000 cerc./animal single challenge infection. The same effect is observed when the 100 cerc./animal challenge infection is repeated two or three times keeping a one week interval between each one. 
     The protocols for this Example are as follows. 
     The data of Example 5 are summarized in Tables IV and V, respectively. 
     EXAMPLE 6 
     To demonstrate the reactivity of sera from schistosomiasis patients against fatty acid binding protein from Schistosoma mansoni--rSm-14, the Example is carried out as follows. 
     The sera from human patients from a Brazilian endemic area and sera from young men living out of the endemic area is tested by immunobloting against the recombinant Sm-14 antigen. Patients are classified in groups according to clinical form and eggs are counted. Parsitological diagnosis is achieved by Kato-Katz method. 
     The results show that sera from all infected individuals recognized rSm-14 in immunobloting, independently of age, worm burden or clinical form, thus reflecting the immunogenicity of rSm-14. 
     EXAMPLE 7 
     This Example shows the vaccination of Swiss mice with rSm-14 against infection with Fasciola hepatica and complete protection achieved against Fasciolosis. 
     Example 7 was carried out as follows. 
     Two groups of 15 mice were immunized with rSm-14 with or without adjuvant. The protocol of vaccination is: (a) two weekly injections of antigen (10 ug/dose/animal rSm 14) emulsified or not in FCA (adjuvant); (b) applying a new dose of injection of antigen three weeks later; and, (c) forty five days after the third dose they were challenged with three Fasciola hepatica metacercariae and sacrificed thirty days after infection. 
     This Example shows cross-reactive protective antigens between different helminths as Schistosomes and Fasciola hepatica. 
     It was recently reported that an antigen named FSh15 cloned from the related parasite, the liver fluke Fasciola hepatica, has significant level of homology at the level of predicted amino acid sequence with Sm-14 and present results showing Sm 14 to be the homologue of this protein in Fasciola hepatica. 
     Recombinant Sm-14 was thus tested as a vaccinating antigen against Fasciola hepatica infection as described in this Example. 
     References to FIGS. 9, 10 and 11 will follow, showing the liver of non-vaccinated (FIGS. 9 and 10) versus vaccinated animals (FIG. 11). 
     After the parasitological test to evaluate the infection by the Fasciola hepatica of the rSm 14 vaccinated and non-vaccinated (controls) animals, subjected to the same infection with three metacercarie/mouse, the liver, intestines and other organs were examined by classical histological processes to evaluate the pathology which developed in the animals of the two groups. It should be pointed out that mainly the liver and the intestines are the most affected organs by the Fasciola hepatica and, therefore, they were extensively examined. 
     Thus, thirty days after oral infection by the classical method with three metacercarie of Fasciola hepatica per mouse, the animals were sacrificed for an evaluation of the infection burden acquired in the presence of the previous vaccination with rSm 14 as compared to non-vaccinated animals. The organs were fixed in Milloning solution, cut, stained by the Hematoxylin-Eosin technique, and examined under the optical microscope. 
     It is conclusively demonstrated by means of FIGS. 8A, 8B, 9, 10 and 11 that rSm-14 is capable of inducing protection against Fasciola hepatica infection on the basis of parasitological and anatomopathological data. Out of the rSm-14 vaccinated animals virtually no individual acquired the infection, after exposure to three (maximum dose allowed for mice) metacercarie of Fasciola hepatica. On the contrary all non-vaccinated control animals became infected after the same exposure. 
     From the anatomopathological point of view, the liver parenchryma of all individuals that were vaccinated with rSm-14 did not show any alteration related to Fasciola hepatica infection except for small fibrotic areas at the level of Glisson capsule. This finding shows that the challenging parasites have been killed by effect of vaccination, very early in their life cycle at the vertebrate host. On the contrary all the non vaccinated/infected animals exhibited extensive areas of destruction of hepatocytes with severe hemorragical regions that were extensive until Glisson capsule. 
     As can be seen in FIGS. 9 and 10 extensive destruction of parenchryma was observed together with the presence of the adult parasites in several individuals. 
     
                       TABLE I______________________________________PROTECTIVE ACTICITY OF SE AND rSm 14 IN SWISS Mice Immunization                    Protection Antigen ( 3 doses)               n.sup.o  of mice                        Worm Burden                                 %______________________________________Exp 1.: 10 ug Sm 14 + FCA               20       12.1     50.6 10 ug Sm 14   19       9.9      59.6 10 ug Gene 10 + FCA               22       28.4     0 10 ug Gene 10 22       27.7     0 PBS           12       24.5     0Exp 2.: 300 ug SE + FCA               21       7.8      72.1 300 ug SE     20       12.9     53.9 10 ug Sm 14 + FCA               10       9.6      65.7 10 ug Sm 14   14       13.6     51.4 PBS           8        28.0     0Exp 3.: 300 ug SE + FCA               11       11.6     56.7 300 ug FCA    10       25.9     0 10 ug Sm 14 + FCA               11       10.1     62.3 10 ug Sm 14   12       8.6      67.9 PBS           8        26.8     0Exp 4.: 300 ug FCA    10       23.2     0 10 ug Sm 14 + FCA               9        10.1     64.0 10 ug Sm 14   9        12.5     55.3 PBS           7        28.0     0______________________________________ 
    
     
                       TABLE II______________________________________PROTECTIVE ACTICITY OF SE AND rSm 14 IN RABBITS(NEW ZEALAND)Immunization Number of            ProtectionAntigen + FCA 3 doses        rabbits    X = sem   (%)______________________________________600 ug SE + FCA        4          7.4 ± 3.9                             9380 ug Sm 14 + FCA        4          12.0 ± 4.1                             89Control      4          109.5 ± 11.0______________________________________                             -- 
    
     
                                           TABLE III__________________________________________________________________________Protective Activity of rSm 14 in outbred miceDistribution of Worm Burden Frequency__________________________________________________________________________Experiment 1Worm Burden  Sm14 + FCA         Sm 14   Gene 10 + FCA                         Gene 10                                Control (PBS)__________________________________________________________________________0-10   65.0   57.9    --      --     --11-20  20.0   31.6    4.5     --     19.721-30  15.0   10.5    59.1    68.2   61.731-40  --     --      31.8    27.3   10.541     --     --      4.5     4.5    8.1N = mice/gp  20     19      22      22     88Experiment 2  SE + FCA         SE      Sm14 + FCA                         Sm14   Control (PBS)__________________________________________________________________________0-10   76.2   40.0    60.0    35.7   --11-20  23.8   55.0    40.0    64.3   19.721-30  --     5.0     --      --     61.731-40  --     --      --      --     10.541     --     --      --      --     8.1N = mice/gp  21     20      10      14     88Experiment 3  SE + FCA         FCA     Sm14 + FCA                         Sm14   Control (PBS)__________________________________________________________________________0-10   77.8   --      63.6    66.7   --11-20  11.1   40.0    36.4    33.3   19.721-30  11.1   30.0    --      --     61.731-40  --     30.0    --      --     10.541     --     --      --      --     8.1N = mice/gp  9      10      11      12     88Experiment 4  FCA    Sm14 + FCA                 Sm14    Control (PBS)__________________________________________________________________________0-10   --     44.4    22.2    --11-20  40.0   44.4    77.8    19.721-30  30.0   11.2    --      61.731-40  30.0   --      --      10.541     --     --      --      8.1N = mice/gp  10     9       9       88__________________________________________________________________________ 
    
     
                                           TABLE IV__________________________________________________________________________PROTECTIVE ACTIVITY OF rSm IN OUTBRED MICE AS A FUNCTION OFVARIATION OF CHALLENGE INFECTIONVACCINATION WITH Sm14 + FCA AGAINST DIFFERENT INFECTIONS           NUMBER OFGROUPS NUMBER OF MICE           CERCARIAE/MICE                     X ± SEM                           PROTECTION (%)__________________________________________________________________________1     20        1.000       58 ± 13.2                           65.9CONTROL 20        1.000       170 ± 15.0                           --2     20          500     31.5 ± 2.3                           49.7CONTROL 20          500     62.6 ± 2.1                           --__________________________________________________________________________ IMUNIZATION SCHEME: X3 DOSES: 10 μg OF rSm14 + FCA WITH 1 WEEK INTERVAL, CHALLENGE INFECTION, 45 DAYS AFTER THE LAST VACCINATION DOSE. P &lt; 0.05 
    
     
                                           TABLE V__________________________________________________________________________PROTECTIVE ACTIVITY OF rSm 14 IN OUTBRED MICE AS A FUNCTIONOF MULTIPLE CHALLENGE INFECTIONS.VACCINATION WITH SM14 + FCA AGAINST DIFFERENT INFECTIONS           NUMBER OFGROUPS NUMBER OF MICE           CERCARIAE/MICE                     X ± SEM                           PROTECTION (%)__________________________________________________________________________1     20        100        11.2 ± 1.09                           65.9CONTROL 20        100       27.2 ± 2.2                           --2     20        100 (X2)  33.0 ± 1.7                           57.3CONTROL 20        100       52.6 ± 1.5                           --3     20        100 (X3)  42.3 ± 2.3                           59.2CONTROL 20        100       47.3 ± 3.3                           --__________________________________________________________________________ IMUNIZATION SCHEME: X3 DOSES: 10 μg OF rSm14 + FCA WITH 1 WEEK INTERVAL, CHALLENGE INFECTION, 45 DAYS AFTER THE LAST VACCINATION DOSE. P &lt; 0.05 
    
     
         __________________________________________________________________________SEQUENCE LISTING(1) GENERAL INFORMATION:(iii) NUMBER OF SEQUENCES: 1(2) INFORMATION FOR SEQ ID NO:1:(i) SEQUENCE CHARACTERISTICS:(A) LENGTH: 133 amino acids(B) TYPE: amino acid(C) STRANDEDNESS: single(D) TOPOLOGY: linear(ii) MOLECULE TYPE: PROTEIN(xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:MetSerSerPheLeuGlyLysTrpLysLeuSerGluSerHisAsnPhe151015AspAlaValMetSerLysLeuGlyValSerTrpAlaThrArgGlnIle202530GlyAsnThrValThrProThrValThrPheThrMetAspGlyAspLys354045MetThrMetLeuThrGluSerThrPheLysAsnLeuSerCysThrPhe505560LysPheGlyGluGluPheAspGluLysThrSerAspGlyArgAsnVal65707580LysSerValValGluLysAsnSerGluSerLysLeuThrGlnThrGln859095ValAspProLysAsnThrThrValIleValArgGluValAspGlyAsp100105110ThrMetLysThrThrValThrValGlyAspValThrAlaIleArgAsn115120125TyrLysArgLeuSer130__________________________________________________________________________