Two epitopes shared by Taenia crassiceps and Taenia solium confer protection against murine T. crassiceps cysticercosis along with a prominent T1 response

Vaccination against cestode parasites: anti-helminth vaccines that work and why

Highly effective recombinant vaccines have been developed against the helminth parasites Taenia ovis, Taenia saginata and Echinococcus granulosus. These vaccines indicate that it is possible to achieve a reliable, high level of protection against a complex metazoan parasite using defined recombinant antigens. However, the effectiveness of the vaccines against the taeniid cestodes stands in contrast to the more limited successes which characterise attempts to develop vaccines against other platyhelminth or nematode parasites. This review examines the features of the host-parasite relationships among the taeniid cestodes which have formed the basis for vaccine development. Particular consideration is given to the methodologies that have been used in making the cestode vaccines that might be of interest to researchers working on vaccination against other helminths. In developing the cestode vaccines, antigens from the parasites' infective larval stage contained within the egg (oncosphere) were identified as having the potential to induce high levels of protection in vaccinated hosts. A series of vaccination trials with antigen fractions, and associated immunological analyses, identified individual protective antigens or fractions. These were cloned from cDNA and the recombinant proteins expressed in Escherichia coli. This strategy was independently successful in developing vaccines against T. ovis and E. granulosus. Identification of protective antigens for these species enabled rapid identification, cloning and expression of their homologues in related species and thereby the development of effective vaccines against T. saginata, E. multilocularis and, more recently, T. solium. The T. saginata vaccine provides an excellent example of the use of two antigen components, each of which were not protective when used individually, but when combined they induce a reliable, high level of protection. One important contributing factor to the success of vaccine development for the taeniid cestodes was the concentration on studies seeking to identify native host-protective antigens, before the adoption of recombinant methodologies. The cestode vaccines are being developed towards practical (commercial) application. The high level of efficacy of the vaccines against T. solium cysticercosis and hydatid disease suggests that they would be effective also if used directly in humans.

Th1 and Th2 indices of the immune response in pigs vaccinated against Taenia solium cysticercosis suggest various host immune strategies against the parasite

Kinetics of the production of serum antibody levels and Th1 (IL-2, IFN-gamma) and Th2 (IL-4, IL-10) cytokines was studied in five pigs vaccinated with a synthetic tri-peptide vaccine (S3Pvac) against Taenia solium, a vaccine that has been shown protects pigs against naturally acquired infection. Healthy pigs of mixed genetic background, similar to those bred in rural villages of Mexico, were vaccinated with S3Pvac or with adjuvant alone, kept in sanitary conditions and bled at different times after vaccination to study the development of their specific immune response. Peripheral blood mononuclear cells (PBMCs) of vaccinated pigs showed a significant increment in the production of Th1 cytokines (IL-2 and IFN-gamma) but not of Th2 cytokines (IL-4 and IL-10) after specific PBLs stimulation with all the individual peptides. A Th1-inclined cytokine profile leading to an exacerbated local inflammation at the early installation stage of the cysticercus may possibly interfere with their successful establishment in the serum antibodies against total cysticercus antigens and against each of the three different peptides comprising S3Pvac were detected 7-51 days after vaccination. Antibodies against GK-1 interfered with the cysticerci development into intestinal tapeworms in prednisolone-treated hamsters. The sub-lethal crippling effect of anti-GK-1 antibodies upon cysticerci indicates to a therapeutic application of S3Pvac in infected pigs having potential epidemiological consequences, as it could aid in decreasing the number of tapeworms expected to develop from the few cysticerci that survive in the vaccinated pigs.

Vaccines for prevention of cysticercosis

Neurocysticercosis due to Taenia solium infection is an important cause of human morbidity and mortality. Despite the availability of effective anthelmintics, the disease remains prevalent in many parts of the world and there is a need for new and improved measures for control of the infection. An effective vaccine to prevent infection in pigs, the parasite's natural intermediate host, would be a valuable new option to assist with T. solium control. Several approaches are being used currently towards the development of a T. solium vaccine and these approaches are reviewed briefly, with emphasis on the use of recombinant oncosphere antigens. Highly effective vaccines have been developed against cysticercosis in sheep and cattle caused by Taenia ovis and Taenia saginata, respectively. This success has encouraged the adoption of a similar strategy for T. solium. The recent finding that one oncosphere antigen, TSOL18, can induce complete protection against T. solium infection in pigs, highlights the potential for development of a practical vaccine. A vision is proposed for the development of a safe, effective, inexpensive vaccine for pigs, which can be administered in an edible form. Through an international collaborative effort, research is progressing towards the realisation of such a vaccine and its use to reduce the global burden of neurocysticercosis.

Immune response and protection elicited by DNA immunisation against Taenia cysticercosis

The study evaluated DNA vaccination in Taenia solium cysticercosis prevention by using cDNA of an antigen (cC1) from T. solium metacestode. pcDNA3-cC1 DNA vaccine was constructed by inserting the cDNA into the eukaryotic expression plasmid pcDNA3. Positive expression of the pcDNA3-cC1 product was confirmed by its transfection into COS7 cell and enzyme-linked immunoabsorbent assay using serum of pigs infected with T. solium metacestode. Immunisation of BALB/c mice with three injections of pcDNA3-cC1 induced antigen-specific immune responses of the Th1 phenotype. Inoculation of new-born pigs induced protection against challenge with T. solium by 73.3% reduction of the metacestode number. Antibodies elicited by DNA immunisation with pcDNA3-cC1 specifically reacted with native cC1 protein, which was mainly restricted to the cyst wall of T. solium metacestode. Positive apoptosis signals were also detected in the cyst wall cells of metacestode slices from pigs immunised with pcDNA3-cC1 by TUNEL staining method. Those suggested that apoptosis played a role in protecting pigs immunised with pcDNA3-cC1 nucleic acid vaccine from pathogen challenge.

Protective immunity against Taenia crassiceps murine cysticercosis induced by DNA vaccination with a Taenia saginata tegument antigen

This study investigated the protective capacity of the recombinant Taenia saginata Tso18 antigen administered as a DNA vaccine in the Taenia crassiceps murine model of cysticercosis. This Tso18 DNA sequence, isolated from a T. saginata oncosphere cDNA library, has homologies with Taenia solium and Echinococcus sp. It was cloned in the pcDNA3.1 plasmid and injected once intramuscularly into mice. Compared to saline-vaccinated control mice, immunization reduced the parasite burden by 57.3-81.4%, while lower levels of non-specific protection were induced in control mice injected with the plasmid pcDNA3.1 (18.8-33.1%) or a plasmid with irrelevant construct, pcDNA3.1/3D15 (33.4-38.8%). Importantly, significant levels of protection were observed between the pcDNA3.1/Tso18 plasmid and pcDNA3.1/3D15 plasmid immunized mice. Mice immunized with pTso18 synthesized low levels of, primarily IgG1 sub-class, antibodies. These antibodies were shown to recognize a 66 kDa antigen fraction of T. crassiceps and T. solium. Splenocytes enriched in both CD4+CD8- and CD4-CD8+ T cells from these vaccinated mice proliferated in vitro when exposed to antigens from both T. solium and T. crassiceps cestodes. Immunolocalization studies revealed the Tso18 antigen in oncospheres of T. saginata and T. solium, in the adult tapeworm and in the tegument of T. solium cysticerci. The protective capacity of this antigen and its extensive distribution in different stages, species and genera of cestodes points to the potential of Tso18 antigen for the possible design of a vaccine against cestodes.

Inhibition of p-450 aromatase prevents feminisation and induces protection during cysticercosis

Cysticercotic male mice undergo an impressive feminisation process, characterised by 200 times increased serum 17beta-estradiol levels while testosterone and dihydrotestosterone are 90% reduced, which results in elevated parasite burden. Administration of Fadrozole (an aromatase inhibitor) in male and female mice suppressed the production of 17beta-estradiol, accompanied with a 70% reduction in parasite burden. This protective effect was associated in male mice with a recovery of the specific cellular immune response. Interleukin-6 (IL-6) serum levels, and its production by splenocytes, was augmented by 80%, together with a 10-fold increase in its expression in testes of infected male mice. Fadrozole treatment returned these levels to baseline values. Aromatase expression in the testes of infected male mice was not affected by Fadrozole. These results suggest that aromatase and IL-6 are key molecules in the production of the feminisation undergone by infected male mice and to Fadrozole treatment as a possible new therapeutic approach to cysticercosis.

New approaches to improve a peptide vaccine against porcine Taenia solium cysticercosis

Cysticercosis caused by Taenia solium frequently affects human health and rustic porciculture. Cysticerci may localize in the central nervous system of humans causing neurocysticercosis, a major health problem in undeveloped countries. Prevalence and intensity of this disease in pigs and humans are related to social factors (poor personal hygiene, low sanitary conditions, rustic rearing of pigs, open fecalism) and possibly to biological factors such as immunity, genetic background, and gender. The indispensable role of pigs as an obligatory intermediate host in the life cycle offers the possibility of interfering with transmission through vaccination of pigs. An effective vaccine based on three synthetic peptides against pig cysticercosis has been successfully developed and proved effective in experimental and field conditions. The well-defined peptides that constitute the cysticercosis vaccine offer the possibility to explore alternative forms of antigen production and delivery systems that may improve the cost/benefit of this and other vaccines. Encouraging results were obtained in attempts to produce large amounts of these peptides and increased its immunogenicity by expression in recombinant filamentous phage (M13), in transgenic plants (carrots and papaya), and associated to bacterial immunogenic carrier proteins.

Immunoendocrine interactions during chronic cysticercosis determine male mouse feminization: role of IL-6

Taenia crassiceps cysticercosis results in an impressive feminization in male mice during chronic infection, characterized by increased serum estradiol levels 100 times their normal values, while those of testosterone and dihydrotestosterone are decreased by 85 and 95% respectively. Concomitantly, the levels of follicle-stimulating hormone and IL-6 are increased 70 and 90 times their normal values in the infected male mice. Since a specific Th1/Th2 shift of the immune response has been previously reported during the chronic infection, and this shift may be associated with the feminization process, we proposed that this shift is induced by immunoendocrine interactions during the disease, and this gives way to a change in the initial resistance to the infection in the male mice, which become as susceptible as female mice. To confirm this hypothesis, we depleted immune system activity in two different ways: total body irradiation and neonatal thymectomy. Our results show that when immune system activity is depleted using either strategy, the male mice do not feminize, and the levels of follicle-stimulating hormone and IL-6 are inhibited. Depletion of IL-6 using IL-6(-/-) knockout mice does not produce the feminization process stated above, while restitution of the IL-6(-/-) knockout, irradiated, and thymectomized mice with murine recombinant IL-6 restores the feminization process. Expression of the IL-6 gene was found only in the testes and spleen of infected animals. Our results illustrate the importance of immunoendocrine interactions during a parasitic disease and show a possible new mechanism of parasite establishment in an initially resistant host.

Synthetic peptide vaccine against Taenia solium pig cysticercosis: successful vaccination in a controlled field trial in rural Mexico

Taenia solium cysticercosis seriously affects human health when localised in the central nervous system (CNS) and causes great economic loss in pig husbandry in rural areas of endemic countries. Increasing the resistance to the parasite in the obligatory host pig may help in curbing transmission. Three synthetic peptides based on protein sequences of the murine parasite Taenia crassiceps, which had previously been shown to induce protection in mice against homologous challenge, were tested as a vaccine against T. solium cysticercosis in pigs. Vaccinated and unvaccinated piglets (240 in all) were distributed in pairs among the peasants' households of two rural villages in Mexico in which 14% of the native pigs were cysticercotic. Ten to twelve months later, the effect of vaccination was evaluated at necropsy. Vaccination decreased the total number of T. solium cysticerci (98.7%) and reduced the prevalence (52.6%). The natural challenge conditions used in this field trial strengthen the likelihood of successful transmission control to both pig and human through a large-scale pig vaccination program. We believe this is a major contribution in anticysticercosis vaccine development as these rather simple yet protective peptides are potentially more cost-effective to produce and less variable in results than antigens that are more complex.