Characterisation of antibody responses in pigs induced by recombinant oncosphere antigens from Taenia solium.

Recombinant antigens cloned from the oncosphere life cycle stage of the cestode parasite Taenia solium (T. solium) have been proven to be effective as vaccines for protecting pigs against infections with T. solium. Previous studies have defined three different host protective oncosphere antigens, TSOL18, TSOL16 and TSOL45. In this study, we evaluated the potential for combining the antigens TSOL16 and TSOL18 as a practical vaccine. Firstly, in a laboratory trial, we compared the immunogenicity of the combined antigens (TSOL16/18) versus the immunogenicity of the antigens separately. Secondly, in a field trial, we tested the ability of the TSOL16/18 vaccine to induce detectable antibody responses in animals living under environmental stress and traditionally reared in areas where T. solium cysticercosis is endemic; and finally, we characterised the immune response of the study population. Pigs of 8-16 weeks of age were vaccinated with 200 µg each of TSOL16 and TSOL18, plus 5mg of Quil-A. Specific total IgG, IgG(1) and IgG(2) antibody responses induced by TSOL16 and TSOL18 were determined with ELISA. The immunogenicity of both antigens was retained in the combined TSOL16/18 vaccine. The combined vaccine TSOL16/18 induced detectable specific anti-TSOL18 antibody responses in 100% (113/113) and specific anti-TSOL16 in 99% (112/113) of the vaccinated animals measured at 2 weeks following the booster vaccination. From the two IgG antibody subtypes analysed we found there was stronger response to IgG(2).

Successful immunization of naturally reared pigs against porcine cysticercosis with a recombinant oncosphere antigen vaccine.

Taenia solium causes cysticercosis in pigs and taeniasis and neurocysticercosis in humans. Oncosphere antigens have proven to be effective as vaccines to protect pigs against an experimental infection with T. solium. A pair-matched vaccination trial field, using a combination of two recombinant antigens, TSOL16 and TSOL18, was undertaken in rural villages of Peru to evaluate the efficacy of this vaccine under natural conditions. Pairs of pigs (n=137) comprising one vaccinated and one control animal, were allocated to local villagers. Animals received two vaccinations with 200 µg of each of TSOL16 and TSOL18, plus 5mg Quil-A. Necropsies were performed 7 months after the animals were distributed to the farmers. Vaccination reduced 99.7% and 99.9% (p<0.01) the total number of cysts and the number of viable cysts, respectively. Immunization with the TSOL16-TSOL18 vaccines has the potential to control T. solium transmission in areas where the disease is endemic, reducing the source for tapeworm infections in humans.

Elimination of Taenia solium transmission to pigs in a field trial of the TSOL18 vaccine in Cameroon.

A pilot field trial of the TSOL18 vaccine was undertaken in Cameroon. Two hundred and forty, 2-3 month-old piglets were distributed to 114 individual households in pairs. Vaccinated animals received three immunisations with 200 microg TSOL18 plus 5 mg Quil A and 30 mg/kg oxfendazole at the time of the second immunisation. Necropsies were undertaken when the pigs were approximately 12 months of age. Viable Taenia solium cysticerci were identified in 20 control pigs (prevalence 19.6%); no cysticerci were found in any of the vaccinated animals (P<0.0001). Combined application of TSOL18 vaccination and a single oxfendazole treatment in pigs may be a relatively simple and sustainable procedure that has the potential to control T. solium transmission in endemic areas and, indirectly, reduce the number of new cases of neurocysticercosis in humans.

Localisation of three host-protective oncospheral antigens of Taenia ovis.

Immunohistochemistry, confocal immunofluorescence and immunogold labelling were used to determine the localisation of the host-protective antigens To16, To18 and To45W in Taenia ovis oncospheres. During maturation of the adult tapeworm the antigens were initially seen as diffuse staining in the developing oncospheres but in mature oncospheres four distinct cells stained positively for the antigens. Confocal fluorescence microscopy using different fluorophores revealed that each of the antigens co-localises within the same cells in the oncosphere. No surface localisation was seen in non-activated or recently activated parasites. Immunogold labelling of non-activated oncosphere sections viewed in transmission electron microscopy revealed labelling of bilateral cells, however the identities of these cells was unclear due to deficiencies in the current level of understanding of oncosphere ultrastructure. Localisation of all the antigens changed dramatically after oncospheres were activated in vitro with each of the antigens being dispersed more generally throughout the parasite parenchyma. During development of the parasites in in vitro culture, surface localisation of the proteins was seen in parasites after 3 or more days in culture. All three antigens were found to be completely absent in parasites by 15 days of culture. The location of the host-protective antigens suggests that initially the invading oncospheres are not susceptible to vaccine-induced antibody and complement mediated attack, but that as the parasites mature, the host-protective antigens come to be associated with the parasite's surface, rendering them susceptible to immune attack.

Vaccination with recombinant oncosphere antigens reduces the susceptibility of sheep to infection with Taenia multiceps.

Taenia multiceps is a cestode parasite, the larval stage of which encysts in the brain of sheep, goats and cattle causing an often fatal condition. The parasite also causes zoonotic infections in humans. Homologues of the recombinant oncosphere vaccine antigens from Taenia ovis and other Taenia species were identified in T. multiceps. Sequencing of the associated T. multiceps genes and cloning of the encoding mRNA has revealed conserved features in the genes and proteins. The T. multiceps oncosphere proteins, designated Tm16 and Tm18, contain a predicted secretory signal and fibronectin type III domain. The recombinant Tm16 and Tm18 proteins were successfully expressed in Escherichia coli as fusion proteins with GST. The antigens, formulated with Quil A adjuvant, were tested in a vaccine trial in sheep. The antigens stimulated immunity in sheep against challenge infection with T. multiceps eggs. Five of nine control sheep died due to a challenge infection with T. multiceps whereas none of 20 vaccinated animals died as a result of the parasite challenge (P=0.001). In addition, vaccination with the Tm16 protein, or Tm16 plus Tm18, induced significant protection against the number of parasites encysting in the brain as a result of the challenge infection (P=0.023, P=0.015, respectively). No clear relationship was apparent between the level of specific serum antibody in vaccinated animals and either the presence or absence of parasites or the number of parasites that occurred in some of the vaccinated animals. We believe this study is the first description of recombinant vaccine-related investigations for T. multiceps. The recombinant oncosphere antigens identified may allow development of effective vaccination strategies against T. multiceps infection in sheep. They raise the potential for the development of a combined vaccine with the Echinococcus granulosus EG95 antigen for prevention of T. multiceps as well as preventing the transmission of cystic hydatid disease.

In vitro oncosphere-killing assays to determine immunity to the larvae of Taenia pisiformis, Taenia ovis, Taenia saginata, and Taenia solium.

Taeniid cestodes infect humans and livestock, causing considerable morbidity and mortality, as well as economic loss. Substantial progress has been made toward the production of recombinant vaccines against cysticercosis in livestock animals. Further development of these vaccines would be aided if a reliable in vitro test were available to measure host-protective immune responses in vaccinated animals. Here, we describe in vitro oncosphere-killing assays for the quantification of host-protective serum antibodies against Taenia pisiformis, Taenia ovis, Taenia saginata, and Taenia solium in rabbits, sheep, cattle, and pigs, respectively. Activated oncospheres of T. pisiformis, T. ovis, T. saginata, and T. solium were incubated in vitro in culture medium, test serum, and a source of complement, and oncosphere killing was assessed after 10 days of culture. In vitro oncosphere killing reflected the presence of specific antibody, and the oncosphere-killing assay typically indicated immunity to the homologous parasite that had been determined in vivo. This study describes the first reliable oncosphere-killing assays for T. pisiformis, T. ovis, T. saginata, and T. solium. These assays will be used for further research into the optimization of recombinant vaccines against cysticercosis.