SjTat-TPI facilitates adaptive T-cell responses and reduces hepatic pathology during Schistosoma japonicum infection in BALB/c mice

GLYCOLYTIC ENZYMES AS VACCINES AGAINST SCHISTOSOMIASIS: TESTING SCHISTOSOMA MANSONI PHOSPHOGLYCERATE MUTASE IN MICE

Schistosomiasis is a globally burdensome parasitic disease caused by flatworms (blood flukes) in the genus Schistosoma. The current standard treatment for schistosomiasis is the drug praziquantel, but there is an urgent need to advance novel interventions such as vaccines. Several glycolytic enzymes have been evaluated as vaccine targets for schistosomiasis, and data from these studies are reviewed here. Although these parasites are canonically considered to be intracellular, proteomic analysis has revealed that many schistosome glycolytic enzymes are additionally found at the host-interactive surface. We have recently found that the intravascular stage of Schistosoma mansoni (Sm) expresses the glycolytic enzyme phosphoglycerate mutase (PGM) on the tegumental surface. Live parasites display PGM activity, and suppression of PGM gene expression by RNA interference diminishes surface enzyme activity. Recombinant SmPGM (rSmPGM) can cleave its glycolytic substrate, 3-phosphoglycerate and can both bind to plasminogen and promote its conversion to an active form (plasmin) in vitro, suggesting a moonlighting role for this enzyme in regulating thrombosis in vivo. We found that antibodies in sera from chronically infected mice recognize rSmPGM. We also tested the protective efficacy of rSmPGM as a vaccine in the murine model. Although immunization generates high titers of anti-SmPGM antibodies (against both recombinant and native SmPGM), no significant differences in worm numbers were found between vaccinated and control animals.

Transmission-Blocking Vaccines against Schistosomiasis Japonica

Control of schistosomiasis japonica, endemic in Asia, including the Philippines, China, and Indonesia, is extremely challenging. Schistosoma japonicum is a highly pathogenic helminth parasite, with disease arising predominantly from an immune reaction to entrapped parasite eggs in tissues. Females of this species can generate 1000-2200 eggs per day, which is about 3- to 15-fold greater than the egg output of other schistosome species. Bovines (water buffalo and cattle) are the predominant definitive hosts and are estimated to generate up to 90% of parasite eggs released into the environment in rural endemic areas where these hosts and humans are present. Here, we highlight the necessity of developing veterinary transmission-blocking vaccines for bovines to better control the disease and review potential vaccine candidates. We also point out that the approach to producing efficacious transmission-blocking animal-based vaccines before moving on to human vaccines is crucial. This will result in effective and feasible public health outcomes in agreement with the One Health concept to achieve optimum health for people, animals, and the environment. Indeed, incorporating a veterinary-based transmission vaccine, coupled with interventions such as human mass drug administration, improved sanitation and hygiene, health education, and snail control, would be invaluable to eliminating zoonotic schistosomiasis.

Crystal structures of Triosephosphate Isomerases from Taenia solium and Schistosoma mansoni provide insights for vaccine rationale and drug design against helminth parasites

Triosephosphate isomerases (TPIs) from Taenia solium (TsTPI) and Schistosoma mansoni (SmTPI) are potential vaccine and drug targets against cysticercosis and schistosomiasis, respectively. This is due to the dependence of parasitic helminths on glycolysis and because those proteins elicit an immune response, presumably due to their surface localization. Here we report the crystal structures of TsTPI and SmTPI in complex with 2-phosphoglyceric acid (2-PGA). Both TPIs fold into a dimeric (β-α)₈ barrel in which the dimer interface consists of α-helices 2, 3, and 4, and swapping of loop 3. TPIs from parasitic helminths harbor a region of three amino acids knows as the SXD/E insert (S155 to E157 and S157 to D159 in TsTPI and SmTPI, respectively). This insert is located between α5 and β6 and is proposed to be the main TPI epitope. This region is part of a solvent-exposed 3₁₀–helix that folds into a hook-like structure. The crystal structures of TsTPI and SmTPI predicted conformational epitopes that could be used for vaccine design. Surprisingly, the epitopes corresponding to the SXD/E inserts are not the ones with the greatest immunological potential. SmTPI, but not TsTPI, habors a sole solvent exposed cysteine (SmTPI-S230) and alterations in this residue decrease catalysis. The latter suggests that thiol-conjugating agents could be used to target SmTPI. In sum, the crystal structures of SmTPI and TsTPI are a blueprint for targeted schistosomiasis and cysticercosis drug and vaccine development.

Because of the worldwide prevalence of schistosomiasis and cysticercosis, it is critical to develop drugs and vaccines against their causative agents. The glycolytic enzyme triosephosphate isomerase (TPI) is a dual-edged sword against diseases caused by parasitic helminths. This is because helminths heavily depend on glycolysis for energy and because the surface localization exhibited by TPIs that elicits an immune response against those organisms. Here we provide the crystal structures TPIs from Taenia solium and Schistosoma mansoni as a first step for vaccine and drug design. As a proof of concept we found that modifications in the single solvent exposed cysteine of TPI from S. mansoni decreases catalysis, making this enzyme a novel target against schistosomiasis.

Protective Immune Responses Generated in a Murine Model Following Immunization with Recombinant Schistosoma japonicum Insulin Receptor

There is a pressing need to develop vaccines for schistosomiasis given the current heavy dependency on praziquantel as the only available drug for treatment. We previously showed the ligand domain of the Schistosoma japonicum insulin receptor 1 and 2 (rSjLD1 and 2) fusion proteins conferred solid protection in mice against challenge infection with S. japonicum. To improve vaccine efficacy, we compared the immunogenicity and protective efficacy of rSjLD1 on its own and in combination with S. japonicum triose-phosphate isomerase (SjTPI), formulated with either of two adjuvants (QuilA and montanide ISA 720VG) in murine vaccine trials against S. japonicum challenge. The level of protection was higher in mice vaccinated only with rSjLD1 formulated with either adjuvant; rSjTPI or the rSjTPI-rSjLD1 combination resulted in a lower level of protection. Mirroring our previous results, there were significant reductions in the number of female worms (30–44%), faecal eggs (61–68%), liver eggs (44–56%), intestinal eggs (46–48%) and mature intestinal eggs (58–63%) in the rSjLD1-vaccinated mice compared with the adjuvant only groups. At 6-weeks post-cercarial challenge, a significantly increased production of interferon gamma (IFNγ) in rSjLD1-stimulated splenic CD4⁺ T cells was observed in the rSjLD1-vaccinated mice suggesting a Th1-type response is associated with the generated level of protective efficacy.

Molecular characterization of triosephosphate isomerase from Echinococcus granulosus

Cystic echinococcosis (CE) is a zoonosis that can be caused by the larvae of Echinococcus granulosus; this disease occurs worldwide and is highly endemic in China. E. granulosus can produce energy by glycolysis as well as both aerobic and anaerobic respirations. Triosephosphate isomerase is a glycolytic enzyme present in a wide range of organisms and plays an important role in glycolysis. However, there has been little research on triosephosphate isomerase from E. granulosus (Eg-TIM). Here, we present a bioinformatic characterization and the experimentally determined tissue distribution characteristics of Eg-TIM. We also explored its potential value for diagnosing CE in sheep using indirect enzyme-linked immunosorbent assay (ELISA). Native Eg-TIM was located in the neck and hooks of protoscoleces (PSCs), as well as the tegument and parenchyma tissue of adult worms. The entire germinal layer was also Eg-TIM positive. Western blots showed that recombinant Eg-TIM (rEg-TIM) reacts with positive serum from sheep and had good immunogenicity. Indirect ELISA exhibited low specificity (53.6%) and low sensitivity (87.5%) and cross-reacted with both Taenia multiceps and Taenia hydatigena. Our results suggest that TIM may take part in the growth and development of E. granulosus. Furthermore, we determined that rEg-TIM is not a suitable serodiagnostic antigen for CE in sheep.