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. 2012;6(3):e1564.
doi: 10.1371/journal.pntd.0001564. Epub 2012 Mar 13.

Enhanced protective efficacy of a chimeric form of the schistosomiasis vaccine antigen Sm-TSP-2

Affiliations

Enhanced protective efficacy of a chimeric form of the schistosomiasis vaccine antigen Sm-TSP-2

Mark S Pearson et al. PLoS Negl Trop Dis. 2012.

Abstract

The large extracellular loop of the Schistosoma mansoni tetraspanin, Sm-TSP-2, when fused to a thioredoxin partner and formulated with Freund's adjuvants, has been shown to be an efficacious vaccine against murine schistosomiasis. Moreover, Sm-TSP-2 is uniquely recognised by IgG(1) and IgG(3) from putatively resistant individuals resident in S. mansoni endemic areas in Brazil. In the present study, we expressed Sm-TSP-2 at high yield and in soluble form in E. coli without the need for a solubility enhancing fusion partner. We also expressed in E. coli a chimera called Sm-TSP-2/5B, which consisted of Sm-TSP-2 fused to the immunogenic 5B region of the hookworm aspartic protease and vaccine antigen, Na-APR-1. Sm-TSP-2 formulated with alum/CpG showed significant reductions in adult worm and liver egg burdens in two separate murine schistosomiasis challenge studies. Sm-TSP-2/5B afforded significantly greater protection than Sm-TSP-2 alone when both antigens were formulated with alum/CpG. The enhanced protection obtained with the chimeric fusion protein was associated with increased production of anti-Sm-TSP-2 antibodies and IL-4, IL-10 and IFN-γ from spleen cells of vaccinated animals. Sera from 666 individuals from Brazil who were infected with S. mansoni were screened for potentially deleterious IgE responses to Sm-TSP-2. Anti-Sm-TSP-2 IgE to this protein was not detected (also shown previously for Na-APR-1), suggesting that the chimeric antigen Sm-TSP-2/5B could be used to safely and effectively vaccinate people in areas where schistosomes and hookworms are endemic.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Vaccine antigen production.
(A) Sm-TSP-2 was ligated to a pET41a vector backbone in-frame with the C-terminal ×ばつHis tag, expressed in E. coli.by autoinduction and purified by IMAC followed by CEX chromatography and desalting into PBS. 1 = uninduced soluble fraction; 2 = autoinduced soluble fraction; 3 = purified protein. (B) Sm-TSP-2/5B was ligated to a pET41a vector backbone in-frame with the C-terminal ×ばつHis tag, expressed in E. coli.by IPTG induction and purified by IMAC and desalting into PBS. 1 = uninduced soluble fraction; 2 = IPTG-induced soluble fraction; 3 = purified protein.
Figure 2
Figure 2. Anti-Sm-TSP-2/5B antibodies bind to parasite-derived Sm-TSP-2.
Immunofluorescence micrograph showing adult male Schistosoma mansoni sections probed with either (A) rabbit anti-TSP-2/5B serum or (B) naïve rabbit serum followed by goat anti-rabbit IgG-Cy3. Both sections were also stained with Alexa-Fluor 488 (green staining of actin filaments) and DAPI (blue staining of nuclei). All images are shown at original magnification ×ばつ63.
Figure 3
Figure 3. Chronically infected individuals do not make IgE against Sm-TSP-2.
Graph showing human anti-Sm-TSP-2 IgE responses towards soluble egg antigen (SEA), soluble adult worm antigen (SWAP) and Sm-TSP-2. Antibody responses were determined by indirect ELISA. Dots reflect OD values of individual people and bars reflect the mean OD values of the groups.
Figure 4
Figure 4. Worm burdens of vaccinated C57BL/6 mice.
All vaccinees were necropsied on day 91, 7 weeks post-challenge. Worms were perfused from the vasculature with PBS into petri dishes and counted. Reductions and significance (*P<0.05; **P<0.01; *** P<0.001) are represented relative to the Maltose Binding Protein (MBP) control group. (A) Trial 1 total worms. (B) Trial 2 total worms.
Figure 5
Figure 5. Liver egg burdens of vaccinated C57BL/6 mice.
All vaccinees were necropsied on day 91, 7 weeks post-challenge. Livers were removed, weighed, digested in 5% KOH overnight at 37°C and the rsulting eggs resuspended in 1 ml formalin. The amount of eggs in multiple 50 μl aliquots were counted and the number of eggs per gram of tissue (EPG) determined. Reductions and significance (*P<0.05; **P<0.01; ***P<0.001) are represented relative to the Maltose Binding Protein (MBP) control group. (A) Trial 1 - liver EPG. (B) Trial 2 - liver EPG.
Figure 6
Figure 6. Protection against parasite challenge is associated with increased IFN-γ production.
Graphs of ELISA data showing IL-4 (left axis), IL-10 (right axis) and IFN-γ (right axis) production by splenocytes taken from mice at necropsy and restimulated with either (A) schistosome soluble egg antigen (SEA) or (B) schistosome soluble adult worm antigen (SWAP). All significant differences are compared to the control MBP-vaccinated, infected group (MBP inf) by ANOVA (**P<0.01, ***P<0.001). Unless otherwise indicated, levels are not significantly different to controls.

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