Oral Delivery of the Sj23LHD-GST Antigen by Salmonella typhimurium Type III Secretion System Protects against Schistosoma japonicum Infection in Mice

Abstract

Background Schistosomiasis japonica is a zoonotic parasitic disease and oral vaccine delivery system would be benefit for prevention of this disease. Although attenuated salmonella has been used as an antigen expression vector for oral vaccine development, the membrane-bound vacuoles in which bacteria reside hinders the presentation of expressed heterologous antigens to the major histocompatibility complex (MHC) molecules. The present work used an attenuated Salmonella typhimurium strain VNP20009 to secretory expression of Sj23LHDGST bivalent antigen from Schistosoma japonicum and tested the protective efficacy against S. japonicum infection in orally immunized mice.Methodology/Principal FindingsPromoters (nirB or pagC) were used to express the antigen (Sj23LHDGST) and the Salmonella type III or α-hemolysin secretion system was employed to secrete it. The immunoblotting analysis and fluorescent microscopy revealed that the antigen was effectively expressed and delivered to the cytosol of macrophages in vitro. Among recombinant vaccine strains, an engineered VNP20009 which expressed the antigen by nirB promoter and secreted it through type III secretion system (nirB-sopE1–104-Sj23LHD-GST) efficiently protected against S. japonicum infection in a mouse model. This strain elicited a predominantly IgG2a antibody response and a markedly increase in the production of IL-12 and IFN-γ. The flow cytometric analysis demonstrated that this strain caused T cell activation as evidenced by significantly increased expression of CD44 and CD69.Conclusion/SignificanceOral delivery of antigen by nirB-driven Salmonella typhimurium type III secretion system is a novel, safe, inexpensive, efficient and convenient approach for schistosome vaccine development.

Vaccination against the digestive enzyme Cathepsin B using a YS1646Salmonella entericaTyphimurium vector provides almost complete protection againstSchistosoma mansonichallenge in a mouse model

“…The promoter/T3SS pairs were inserted in-frame with either S. mansoni CatB or eGFP. In monomicrobial culture, CatB expression was effectively driven by the nirB_SspH1, SspH1_SspH1 and SteA_SteA plasmids (Fig 3A) with the greatest production from the nirB promoter in low oxygen conditions as previously reported [29]. Secreted CatB was detectable in the monomicrobial culture supernatants only with YS1646 bearing the SspH1_SspH1 construct (Fig 3A).…”

“…Administered IM, rCatB alone consistently elicited high systemic antibody responses and provided a modest level of protection without any measurable mucosal response. Chen and colleagues have also used YS1646 as a vector to test single- and multi-modality approaches for a bivalent vaccine candidate (Sj23LHD-GST) targeting S. japonicum in a similar murine model [29]. Although some authors have promoted so-called ‘prime-pull’ strategies to optimize mucosal responses (ie: ‘prime’ in the periphery then ‘pull’ to the target mucosa) [50], it is interesting that both the Chen group and our own findings suggest that PO→IM dosing may be the optimal strategy.…”

“…Although some authors have promoted so-called ‘prime-pull’ strategies to optimize mucosal responses (ie: ‘prime’ in the periphery then ‘pull’ to the target mucosa) [50], it is interesting that both the Chen group and our own findings suggest that PO→IM dosing may be the optimal strategy. In the S. japonicum model targeting the long hydrophobic domain of the surface exposed membrane protein Sj23LHD and a host-parasite interface enzyme (glutathione S-transferase or GST), the PO→IM vaccination schedule led to important reductions in both worm numbers (51.4%) and liver egg burden (62.6%) [29].…”

“…Although there is considerable experience with the attenuated S. typhi vaccine strain (Ty21a: Vivotif™) in the delivery of heterologous antigens [21, 28], far less is known about the potential of other Salmonella strains. Of direct relevance to the current work, Chen and colleagues used YS1646 to express a chimeric S. japonicum antigen that induced both strong antibody and cellular responses after repeated oral dosing and provided up to 62% protection in a murine challenge model [29].…”

Recombinant Salmonella enterica Serovar Typhimurium as a Vaccine Vector for HIV-1 Gag

“…The induction of the promoter, only inside the macrophage, prevents loss of the expression plasmid during infection. The NirB promoter has also been successfully used in the expression of other foreign antigens to be delivered by Salmonella vaccines [110,111]. Other promoters that can be investigated for use in the in vivo expression of HIV-1 antigens are the htrA, groEL, PgaC, and other Salmonella -SPI2-derived promoters, which are activated after uptake of the recombinant bacteria by antigen-presenting cells [112,113,114].…”