# Evaluating the Immunogenicity of a Recombinant Bacillus subtilis Expressing LTB-Fused Protective Antigen of Transmissible Gastroenteritis Virus in a Murine Model

## TL;DR

Researchers developed an oral vaccine using Bacillus subtilis to protect against transmissible gastroenteritis in piglets, showing strong immune responses in mice.

## Contribution

A recombinant Bacillus subtilis strain expressing a TGEV antigen fused with an adjuvant was shown to induce robust mucosal and systemic immunity in a murine model.

## Key findings

- The recombinant Bacillus subtilis strain successfully expressed the LTB-fused TGEV antigen.
- Oral administration of the strain in mice induced strong mucosal, humoral, and cellular immune responses.
- The vaccine candidate generated effective virus-neutralizing antibodies.

## Abstract

Transmissible gastroenteritis is a severe intestinal disease that causes high mortality in newborn piglets, leading to major economic losses in the swine industry worldwide. Since the pathogen infection starts in the gut, it is crucial to develop an oral vaccine that could trigger strong immune responses in the intestinal mucosa. In the study, a food-grade bacterium, Bacillus subtilis, was used to deliver a key viral protein fused with an immune-boosting component to create a safe oral vaccine candidate. After constructing the recombinant strain and confirming protein expression, we administered it orally to mice. The results showed that this candidate successfully stimulated comprehensive immune protection, including gut immunity, antibody production, and cellular responses, while also generating effective virus-neutralizing antibodies. Our findings demonstrate that this Bacillus subtilis-based oral vaccine candidate is a promising candidate for controlling transmissible gastroenteritis, offering a practical and effective solution to protect piglets and reduce economic impacts on the swine industry.

Transmissible gastroenteritis (TGE), caused by the TGE virus (TGEV), is a highly contagious enteric disease characterized by vomiting, dehydration, and watery diarrhea. It mainly endangers piglets within two weeks of age, with a 100% mortality rate, inflicting severe economic losses on the global swine industry. Since enteric tropism of the virus and mucosa serves as the first line of defense against viral invasion, an oral vaccine inducing sufficient secretory immunoglobulin A (SIgA) antibodies in animals should be developed. Being a generally recognized as safe (GRAS) microorganism, Bacillus subtilis can form endospores under extreme environmental conditions, which confer resistance to the hostile gastric environment and have been widely employed as delivery vehicles for oral vaccines owing to their immunoadjuvant activity and non-specific antidiarrheal effects. In this study, the AD antigenic epitope of the TGEV S protein was selected as the immunogen. The mature peptide of the B subunit of the heat-labile enterotoxin from enterotoxigenic Escherichia coli served as a mucosal adjuvant, and B. subtilis WB800N was used as the delivery host to construct the recombinant strain pHT43-LTB-AD/WB800N. After confirming the successful expression of the target protein, oral immunization was performed using mice as a model. The results demonstrated that this recombinant strain induced robust mucosal, humoral, and cellular immunity, along with considerable levels of neutralizing antibodies. These findings indicate that recombinant B. subtilis could serve as an oral vaccine candidate to combat TGEV infections.