# Exploring BCG to deliver avidin fusion antigens from Schistosoma mansoni

## TL;DR

Researchers tested using the BCG vaccine to deliver a Schistosoma mansoni antigen fused with rhizavidin, but found low immunogenicity despite successful biotinylation.

## Contribution

Demonstration of BCG's potential as a carrier for avidin-fused antigens, with biotinylation and antigen coupling achieved in vitro.

## Key findings

- BCG was successfully biotinylated and coupled with Rzv:TSP-2 at 35% efficiency.
- The BCG-Rzv:TSP-2 vaccine showed low immunogenicity in mice.
- Optimizations are needed to improve antigen stability and immune response.

## Abstract

Bacillus Calmette-Guérin (BCG) is one of the most successful vaccines in the world and evidence suggests it can be used as a bacterial vector to deliver heterologous antigens.

We evaluated whether BCG could be biotinylated and used as a carrier of Schistosoma mansoni antigen tetraspanin-2 (TSP-2) fused with rhizavidin, an avidin analog.

BCG was grown and biotinylated. The recombinant protein Rzv:TSP-2 was produced and purified from Escherichia coli. The biotinylation and antigen coupling was analysed by flow cytometry, enzyme-linked immunosorbent assay (ELISA) and Western blot. Vaccine immunogenicity was tested in immunised mice by the assessment of lung and splenic T cells.

BCG can be biotinylated, which in turn, can be coupled with Rzv:TSP-2. After a series of optimisations which involved molarity of the biotin, ratio of BCG:reagent and the concentration of Rzv:TSP-2 used, almost 50% of the bacteria were biotinylated and 35% coupled with antigen. Although a clear adjuvant effect of BCG was observed, evaluation of immune response in immunised mice demonstrated an overall low immunogenicity of the BCG-Rzv:TSP-2.

These results demonstrated the use of BCG as a carrier of avidin-tagged antigens. Further optimisations are needed in order to strengthen the stability of tagged proteins in order to produce antigen-specific immune responses.