Strategies for Optimal Expression of Vaccine Antigens from Taeniid Cestode Parasites in Escherichia coli

Abstract

Investigations were undertaken into optimizing the expression of Cestode parasite vaccine antigens in the bacterium, Escherichia coli to levels sufficient for mass production. A strategy to genetically engineer the antigens and improve their expression in E. coli was investigated. Plasmid constructs encoding truncated parasite antigens were prepared, leading to removal of N and C-terminal hydrophobic domains of the antigens. This approach was found to be an effective strategy for improving expression of the TSOL18 recombinant antigen of Taenia solium in E. coli. Clear demonstration that plasmid construct modification can be used to significantly improve heterologous expression in E. coli was shown for the EG95 antigen of Echinococcus granulosus. Removal of hydrophobic stretches of amino acids from the N and C termini of EG95 by genetic manipulation led to a substantial change in expression of the protein from an insoluble to a soluble form. The data demonstrate that the occurrence of hydrophobic regions in the antigens are a major feature that hindered their expression in E. coli. It was also shown that retaining a minimal protein domain (a single fibronectin type III domain) led to high level expression of functional protein that is antigenic and host protective. Two truncated antigens were combined from two species of parasite (EG95NC⁻ from E. granulosus and Tm18N⁻ from Taenia multiceps) and expressed as a single hybrid antigen in E. coli. The hybrid antigens were expressed at a high level and retained antigenicity of their respective components, thereby simplifying production of a multi-antigen vaccine. The findings are expected to have an impact on the preparation of recombinant Cestode vaccine antigens using E. coli, by increasing their utility and making them more amenable to large-scale production.