Towards the production of “Shigella plus” a low-cost recombinant Shigella glycoconjugate vaccines

Summary

For the past 18 years the Wren group and others have pioneered Protein Glycan Coupling Technology (PGCT) for the production of low-cost recombinant glycoconjugate vaccines in host cells such as E. coli. The technology involves coupling a protein carrier to a glycan of vaccine potential (e.g. O-antigen or capsules) using a bacterial oligosaccharyltransferase in E. coli cells. This allows the production of an inexhaustible and renewal supply of pure cloned bioconjugate vaccine in a single step process. Low cost vaccines produced by the Wren group using PGCT include those to protect against pneumonia, tularemia and melioidosis. In addition, GSK/GlycoVaxyn have shown that PGCT can be used for the production of Shigella dysenteriae type 1 O-antigen coupled to the Pseudomonas carrier protein ExoA, this is currently in human vaccine trials. We will improve on this vaccine by 1) coupling Shigella carrier proteins, that the Baker group have shown in Vietnam to have vaccine potential in their own right, to the Shigella dysenteriae O-antigen and 2) couple the best Shigella protein candidates to additional Shigella O-antigens including Shigella sonnei. The double-hit approach of coupling candidate protein and glycan immunogens should allow for the production of broad-coverage effective Shigella vaccines. This pump priming grant will enable significant steps to be made towards producing a new generation of recombinant “Shigella plus” vaccines. The subsequent testing of these candidates will facilitate significant funds towards a human trialled vaccine and the overall aim to produce an effective low-cost broad-coverage Shigella vaccine – a current imperative in LMICs.

Project outcomes

Shigellosis remains a major cause of diarrheal disease in low income countries and causes substantial morbidity and mortality. A safe, effective Shigella vaccine that include coverage of Shigella sonnei is a current global imperative. In previous research the Baker lab identified 12 proteins by protein microarray analyses to be highly immunogenic in children infected with Shigella. Eight of these proteins were shown to raise antibody responses when injected into rabbits. Upon testing of the respective rabbit polyclonal sera for complement-mediated serum bactericidal activity (SBA) against Shigella, 6 of the 8 proteins had raised antibody responses with strong SBA activity.

In this study we cloned these six proteins (with glycotags) in an appropriate E. coli strain and demonstrated expression of these proteins. In parallel, we were also able to express the O-antigens from S. dysenteriae and S. sonnei appropriate E. coli strains. We were able to couple three of the six proteins (all from S. sonnei) to the S. dysenteriae O-antigen using our protein glycan coupling technology. The three new “Shigella plus” vaccine candidates are available for testing and evaluation.