Development and Immunogenicity of a Prototype Multivalent Group B Streptococcus Bioconjugate Vaccine

Abstract

Group B Streptococcus (GBS) is a leading cause of neonatal infections and invasive diseases in nonpregnant adults worldwide. Developing a protective conjugate vaccine targeting the capsule of GBS has been pursued for more than 30 years; however, it has yet to yield a licensed product. In this study, we present a novel bioconjugation platform for producing a prototype multivalent GBS conjugate vaccine and its subsequent analytical and immunological characterizations. Using a glycoengineering strategy, we generated strains of Escherichia coli that recombinantly express the type Ia, type Ib, and type III GBS capsular polysaccharides. We then combined the type Ia-, Ib-, and III-capsule-expressing E. coli strains with an engineered Pseudomonas aeruginosa exotoxin A (EPA) carrier protein and the PglS oligosaccharyltransferase. Coexpression of a GBS capsule, the engineered EPA protein, and PglS enabled the covalent attachment of the target GBS capsule to an engineered serine residue on EPA, all within the periplasm of E. coli. GBS bioconjugates were purified, analytically characterized, and evaluated for immunogenicity and functional antibody responses. This proof-of-concept study signifies the first step in the development of a next-generation multivalent GBS bioconjugate vaccine, which was validated by the production of conjugates that are able to elicit functional antibodies directed against the GBS capsule.

Discovery and characterization of a new class of O-linking oligosaccharyltransferases from the Moraxellaceae family

“…Intact protein MS of purified EPA-Pil 20 -GBSIII supported a glycan:protein ratio of 20% ( Fig. 6E ) calculated using methods reported in Duke et al. (2021) .…”

“…1993 ), the E. coli O16 wbbL gene from plasmid pMF19 (Sp R ) ( Feldman et al. 2005 ), and the GBSIII glycan was from a pBBR1MCS2 derivative we reported recently ( Duke et al. 2021 ).…”

“…Protein concentrations for immunization and western blots were determined using a Pierce BCA Protein Assay kit (Thermo Fisher). The ratio of polysaccharide to protein calculate for vaccine dosing was determined using the method described in Duke et al. (2021 ).…”

Current research update on group B streptococcal infection related to obstetrics and gynecology

“…Currently, two GBS vaccines have entered Phase II or III clinical trials. The first is a multivalent conjugate vaccine aimed at targeting the majority of pathogenic serotypes, while the other is a protein subunit vaccine ( Duke et al, 2021 ). The multivalent conjugate vaccine has the potential to prevent 95% of GBS infections in pregnant women, 99% of stillbirths, and 99% of neonatal GBS infections by targeting the majority of pathogenic serotypes.…”

A combinatorial DNA assembly approach to biosynthesis ofN-linked glycans inE. coli

“…Traditionally, PGCT involves transforming Escherichia coli cells with three plasmids that encode the requisite components for glycoconjugate production: a substrate protein, an oligosaccharyltransferase, and a glycan biosynthesis locus. The typical approach in the PGCT vaccine field is to attempt to transfer a complete, unmodified glycan biosynthetic gene cluster from a native host into E. coli ( Cuccui et al 2013 ; Kay et al 2016 ; Harding et al 2019 ; Duke et al 2021 ). In some cases, this results in functional, although usually not optimal, glycan biosynthesis.…”