Gram-positive Streptococcus agalactiae or group B Streptococcus (GBS) is a leading cause of invasive
infections in pregnant women, newborns, and elderly people. Vaccination of pregnant women represents the best strategy for prevention of
neonatal disease, and GBS
polysaccharide-based
conjugate vaccines are currently under clinical testing. The potential of GBS pilus
proteins selected by genome-based reverse vaccinology as protective
antigens for anti-
streptococcal vaccines has also been demonstrated. Dressing pilus
proteins with surface
glycan antigens could be an attractive approach to extend
vaccine coverage. We have recently developed an efficient method for
tyrosine-directed
ligation of large
glycans to
proteins via
copper-free
azide-
alkyne [3 + 2] cycloaddition. This method enables targeting of predetermined sites of the
protein, ensuring that
protein epitopes are preserved prior to
glycan coupling and a higher consistency in
glycoconjugate batches. Herein, we compared conjugates of the GBS type II
polysaccharide (PSII) and the GBS80 pilus
protein obtained by classic
lysine random conjugation and by the recently developed
tyrosine-directed
ligation. PSII conjugated to
CRM197, a
carrier protein used for
vaccines in the market, was used as a control. We found that the constructs made from PSII and GBS80 were able to elicit murine
antibodies recognizing individually the
glycan and
protein epitopes on the bacterial surface. The generated
antibodies were efficacious in mediating opsonophagocytic killing of strains expressing exclusively PSII or GBS80
proteins. The two
glycoconjugates were also effective in protecting newborn mice against GBS
infection following vaccination of the dams. Altogether, these results demonstrated that
polysaccharide-conjugated GBS80 pilus
protein functions as a carrier comparably to
CRM197, while maintaining its properties of protective
protein antigen. Glycoconjugation and reverse vaccinology can, therefore, be combined to design
vaccines with broad coverage. This approach opens a path to a new generation of
vaccines.
Tyrosine-
ligation allows creation of more homogeneous
vaccines, correlation of the immune response to defined connectivity points, and fine-tuning of the conjugation site in
glycan-
protein conjugates.