Anti-Group B Streptococcus Glycan-Conjugate
Vaccines Using Pilus Protein GBS80 As Carrier and Antigen: Comparing
Lysine and Tyrosine-directed Conjugation
posted on 2015-07-17, 00:00authored byAlberto Nilo, Laura Morelli, Irene Passalacqua, Barbara Brogioni, Martin Allan, Filippo Carboni, Alfredo Pezzicoli, Francesca Zerbini, Domenico Maione, Monica Fabbrini, Maria
Rosaria Romano, Qi-Ying Hu, Immaculada Margarit, Francesco Berti, Roberto Adamo
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.