Group B Streptococcus capsular polysaccharide (serotypes Ia, Ib, II, III, IV, V) (GBS CPS)

Group B Streptococcus (GBS), or Streptococcus agalactiae, is a leading cause of life-threatening neonatal infections, including sepsis, pneumonia, and meningitis (Madhi et al., 2023, NEJM). The capsular polysaccharide (CPS) is the primary virulence factor of GBS, forming a protective layer that inhibits opsonophagocytosis by the host's immune system (Paoletti & Kasper, 2019, Vaccine). While ten GBS serotypes have been identified, six specific serotypes—Ia, Ib, II, III, IV, and V—account for approximately 98% of invasive GBS disease cases globally (Pfizer, 2023). The IVT GBS-06 (GBS6) vaccine is a hexavalent conjugate vaccine designed to target these six serotypes by linking the polysaccharides to a CRM197 carrier protein. This conjugation converts the polysaccharides into T-cell dependent antigens, stimulating the production of high-affinity IgG antibodies in pregnant women. These antibodies are then transferred across the placenta to the fetus, providing passive protection to the newborn during the period of highest vulnerability (Absba et al., 2022, Frontiers in Immunology). Clinical efficacy is measured by the ability of these antibodies to induce opsonophagocytic killing of the bacteria. This target is critical for reducing the global burden of neonatal GBS disease, for which no vaccine is currently licensed.

Other names

Streptococcus agalactiae capsular polysaccharideGBS capsular polysaccharideGBS6 antigensHexavalent GBS polysaccharidePF-06760805 antigens

Induction of serotype-specific opsonophagocytic antibodies (IgG) that facilitate bacterial clearance via the host immune system and provide passive immunity to neonates through transplacental transfer (Madhi et al., 2023, NEJM).