Group B Streptococcus capsular polysaccharide serotype II (GBS CPS II)

Group B Streptococcus (GBS) capsular polysaccharide serotype II is a critical virulence factor of Streptococcus agalactiae, a leading cause of invasive neonatal disease, including sepsis, meningitis, and pneumonia (StatPearls, 2025). The serotype II CPS is a complex carbohydrate structure that forms the outermost layer of the bacterium, characterized by a repeating unit containing glucose, galactose, N-acetylglucosamine, and a terminal sialic acid residue (Infection and Immunity, 2002). Its primary biological function is to facilitate immune evasion by inhibiting opsonophagocytosis and interfering with the host's complement-mediated killing pathways (Infection and Immunity, 2002; ResearchGate, 2012). As a therapeutic target, it is a key component of multivalent glycoconjugate vaccines, such as Pfizer's hexavalent GBS6 vaccine, which is currently in clinical development (NEJM, 2023; Pfizer, 2024). These vaccines aim to induce high titers of serotype-specific IgG antibodies in pregnant women, which are then passively transferred across the placenta to provide protection to the newborn during the first months of life (WHO, 2023). Clinical trials have demonstrated that targeting this polysaccharide can elicit robust maternal antibody responses that are efficiently transferred to infants (NEJM, 2023).

Other names

GBS type II polysaccharideStreptococcus agalactiae serotype II capsular polysaccharideType II capsular polysaccharide of Group B StreptococcusGBS serotype II CPS

Induction of protective opsonophagocytic antibodies (IgG) that facilitate bacterial clearance by the host immune system.