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Group B Streptococcus (GBS) vaccines using purified polysaccharides show promise for preventing infant infections. Immunization of pregnant women could transfer protective antibodies, reducing neonatal GBS disease.
Area of Science:
- Obstetrics and Gynecology
- Infectious Diseases
- Vaccinology
Background:
- Group B Streptococcus (GBS) is a significant perinatal pathogen.
- Infant susceptibility to GBS infection is linked to maternal antibody deficiency.
- Vaccination strategies aim to induce protective antibodies via maternal immunization.
Purpose of the Study:
- To evaluate the safety and immunogenicity of purified GBS type-specific polysaccharides as candidate vaccines.
- To assess the potential for placental transfer of vaccine-induced antibodies for infant protection.
Main Methods:
- Purification and characterization of native GBS type Ia, II, and III polysaccharides.
- Administration of polysaccharides as immunogens to healthy adult volunteers.
- Measurement of antibody responses, including isotype and functional activity (opsonophagocytosis).
Main Results:
- Native GBS polysaccharides were safe and non-toxic in adults.
- Immunogenicity varied by serotype: Type Ia (65%), Type II (95%), Type III (70%) in non-immune adults.
- Antibody responses were near 100% in previously immune volunteers.
- Vaccine-induced antibodies demonstrated in vitro opsonophagocytosis and in vivo protection in animal models.
Conclusions:
- Purified GBS polysaccharides are safe and immunogenic candidate vaccines.
- Further studies in pregnant women are needed to confirm efficacy in preventing neonatal GBS disease.
Abstract:
In recent years group B Streptococcus (GBS) has been recognized as a major perinatal pathogen. As with other encapsulated bacteria, protective immunity appears to correlate with serum antibody specific for the homologous capsular polysaccharide antigen of each serotype. Since susceptibility of the young infant to disseminated GBS infection relates to type-specific antibody deficiency in maternal serum, immunization of women with purified GBS type-specific polysaccharides has been proposed as a method for the prevention of infant disease through placental transport of protective antibodies. Candidate native polysaccharides from GBS have been purified, immunochemically and structurally characterized, and employed as immunogen in healthy adult volunteers. Native type Ia, II, and III polysaccharides have been shown to be nontoxic, safe, and immunogenic in approximately 65%, 95%, and 70%, respectively, of nonimmune adults. Antibody response to immunization approaches 100% in previously immune volunteers. Vaccine-induced type-specific antibodies to these candidate polysaccharide vaccines promote in vitro opsonophagocytosis, protect animals given a lethal challenge of homologous organisms, and are predominantly of the IgG isotype. Once similar results can be documented in women immunized during the last half of pregnancy, efficacy of these candidate GBS polysaccharide vaccines in the prevention of neonatal and young infant GBS disease should be evaluated.