Protective levels of human immunoglobulin G antibody to group B streptococcus type Ib

Advances towards licensure of a maternal vaccine for the prevention of invasive group B streptococcus disease in infants: a discussion of different approaches

Group B streptococcus (Streptococcus agalactiae, GBS) is an important cause of life-threatening disease in newborns. Pregnant women colonized with GBS can transmit the bacteria to the developing fetus, as well as to their neonates during or after delivery where infection can lead to sepsis, meningitis, pneumonia, or/and death. While intrapartum antibiotic prophylaxis (IAP) is the standard of care for prevention of invasive GBS disease in some countries, even in such settings a substantial residual burden of disease remains. A GBS vaccine administered during pregnancy could potentially address this important unmet medical need and provide an adjunct or alternative to IAP for the prevention of invasive GBS disease in neonates. A hurdle for vaccine development has been relatively low disease rates making efficacy studies difficult. Given the well-accepted inverse relationship between anti-GBS capsular polysaccharide antibody titers at birth and risk of disease, licensure using serological criteria as a surrogate biomarker represents a promising approach to accelerate the availability of a GBS vaccine.

Immunoglobulin G Determination in Human Serum and Milk Using an Immunosensor of New Conception Fitted with an Enzyme Probe as Transducer

To completely overcome the problem of the presence of urea in the serum, which can be the cause (especially at low immunoglobulin G concentrations) of a small but non negligible interference in the enzyme reaction of the enzymatic marker, when the measurement was performed by a potentiometric immunosensor that we constructed and characterized in previous work, and which used urease as marker, we have now constructed an entirely different and highly innovative immunosensor. This new device uses the enzyme alkaline phosphatase as marker, sodium phenylphosphate as substrate but above all, a tyrosinase biosensor obtained by coupling a Clark type gas diffusion amperometric electrode and the tyrosinase enzyme, immobilized in a cellulose triacetate membrane, as transducer. After optimizing the ‘competitive’ measurement procedures, the new immunosensor was used to determine both HIgG and the anti-HIgG, with a limit of detection (LOD) of the order of 3×10^-11 M. Clearly this highly innovative construction geometry makes the immunosensor extremely selective. This makes it possible to determine immunoglobulin G both in human serum and milk without the slightest interference by any urea present in these biological matrixes.

Serotypes and clinical manifestations of group B streptococcal infections in western Sweden

OBJECTIVES

To study the serotype distributions of group B streptococci (GBS) isolated from blood and cerebrospinal fluid and from the genital tract of pregnant women and to investigate any possible relation between serotype, age and clinical manifestation.

METHODS

Invasive strains were collected from 1988 to 1997 and genital strains from 1995 to 1996. Strains of GBS were serotyped with coagglutination. Clinical data were obtained from hospital notes.

RESULTS

A total of 144 invasive strains, 78 from neonates and infants and 66 from adults, were serotyped. The most common isolates from neonates and infants were types III (62%), Ia (18%), and V (9%). The most common isolates from adults were types III (29%), Ib (23%), V (21%) and II (15%). A majority of the adults (94%) had an underlying medical condition. The most common serotypes of the 114 strains isolated from the genital tract of pregnant women were types III (32%), V (22%), Ia (13%), Ib (13%) and II (11%).

CONCLUSIONS

Serotype III was the single most frequent GBS isolate from infants and adults. Serotype V, which appeared first in 1992, was the third most frequent isolate. A vaccine containing five GBS capsular polysaccharides appears to be appropriate for the Swedish population.

Neonatal mouse protection against infection with multiple group B streptococcal (GBS) serotypes by maternal immunization with a tetravalent GBS polysaccharide-tetanus toxoid conjugate vaccine

Most cases of neonatal sepsis and meningitis caused by group B streptococci (GBS) are attributable to one of four major capsular serotypes: Ia, Ib, II, or III. Because resistance to infection with GBS has been correlated with the presence of serum antibodies to the type-specific capsular polysaccharides in both experimental animals and human neonates, efforts have been made to elicit protective immunity with GBS capsular polysaccharide vaccines. However, the GBS capsular polysaccharides alone are not highly immunogenic in either animals or human volunteers. Therefore, we and other investigators have attempted to enhance immunogenicity by coupling individual capsular polysaccharides to a carrier protein. Here we report the synthesis and immunogenicity in rabbits of a GBS type Ib polysaccharide-tetanus toxoid vaccine prepared by the direct, covalent attachment of tetanus toxoid to a selected number of sialic acid residues on the type-specific polysaccharide. In addition, the Ib polysaccharide-tetanus toxoid conjugate vaccine was combined with similar tetanus toxoid conjugates of GBS type Ia, II, and III polysaccharides to form a tetravalent GBS conjugate vaccine. Protective efficacy of the GBS tetravalent conjugate vaccine was demonstrated in a mouse maternal immunization-neonatal challenge model of GBS infection. The results support testing in human subjects of a multivalent GBS conjugate vaccine of this design, with the eventual goal of protecting newborns against GBS infection.

Immunologic basis for increased susceptibility of the neonate to infection

Neonatal infection with the GBS occurs in a small fraction of exposed infants who lack specific antibody. Diminished influx of PMNs to sites of infection as a result of abnormalities in chemotaxis, bone marrow exhaustion, and to a lesser degree relative complement deficiency and decreased microbicidal activity of PMNs may be additional predisposing factors. Infection with HSV occurs more often in infants born to mothers with primary rather than secondary infection; the lack of passively acquired antibody in such infants is a possible but unproved susceptibility factor. The failure of neonates to control HSV may also be related to decreased production of or response to interferon or to decreased activity of nonimmune and immune cellular cytotoxic mechanisms. Similarly, infection with Toxoplasma and intracellular bacterial pathogens, such as Listeria, may be more severe because of the decreased generation of lymphokines and interleukins, which attract macrophages to the site of infection and enable them to kill these organisms. Much of this analysis based on in vitro and animal studies summarizes current information in a rapidly changing field rather than stating established fact. The precise age at which most of the immune functions discussed reach maturity is unknown. However, the risk of severe infection with these pathogens appears to wane by 2 to 3 months of age. Although this may partly reflect decreased exposure, we might hypothesize that immune functions that are mature by this age are those most critical for protection. Future studies focusing on changes in immune function during the first months of life may provide useful insights into the immunobiology of these diseases and direct attention to the most fruitful areas for immunologic intervention.