Vaccine against group B Streptococci

The search for a vaccine against group B streptococci Group B streptococci are one of the leading causes of infection in newborn infants, causing pneumonia, septicaemia or meningitis.

A group of Portuguese researchers and a team in a CNRS-associated laboratory at the Institut Pasteur have just identified a protein in this micro-organism which allows it to colonise a host by modulating its immune system. According to these scientists, who have published this study in the Journal of Immunology, the protein thus identified is a possible candidate for the development of a vaccine against Group B Streptococci.

Infections caused by group B streptococci (Streptococcus agalactiae) are an important public health problem. Some 800 cases of invasive infections in newborn infants are recorded each year in France; they mainly result from transmission from the mother to the infant. Mortality linked to these infections remains high (50 to 100 deaths each year), and despite antibiotic therapy, 25 to 50% of the infants who survive suffer from neurological after-effects.

A new prospect for the development of a vaccine against group B streptococci has just been discovered, thanks to a study carried out in the laboratory headed by Paula Ferreira, at the Institute for Biomedical Sciences - Abel Salazar - in Porto, working in collaboration with Patrick Trieu-Cuot, head of the CNRS-associated Unit for the Biology of Pathogenic Gram-positive Bacteria at the Institut Pasteur.

Some proteins produced by pathogenic micro-organisms are capable of interfering with the immune system of the host in order to facilitate microbial colonisation.

The scientists have shown that a protein secreted by group B streptococci, called GAPDH, was capable of raising the level of one of the "messengers" in the immune system, a cytokine called IL-10 (interleukin-10). Such an increase in IL-10 diminishes the immune defences, so that invasive bacterial infection is facilitated. The researchers also showed that IL-10-deficient mice were much more resistant to infection by group B streptococci.

The team thus concluded that GAPDH could be used to ensure immune protection against group B streptococci. Preliminary immunization studies in the mouse demonstrated a protective effect of GAPDH against group B streptococcal infection, thus confirming that this protein should be a good vaccine candidate.

"The ideal vaccination strategy would consist in inducing mucosal immunity, and thus eliminate the vaginal carriage of group B streptococci," explains Patrick Trieu-Cuot. "This vaccination would make it possible to eliminate the antibiotic prophylaxis given at the onset of labour to women who are infected by this micro-organism." It should be remembered that systematic screening is currently ensured between the 34th and 37th weeks of amenorrhoea.

The researchers are now working on the development of this vaccination strategy.