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Blocking Every Bug

30 June 2005 (All day)
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The enemy. The Strep B bacterium kills around 100 newborns in the United States each year.

As anyone who's gotten sick despite a flu shot knows, a vaccine that protects against one strain of a pathogen doesn't necessarily protect against the others. Now researchers have used a new strategy to develop a vaccine that protects mice from multiple variants of the Strep B bug, which kills around 100 newborns in the United States each year. Experts believe the strategy could help tackle other diseases as well.

Group B streptococcus (GBS) bacteria live in the genital tracts of about a quarter of healthy women. Those infected experience few problems, but their children can develop sepsis, meningitis, or pneumonia if they contract the bug during birth. Babies inherit protective antibodies from their mothers via the placenta, so a GBS vaccine for pregnant women would go a long way toward preventing infections. However, because there are so many disease-causing strains of GBS, developing a widely effective vaccine has been a formidable challenge.

To make the new vaccine, the researchers first sequenced the complete genome of eight GBS strains. Then a computer program identified 589 proteins likely to be on the surface of the bacterium, where they could be detected by the immune system. Only about two-thirds of these were present in all eight strains, revealing a surprising degree of heterogeneity in GBS genomes, says infectious disease physician Lawrence Madoff of Harvard Medical School, a co-author. The researchers purified 312 of the proteins, injected them individually into female mice, waited for the mice to develop antibodies against the proteins, and then tested the offspring of the injected mice for their susceptibility to the bugs.

Four promising proteins emerged. A mixture of the four protected mice against the 12 strains responsible for the majority of GBS disease in humans. No one protein protected against all of the strains; the combination was essential for the broad effectiveness, the team reports 1 July in Science.

Craig Rubens of Children's Hospital in Seattle, Washington, calls the strategy "an important new approach." But he cautions that the cocktail of proteins that make up the vaccine might need to be updated as new disease-causing strains of GBS emerge.

Related sites
Madoff's home page
CDC's info on Strep B

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