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The events of the fall of 2001 highlighted the need for an effective treatment against anthrax used as a weapon. Antibiotics can kill the bacterium, but the toxin it secretes may already be present at lethal levels within the body when this treatment is administered. The current vaccine, meanwhile, only targets one of the three parts of the toxin released by Bacillus anthracis. A new approach described in a report published online this week by the Proceedings of the National Academy of Sciences provides a more effective defense against the disease in mice.
B. anthracis not only secretes toxins that irreversibly damage immune system cells but also coats itself with molecules known as poly-gamma-D-glutamic acid (PGA) to form a protective capsule and avoid detection as it spreads. Julia Y. Wang and her colleagues at Harvard Medical School and Brigham and Women's Hospital used Bacillus licheniformis, a harmless bacterium that has a similar shielding capsule as anthrax, to purify PGA for use in the novel vaccine. In addition, the vaccine contained so-called protective antigen (PA), one of anthrax's three toxins that is the basis of the existing vaccine. "Clearly there is a need for a better anthrax vaccine," Wang says. "The bivalent vaccine we came up with is likely to be much more effective at protecting against systemic anthrax because it targets both virulence factors of Bacillus anthracis--its toxin and its capsule."
The researchers tested the new treatment on mice by injecting the animals with the new vaccine three times over the course of four weeks. At the end of this period, the researchers found increased levels of antibodies for both PGA and PA in the animals. In addition, treated mice survived exposure to anthrax that killed control animals within 24 hours. The authors suggest that the dual vaccine allows a more effective disease response by synergistically enhancing the immune system's reaction to two separate parts of anthrax's attack. They conclude that the vaccine design "may be widely applicable against infectious diseases and provides additional tools in medicine and biodefense."