Researchers at the University of Texas Southwestern Medical School report in the 10 September issue of Vaccine that an engineered ricin vaccine protects mice against ricin's toxic effects while being non-toxic itself. Previous attempts to make ricin vaccines have failed because of toxicity. The U.S. Centers for Disease Control (CDC) considers ricin a class B bioterrorism agent.

Ricin is a potent toxin, which kills by eliminating the protein synthetic capability of a cell. A single molecule of the ribotoxic A chain can kill a cell; an extremely low dose can kill a human. Ricin's reputed use in espionage is difficult to prove since the molecule is lethal at undetectable doses. However, in one famous Cold War assassination, Bulgarian dissident Georgi Markov died in London after being pricked by an umbrella. A pellet in the umbrella tip was later discovered to contain ricin.

In July 2002, CIA and Pentagon observers reportedly...

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