How easy is it to make ricin poison? “You just get a bunch of castor beans and grind them up,” says immunologist Ellen Vitetta of the University of Texas Southwestern Medical Center. Stockpiles were recently discovered in Afghan caves used by al Qaeda; Iraq is also known to have supplies. Scientists have worked for years to find a vaccine (the poison is so hard to recognize in its victims that an antidote would be impractical) but without success-until Vitetta and colleagues came upon it.

The poison is best known for its role in a notorious cold war espionage murder.
In 1978 Georgi Markov-a Bulgarian dissident who had left his country a few years earlier-was on his way to work at the BBC in London when he felt a stinging pain in the back of his right thigh. Markov turned and saw a man picking up an umbrella from the street; the man apologized and walked away. But the pain in Markov’s thigh increased, and that night he developed a high fever. Three days later, he was dead. An autopsy revealed that a tiny amount of ricin had been delivered by means of a pellet, likely shot into Markov’s thigh with a weapon disguised as an umbrella.

Recently, Vitetta was using ricin poison in her search for a cancer drug. “We were attaching a part of the ricin toxin to antibodies directed against tumors,” she says. “You could say the antibody was the delivery system for a warhead and the warhead was the toxin.” There were side effects to the treatment, but Vitetta and colleagues were able to eliminate them through genetic engineering of the toxin. Then it occurred to them: Because they were able to eliminate the side effect, they could probably eliminate the toxicity as well, thus producing a vaccine for the poison.

Initial tests in animals have proven safe and effective, and Vitetta estimates that a drug could be available in a few years.