The first human tests of a vaccine to prevent ricin poisoning show that it is safe and effective, researchers at the University of Texas Southwestern Medical Center report.

Ricin is a lethal poison made from the remains of processing castor beans. With more than 50,000 tons of castor bean extract available globally, public health officials warn that ricin could easily be obtained and used by terrorists.

The New Research

In the pilot study, 15 participants were divided into three groups of five. Each group received a different dose of the vaccine, called RiVax, in a series of three injections. The group that received the highest dose produced ricin-neutralizing antibodies in their blood, indicating that their immune systems had responded, the researchers found.

A vaccine that we developed against ricin is safe and it elicited antibodies in human volunteers," says lead researcher Ellen Vitetta, director of the Cancer Immunobiology Center.

To determine whether the antibodies would prevent ricin poisoning, Vitetta's team tested the human antibodies in mice that had been infected with active ricin. The mice survived.

Development Will Take Time

While this small study is encouraging, the actual development of the vaccine may take some time, Vitetta says. First, the researchers need to establish a large stockpile of the vaccine to test on many people, and they must find the best way to store the vaccine to keep it stable. In addition, the researchers need to test its effectiveness against the various ways that ricin can be delivered. "We need to determine whether the vaccine will protect against ricin aerosol, ricin given orally or in water or food," Vitetta says.

Dr. Christopher P. Holstege, director of the Blue Ridge Poison Center in the division of medical toxicology at the University of Virginia, thinks that developing a successful vaccine against ricin is important to thwart a potential bioterror attack. There is a pressing need for an effective vaccine for ricin poisoning, Holstege says. "Ricin is a bioterrorism agent that is very potent," he says. "This is something that is a risk to the general public and to the military."

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