Winter 2006-07
Ricin: Vaccine Passes First Clinical Test
The most notorious case of ricin poisoning reads like something borrowed from the pages of a cold war potboiler. A Bulgarian journalist named Georgi Markov is attacked in 1978 London by a man wielding an umbrella rigged with a poisoned tip loaded with the deadly toxin. The umbrella pierces the skin, the tip releases its poison, the poison attacks the journalist, and Markov dies a few days later.
This story highlights the concern over ricin as a potential agent of biological terrorism. Terrorists would not have to rely on weapons as unwieldy as umbrellas because ricin, a byproduct of the production of castor oil, can be powdered and aerosolized and delivered by air, food, or water. Worst of all, no proven antidotes or vaccines exist against it.
For the last few years, a team of scientists at the University of Texas Southwestern Medical Center has been developing a ricin toxin vaccine. Led by Dr. Ellen Vitetta, the team’s preclinical research has been supported by the NIAID, and the researchers recently reported the results of the first human clinical trial that tested their experimental vaccine. NIAID did not fund the clinical trial.
Recently, Dr. Vitetta’s team reported that injections of their experimental vaccine were well-tolerated with only mild side effects in the 15 people who were vaccinated as part of the Phase I safety trial. The trial compared different dosages of the vaccine, each administered in three separate shots to a group of five individuals. When the participants had their blood drawn 14 days after the third vaccination, 1/5 in the low dose group, 4/5 in the middle dose group and 5/5 in the high dose group had developed active anti-ricin antibodies capable of neutralizing the toxin.
Now Dr. Vitetta and her colleagues are looking at how successfully the vaccine can protect laboratory rodents against ricin toxin delivered by aerosol or orally instead of by injection. In ongoing experiments, the vaccine does protect against oral administration. In addition, the group is testing the use of an adjuvant (a compound added to the vaccine) to enhance the immune response to the vaccine so that lower doses will become more effective.
—Jason Bardi
Reference
Vitetta, E. et al. A pilot clinical trial of a recombinant ricin vaccine in normal humans. PNAS DOI: 10.1073/pnas.0510893103 (2006).
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