January 30, 2006

Vaccine Against Biowarfare Agent Shows Promise

By Anthony J. Brown, MD

NEW YORK -- U.S. researchers have developed a genetically engineered vaccine against ricin, a highly lethal toxin derived from castor beans, which appears safe and stimulates an immune response at high doses, according to the results of a small study.

"Ricin represents a potential agent for use in biological warfare and is classified by the Centers for Diseases Control and Prevention as a level B biothreat," the investigators report in the Proceedings of the National Academy of Science.

Probably the most famous case of the use of ricin as a bioweapon was when the Bulgarian dissident Georgie Markov was killed in 1978 after being stabbed in the leg with an umbrella tipped with the lethal toxin, lead author Dr. Ellen S. Vitetta, of the University of Texas Southwestern Medical Center in Dallas, told Reuters Health. "With more and more spottings of ricin use after 9/11, interest in developing a vaccine grew," she added.

Vitetta said her group's vaccine, called RiVax, is one of several currently in development by researchers in the U.S. and elsewhere. The vaccine is based on a mutated version of the ribotoxic A chain of ricin, combined with the bacteria E. coli.

After showing that RiVax was safe in mice and rabbits in previous studies, the researchers tested the vaccine in 15 human subjects, who were given a low, intermediate or high dose. Three groups of five subjects were given the assigned dosage three times at monthly intervals.

The vaccine appeared to be safe with only minor side effects, such as injection site pain and headache. One of five subjects in the low-dose group, four of five in the intermediate-dose group, and all five in the high-dose group developed antibodies to ricin.

"There was a dose-response relation, if you can call it that since we only had 15 patients," Vitetta said.

The researcher added that her group is planning further studies to examine the effects of various vaccine supplements and to better understand the protection provided by the vaccine. "If money were no object, a ricin vaccine could be on the market in a few years," she said.

SOURCE: Proceedings of the National Academy of Science, January 30, 2006.