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Ricin Vaccine Shown Safe in Humans By Chris Schneidmiller WASHINGTON — The first tests of the experimental ricin vaccine on humans indicate that it would safely provide protection if the poison was used in an act of bioterrorism, researchers said this week (see GSN, Dec. 1, 2004). Scientists at the University of Texas Southwestern Medical Center in Dallas tested the RiVax vaccine on three groups of volunteers, each consisting of five participants, according to an article published online in the Proceedings of the National Academy of Sciences. All volunteers received three doses over three months. The five volunteers who received the highest dose of 100 micrograms produced blood-borne antibodies that would neutralize the toxin. Scientists also found antibodies in four volunteers who received the medium dose of 33 micrograms and in one participant who received the low dosage of 10 micrograms. Antibodies from the volunteers were tested in mice injected with live ricin. The mice lived, and researchers believe the vaccine would similarly safeguard humans against a lethal dose of ricin. The volunteers themselves suffered minimal side effects from the vaccine, including mild headaches and soreness at the site of injection. Such problems are expected with most intramuscular shots, researchers said in a university press release. “The vaccine that we’re developing … is safe in humans, at least at the doses we tested, and is able to produce an immune response,” lead research article author Ellen Vitetta, director of the Cancer Immunobiology Center at UT Southwestern, said in an interview. There is no approved vaccine for ricin, a poison that can be extracted from the waste left by processing castor beans into castor oil. A 500-microgram dose of ricin could kill an adult, according to the Centers for Disease Control and Prevention, and death is assured for those who do not receive treatment within a few hours of exposure. The toxin is a known terror and espionage agent. Ricin-laced mail was sent two years ago to the office of Senate Majority Leader Bill Frist (R-Tenn.) (see GSN, Feb. 3, 2005). Bulgarian dissident Georgi Markov died in 1978 after being jabbed with an umbrella that inserted a ricin pellet into his leg. Miami pharmaceutical firm DOR BioPharma plans to produce RiVax if it is licensed by the Food and Drug Administration. The company announced last week that it had completed development of the manufacturing process for an important protein to be used in the vaccine. Work on the vaccine at UT Southwestern began in 1999. Vitetta said it could take another two years before the treatment is ready for consideration by the Food and Drug Administration. “It’s hard to know. It depends on the progress of the work and the funds available,” she said. “A lot more work remains to be done.” A National Institutes of Health grant will provide funding through February 2007. Vitetta said she is waiting to hear whether the agency plans to offer additional money. Researchers are now developing a vaccine adjuvant — material that would be combined with the inoculation to boost its strength and longevity. Participants in the clinical trial had antibodies in their blood for up to 127 days following the final dose, researchers found. They hope to produce a vaccine that provides protection for a year or longer, Vitetta said. Also being studied is whether the vaccine safeguards mice against aerosolized ricin or poison taken orally. A ricin attack would be more likely to come in those forms than through a needle, Vitetta said. The vaccine is presently being considered only as a prophylactic to be administered in advance of potential exposure to ricin, said DOR BioPharma president and CEO Michael Sember. The company is planning additional clinical trials, but Sember said he could not discuss details of those efforts. No federal agency has issued a request for bids for production of a ricin vaccine, Sember said. The Centers for Disease Control designates ricin as a Category B biothreat, meaning it is moderately easy to disseminate and would be expected to result in low mortality rates. The United States has focused resources against biological terrorism on countering Category A diseases such as plague and smallpox, which can be easily transmitted from person to person and could cause a large number of deaths. Sember said, though, that history has proven the need for a ricin vaccine. “We can’t quantify the size of the market,” he said. “What we can say, is that it’s well known that ricin is a toxin that can be used and has been used around the world for some time.”
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