Human trials initiated for ricin vaccine
agent, is to proceed with the first phase of human clinical testing
of RiVax, a genetically engineered vaccine for the toxin for which
there is currently no effective vaccine or treatment for ricin
poisoning in humans.
Ricin, which is extracted from castor beans, can cause fever, nausea abdominal pain or lung damage before dying within a few days of exposure. Because castor beans are readily available, public health officials warn that ricin could be used for terrorism. There have been several recent incidents involving the toxin in the United States and Europe.
The pilot phase I trial is designed to confirm the vaccine's safety at doses that induce effective antibody levels in healthy humans. DOR BioPharma, has received an exclusive license for the vaccine and is developing manufacturing processes for the genetically engineered vaccine.
DOR is planning to produce a large stockpile for more advanced human clinical testing, product licensing and potential purchases from the US government and other interested parties.
Ricin is one of several types of toxalbumins that exert their toxicity by inhibiting protein synthesis in eukaryotic cells, which may ultimately lead to cell death. The Centres for Disease Control classifies ricin as a "Category B" biological agent, which means it is "relatively easy to disseminate."
In creating the new vaccine, DNA encoding the active "A" chain of the toxin was mutated. Deleting the chain's site that inhibits the cell's ability to synthesize proteins, as well as being responsible for inducing vascular leak in the host achieved this.
DOR BioPharma, in conjunction with UT Southwestern scientists, eventually created three genetically distinct non-toxic versions of the ricin A chain, two of which were effective as vaccines in mice. E. coli bacteria are used to produce the A chain protein, making vaccine production inexpensive and safe.
Injected RiVax has been known to protect mice against 10 lethal doses of ricin and has no side effects in mice when given at 100 times the dosage required for an immune response. A similar study in rabbits also showed no side effects, and the animals also produced high levels of ricin-neutralizing antibodies
Dr. Ellen Vitetta, director of the Cancer Immunobiology Centre at UT Southwestern said: "This is a safety and immunogenicity trial to test the immune response induced by the vaccine, the sera (blood products) from our injected human volunteers who will be tested for levels of specific ricin-neutralizing antibodies."
"These antibodies, in turn, will be evaluated for their ability to protect mice against a lethal ricin challenge. As far as we can tell, the vaccine is completely safe and has no side effects."
The threat of bioterrorism using ricin has led to many companies and research institutions devote R&D resources into the development of a vaccine. Scientists at the US Army Medical Research Institute of Infectious Diseases have also developed an experimental vaccine that could protect individuals against ricin. The treatment has proved effective in mice, and if further animal studies are successful, the vaccine could soon be tested in humans.
