The nearly year-long pilot study involved three groups of five volunteers each. Individuals in each group received a series of three injections of various doses of the vaccine, called RiVax, over the study period. As a recombinant vaccine, RiVax is a form of ricin that consists of a genetically modified subunit of the toxin, rather than an inactivated whole toxin.
All five of the individuals in the group receiving the highest vaccine dose produced ricin-neutralizing antibodies in their blood, indicating their immune systems had responded. Four of five in the intermediate dose group produced antibodies, while one of five in the lowest dose group did so.
The human-produced antibodies were then injected along with active ricin toxin into test mice, and the mice survived.
The results of the vaccine trial will be available this week online and in an upcoming issue of the Proceedings of the National Academy of Sciences.
"Our major concern in this trial was safety," said Dr. Ellen Vitetta, director of the Cancer Immunobiology Center at UT Southwestern and lead author of the study. "We have taken a very deadly toxin and genetically engineered it to be safe and to induce protective immunity in humans."
Dr. Vitetta's work with ricin received international attention when she and a team of UT Southwestern researchers in the Cancer Immunobiology Center developed the experimental vaccine for the deadly toxin as an outgrowth of their cancer-therapy work. Dr. Vitetta, Dr. Joan Smallshaw, assistant professor in the center, and their colleagues showed in pre-clinical studies that the subunit of the ricin toxin used to make RiVax was non-toxic but
Contact: Amanda Siegfried
UT Southwestern Medical Center