Ricin vaccine enters Phase 1B clinical trial

Soligenix, Inc., has completed enrollment of its Phase 1B clinical trial of RiVax, a ricin subunit vaccine, in healthy volunteers.

According to preliminary results, RiVax has shown to be safe at all doses tested in volunteers. The Phase 1B trial will assess the duration of immune responses using an adjuvant formulation of RiVax over a period of more than one year after vaccination.

The trial is expected to result in both longer lasting and higher levels of protective antibodies. The trial, which is funded by a grant from the FDA's Orphan Products Division, employs an escalating dose of strategy in which volunteers receive three intramuscular doses of vaccine at six week intervals, which matches many commonly employed vaccination regimes.

Ellen Vitetta, director of the University of Texas Southwestern Medical Center's Cancer Immunobiology Center, is the principal investigator of the study.

Analysis of human immunogenicity and complementary non-human primate efficacy from the test is expected during the first half of 2011.

In a Phase 1 clinical trial of the subunit vaccine without an adjuvant, RiVax's safety and immunogenicity was observed, with results showing that adjuvant-free RiVax was well tolerated and induced antibodies in humans that neutralized ricin toxin in tissue culture and in mice.

"We are very encouraged that we have demonstrated safety at the highest vaccine doses in the current trial volunteers," Vitetta said. "This study with the adjuvanted formulation will further guide us in determination of safe dose levels of RiVax that induce the highest levels of antibodies that are correlated to efficacy. We are looking forward to completing the analysis of the immune responses induced by RiVax in the sera of volunteers up to one year after the last vaccination."