Promising results from Soligenix' RiVax vaccine against ricin toxin

Dec 29 2009

Soligenix, Inc. (OTC Bulletin Board: SNGX) (Soligenix or the Company), formerly known as DOR BioPharma, Inc., a late-stage biotechnology company, announced today the publication of an article in the January 2010 edition of Infection and Immunity, detailing the characteristics of several immunodominant regions of ricin A chain, the antigenic component of RiVax((TM)). RiVax((TM)) is Soligenix's vaccine to protect against exposure to ricin toxin and is currently being evaluated in Phase 1 human safety and immunogenicity trials, as well as nonhuman primate trials for efficacy.

The article, entitled "A Monoclonal Immunoglobulin G Antibody Directed against an Immunodominant Linear Epitope on the Ricin A Chain Confers Systemic and Mucosal Immunity to Ricin," is the result of collaborative efforts between the Wadsworth Center of the New York State Department of Health (Albany, NY) and Soligenix. The research was funded in large part by several National Institutes of Health (NIH) grants to the Company for the development of RiVax((TM)). The full article (Neal et al., Infection and Immunity, 2010, volume 78: pp. 552-561) is available online at: http://iai.asm.org/cgi/content/abstract/78/1/552.

In this study, the investigators produced and characterized a monoclonal antibody directed against a region ("epitope") of the ricin A chain previously known to be highly immunologically stimulatory ("immunodominant") in humans. The monoclonal antibody was shown to bind the ricin A chain with high affinity, and to be capable of neutralizing ricin toxin in a cell-based killing assay. Moreover, when administered passively to mice, the neutralizing antibody was sufficient to protect the animals against both systemic (i.e., intraperitoneal) and mucosal (i.e., intragastric) ricin challenge. These results advance the concept that antibodies present in the circulation at the time of toxin exposure not only protect animals against death, but may also prevent the toxin's effects on mucosal tissues. This is an important finding, as ricin is toxic to humans following ingestion and inhalation. The study is also significant because it raises the possibility of using specific linear determinants on the ricin A chain as markers for protective immune responses in humans. Immunological readouts, such as the ability of serum antibodies to react with specific neutralizing epitopes on the ricin A chain, along with other markers that are currently in use to investigate human immune responses, will be essential in fully evaluating the efficacy of candidate ricin vaccines such as RiVax(TM), in the absence of the ability to perform vaccine efficacy trials in humans.

"These data are important in terms of ricin vaccine development, since they firmly establish that pre-existing serum antibodies directed against linear determinants on the ricin A chain are sufficient to confer both systemic and mucosal immunity to ricin," stated Nicholas Mantis, Ph.D., Research Scientist IV, Wadsworth Center, and lead author of the study.

"Vaccination by injection primarily induces antibodies in the circulation, and in the case of RiVax((TM)), these fundamental results further indicate that intramuscular vaccination will be expected to protect humans against ingestion of toxin or aerosolized toxin exposure," said Robert N. Brey, Ph.D., Chief Scientific Officer of Soligenix, and a co-author of the study. "The publication of these results is exciting as they lead the way to the potential development of new applications utilizing a key target of neutralizing antibodies in vivo."