Soligenix, a development stage biopharmaceutical company based in Princeton, N.J., released results of a phase Ib trial of an aluminum hydroxide (Alum) adjuvanted formulation of RiVax, designed to improve the immunogenicity of the vaccine.

The results of the study indicate that Alum adjuvanted RiVax is safe and well tolerated, and induces greater ricin neutralizing antibody levels in humans than adjuvant-free RiVax.

"The phase IB results demonstrate that well characterized adjuvants can improve the performance of highly purified subunit antigens such as the one contained in RiVax,” said Robert N. Brey, PhD, CSO of Soligenix. “The next steps for the development of RiVax will include the evaluation of secondary adjuvants to enhance the induction of neutralizing antibodies in fewer doses and the employment of our ThermoVax technology to stabilize the ingredients of the vaccine for long term storage at ambient temperature conditions."

The phase Ib trial enrolled healthy volunteers and was designed to evaluate the long term safety and immunogenicity of escalating doses of the vaccine up to one year after a primary vaccination, in which the vaccine was administered by intramuscular injections at 0 weeks, 6 weeks and 6 months in doses of 10µg to 100µg.

At peak antibody titers determined two weeks after the third vaccination, all of the subjects developed neutralizing antibodies against ricin toxin. When comparing peak antibody titers obtained in the phase Ib trial to that of the prior phase Ia trial, which used an adjuvant-free formulation of RiVax, all subjects in the 10µg dose group of the phase Ib trial developed neutralizing antibodies with the Alum formulation of RiVax compared to only one of five subjects in the 10µg group of the adjuvant-free vaccine.  For the 100µg dose vaccine, peak neutralizing titers were four-fold higher with the Alum formulation of RiVax as compared to the adjuvant-free vaccine, with total antibody titers (including all antibodies directed against the vaccine) 17 fold higher. Of all vaccine recipients of both the high dose and the low dose in the phase Ib trial, 100% were seropositive at nine months after the first vaccination, with 60% remaining positive at one year.

"These positive results indicate a route forward for the further development of the vaccine in larger and more definitive trials in humans and to provide the additional correlates of protective immunity in pivotal animal studies," said Brey. "With the formal Request for Information (RFI) from the Department of Defense regarding the status of ricin toxin vaccine development, we believe that Soligenix is well positioned to collaborate with the DoD on the future development of RiVax."

The phase Ib trial was conducted by investigators at the University of Texas Southwestern Medical Center (UTSW) led by Dr. Ellen Vitetta, director of the cancer immunobiology center at UTSW and supported by a combination of grants including a $940,000 grant from the FDA’s office of orphan products development.