The purpose of this study was to establish preliminary conditions for long-term stability of RiVax with the intent of avoiding the cold chain, usually required for storage of vaccines. In this publication, a series of formulations of the RiVax immunogen, a modified recombinant ricin A chain protein, were examined for comparative effects of storage at room temperature versus refrigeration.
The formulations were designed with excipients expected to add to protein stability and then processed by lyophilization to remove water. One combination of lyophilization conditions and excipients was found to result in a vaccine that retained immunogenicity in animals, an index of vaccine potency, for one year at room temperature.
The lead formulation showed no evidence of degradation, whereas unstable control formulations aggregated when reconstituted with water. Moreover, the stabilized vaccine formulation was potent when adsorbed to aluminum hydroxide adjuvant, which is used in many approved vaccines.
As shown previously, the aluminum adjuvant enhanced the immunogenicity and potency of RiVax. The lyophilized vaccine was also tested for immunogenicity in mouse challenge models, in which vaccinated mice were exposed to ricin by the aerosol or oral route. In each case, the reconstituted vaccine was demonstrably protective in comparison to control vaccine preparations.
Robert Brey, chief scientific officer of Soligenix, said: “These results are very promising not only for the future development of RiVax in particular, but also for the potential development of other vaccines with long-term stability, especially those using conventional adjuvants composed of aluminum salts.
“Our current efforts are centered on combining conventional adjuvant and scalable lyophilization techniques to examine formulations that retain stability at elevated temperatures, building on the results that Dr Vitetta and her colleagues have reported in this publication.”