Because of the rapid internalization of ricin toxin, vaccination is the best strategy for dealing with ricin intoxication. Antibodies generated in response to vaccination are continuously present and can “mop up” ricin as soon as it is present.
The RiVax® vaccine candidate uses one of the safest vaccination approaches known – using a modified inactivated protein component of the ricin toxin itself to raise antibody responses, combined with an alum adjuvant to boost the body’s response to the vaccine.
RiVax® also uses Soligenix’s proprietary ThermoVax® technology to create a vaccine which is stable for long term storage even at very high temperatures (e.g., 40°C or 104°F). This means the RiVax® protein may be stored for long periods of time allowing it to be stockpiled for future use.
What is RiVax®?
RiVax® primarily consists of two components:
- A modified form of the A-chain of the ricin toxin. The modifications have removed the biological activity of the protein while still retaining its shape to trigger an effective antibody response.
- Aluminum (“alum”) as an adjuvant. Alum is a very well-known adjuvant, used in many commercial vaccines, with well known safety profiles.
RiVax® is administered as an intramuscular injection on 2 or 3 occasions, resulting in the adaptive immune system mounting an antibody response.
Mechanism of Action
RiVax® induces the adaptive immune system to produce antibodies that recognize and bind ricin toxin, preventing it from getting inside cells and killing them. After intramuscular injection with RiVax®, IgG and other antibodies are produced and circulate within the body and are able to mop up ricin whether it was inhaled, eaten or injected.
How is RiVax® Thermostabilized?
The initial alum-adjuvanted RiVax® vaccine generated antibodies that degraded very quickly. By using Soligenix’s proprietary technology, ThermoVax®, a thermostabilized version of RiVax® was produced so it can be stored for long periods of time (i.e., 12 months) even at elevated temperatures (e.g., 40°C or 104°F).
The thermostabilized version of RiVax® is produced by lyophilizing (freeze-drying) the vaccine in individual vials to form a solid white cake. This removes water and other components from the material which would otherwise destabilize the protein. By using a proprietary process, the protein-aluminum combination remains intact.
The solid, lyophilized material can then be returned to a liquid form immediately before use by simply adding sterile water and mixing prior to injection. Because sterile water is also very common and very stable, this results in an extremely convenient product that can be stored for extended periods. Long term storage and ease of use are key attributes for a product that may be stockpiled.
This same thermostabilization process has been demonstrated to be compatible with other subunit protein vaccines.