Adjuvants designed for veterinary and human vaccines.

Adjuvants play an important role in the efficacy of vaccines as the antigens become more and more purified. Indeed recombinant proteins or synthetic peptides are safer than crude inactivated micro-organism, but less immunogenic. This can be balanced by specific adjuvants. But there is no universal adjuvants and their action is not yet clear and rely on different mechanisms. Then, they must be adapted according to several criteria, like the target species, the antigens, the type of immune response, the route of inoculation, or the duration of immunity. For this purpose different type of emulsions have been developed. Water in oil (W/O) emulsions induce a strong and long term immune response. Those based on mineral oils are known to be very efficient but can sometimes induce local reactions with reactive antigens. Non mineral oils are well tolerated but less efficient with poor immunogens. Multiphasic (W/O/W) emulsions can induce short and long term immune responses with various antigens and oil in water (O/W) emulsions are well tolerated and induce a short term immune response. New generation of adjuvants are based on a new concept called 'immunosol' and stem from the association of nanoparticles with a new immunostimulant. They can be used when emulsions are not suitable to obtain a good balance between safety and immunogenicity.