Immunologic adjuvant

In immunology an adjuvant is an agent which, while not having any specific antigenic effect in itself, may stimulate the immune system, increasing the response to a vaccine. Adjuvants are sometimes called the dirty little secret of vaccines [1] in the scientific community, as not much is known about how adjuvants work. The aluminum salts aluminum phosphate and aluminum hydroxide are the two most common adjuvants in human vaccines. Squalene is also used in some human vaccines and more vaccines with squalene and phosphate adjuvants are being tested on humans. Oil adjuvants are used in animal vaccines. Aluminum salts used in many human vaccines are generally regarded as safe, however, a recent study revealed that aluminum adjuvants at levels comparable to those administered to Gulf War veterans can cause motor neuron death. The compound QS21 is under investigation as a possible immunological adjuvant as is Novartis' (formerly Chiron) MF59. Another market-approved adjuvant and carrier system is virosomes. During the last two decades a variety of technologies have been investigated to improve the widely used, but unfavorable adjuvants based on aluminum salts. These salts develop their effect by inducing a local inflammation, which is also the basis for the extended side-effect pattern of this adjuvant. By contrast, the adjuvant capabilities of virosomes are independent of any inflammatory reaction. Virosomes contain influenza virus-derived membrane-bound hemagglutinin and neuraminidase, which amplify fusogenic activity and therefore facilitate the uptake into antigen presenting cells (APC) and induce a natural antigen-processing pathway. The delivery of the antigen by virosomes to the immune system in an almost natural way may be a main reason why virosome-based vaccines stand out due to their excellent safety profile.
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