Aluminium Adjuvants – A Nanomaterial used as Adjuvants in Human Vaccines for Decades

Aluminium salts have been used for decades in vaccines as adjuvants to facilitate the adaptive immune response against co-administered antigens. Two types of aluminium adjuvant are mostly used, aluminium oxyhydroxide and aluminium hydroxyphosphate. Both types of aluminium adjuvant consist of nanoparticles that form loose, micrometre sized aggregates at circumneutral pH.

Aluminium adjuvants constitute a well-documented example of administration of nanomaterials to humans with infrequent side effects and a safety record generally regarded as excellent. However, despite its prolonged use in human and veterinary medicine, the mechanisms behind the enhanced response and the immune stimulatory effect are still by and large unknown.

The present paper reviews existing ideas regarding the immunostimulatory effects of aluminium adjuvants, with a focus on the induction of an inflammatory response by cellular stress. Reviewed information was obtained from peer-reviewed scientific papers published in 1988 to date with one exception, a paper published 1931.

Cellular stress causes extra cellular signalling of Danger Associated Molecular Patterns (DAMPs) and upon phagocytosis of aluminium adjuvants the cells need to manage the ingested particles.

A persistent intracellular accumulation of aluminium adjuvants will be a solid depository of sparingly soluble aluminium salts maintaining a constant concentration of Al³⁺ ions in the cytoplasm and this will affect multiple biochemical processes. The cell will be under constant stress and DAMP signalling will occur and we would like to suggest the maintenance of a constant concentration Al³⁺ ions in the cytoplasm as a general underlying feature of the immune stimulation properties of aluminium adjuvants.