(How) do aluminium adjuvants work?

The aluminium compounds, originally identified as adjuvants over 70 years ago, remain unique in their widespread application to human vaccines. Given this history, it is surprising that the physicochemical interactions between aluminium compounds and antigens are relatively poorly understood. This has clearly been a contributing factor to vaccine failures, for example, through inappropriate selection of aluminium species or buffers. Similarly, the mechanism(s) of action of aluminium adjuvants are relatively unstudied, although it appears that these agents fail to fit within the current principles underlying activation of the immune response. This review aims to examine recent developments in our understanding of the physicochemical and biological aspects of research into aluminium adjuvants.