Alum is the most widely used clinical adjuvant, but its mode of action remains contentious, although the formation of depots for the slow release of antigen is often cited as one of its main immunostimulatory mechanisms. In the FASEB Journal, Brewer and colleagues use an approach of trangenic expression of a T cell antigen receptor and the model antigen EαGFP to rule out the of the possiblity that the formation of a depot of alum is responsible for its adjuvanticity. After antigen priming with alum or the Toll-like receptor agonist CpG, which is an adjuvant but cannot form a depot, they find no difference in the kinetics or magnitude of the T cell response or in the delivery of antigen to a variety of antigen-presenting cells. Alum forms discrete and removable foci at its injection site, and excision of these foci, even as early as 2 hours after injection, has no effect on either primary or recall responses. Rather than being adsorbed to the alum, antigen is therefore rapidly disseminated in soluble form.

FASEB J. 26, 1272–1279 (2012)