Vaccine Adjuvants Revisited

Abstract

A huge amount of evidence has been made available on various adjuvants as immunological auxiliaries. Very few of them, however, have made it into commercial vaccines. Their defining properties and uses are discussed in the fol- lowing mini-review. WHAT IS AN ADJUVANT? In Freund's words (1) an adjuvant should "evoke very abundant serum antibody production sustained for an unex- pectedly long time". In other words, it is something very practical. It must work in animals at least the size of sheep and of course in both veterinary and human vaccination. To this end it must be thoroughly biocompatible, easy to handle and to store, sterile, safe, acceptable for registration as an auxiliary in vaccination and, last but not least, must have an affordable price. "Abundant serum antibody production" moreover always seems to go hand-in-hand with a host of other beneficial cel- lular immunostimulatory effects. WHAT IS NOT AN ADJUVANT? The following are not adjuvants: Any soluble or insolu- ble substance producing antibodies only in mice (which then have to take the blame for "lying"), and also immunopoten- tiators (showing saturation doses) or immunomodulators (showing dose optimum and even inhibition at the high end). Examples are: water soluble muramyl peptides, saponins, liposaccharides, hormones. These one might characterize as "adjuvants for adjuvants", or, in a word, pseudo-adjuvant. Undoubtedly they are important in special cases, but their usefulness is more remote.