During the last decade or so vaccine development has been facilitated by rapid advances in molecular and cell biology. These have laid the foundations of a new generation of vaccines exemplified by subunit vaccines produced through gene cloning and by synthetic peptides mimicking small regions of proteins on the outer coat of viruses. Such peptide are capable of eliciting virus-neutralizing antibodies. Unfortunately, subunit and peptide vaccines are only weakly or non immunogenic in the absence of immunological adjuvants that are known to augment specific cell-mediated immune responses to the...