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...