STRATEGIES FOR EXPLOITING THE IMMUNE-SYSTEM IN THE DESIGN OF VACCINES

There are three types of vaccines in medical use today-live, attenuated agents, mainly viruses; inactivated whole organisms; and subunit preparations. Though there are examples in each category of successful preparations, live attenuated viruses have almost invariably given long-lasting immunity after one or two administrations. Contributing reasons for this are gleaned, not from human vaccine studies, but from model systems and it is concluded that a vaccine needs to achieve four goals: activation of antigen-presenting cells; overcoming genetic variability in T cell responses; generation of high levels of T and B memory cells; and persistence of antigen for recruitment of B memory cells. Of the newer approaches to vaccine development, synthetic peptides have substantial limitations but should be successful in some cases. Subunit preparations may also be limited as a general method. Some live viral or bacterial vaccines, used as vectors of nucleic acid coding for other antigens, hold considerable promise as is illustrated by recent examples.