ABSTRACT
Preventive vaccines have historically represented one of the most cost-effective and most common forms of public health measures. The worldwide market for vaccines is $2.8 billion per year (1). The Centers for Disease Control and Prevention estimates that 5 million doses of vaccines are given yearly in the United States alone (2). In the past, vaccine technology was composed of two basic approaches to the generation of protective immunity: live attenuated vaccines and killed vaccines. Live attenuated vaccines elicit prophylactic immunity through both antibody and relatively weak cellular responses, whereas killed vaccines function primarily through humoral immune response. These traditional approaches to vaccine development together with more modem recombinant methods have failed for infectious diseases such as tuberculosis and malaria (2). Recently, however, a revolution occurred in vaccine research with the arrival of "naked" DNA vaccines.
