DNA VACCINES

Abstract

Traditionally, protection against infectious diseases has relied on the use of attenuated or killed vaccines. However, many such vaccines are inadequate for reason of efficacy, safety, and cost effectiveness. Live-attenuated vaccines may be immunosuppressive, cause disease if not attenuated sufficiently, or provide limited immunity if too much attenuated. A major concern regarding the use of live vaccines is the possibility of outgrowth of more virulent organisms. Killed vaccines are often unable to generate protective levels of immunity for reasons of Ag load and loss of important epitopes during inactivation. In addition, they are frequently inconvenient, given that repeated immunization is often necessary to achieve effective levels of immunity. Further, because killed viral vaccines do not provide endogenously synthesized proteins, they are in general unable to induce cytotoxic T cells, possibly a required component of a truly effective vaccine. Subunit vaccines are generally safe but costly and poorly immunogenic. Live recombinant vaccine vectors are effective, but their repeated use in the same host may be limited by vector immunity; furthermore, they are subject to reversion events and can cause disease or death in immunocompromised hosts. There is a need for better vaccines, and recently DNA vaccines have been developed (1).