Gene vaccines.

A most surprising finding was that naked DNA when injected into animal tissue is taken up and expressed by cells with great efficiency. The DNA is given as a plasmid which includes a promoter and an enhancer. When inoculated, it is not stably integrated within the chromosomal DNA, but persists as extrachromosomal nuclear episomes. Both purified DNA and RNA have been shown to be expressed in somatic cells. It is now well established that injection of DNA by many routes is expressed in vivo and the proteins immunogenic. DNA vaccines appear to induce efficient and complete immune responses. The immunizations produce long-term humoral and cellular responses, qualitatively similar to live attenuated vaccines but without the safety hazards of infectious agents. These findings will have important implications for the continued development of human vaccines.