The feasibility of using DNA as a treatment has been demonstrated in animal models, but clinical applications of this form of technology remain elusive. When gene therapy does come into wide medical use, it may be as a vaccine. Difficulties in developing vaccines against chronic infections with viral agents such as the human immunodeficiency virus (HIV), herpes simplex virus, and hepatitis C virus are partly due to the poor immunogenicity of standard vaccines; these problems have spurred the development of new vaccine strategies that use DNA instead of protein.DNA vaccines contain the gene or genes for an antigenic portion . . .