Targeting gene expression in specific tissues or cells is a molecular technique under intensive study. Although a challenging task, gene targeting is the main tool of gene therapy, with a potential to develop new treatments for many diseases caused by specific gene defects.

Genes can be targeted for various reasons, such as promoting or increasing gene expression (transductional or transcriptional targeting), preventing protein production from a targeted gene (antisense therapy), delivering anticancer drugs to tumor cells, tagging a given gene with a radioactive compound, for experimental or diagnostic purposes, or to deliver a missing gene into cells (gene transfection).

Gene targeting techniques may involve viral vectors such as adenovirus or herpes simplex virus. Gene targeting techniques may also involve non-viral vectors, such as plasmids. Vectors are vehicles for transportation of either DNA and RNA molecules into cells. Viral and retroviral vectors are genetically modified viruses that...