Cell transfection is a method of gene delivery that introduces foreign DNA into a cell. It is the basis of gene therapy and much modern genetic research.
Transfection is either transient or stable in nature. When foreign DNA is introduced, but is eliminated by the cell prior to or during mitosis, it is transient transfection. Much more rarely, foreign DNA is introduced and enters the cell nucleus, adding to or replacing a portion of the cell's native DNA. This type of transfection transforms the cell so that the DNA change is duplicated during mitosis, and is called stable transfection.
Through the use of chemical reagents and carefully-structured methodologies, researchers can induce enough stable transfections in cells to grow a cell culture with a desired genetic change. This is the core of gene therapy.
Cell transfection is accomplished through several different methods, including microinjection of foreign DNA into the cell or through the creation of a "gate" with a chemical or biological reagent. New and better methods for inducing cell transfections are being developed on an ongoing basis.
Web Resources On Cell Transfection
Promega Transfection Guides
Wikipedia: Gene Transfection
Book Resources On Cell Transfection
Gene Delivery to Mammalian Cells by Heiser & Walker (Editors)
Gene Delivery to Mammalian Cells: Methods and Protocols by William C. Heiser