Homologous Recombination with DNA Introduced into Mammalian Cells

The ultimate objective of the work described below is gene therapy; i.e., the controlled introduction of DNA into cells so as to correct faulty chromosomal genes. Conditions caused by the absence or low level of some normal gene product (generally, but not always, inherited recessively) can, in principle, be corrected by simple insertion of a copy of the normal gene into any of a potentially large number of sites in the genome, provided that no other gene function is upset by the insertion and provided that adequate and controlled function of the introduced DNA can be obtained. In-herited conditions (usually dominant) caused by a mu-tant gene producing a harmful product cannot be cor-rected by the simple presence of a normally functioning