Stable cell lines are crucial laboratory tools that can be used to express large amounts of a protein of interest. This can be necessary for a variety of reasons; high protein production may be necessary for the screening of experimental drugs, studying of gene functions, or production of therapeutic proteins (including recombinant antibodies).
Stable cell lines contrast strongly with transiently-transfected cells, which do not have stable genetic and protein expression characteristics. Transient transfection results in temporary changes to cell lines, which may aid in one-time production of proteins or short-term experiments. This makes transiently-transfected cell lines ideal for simple experiments, but problematic for studies that last for several days or more. As such, genetic modifications of cells used for longer studies must be permanent (i.e be present in the genome), and hence require advanced transfection techniques.