In vitro expansion of tissue cells by conditional proliferation.

Cell therapies rely on the implantation of well-characterized functional cells with defined properties. Often, the cells of interest do not proliferate in vitro and thus cannot be expanded to the amount needed for characterization, purification, manipulation, or cloning. Here, we describe a method that allows the reversible expansion of cells by the introduction of a proliferator gene controlled by a regulatable expression module. The module is transferred by DNA transfer or by lentiviral transduction. The addition of a clinically accepted regulator [Doxycycline (Dox)] induces proliferator expression and expansion of the cells ad infinitum. Removal of the regulator eliminates the effect of the proliferator and leaves the cells in a non-proliferating status. The method has been applied to different mouse and human tissues. This chapter describes the method for the well-examined example of mouse embryonic fibroblast (MEF) expansion.