An optimized conditional suicide switch using doxycycline-dependent expression of human tBid.

We have examined in a HeLa model system whether tight doxycycline-dependent expression of human tBid can be used as a fast and efficient suicide switch. A stably transfected cell line expressing human tBid in a strictly dox-dependent manner showed fast and efficient killing with up to 98 % specific cell death 24 h after induction. The survival rate was only 0.6 % after eleven days of dox treatment. Very low amounts of tBid were sufficient to induce apoptosis indicating that stringent control of the dox-dependent suicide gene is essential for cell survival in the absence of inducer. Using human tBid, an endogenous effector protein with low immunogenic potential, and doxycycline, an inducer with low cytotoxicity and a long record of safe use in humans, this conditional suicide switch provides a tool for various applications, e.g., adoptive immune transfer.