Cell lines stably expressing the (-1) or (0) dual-luciferase HIV reporter, or the in-frame construct, were generated following the manufacturer's instructions, using 293T Flp-in TM cells (Invitrogen). Individual clones that stably incorporated the plasmids were selected on the basis of their resistance to hygromycin B (Wisent) (250 mg/ml) and maintained in hygromycin B.