To prepare pseudoviruses and live viruses, 293FT cells were cotransfected with 7.5 mg wild-type or mutant pNL4-3-DE-EGFP, and 2.5 mg pHEF-VSV-G, or 10 mg wild-type or mutant pLAI.2 using Lipofectamine 2000 (Invitrogen, USA) according to the manufacturer's instructions. Supernatants were collected 48 h after transfection and stored at 280uC after spinning down and filtering to remove cell debris. The cells were rinsed with ice-cold phosphate-buffered saline (PBS), scraped from each plate and lyzed in cell lysis buffer (Boehringer, Germany) and 16 protease inhibitor cocktail (Roche, USA) on ice for 30 min. Cell lysates were stored at 220uC after centrifugation at 13,0006g at 4uC for 15 min to remove cell debris.