Kinetics of lentiviral vector production. The CH-eGFP-WS-derived lentiviral vector was produced in two CF2 modules by triple transient transfection in serum-free medium. Starting at 2 days post-transfection, cell-culture medium was harvested once a day for five consecutive days and concentrated by low-speed centrifugation. The p24 content (pg p24/ml) of vector preparations was determined by ELISA, the transducing titers (TU/ml) by FACS analysis and the RNA equivalents (RNA/ml) by one-step RT-qPCR with LTR primers. Data represent the mean value ± standard deviation and represent 3 independent experiments. A decrease in vector titer starting at 3 days post-transfection was evidenced by all methods. The specific activities (TU/pg and TU/RNA) are depicted in the inset.