Is the TRC lentiviral vector (pLKO.1) 2nd or 3rd generation?

The pLKO.1 vector is a 3rd generation vector because of the chimeric 5' LTR (U3 replaced with CMV) which makes it TAT independent. Researchers can use second or third generation packaging systems. However, second generation packaging systems are used and recommended by the TRC and give much higher titers. This is because even though transcription can be driven by CMV, the presence of the TAT transcativator in the second generation packaging system enhances transcription by binding to TAR (element present in the 5' LTR).