The recent development of lentivirus-derived vectors is an important breakthrough in gene transfer technology because these vectors allow transduction of nondividing cells such as hematopoietic stem cells (HSC), due to an active nuclear import of reverse-transcribed vector DNA. We recently demonstrated that addition of the central DNA flap of HIV-1 to an HIV-derived lentiviral vector strikingly increases transduction of CD34(+) cells. We now describe improvements of the transduction protocol designed to preserve HSC properties and two modifications of the previously described TRIP-CMV vector. First, deletion of the enhancer/promotor of the 3 ' LTR in the TRIP-CMV vector resulted in a safer vector (TRIP Delta U3-CMV) with conserved transduction efficiency and increased EGFP transgene expression. Second, the original internal CMV promoter was replaced with the promoter for the ubiquitously expressed elongation factor 1 alpha (EF1 alpha). This promoter substitution resulted in a significantly more homogeneous expression of the EGFP transgene in all hematopoietic cell types, including CD34(+)-derived T lymphocytes, in which the CMV promoter was inactive, and NOD/SCID mouse repopulating cells. We thus present here an HIV-derived lentiviral vector, TRIP Delta U3-EF1 alpha, which can very efficiently transduce human cord blood HSC and results in high long-term transgene expression in CD34(+)-derived T, B, NK, and myeloid hematopoietic cells.
