Retroviral Vector-Mediated Gene Expression in Human CD34+CD38- Cells Expanded in Vitro: Cis Elements of FMEV Are Superior to Those of Mo-MuLV

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Abstract
A novel murine stromal cell line, HESS-M28, was established, which supports the expansion of human CD34+ CD38- cells more than 300-fold in vitro in the presence of human IL-3 and SCF. These cells were used in an attempt to evaluate cis-acting elements of retroviral vectors in human primitive hematopoietic cells. Cord blood cells were cultured on top of the mixed cell layers of the stromal cell line, HESS-M28, and retroviral vector-producing cells. The FM EV-type vector SF/Lyt contained the spleen focus-forming virus U3 and the M ESV primer-binding site (PBS), while MO3/Lyt contained the U3 region and PBS from Mo-MuLV. After transduction by the FM EV-type and Mo-MuLV-based vectors, expression of the marker gene murine CD8 (mCD8) was examined in CD34-, CD34+, and CD34+ CD38- cells. In CD34+ and CD34+ CD38- cells, expression of mCD8 was higher with the FMEV-type vector, SF/Lyt, compared with the cells transduced by the Mo-M uLV-based vector M O3/Lyt, although the expression was comparable in CD34- cells. Expression of marker genes was also confirmed in long-term culture-initiating cells (LTC-ICs) and SCID-repopulating cells (SRCs).