Development of novel packaging cells for refrovirus vectors based on stromal cells

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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.Utilizing this cells, attempt was made 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 FMEV- type vector, SF/Lyt, contained the spleen focus- forming virus U3 and the MESV pimer binding site (PBS), while MO3/Lyt contained the U3 region ard PBS from McMLV.Following transduction by the FMEV- type and the MonLV- 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 to the cells transduced by the MoMLV- based vector, MO3/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).