Retroviral Transfer of the nlsLacZ Gene into Human CD34+Cell Populations and into TF-1 Cells: Future Prospects in Gene Therapy

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Abstract
Few data are available concerning behavior of reimplanted human hematopoietic cells after autologous stem cell transplantation. This paper reports the possibility to transfer gene markers coding for β-galactosidase (β-Gal) activity by retroviral vectors into a human leukemic growth factor-dependent cell line, TF-1, and into human hematopoietic progenitors isolated from peripheral blood or bone marrow. Using various combinations of retroviral vectors and packaging cell lines, we demonstrated high expression of a bacterial β-Gal activity induced by the LacZ gene, the nlsLacZ gene, or the Sh-ble/LacZ gene, in human hematopoietic cells. The expression of the nlsLacZ construct was stable until the end of the culture in infected CD34+ cell-enriched cell populations, and a slow decrease of transgene expression was observed in a transduced TF-1 cell population during a 1-year long-term culture. Data obtained with the nlsLacZ gene demonstrate that both retroviral transfer and corresponding gene expression were not found to modify the pattern of cell proliferation and differentiation. These results open interesting prospectives for the use of the nlsLacZ gene to mark and follow the fate of progenitor cells isolated from patients with cancers prior to reimplantation. Gene transfer into human hematopoietic stem cells represents a fascinating approach to study the differentiation process of stem cells and to perform the gene therapy of some genetic or acquired diseases. However some questions remain about the possibility to transfer and to express a transgene for a long period of time in human stem cells. Moreover, the possibility to achieve complete hematopoietic reconstitution by transplanting human stem cells isolated on the basis of CD34 expression remains to be demonstrated. In this paper, we address these questions by transferring gene markers coding for a β-Gal activity with retroviral vectors into human CD34+ cell populations and into TF-1 cells. Results obtained with the nlsLacZ gene open interesting prospectives to mark peripheral blood progenitor cells isolated from patients with cancers and to follow the hematopoietic reconstitution by studying in vivo gene expression.