Comparison of the effects of growth factors on retroviral vector-mediated gene transfer and the proliferative status of human hematopoietic progenitor cells.

We have examined the ability of the recombinant hematopoietic growth factors (HGF) interleukin-3 (IL-3), IL-6, and granulocyte-macrophage colony-stimulating factor (GM-CSF) to increase retroviral vector-mediated gene transfer into human hematopoietic progenitor cells (HPC). The efficiency of neo gene transfer by the N2 vector into human HPC was enhanced by preculture with either GM-CSF or IL-3 (but not IL-6) and with each combination of the three factors. The combination of IL-3 plus IL-6 consistently produced significantly higher levels of G418-resistant colonies (50-60%) than any of the other combinations of HGF tested. Following preculture with HGF and transduction by N2, marrow was maintained in long-term bone marrow culture (LTBMC) for 2 months. The levels of G418-resistant HPC remained stable, and no apparent depletion of total HPC content resulted from the prior exposure to highly stimulatory doses of factors. The proliferative status of the HPC, following exposure to the HGF, was measured as the percentage of HPC that were inhibited from forming colonies by exposure to the S-phase-specific drug, hydroxyurea. The ability of the different HGF to increase the rate of gene transfer by N2 correlated significantly with the extent to which they stimulated HPC proliferation. These results suggest that the mechanism by which HGF increase rates of gene transfer into HPC is by stimulating cell proliferation. Techniques that produce high rates of gene transfer into long-lived human HPC will facilitate studies to quantitate expression of exogenous genes in hematopoietic cells and may be applicable to clinical gene therapy.