Human multidrug resistance-1 gene transfer to long-term repopulating human mobilized peripheral blood progenitor cells. 
Mobilized peripheral blood progenitor cells (PBPC) are an attractive target for the retrovirus-mediated transfer of cytostatic drug resistance genes.  We analyzed NOD/SCID mouse repopulating CD34+ PBPC from cancer patients following retroviral Transwell transduction in various cytokine combinations with the FMEV-based (Friend-mink cell focus forming/murine embryonic stem cell virus) hybrid vector SF-MDR carrying the human multidrug resistance-1 (MDR1) gene.  Five to 10 weeks following transplantation of 2.0 x 10(6) CD34+ PBPC into NOD/SCID mice we observed medium to high levels of human cell engraftment with up to 33%.  The extent of vector-marked human cells was assessed by a quantitative real-time polymerase chain reaction (PCR).  SF-MDR gene transfer into long-term in vivo repopulating human hematopoietic cells was optimal in the presence of either IL-3/IL-6/SCF/FL or FL/TPO/SCF resulting in three-fold (12.4% +/- 1.7%) or four-fold (16.5% +/- 6.8%) higher average proportions of gene-marked human cells in NOD/SCID mice as compared to IL-3 alone (P < 0.01).  In conclusion, we could optimize the engraftment capacity and the retroviral gene transfer to CD34+ PBPC using cocktails of early acting cytokines in combination with the recombinant fibronectin fragment CH-296.  Our data suggest that the NOD/SCID model provides a valid assay to estimate the gene transfer efficiency to repopulating human PBPC that may be achievable in clinical autologous transplantation settings.