Stable producer cell lines generated by transduction of 293GPG cells. A. 293GPG stable producer cell lines for the GFP-empty vector control virus and the human EAR-2 -GFP virus are stable in expression of GFP. Flow cytometry performed after two months continuous culture shows GFP expression in > 99.5% of cells. B. 293GPG-EAR-2 cell lines were stable with respect to protein expression. Immunoblot analysis performed on transduced cells after two months continuous culture shows strong expression of EAR-2 protein. C. 293GPG stable producer cell lines were able to produce virus at titers significantly higher than those achieved by transient transfection. Virus was concentrated (one round). Error bars denote standard deviation. D. Transduction of bone marrow using virus produced from stable producer cell lines (1 round of ultracentrifugation) is not able to achieve high transduction rates in primary murine bone marrow cells.