Increased efficiency of gene transfer with retroviral vectors in neonatal hematopoietic progenitor cells.

The retroviral vector N2, which is derived from the Moloney murine leukemia retrovirus, was used to transfer the bacterial NeoR gene (conferring resistance to the neomycin analogue G418) into hematopoietic progenitor cells from fetal, neonatal, and adult dogs and cats. Infection of canine and feline bone marrow cells with the N2 vector resulted in resistance of granulocyte-macrophage colony-forming units (CFU-GM) to G418. Approximately 2%-4% of fetal liver, fetal bone marrow, and adult bone marrow day-7 CFU-GM were resistant to 1.75 mg/ml G418, a dose toxic to cells not expressing the NeoR gene, after infection with the N2 retrovirus. In sharp contrast to the low rate of infectivity of both fetal and adult marrow samples, the mean +/- SD of G418-resistant CFU-GM was 11.7% +/- 14.1% and 14.0% +/- 18.1% for neonatal dog and cat marrow samples, respectively. The neomycin phosphotransferase enzyme activity was detected in G418-resistant CFU-GM, confirming that G418-resistant CFU-GM expressed the NeoR gene. The increased efficiency of retroviral vector-mediated gene transfer into neonatal hematopoietic progenitor cells was not due to an increased fraction of actively dividing cells, as determined by tritiated thymidine suicide. Understanding the basis for increased gene transfer into neonatal hematopoietic progenitor cells may be helpful in designing effective retroviral vectors/gene transfer protocols for gene therapy.