Differential transduction efficiency of SCID-repopulating cells derived from umbilical cord blood and granulocyte colony-stimulating factor-mobilized peripheral blood

The gene transfer efficiency into nonobese diabetic/severe combined immunodeficient (NOD/SCID)-repopulating cells (SRCs) derived from umbilical cord blood (UCB) (n = 11 NOD/SCID mice) and granulocyte-colony stimulating factor (G-CSF)-mobilized peripheral blood (MPB) (n = 64 NOD/SCID mice) was compared using a clinically relevant protocol and a retrovirus vector expressing the enhanced green fluorescent protein (EGFP). At 6-9 weeks after transplantation, the frequency of transduced human cells in the bone marrow (BM) (40.5% ± 2.4% [mean ± SE]) and spleen (SPL) (36.4% ± 3.2%) in recipients of UCB cells was significantly higher (p < 0.001) than that observed in the BM (2.2% ± 1.8%) and SPL (2.0% ± 2.6%) in recipients of MPB. In subsequent studies, MPB was cultured for 2-8 days in cytokines prior to transduction to determine if longer prestimulation was required for optimal gene transfer. A significant increase in gene transfer into CD45⁺ human cells and clonogenic cells derived from MPB SRCs was observed when cells were prestimulated for 6 days compared to 2 days prior to transduction (p = 0.019). However, even after 6 days of prestimulation, transduction was still significantly less than UCB. A substantial discrepancy exists in the ability to introduce genes effectively via retrovirus vectors into SRCs derived from MPB as compared to UCB.