Competitive repopulation experiments. In 2 animals (RQ3636 [A] and RQ3590 [B]), a single dose of AMD3100 (1 mg/kg) was administered subcutaneously. PB cells were collected by leukapheresis, enriched for CD34⁺ cells, transduced with G1Na retroviral vectors (animal RQ3590) or a second distinguishable Neo^R-containing vector, LNL6 (animal RQ3636), and frozen for subsequent reinfusion in the animals. One month after the first mobilization, recombinant human G-CSF was administered, and hematopoietic cells were collected by leukapheresis on day 5. CD34⁺ cells were subsequently enriched and transduced with the alternative distinguishable retroviral vectors (LNL6 for animal RQ3590 and G1Na for animal RQ3636). Cells were frozen and soon after reinfused in the animals along with the previously transduced AMD3100-mobilized fraction. Gene marking levels were determined at different time points after transplantation by real-time PCR in PBMCs and GRANs. Gene marking levels were also determined in B and T cells 24 months after transplantation in animal RQ3636 (B cells, 2%; T cells, 3%) and animal RQ3590 (B cells, 0.3%; T cells, 0.1%).