PCR analysis from 1 representative long-term hematopoietic culture initiated with all 7 groups of transduced and untransduced CD34⁺ cells outlined in Fig 1. In this experiment, cells were transduced on d1 with G1Na and with LNL6 on d5 and d6. LTCs were initiated on d0, d1, d5, or d6 with the indicated cell group and maintained with cytokines. Cultures were demidepopulated every week, followed by replenishment of half of the medium and cytokines. Harvested cells were used for clonogenic assays in the presence or absence of G418. Values were normalized to represent data obtained from cultures initiated with 10⁴ cells. The origin of the neo^R gene detected in single colonies at weeks 2, 3, 4, and 5 is indicated. Each bar is divided into 3 sections reflecting the percentage of colonies at each time point containing G1Na sequences, LNL6 sequences, or both. For every data point, between 7 and 15 colonies were analyzed. Numbers on top of each bar indicate the transduction efficiency. Similar results were obtained in 1 additional experiment using this sequence of transduction.