Replating ability of Lin^- cells depends on vector design. Correcting the frequency of replating cells for the average vector copy number detected on day 7 after transduction, LTR vectors showed a significantly increased risk for transforming Lin^- cells to acquire replating potential. The median is indicated as a thick black line. If no clones were obtained, the frequency of 1 in 9550 was taken for calculation; if all 96 wells contained replating cells, the frequency was estimated as (at least) 1 in 22 cells.