Schematic representation of the maximum distance between individual hits within RV and LV hot spots. Symbols represent single hot spots originated from 2 (♦), 3 (♦), or 4 (◇) hits in the genome of CD34⁺ HSCs (1030 RV and 849 LV integrations) and HeLa cells (869 RV integrations), plotted according to the maximum distance between individual integrations (in base pairs, log scale). Also shown are “false positive” hot spots generated by applying the definition criteria to a library of LM-PCR–amplified random sequences of human CD34⁺ DNA (798 sequences). A total of 26.0% of the 97 RV hot spots in CD34⁺ cells and almost one-half (40.4%) of the 52 RV hot spots in HeLa cells contained 2 independent integrations in less than 2 kb, compared with only 1 of the 33 LV hot spots.