Level of gene marking expressed as number of copies of vector (WPRE) per 100 blood cells analyzed over time. Unique patient identifiers are listed in the upper right corner of the graph. Limits of quantification (stippled) and limits of detection (diagonal lines) values were determined for each amplification reaction and typically were in the range of 0.05% (500 cells/million) to 0.01% (100 cells/million), respectively. Reproduced with permission from DiGiusto et al.³⁸