Schematic illustration of alteration of clonal pattern of Ig and TCR gene rearrangements between presentation and relapse in 10 children with ALL. Germ-line gene segments are presented with more than 98% identity. Original IgH targets are shown in white; new IgH targets are shown as hatched circles. TCR targets identified at diagnosis are shown in gray, and new TCR targets are shown as dotted circles. Ongoing rearrangements (V_H-V_H replacement and V_H to DJ_H joining) were found in 2 cases (11 and 449). It is possible to amplify the clones identified at relapse using ASO-PCR approaches on diagnostic samples in 7 patients with ALL, as shown here with arrows for cases 170, 178, 191, 366, 449, 452, and 472. In 2 cases identified with an asterisk (^*), Ig-κde rearrangement was later identified at presentation and preserved at relapse.