Unique Ig rearrangement patterns in purified CD19⁺CD127⁺ and CD19⁺CD127⁻ populations. (A-F) The levels of D_H-J_H, V_H-DJ_H, Vκ-Jκ, Vκ-Kde, IntronRSS-Kde, and Vλ-Jλ rearrangements were quantified in FACS-purified CD127⁺ and CD127⁻ populations and compared with freshly isolated pediatric BM pro-B cells (dotted line) and small pre-B cells (gray shaded area). The quantitative standards used to determine the percentage of rearranged alleles were a mixture of leukemic cell lines with monoallelic rearrangements set at 100%. All data were obtained from triplicate experiments using cells isolated from 3 separate xenogeneic cultures. (G-I) The size distributions of complete V_H-DJ_H, Vκ-Jκ, and Vλ-Jλ were assessed using GeneScan analysis. These patterns are not consistent with in-frame selection, which would be indicated by a characteristic trinucleotide spacing (triplet peaks) shown on the x-axis of each plot. Size standard peaks are shown in light gray at positions 139, 160, 246, and 300.