CD19⁺CD5⁺ B cells from DTG mice are leukemogenic. (A) CD19⁺CD5⁺ splenocytes (10⁶ cells) were purified by FACS from 2 different DTG mice and injected into the tail vein of recipient SCID mice. Mice were bled every 6 weeks, and analyzed for the appearance of CD19⁺CD5⁺ cells using flow cytometry. Normal C57Bl/6 mice and sham-injected SCID mice were included as controls. CD19⁺CD5⁺ B cells were readily detected in SCID recipients but not control animals at 6 weeks posttransfer. (B) Genomic DNA prepared from spleens of 36-week-old WT, dnRAG1, Eμ-TCL1, and DTG mice (lanes 2-14), as well as DTG donor and SCID recipient mice in panel A (lanes 15-18), was subjected to Southern hybridization using a J_H-probe. *Nongermline bands. The J_H probe contains a portion of the Eμ enhancer, and therefore also detects the dnRAG1 transgene which contains this element.¹²  (C) V_H-to-DJ_H and Vκ-to-Jκ rearrangements were amplified by PCR from genomic DNA samples described in panel B. Rearrangements to a given J segment are shown at right. The non-rearranging CD14 locus was amplified from the diluted genomic DNA templates as a loading control. (D) The most represented IgVH and IgVκ gene sequences from three ill Eμ-TCL1 and DTG mice were analyzed to identify gene usage, mutation status, CDR3 composition and pI, and reported reactivity profile (summarized from supplemental Tables 1-2).