Development of a fully penetrant, highly aggressive B-ALL in Kras^G12D/+and Ink4a/Arf double-mutant mice. (A) Representative images of enlarged LNs (middle, white arrows) and spleen (right) from a CD19^Cre/+Kras^G12D/+Ink4a/Arf^L/+ mouse with pre-B-ALL. Representative whole-body photograph of CD19^Cre/+Kras^G12D/+Ink4a/Arf^L/+ mouse with pre-B-ALL (left). White arrow denotes cervical lymphadenopathy; black arrow denotes lagging hind-limb paralysis due to peridural space involvement. Scale bar, 1 cm. (B) Histologic, IHC, and immunofluorescent stains of indicated markers in LN and BM from a representative CD19^Cre/+Kras^G12D/+Ink4a/Arf^L/+ mouse with B-ALL. CD19 staining is shown in green with blue DAPI nuclear counterstain. Note cytoplasmic expression of IgM in B-ALL cells and infiltration of B-ALL cells in the BM and peridural space (PDS) contributing to paralysis (bottom H&E). Scale bars: white, 25 µm; black, 50 µm (see supplemental Figure 5). (C) Southern blot analysis for IgH (left) and TCR (right) genes in the same genomic DNA isolated from CD19^Cre/+Kras^G12D/+Ink4a/Arf^L/+ leukemias. Clonal bands are present for the IgH gene (arrows) but not for TCR. Absence of GL band in some tumor DNA samples indicates almost complete replacement with lymphoma cells.