Combination of B-cell–specific BCL2 overexpression and Myd88p.L252P expression drives ABC-DLBCL development in vivo. (A) Kaplan-Meier curve illustrates overall survival of M-B-Cd19 mice. M-B-Cd19 mice display a significantly reduced survival compared with the respective controls (log-rank test). (B) M-B-Cd19 mice develop splenomegaly at 25 to 35 weeks. MRI scans and quantification of spleen weights at autopsy are shown (two-tailed Student t test). (C) The architecture of spleens and lymph nodes isolated from M-B-Cd19 mice was completely disrupted by a homogeneous infiltrating population of large lymphoblastoid cells (DLBCL column). Small areas of more heterogeneous lymphoid cell populations consisting of small lymphoid cells were occasionally detectable (LPD column). The livers of M-B-Cd19 mice were diffusely infiltrated by large blastoid cells with DLBCL-like morphology. (D) Variable-diversity-joining–recombination analysis by Southern blot analysis revealed the presence of clonal populations in tumors of M-B-Cd19 mice. Tumors from leukemic Eµ:TCL1 mice were used as oligoclonal controls. The germ line configuration is also present in the WT controls and is depicted as “G.” Asterisks indicate clonal rearrangements. Samples of mice with lymphoma detected by histologic analyses are marked with white triangles (top). (E) Genealogic trees of murine DLBCL isolated from M-B-Cd19 mice. Igh rearrangements were cloned and individual clones were sequenced. Analysis focused on the Ighv segments starting with FR1. Genealogic tree was derived from 32 sequences. The tree-like structures demonstrate ongoing somatic hypermutation. Numbers in circles show number of sequence reads; numbering of mutations is in regard to the germ line sequence of Ighv1-26. (F) The Ki-67 index of DLBCL lesions from M-B-Cd19 mice was significantly higher than that in M-Cd19 mice (P = 2.27 × 10−12, two-tailed Student t test; n = 3 mice per genotype; 20 fields of view per lesion). (G) Lymphoma infiltrates of M-B-Cd19 mice were immunohistochemically analyzed and stained positive for Irf4 and Cd138 and negative for B220 and Bcl6. The Ki-67 stainings are quantified in (F).
