IµHABcl6 Ung^−/−Msh2^−/− and IµHABcl6 Msh2^−/− mice die of early onset DLBCL. (A) Clonality analysis of mature B-cell lymphomas was carried out on all B-cell tumors using Ig variable region amplification. Four major PCR fragments corresponding to respective JH1, JH2, JH3, and JH4 arrangement are labeled on the left. Multiple bands are present in a polyclonal population of healthy B cells (lane 1), and a single or dominant band indicates a clonal population. Representative specimens are shown. Lanes 2 to 4: DLBCLs from IµHABcl6 mice. Lanes 5 to 7: FLs from IµHABcl6 Ung^−/− mice. Lanes 8, 9: DLBCLs from IµHABcl6 Msh2^−/− mice. Lanes 10 to 12: DLBCLs from IµHABcl6 Ung^−/−Msh2^−/− mice. M, 1-kb DNA marker. (B) Unsupervised hierarchal clustering of gene expression profiles obtained from Illumina Mouse WG-6 v2.0 microarrays of representative B220⁺ IgM⁺ CD138⁻IµHABcl6 (n = 3), IµHABcl6 Ung^−/−Msh2^−/− (n = 4), and IµHABcl6 Msh2^−/− (n = 2) mature GC B-cell lymphomas (color coded). Rows represent different gene probes, and columns denote individual samples. The scale indicates relative changes in gene expression normalized by the standard deviation (−2 to 2 in log₂ units; 0 represents the mean expression level of a given gene across samples). (C) Supervised hierarchical clustering of gene expression data from representative IµHABcl6 (n = 3), IµHABcl6 Ung^−/−Msh2^−/− (n = 6), and IµHABcl6 Msh2^−/− (n = 5) B-cell lymphomas. The pre-B-cell lymphomas and DLBCLs (defined by immunophenotyping and histology) are noted on the bottom and have distinct gene expression profiles (supplemental Table 2). (D) Median time to development of DLBCL in IµHABcl6 mice (squares) was 16.2 months compared with 6.5 months in the IµHABcl6 Ung^−/−Msh2^−/− mice (circles) and 5.8 months in IµHABcl6 Msh2^−/− mice (triangles). Bars denote the median. P values were calculated using the 1-tailed Mann-Whitney U test. (E) Kaplan-Meier overall survival curves for IµHABcl6 mice with indicated genotypes that developed DLBCLs. P values were calculated using the log-rank (Mantel-Cox) test.