B-cell–specific SOX11 expression produces MCL phenotype. (A) Schematic representation of the gene cassette for the coexpression of SOX11 and EGFP in the B cells of a C57BL/6 mouse model. (B) Single-cell mass cytometry (CyTOF) data analyzed using SPADE to comprehensively characterize splenocytes from WT vs age-matched Tg-SOX11 mice. Major immune subsets are annotated based on canonical marker expression patterns, and the SPADE tree is colored by [log10([% of total in SOX11]/[% of total in WT])], highlighting selective expansion of a specific B-cell subset in Tg-SOX11 mice. (C) Further analysis of B-cell subsets by viSNE highlights the phenotype of the expanded population of cells as CD19⁺CD21⁻CD23⁻CD5⁺ (black arrows). (D) Frequency of CD5⁺CD19⁺CD23⁻ B1 cells in peripheral blood, spleens, lymph nodes, and bone marrow of Tg-SOX11 mice vs WT littermates analyzed by flow cytometry (N = 3/group). (E) Frequency of CD5⁺CD19⁺CD23⁻ B1 cells in the peripheral blood of 1.5- to 36-month-old Tg-SOX11 mice vs WT littermates analyzed by flow cytometry (N = 3/group). (F) Spleens from 6-month-old mice showing splenomegaly in Tg-SO11 mice compared with WT littermate controls (N = 3/group). (G) Pathological analysis of spleen sections from a Tg-SOX11 mouse confirming a neoplastic B220⁺CD3⁻CD34⁻BCL6⁻ immunophenotype. Fo, follicular; GC, germinal center; H&E, hematoxylin and eosin; Mono/Mac, monocytes/macrophages; MZ, marginal zone; NF, newly formed transitional; NK, natural killer; pDC, plasmacytoid dendritic cells.