CLL development in Tcl-1 tg mice with and without IRF4 expression. (A) CD19⁺ CD5⁺ CLL cells were measured in the peripheral blood using flow cytometry and (B) analyzed over time. N = 6 (Tcl-1 tg IRF4^+/+, red), N = 8 (Tcl-1 tg IRF4 ΔB/ΔB, blue). Arrows indicate mice euthanized because of overt CLL development. (C) Kaplan-Maier analysis showing overall survival of Tcl-1 tg IRF4^+/+ mice (N = 36) and Tcl-1 tg IRF4 ΔB/ΔB mice (N = 28). The study end point of this analysis was 400 ± 20 days. (D) Spleen size and weight were analyzed in healthy age-matched littermates of the indicated genotypes (green) and leukemic Tcl-1 tg mice with WT IRF4 expression (red) or without IRF4 expression (blue). Analyzed mouse numbers are depicted on the y-axis. (E) CD19⁺ CD5⁺ CLL cells were measured in lymphoid organs derived from leukemic Tcl-1 tg mice with WT IRF4 expression (red) or without IRF4 expression (blue). (F) CLL clone sizes as measured by BCR sequencing. LNp, peripheral lymph nodes; major, major clone in % of total CLL cells; minor, minor clones in % of CLL cells; PC, peritoneal cavity; WT, wild-type.