miR-125b–induced B-cell leukemia is accelerated in IRF4-deficient mice, and enforced expression of IRF4 inhibits miR-125b–induced development of spontaneous B-cell cancers in mice. (A) Survival curve of Eμ/miR-125b-Tg mice, CD19cre IRF4^flox/flox Tg mice, double-Tg mice, and control mice. The genotypes and number of mice in each group are indicated on the plot. (B) Some Tg mice developed lymphoma. Lymphomas are shown at the superficial cervical or inguinal lymph node sites by red arrows. (C) Representative flow cytometric analysis of leukemic B cells in the blood, bone marrow, and spleen of moribund Eμ/miR-125b, CD19cre IRF4^flox/flox and double-Tg mice. (D) Survival curve of the secondary recipient mice transplanted with bone marrow cells from moribund Eμ/miR-125b-Tg mice, CD19cre IRF4^flox/flox Tg mice, double-Tg mice, and control mice (n = 6 mice per group). (E) Spleen weight of the secondary recipients described in panel D. (F) Frequency of bone marrow B cells (B220⁺) in mice receiving Eμ/miR-125b-Tg donor cells that were transduced with either an IRF4-expressing vector or a control vector. NS, not significant.