IRF-4 suppresses BCR/ABL–stimulated B-lymphoid colony formation. Bone marrow cells freshly isolated from mice were infected with titer-matched MSCV constructs containing BCR/ABL-GFP⁺Neo, BCR/ABL-GFP⁺IRF-4, BCR/ABL-GFP⁺IRF-8, or GFP (A), then triplicates of 2 × 10⁶ cells were plated in soft agar media in the absence of cytokines. Colonies were counted after 10 days. Representative soft agar plates and quantitation of the corresponding colonies are presented in panel B and panel C, respectively.