STAT5aΔN^S711F-expressing cells confer a milder form of MPD, which is restored to aggressive disease by transgenic human bcl-2 expression. STAT5ab^null/null FL cells at E14.5 and E15.5 were transduced with either MSCV/IRES-GFP vector control (IR), STAT5a^S711F, or STAT5aΔN^S711F and transplanted into lethally irradiated recipient mice. Tissues from mice that underwent transplantation were collected and formalin-fixed, and histologic sections were stained with hematoxylin and eosin. Representative sections of liver (A) and spleen (B) are shown. Histologic sections were prepared for mice expressing IR-GFP, STAT5a^S711F, and STAT5aΔN^S711F + bcl-2 groups at < 30 days after transplantation. For mice that received STAT5aΔN^S711F-expressing BM cells that survived long term, the histology was performed at the end of the survival curve (80-90 days). Images were taken using an Olympus BX41 microscope equipped with PanAchromatic objectives (20×) and a mounted Spot In-Sight digital camera (Diagnostic Instruments Inc). The software for image acquisition was Spot Advance. Image processing was done in Adobe Photoshop.