Antileukemic efficacy of AAV2/8-mediated hIFN-β expression in a xenograft AML model. (A) HL-60 tumor burden in β2m^null NOD/SCID mice following AAV2/8 hIFN-β gene transfer; quantitative results from fluorescence-activated cell sorter (FACS) analysis of bone marrow and spleen single-cell suspensions. Control animals included a saline-treated cohort and a cohort receiving AAV2/8 hFIX vector. Error bars represent SEM. (B) Human CD45 immunohistochemistry confirming the widespread tissue infiltration of control hFIX-transduced mice with HL-60 cells, in marked contrast to hIFN-β–transduced animals. (C) TUNEL staining of subcutaneous HL-60 tumor implants following systemic transduction with AAV2/8 hFIX or AAV2/8 hIFN-β. The negative tumor control was stained without prior treatment with TdT enzyme. All slides were counterstained with DAPI. Slides were examined using an Olympus BX-51 microscope equipped with a 40×/0.85 numerical aperture oil objective (Olympus, Melville, NY). Images were captured using an Olympus digital camera model U-TVO using the SIS image analysis system (Soft Imaging Systems, Münster, Germany). Adobe Photoshop version 5 (Adobe Systems, San Jose, CA) was used to edit the images.