In vivo bone marrow transplant/cytidine deaminase (CDD) gene transfer model. Bone marrow cells were harvested from C57 Bl/6 mice, prestimulated with IL-6/SCF, transduced in the presence of fibronectin (FN) fragments and IL-6/SCF, and transplanted by tail vein injection into lethally irradiated recipients. A spleen focus-forming virus-based vector containing the CDD cDNA in combination with the enhanced green fluorescent protein (EGFP) marker gene was used. A vector expressing EGFP only served as control. After hematopoietic reconstitution, animals were treated with repetitive cycles of cytarabine (500-1000 mg/kg administered intraperitoneally on 4 consecutive days). Peripheral blood counts as well as the percentage of EGFP⁺ granulocytes and lymphocytes were analyzed 3 days before and 1, 4, and 8 days after treatment cycle. IRES indicates internal ribosomal entry site.