Frequency of genetically modified cells in the peripheral blood after transplantation. Serial determinations of GFP marking (expressed as percent cells marked in the peripheral blood) were made by flow cytometry (A) or PCR (average copy number × 100 shown) (B). Vector marking in cells transduced with SAR-containing vectors is shown in solid symbols, non–SAR-containing vectors in open symbols. Animal designations and fluorescence assignment are noted: EGFP indicates enhanced green fluorescent protein; EYFP, enhanced yellow fluorescent protein.