FACS analyses of NGFR transgene expression in transduced CD34⁺Lin⁻ cells. Sorted human mPB CD34⁺Lin⁻ cells were activated and transduced with LINGFR or MINGFR vector supernatants. Two days after viral transduction (4 days in culture), expression of CD34 (stained with an SR-conjugated antibody) and the Lin markers (stained with FITC-conjugated antibodies) were analyzed (dot plots in upper panels). Live cells which retained the CD34⁺Lin⁻phenotype were gated (R2 regions) and percentages of gated cells among the total live cells were determined (≈80% in all cases). Efficiencies of gene transfer and expression levels in these CD34⁺Lin⁻ cell populations were assessed by presence of NGFR (stained by a PE-conjugated antibody) and are plotted as histograms in the lower panels. The gates set up to sort cells expressing NGFR (NGFR⁺, R4) and cells lacking the NGFR surface reporter (NGFR⁻, R3) are indicated as are the percentages of NGFR⁺ cells.