Figure 2.

(A) Infection of c-Kit⁺ and c-Kit⁻ cells by SCF-directed bio-AdLuc. Bio-AdLuc linked to avidin was incubated with 250 ng/ml SCF (control vector) or bio-SCF (SCF-directed vector) before infection of the c-Kit⁺ cell lines M-O7e and MB-O2 and the c-Kit⁻ cell lines HL-60 and KG-1a (moi = 165). (B) Specificity of SCF-directed gene transfer to M-O7e cells. SCF-targeted vectors were constructed by incubating Bio-AdLuc (moi = 100) linked to avidin with 50–1,000 ng/ml bio-SCF. In competition experiments, M-O7e cells were incubated with 500 ng/ml nonbiotinylated SCF or IL-3 before infection with 100 μl of the SCF-targeted vector constructed by incubation with 250 ng/ml bio-SCF. In A and B, luciferase activity at 24 hr after infection is reported as the mean ± SE of duplicate determinations and is representative of two experiments. (C) Kinetics of luciferase gene expression after infection of M-O7e cells with SCF-directed vectors. SCF-directed vectors were constructed by adding 250 ng/ml SCF to bio-AdLuc linked to avidin (moi = 120). At various times after infection, M-O7e cells were harvested and assayed for luciferase expression. At all time points, luciferase activity of cells infected with the control vector was less than 2 × 10⁴ RLU/mg protein.