Vector design and evidence for Smad4 overexpression in human cells. (A) Schematic design of control and Smad4 vector constructs. LTR indicates long terminal repeats. (B) Transduction efficiencies of CB cells were determined 2-3 days after transduction. (C) RT-PCR results of Smad4 mRNA expression in CB HSCs. Values are relative to HPRT expression. (D) Western blot analysis showing Smad4 protein expression in human CB cells. Actin was used as loading control.