Transduction of CB Lin^– cells with Smad7 retrovirus. (A) Depletion of myeloid (CD33 and CD15) and B-cell (CD19 and CD20) lineage markers from de novo isolated human CB to generate Lin^– CB cells used for gene transfer. (B) Experimental outline for assessment of Smad7 function in hematopoietic repopulating cells, as described in “Materials and methods.” GTE indicates gene transfer efficiency; SRC, SCID repopulating cell assay; CFU-SRC, colony forming unit–SRC assay. (C) A representative example of CB Lin^– cells 1.5 days after the final exposure to vector or Smad7 retrovirus, assessed by flow cytometric analysis of GFP expression. Dotted histogram indicates cells exposed to supernatant harvested from empty PG13 packaging cells, used to set the GFP⁺ marker. Value represents the average gene transfer efficiency into CB Lin^– cells, measured as the percentage of GFP⁺ cells ± SEM, from 15 independent CB samples. (D) Expression of the primitive hematopoietic marker CD34 on transduced (GFP⁺) CB Lin^– cells 1.5 days after the final virus exposure (± SEM). (E) Relative expression of Smad7 (± SEM) using Q-PCR in vector- (□) versus Smad7-transduced cells (▪).