The in vivo phenotype conferred by Smad7 is dependent on Smad4. (A) GFP contribution in PB of primary recipients as assessed by FACS analysis at 13 weeks after BM transplantation: WT cells transduced with the MIG vector, 16.5% ± 5.0%; WT cells transduced with Smad7 vector, 31.6% ± 8.26%; Smad4^–/– cells transduced with MIG vector, 6.19% ± 0.96%; Smad4^–/– cells transduced with Smad7 vector, 7.97% ± 0.6%. (B) The percentage of GFP⁺ cells in PB of secondary recipients at 12 weeks after BM transplantation: WT cells transduced with MIG vector, 2.3% ± 0.51%; WT cells transduced with Smad7 vector, 62.2% ± 2.7%; Smad4^–/– cells transduced with MIG vector, 0.2% ± 0.06%; Smad4^–/– cells transduced with Smad7 vector, 0.2% ± 0.05%. Data are from 1 representative experiment and calculated as mean values ± SEM (P < .05 between WT/Smad7 and Smad4^–/–/Smad7). A total of 20 primary and 16 secondary recipients were used.