fVIII expression and vector copy number analysis in hemophilia A mice following reduced-intensity TBI or BU-ATS conditioning regimens. Human efVIII and sfVIIIΔB antigen (fVIII:Ag) levels in the plasma of 550 cGy TBI–conditioned (A) or BU-ATS–conditioned (B) hemophilia A mice that received BM cells transduced with FB.efVIII- or MSGV-sfVIIIΔB vectors (at 0.5 MOI × 3 cycles and 5 MOI × 3 cycles, respectively), as measured by ELISA and presented as mean values ± SDs at various time points after transplantation. (C) Vector copy number in the genomic DNA of PB, spleen (SP), and BM cells was quantified by real-time PCR using human fVIII-specific primers at 6 months after transplantation. The vector copy numbers per cell for mice that received MSGV-sfVIIIΔB–transduced BM cells were significantly higher than those that received the FB.efVIII-transduced BM in both the 550 cGy TBI–conditioned (P = .004) and BU-ATS–conditioned (P = .001) groups. Data presented are the mean values of 2 independent experiments ± SDs.