Effect of HOXB4 expression on engraftment, survival, and ROS. (A) Schematic representation of competitive repopulation assay used to assess relative engraftment potential of gene-modified HSC populations. (B) Competitive repopulation of transduced BM as measured by the percentage fluorescent-positive cells in peripheral blood. At the indicated time points after transplantation, the contribution of gene modified cells to the production of peripheral blood leukocytes was analyzed by flow analysis. Percentages: □ represents Fancc^−/− + SF-IG; , Fancc^−/− + SF-FAC-IG; ■, Fancc^−/− + SF-HOXB4-IV; ▨, Fancc^−/− + SF-HOXB4-IV + SF-FAC-IG; , WT + SF-IG–transduced cells in the peripheral blood. Data represent the mean plus or minus SEM of 2 independent experiments incorporating 5 to 14 mice per experimental group. *P < .05, **P < .01 compared with Fancc^−/− + SF-IG group (Wilcoxon rank sum test). NS indicates not significant. (C,D) Apoptosis and ROS levels in transduced BM. LSK BM from C57B6 or Fancc^−/− mice were transduced with either SF-IV or SF-HOXB4-IV. At 2 days after transduction, BM was stained with antibodies directed against lineage markers, c-Kit and Sca-1, in addition to staining with either (C) annexin V or (D) H₂DCFDA. Data represent the least squares mean estimates plus or minus SEM from mixed-effects model analysis of 5 or 6 independent experiments. □ represents Fancc^−/− + SF-IV; ■, Fancc^−/− + SF-HOXB4-IV; , WT + SF-IV; and ▩, WT + SF-HOXB4-IV. *Significant after multiple comparison adjustment (P < .05) by Tukey method.