Retrovirus vectors and in vitro expansion of transduced Fancc^−/− BM cells. (A) Retroviral vectors used in this study. SF indicates enhancer/promoter from the spleen focus forming virus long terminal repeat; FANCC, cDNA encoding the human FA complementation group C protein; HOXB4, cDNA encoding the human homeobox cluster B paralog group 4 protein; IRES, the internal ribososome entry site from encephalomyocarditis virus; eGFP, enhanced green fluorescent protein; Venus, modified version of yellow fluorescent protein; Pre, truncated version of the woodchuck hepatitis virus posttranscriptional regulatory element, which lacks any X protein coding sequence; Ψ, packaging signal. (B) Preservation of colony forming activity after in vitro culture. C57B6 LSK BM cells were transduced twice with either SF-HOXB4-IG or SF-IG at an MOI of 6 and cultured for an additional 14 days. The initial transduction frequency was 48.2% plus or minus 0.6% for SF-HOXB4-IG versus 55.1% plus or minus 1.5% for SF-IG–transduced LSK cells based on fluorescence at day 2 after transduction. BM was then plated out in methylcellulose, as described in “Colony-forming assays” and colonies were scored 7 days later. Data represent the mean of 3 independent experiments plus or minus SEM. □ represents SF-IG; ■, SF-HOXB4-IG. **P < .01 compared with SF-IG–transduced group by Student t test. (C) In vitro expansion of BM cells transduced with SF-HOXB4-IG. LSK BM cells from either C57B6 or Fancc^−/− mice were transduced with either SF-HOXB4-IG or SF-IG and were then cultured for an additional 14 days. The percentage of eGFP⁺ cells in culture was determined at days 4, 9, and 14 after transduction. Data represent the mean of 5 or 6 independent experiments plus or minus SEM. □ represents C57B6 BM; Δ, Fancc^−/− BM; —, SF-IG; , SF-HOXB4-IG. **P < .01 compared with corresponding SF-IG transduced group by Student t test.