Experimental design. (A) Schematic diagram of a lentiviral SIN provirus integrated into the genome of a target cell. Virus boundaries are represented by the 5′ and 3′ LTRs, consisting of a minimal U3 (ΔU3) as well as the R and U5 regions. Transgene expression is driven by the internal SFFV promoter located upstream of eGFP and wPRE. SD indicates splice donor; SA, splice acceptor; Ψ, extended packaging signal encompassing residual gag sequences (ΔGA); RRE, Rev-responsive element; and cPPT, central polypurin tract. (B) Murine Lin⁻ cells were purified and prestimulated for 9-48 hours in STIF medium without heparin. Cells were transduced overnight, and either directly transplanted (Tx) or expanded (Exp.) for another 7 days (168 hours) in STIF medium containing heparin. Each of the 7 mice per group was transplanted with an independently transduced and cultivated batch of cells. Group names (G9-14, G48-14, G9-168, and G48-168) indicate the duration of prestimulation and posttransduction expansion times (in hours). Tx, number of transplanted cells per mouse.