Figure 3.

Composite FB element does not adversely affect performance of SIN gammaretroviral and lentiviral vectors. (A) Schematic representation of gammaretroviral (MSGV1, MSinSB, RMSinFB, RMSinOFB) and lentiviral (SIV-MSCV, SIV-MSCV-FB, SIV-MSCV-OFB) vectors. Plasmid forms of the vectors are illustrated. All vectors include a GFP transgene under the transcriptional control of the LTR (MSGV1), an internal CA promoter (SIN gammaretroviral vectors) or an internal MSCV LTR promoter (SIN lentiviral vectors). Arrows depict the initiation sites of LTR-, the CA-, or the MSCV-promoter directed RNA synthesis. The deletion in the U3 region of the 3′ LTR in the SIN configuration is indicated by ΔU3. Other abbreviations: B (black type), bovine growth hormone poly(A) signal; B (white type), rabbit β-globin poly(A) signal; CMV, cytomegalovirus immediate early enhancer-promoter; cPPT, central polypurine tract; FB, composite FII/BEAD-A element; OPRE, safety-modified woodchuck hepatitis virus posttranscriptional regulatory element; RRE, Rev-responsive element; S, SV40 late poly(A) signal. Vector titers were measured on NIH3T3 cells and are shown for triplicate determinations (right). *Significantly higher than the RMSinFB titer (P < 0.001). **Significantly higher than the SIV-MSCV-FB titer (P < 0.01). (B) Comparison of GFP fluorescence intensity levels (MFI values) of human 293T cells transduced with the indicated gammaretroviral and lentiviral vectors. Cells were transduced once at low MOI (~1) in triplicate and evaluated by flow cytometry 10 days later. Only the transductions with less than 10% positive cells were analyzed to minimize the effects of multiple integrations. *Significantly higher expression level than the MSGV1 vector (P = 0.003), the MSinSB vector (P < 0.02) and the RMSinFB vector (P < 0.01). **Significantly higher expression level than the SIV-MSCV vector (P < 0.001) and the SIV-MSCV-FB vector (P < 0.001).