Transduction of human and monkey cells with HIV-1–based or SIV-based lentiviral vectors. (A) Diagrams of the HIV-1–(pCL20c MSCV-GFP) or SIV-based (pCL20cSLFR MSCV-GFP) transfer vectors. Sequences from the SIVmac_1A11 genome are indicated as solid boxes. Residual nef coding sequences upstream of a KpnI site (accession no. KO3455, nucleotide 9015) were removed from an earlier version of the HIV-1–based vector, pCL10.1 MSCVcGFP, to generate the vector designated pCL20c MSCV-GFP. The SIV-based transfer vector was constructed by replacing each element of the HIV-based vector with a corresponding fragment from the SIVmac_1A11 genome; the fragment sizes of each element differ slightly. Helper plasmids encoding SIV-gag/pol or the SIV-rev/tat proteins were developed using the pCAGGS expression plasmid system as described for the HIV-1–based system, SJ1.⁶  The titers of amphotropic or VSV-G pseudotyped HIV-1 or SIV vectors are indicated as the means and standard errors of the means for 3 to 5 separate preparations. (B) Relative transduction of human (HeLa, left) cells, owl monkey kidney (OMK, middle), or rhesus monkey kidney (LLC-MK2, right) cells at various multiplicities of infection (MOIs). The experiments were performed in duplicate, and the averages are plotted. The vector/envelope for each titration was as follows: HIV-1/amphotropic (▪), HIV-1/VSV-G (•), SIV/amphotropic (□), or SIV/VSV-G (○).