Effect of SIN design and WPRE addition on transgene expression in human CD34⁺ cells.

A total of 10⁵ CD34⁺ cells were transduced with 10⁶ HeLa-TU of the indicated GFP-expressing HIV-derived vectors and analyzed by flow cytometry 4 days later. Vectors were as follows: (A) PGK (2 intact LTRs); PGK-SIN (3′ SIN-LTR deletion, see “Materials and methods”); PGK-SIN-W (addition of WPRE upstream of the 3′ SIN-LTR). (B) Same analysis as in A but with EF1α promoter instead of PGK promoter. Results are represented as contour graphs of CD34 expression versus GFP expression (4-log scale). For each condition, GFP expression is also displayed as histograms of GFP fluorescence intensity (x-axis, 4-log scale) versus number of cells (y-axis, linear). Number in square represents median of fluorescence intensity of GFP⁺ cells.