CCR5 shRNA (1005) is less cytotoxic to PBMC by expressing from the H1 promoter. PHA/IL-2-stimulated PBMCs (4 × 105) were transduced at m.o.i. of 5, 1 or 0.2 with lentiviral vectors encoding CCR5 shRNA (1005) under the H1 [H1 CCR5shRNA (1005)] or the U6 promoter [U6 CCR5 shRNA (1005)] or no shRNA (no shRNA). The expression levels of EGFP were monitored by flow cytometry at day 4, 7 and 12 post transduction. Rectangle, m.o.i. = 5; diamond, m.o.i. = 1; triangle, m.o.i. = 0.2.