I inserted shRNA in pLK0.3G (a lentiviral vector with GFP as a reporter) to generate a shRNA plasmid and produce lentivirus for transduction in Tregs. After 3 days transduction, Tregs were stained with antibody of target protein and went through the FACs. I found that the cells with low target protein expressions (high knockdown efficiency) are not the cells with high GFP (high transduction efficiency). Does anybody know the reason?