Dose–response of HDAC inhibitors on the transduction levels and transgene product yields resulting from IDLV-mediated gene transfer into human cells. (A) Chemical structures of TSA and SAHA made with the aid of ChemBioDraw version: 12.0d560. (B) Flow cytometric analyses at 48 hr posttransduction of myoblasts (1.5×105 cells/well) exposed for 16 hr to IDLV.CMV.eGFP at 1.2×106 vgc/ml in the absence (gray bars) or in the presence of various doses of TSA or SAHA (solid bars). Mock-transduced myoblasts served to set the threshold between background and eGFP-specific fluorescence. The concentrations of TSA and SAHA applied were 0.125, 0.25, 0.5, 0.75, 1.0, 2.0, 4.0, and 8.0 μM. The flow cytometry data are expressed in terms of the percentage of reporter-positive cells and corresponding mean fluorescence intensity (MFI) values (upper and lower graphs, respectively). (C) Flow cytometric analyses at 48 hr posttransduction of hMSCs (1.5×105 cells/well) exposed to IDLV.hPGK.eGFP at 1.35×106 vgc/ml in the absence (gray bars) or in the presence of different doses of SAHA. Eight different concentrations of SAHA were used with each dose varying by a factor of 2 from a minimum of 0.125 μM to a maximum of 16 μM. Mock-transduced hMSCs served to set background fluorescence levels. (D) Flow cytometric analyses at 48 hr posttransduction of HeLa cells transduced with IDLV.hPGK.eGFP at 1.35×106 vgc/ml in the absence (gray bars) or in the presence of different doses of SAHA. Eight different concentrations of SAHA were used with each dose varying by a factor of 2 from a minimum of 0.125 μM to a maximum of 16 μM. Mock-transduced HeLa cells served to set the threshold between background and eGFP-specific fluorescence. hMSCs, human fetal mesenchymal stem cells; SAHA, suberoylanilide hydroxamic acid; TSA, trichostatin.