Targeted Large DNA Insertion Figure 4. Transduction of target cells by CsCl density gradient-purified dHV.F50 and dHV.68/5939.F50 particles. (A) Direct fluorescence microscopy analysis of HeLa cells and DMD myoblasts that were either mock-infected or infected with 4, 20 or 100 HTUs of dHV.F50 or dHV.68/ 5939.F50 per cell. (B) Representative flow cytometry histograms corresponding to HeLa cells and DMD myoblasts transduced with different amounts of dHV.F50 or dHV.68/5939.F50 (i.e. 0, 4, 20 or 100 HTUs/cell). The % of maximum refers to the ratio between the number of events analyzed in each case and the number of events in the sample with the largest number of events. (C) Quantification by flow cytometry of gene transfer into HeLa cells and DMD myoblasts exposed to 4, 20 or 100 HTUs of dHV.F50 or dHV.68/5939.F50 per cell (n = 3). Gene transfer activity is expressed both in terms of the frequency of eGFP-positive cells and the mean fluorescent intensity (MFI) of the transduced cells (which reflects mean intracellular eGFP levels). Error bars represent standard deviations. All measurements were performed at 72 hours postinfection. doi:10.1371/journal.pone.0003084.g004 PLoS ONE | www.plosone.org 6 August 2008 | Volume 3 | Issue 8 | e3084