Normalizing total virus concentration with Ad5 empty vectors and impact on transgene expression. A549 cells were infected as described in figure 1. Detection of gag (A), pol (B), and nef (C) transgene expression in A549 cell lysates infected with monovalent, trivalent or multivalent formulations composed of monovalent vectors and empty vector to normalize total virus concentration. Fluorescence based ELISA signal is measured in relative fluorescence units (RFU). Similar results were observed on an independent set of experiments using OD450 detection (data not shown). The error bars represent 95% confidence interval (error bars for the monovalent and trivalent formulations were not available, n = 1).