Screening human sera samples to investigate a protective role of FX. (a) A549 and (b) SKOV3 cells: Ad5 (2 × 1010 vp ml−1) were incubated with media (control) or 25 different human sera −/+40 μg ml−1 Xbp for 30 min at 37 °C. (c) SKOV3 cells: Ad5 or Ad5T* (2 × 1010 vp ml−1) was incubated with media (CON), human or mouse serum −/+ 40 μg ml−1 Xbp for 30 min at 37 °C. Representative human serum samples which did not show a dependence on FX for protection (pooled sera #17, 22, 24) were used in this experiment. Virus suspensions were diluted 200-fold in serum-free media and 100 μl added to cells for 2 h at 37 °C, then replaced with media with 2% fetal calf serum. Transgene expression was quantified ~16 h post transduction and relative light units (RLUs) were normalised to mg total protein. Graphs show transduction as a percentage of control (Ad transduction with media). Media control (*P<0.05) or matched serum–Xbp conditions (#P<0.05) vs serum+Xbp.