Coupled Effects of Polybrene and Calf Serum on the Efficiency of Retroviral Transduction and the Stability of Retroviral Vectors

The relative concentrations of Polybrene (PB) and calf serum (CS) in retroviral supernatant have considerable effects on the efficiency of retrovirus-mediated gene transfer and the stability of retroviral vectors. The effect of PB on the efficiency of transduction of Moloney murine leukemia virus (MMuLV)-derived vectors is strongly dependent on CS. At a fixed CS concentration, the efficiency of transduction shows a maximum as a function of PB concentration. Increasing the CS concentration shifted this maximum to higher PB concentrations, but the value of the maximum remained the same. Therefore, there were optimal combinations of PB and CS concentrations that maximized the efficiency of gene transfer: 4.4, 8.8, 13.2, and 22 μg/ml of PB for 1%, 2.5%, 5%, and 10% (vol/vol) CS, respectively. Moreover, the presence of PB affected significantly the kinetics of retroviral decay. The loss of retroviral activity did not follow simple exponential decay in the absence of PB during the decay period of the viral supernatant. The dynamics of viral inactivation showed an initial phase during which the transduction efficiency remained constant followed by exponential decay. However, in the presence of high PB concentrations (13.2 μg/ml) during the decay period of retroviral vectors, the initial delay was lost and the decay was exponential right from the outset. The present results suggest that in addition to virus–cell interactions that occur on the target cell surface, other physico-chemical processes may occur in solution that have a profound effect on retroviral activity and therefore they are of particular importance for gene therapy.

Overview summary

The effects of physico-chemical factors such as the polycation Polybrene (PB) and calf serum (CS) on the efficiency of gene transfer are investigated. PB and CS exhibit a coupled action, because the effect of one strongly depends on the concentration of the other. Optimal concentrations exist for which the efficiency of retroviral transduction is maximized. Retroviral decay exhibits sigmoidal kinetics in the presence of PB, but exponential kinetics in the absence of PB from the viral supernatant, during the period of viral decay. These findings suggest that, in addition to virus–cell interactions that occur on the cell surface, physico-chemical processes may occur in solution that play an important role in retrovirus-mediated gene transfer.