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 r etroviral supernatant have considerable effects on the efficiency of r etrovirus-mediated gene transfer and the stability of retroviral vecto rs. The effect of PR on the efficiency of transduction of Moloney muri ne leukemia virus (MMuLV)-derived vectors is strongly dependent on CS: At a fixed CS concentration, the efficiency of transduction shows a m aximum as a function of PB concentration. Increasing the CS concentrat ion shifted this maximum to higher PB concentrations, but the value of the maximum remained the same. Therefore, there were optimal combinat ions of PB and CS concentrations that maximized the efficiency of gene transfer: 4.4, 8.8, 13.2, and 22 mu g/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 vir al inactivation showed an initial phase during which the transduction efficiency remained constant followed by exponential decay. However, i n the presence of high PB concentrations (13.2 mu g/ml) during the dec ay period of retroviral vectors, the initial delay was lost and the de cay was exponential right from the outset. The present results suggest that in addition to virus-ceh interactions that occur on the target c ell surface, other physico-chemical processes may occur in solution th at have a profound effect on retroviral activity and therefore they ar e of particular importance for gene therapy.