INCREASED VIRAL TITER THROUGH CONCENTRATION OF VIRAL HARVESTS FROM RETROVIRAL PACKAGING LINES

Dependent on the viral vector and the specific assay used, viral titer s produced from commonly used retroviral packaging cell lines have an upper limit in the range of 10(5) to 10(7) infectious units/ml. We hav e developed a generally applicable method, using hollow-fiber filtrati on technology, which allows for the concentration of infectious virus derived from packaging lines. This method resulted in a reproducible 1 0- to 30-fold increase in viral titer and can readily be scaled to acc ommodate larger input volumes. Over 80% of the input virus is recovere d in an infectious form in the concentrate. Concentrated virus contain ing media was seen to produce higher infection frequencies in Jurkat T cells as compared to unconcentrated virus containing media; however, this was not proportional to the differences in viral titer observed b y limiting dilution analysis on NIH-3T3 cells. These results are discu ssed in relation to the importance of factors other than viral titer i n determining transduction frequencies.