Sorting vector producer cells for high transgene expression increases retroviral titer.

Vector producer cells are derived from helper cell lines expressing viral proteins that have been transduced to express a transgene-carrying retroviral genome. Vector producing cells express two relevant forms of RNA in their cytoplasm: vector RNA (vRNA) that is packaged as the actual gene transfer agent, and messenger RNA (mRNA) from which transgene is translated. Two premises underlie this study: (1) vRNA is limiting for virus production and (2) mRNA is proportional to vRNA. Together, these premises predict that transgene expression in the vector producing cells will be predictive of the viral titer from those cells. In this case, sorting the vector producing cells for high transgene expression should select for more virus production in vector producing cell supernatants. This prediction was supported, with a greater than fivefold benefit in viral titer. This demonstrates a rapid and simple method by which to obtain significantly increased viral titers from the same vector producing cell preparation.