Screening retroviral packaging cells for highly efficient virus production by using a combined selection procedure.

To facilitate the screening for clones of transfected packaging cells producing a high yield of recombinant retrovirus, we present a fast and simple method for the isolation of overexpressing cells. By this method the efficiency of virus production can generally be enhanced 10- to 100-fold by application of high selection pressure. Cell lines which exhibit titers of up to 10(8) CFU/ml were obtained.