Factors influencing the production of recombinant SV40 vectors

Most gene therapy approaches employ viral vectors for gene delivery. Ideally, these vectors should be produced at high titer and purity with well-established protocols. Standardized methods to measure the quality of the vectors produced are imperative, as are techniques that allow reproducible quantitation of viral titer. We devised a series of protocols that achieve high-titer production and reproducible purification and provide for quality control and titering of recombinant simian virus 40 vectors (rSV40s). rSV40s are good candidate vehicles for gene transfer: they are easily modified to be nonreplicative and they are nonimmunogenic. Further, they infect a wide variety of cells and allow long-term transgene expression. We report here these protocols to produce rSV40 vectors in high yields, describe their purification, and characterize viral stocks using quality control techniques that monitor the presence of wild-type SV40 revertants and defective interfering particles. Several methods for reproducible titration of rSV40 viruses have been compared. We believe that these techniques can be widely applied to obtain high concentrations of high-quality rSV40 viruses reproducibly.