Production of clinical-grade gammaretroviral vectors for ex vivo gene delivery requires a scalable process that can rapidly generate large amounts of vector supernatant, clear large numbers of residual packaging cells with minimal decreases in vector titer, and satisfy all current regulatory guidelines regarding product biosafety. To that end, we have developed a simplified method that is compliant with current good manufacturing practices for the production of clinical-grade gammaretroviral vectors in a clinical research environment. We validated a large-scale production platform utilizing 1,700-cm(2) expanded surface roller bottles and a "modified" step-filtration process consisting of a 40/150-μm dual-screen filter for aggregate removal followed by a Sepacell 500II leukocyte reduction filter for removal of residual packaging cells. This clarification process can clear at least 2 × 10(9) viable producer cells using a single filter set-up without any significant loss of titer post-filtration. This platform typically generates 18 liters of vector supernatant to support small-scale clinical trials, but can easily be scaled up to 70 liters during a single manufacturing run. To date, this platform has generated five clinical-grade gammaretroviral vector products, four of which are now being used in adoptive cell therapy clinical trials for the treatment of a variety of solid cancers.