(328d) Development of a Depth Filtration Recovery for a Viral Vector Product

The use of viral vectors containing recombinant transgenes continues to show promise in gene therapy clinical trials. For recombinant adeno associated virus (AAV) based vectors, a number of manufacturing processes have been developed and successfully utilized to manufacture limited amounts of clinical material.  Expanded therapeutic uses for viral vectors or large potential markets require development of manufacturing processes capable of meeting larger material demands.  This paper describes development of a primary recovery operation employing a two stage filtration train to produce a clarified feedstock suitable for further purification.  Initial membrane filtration experiments indicated that > 25 m² of membrane would be needed to process a single 250 L bioreactor.  Recovery development was undertaken to significantly reduce the needed membrane area.  Key challenges included limited analytical throughput, product loss upon filtration, and concurrent cell process development.  These were met using a two-stage filter evaluation strategy.  In the first stage, the first few drops of filtrate from 29 different filters were screened to evaluate potential adsorption/removal of product.  In the second stage, a detailed throughput and performance assessment of the best filters from the first stage was conducted under conditions of constant flow.  A combined cake-complete blockage model was used to fit the data.  The model should enable prediction of the impact of cell process changes on the recovery operation.  The chosen depth filter was able to process 300 L/m² at <20 psi.