A blueprint for TFF format selection: Hollow fibers and flat sheets for ultrafiltration of AAV

Over decades of development, the roles for tangential flow filter formats used in recombinant protein processing, including monoclonal antibodies, have become well-defined. In upstream applications the low shear environment in hollow fibers is utilized to recirculate cells without impacting product quality. Flat sheet cassettes are typically used in downstream applications, as their higher turbulence enables faster processing in smaller footprints. However, platform processes for many emerging therapies (e.g. viral vectors, cell therapies, nucleic acids) are still in their infancy, and the roles for TFF formats have yet to be defined. Interestingly, there are many examples of drug developers using different filter formats in the same application. With such a broad range of modalities entering the clinic, each with unique product and process requirements, TFF format optimization is likely to become a more routine step in process development. Here we provide a four-step template to optimize TFF filter formats for bioprocessing. The approach is demonstrated using one of the most common viral vectors in development today, adeno-associated virus (AAV). It includes data from several common AAV serotypes at multiple locations along the downstream process. First, design space limits are defined for parameters such as flow and pressure. In the second and third steps, process conditions are optimized and then applied to achieve the process targets for concentration and/or diafiltration. The TFF formats are compared using key performance outputs such as flux, purity, and yield. Finally, a manufacturing assessment is used to compare formats for factors including cost, facility fit, and sustainability.