Prefilters
Virus filters are prone to fouling thus often require the use of a prefilter to achieve the desired virus filter throughput. These prefilters also have limited options for scale-down devices ( See Table 1 for suppliers). This presents a challenge for virus clearance studies, as some prefilters may contribute significantly to the removal of virus when used in-line with the viral filter. To avoid this issue, prefiltration may be performed independently and the resulting prefiltered feedstock can be spiked with virus and applied to the virus filter. In many cases operating the prefilter in-line with the virus filter is necessary to achieve optimal throughput and avoid the reintroduction of filter foulants. Therefore separating the filters may result in lower manufacturing throughput and higher costs. Alternative methods for spiking virus have been developed to introduce the virus spike after an inline prefilter using a highly accurate pump system (Lutz, Chang et al. 2011) to achieve the full benefit of the prefilter without impacting viral titer.