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.