Feed Materials (Load Material and Virus Stock)
Feed materials should be representative of the in-process material from a manufacturing run in terms of product quality attributes and solution conditions. In cases where feed material property is affected by freezing and thawing, it is preferable to obtain feed material soon after a manufacturing scale run and use without freezing, or freshly prepare feed from the preceding unit operation at small scale, or filter thawed material to remove any potentially clogging aggregates or particles that result from freezing and thawing. This can result in not achieving the desired volumetric throughput in the validation study
Impurities present in a virus spike can significantly impact product mass or volume throughput in a virus clearance study (Slocum, Burnham et al. 2013, De Vilmorin, Slocum et al. 2015). Therefore, high purity and high titer virus stocks are desirable to evaluate virus removal while maintaining product filtration capacity. High viral titer can help reduce the required viral spike volume while allowing measurement of full viral removal capacity.