The Virosart HF was next tested with a feed stream comprising PPV spiked buffered human IgG solution at a IgG concentration
of 0.1 g/L. Two spike trials were carried out with different amounts of virus, the first containing 5x105 pfu/mL and the second
5x106 pfu/mL. The log reduction values were determined using permeate grab fractions taken at 25% and 90% flux decay. The
log reduction value was also determined in the post-wash fraction and the overall filtrate and wash pool. As shown in Figure 5, Virosart HF achieved robust log reduction values for human viruses regardless of the extent of blockage. The log reduction
value for PPV was also high in the post-wash fraction, resulting in an overall pool log reduction value >6 in both tests.
Figure 5: PPV retention in a human lgG model protein feed stream at different degrees of flux decay, during post wash and
in the final filtrate and wash pool executed at two different spike levels.
Finally, the flush volume required to achieve the recovery of the target protein was determined by monitoring the permeate
stream using an in-line UV-detector at 280 nm (see Figure 6). A 0.8-m˛ Virosart HF module was challenged with a 2-g/L buffered human IgG model solution until ~40% flow decay was observed,
and then the module was flushed with buffer at 2 bar differential pressure. The protein concentration in the permeate stream
was calculated from the UV measurement based on a previously determined calibration curve. Flushing the membrane with 3 L/m˛
achieved 99% protein recovery.
Figure 6: Analysis of the recovery flush of a 0.8-m˛ Virosart HF process module. The data shows that, already after 3 liter
flushing per m˛ membrane area, 99% of protein is recovered.
The Virosart HF is a novel, high-performance parvovirus filter based on a surface-modified asymmetric PES hollow fiber membrane.
Rigorous testing confirmed its consistently robust retentive properties and high filtration capacity under challenging conditions,
including an inlet pressure of up to 5 bar, up to 90% blockage, loading of up to 7.4-kg antibody/m˛ and spiking with 0.5%
PPV. The hollow fiber membrane can be packed densely into scalable modules with a small footprint ideal for single-use campaigns.
The authors would like to thank Amit Mehta, Alexander Seay, and John Salvador from Genentech, a member of the Roche Group,
for their contributions and support of this development.
Susanne Roederstein is director purification technologies Europe and Volkmar Thom is director precipitation technologies,
Sartorius Stedim Biotech GmbH, August Spindler Str. 11, 37079 Göttingen, Germany.
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