Antibody retention and flux decline during filtration through virus retentive membranes
Open Access
- Author:
- Billups, Matthew
- Graduate Program:
- Chemical Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- December 14, 2020
- Committee Members:
- Phillip Savage, Program Head/Chair
Andrew Zydney, Thesis Advisor/Co-Advisor
Ali Borhan, Committee Member
Stephanie Butler Velegol, Committee Member
Hee Jeung Oh, Committee Member - Keywords:
- virus filtration
ultrafiltration
antibody
retention
fouling - Abstract:
- Virus filtration is a key component of the overall virus clearance strategy in the production of monoclonal antibodies. These virus filtration membranes also provide one of the most selective membrane separations ever demonstrated, with more than 95% recovery of the antibody product in the filtrate with more than 99.99% retention of even small parvovirus, despite the less than 2-fold difference in size between the virus and antibody. However, the filtrate flux through these virus filters can often decrease by more than 100-fold during filtration of these antibody solutions. The objectives of this thesis were to obtain a more quantitative understanding of the intrinsic sieving characteristics and filtrate flux behavior of commercially available virus filters. Experiments were performed with the Viresolve® Pro and PegasusTM SV4 virus filters both with and without stirring to control the effects of concentration polarization. The actual sieving coefficient of a highly purified monoclonal antibody was less than 0.05 for both membranes, demonstrating that the high antibody recovery during typical virus filtration processes is a direct result of the high degree of concentration polarization in these systems. The intrinsic selectivity of the virus filter was in good agreement with predictions of available hydrodynamic models accounting for a log-normal pore size distribution. The actual sieving coefficient also decreased with increasing antibody concentration, consistent with available models for proteins with attractive interactions (negative values of the interaction parameter). The filtrate flux was found to be a strong function of antibody properties, with very low flux for more hydrophobic antibodies that show significant intermolecular attractive interactions. Filtrate flux data were obtained with the asymmetric Viresolve® Pro filter in both orientations, selective skin-up and skin-down, and in combination with different prefilters. The Viresolve® Pro had much higher flux during filtration with the skin-side down, demonstrating the importance of orientation on the virus filter behavior. The use of large pore size prefilters upstream of the Viresolve® Pro skin significantly improved the flux behavior when the filter was oriented skin-side down, but only when the pre-filter was placed directly on top of the Viresolve® Pro. This 100-fold improvement in flux was not seen after batch prefiltration. Data obtained using an in-line prefiltration demonstrated that the critical factor was the residence time between the prefilter and the Viresolve® Pro, suggesting that the prefilter disrupts small aggregates in the antibody solution that then reversibly self-associate leading to a reduction in filtrate flux. This behavior is consistent with the presence of strong intermolecular attractive interactions in these antibody solutions. These results provide important insights into the transport characteristics of virus filters and their effect on the performance of these virus filters in bioprocessing.