Bill Riordan, PhD 2008

Thesis Title: Analysis and design of membrane adsorbers for viral clearance

Anion exchange membrane adsorbers represent an emerging alternative technology for viral clearance required during the purification of monoclonal antibody therapeutics. Rapid mass transfer rates and low trans-membrane pressure drop allow membrane adsorbers to maintain a high dynamic binding capacity for viruses while operating at fast volumetric flow rates. Building on these inherent advantages, the work in this dissertation was directed at developing a fundamental understanding of virus adsorption onto anion exchange ligands, and using this understanding to guide the design of improved membrane adsorbers that meet operational goals specific to viral clearance.

Membrane adsorbers incorporating the quaternary amine (Q) ligand were highly sensitive to salt concentration, with viral clearance decreasing as salt concentration increased. To overcome this limitation, four salt tolerant ligands were discovered that maintained high viral clearance at salt concentrations up to 150 mM. Additionally, the salt tolerant ligands were shown to be capable of removing different viruses, host cell protein, and DNA in the presence of a concentrated protein solution and salt. Further analysis of structural derivatives of these ligands showed that increased salt tolerance was due to higher ligand net charge and additional secondary hydrogen bonding interactions between the virus and the ligand. These factors combined to increase the total number of interactions between the virus and the membrane, results that were well described by an electrostatic free energy model of viral clearance. The results presented in this dissertation have a broad impact on the field of viral clearance.

Membrane adsorbers are disposable devices that eliminate cleaning and validation steps required by traditional beads. When functionalized with a salt tolerant ligand, process and product safety is increased by increasing the number of impurities that can be removed in the presence of salt. Overall, salt tolerant membrane adsorbers represent a robust approach to viral clearance during the purification of protein therapeutics.