Assessing the Effect of Solution Conditions on Viral Filtration of an Fc-Fusion Protein

Validation of adequate virus clearance is critical in order to obtain FDA approval for a manufacturing process of a biotherapeutic produced using a mammalian system. Clearance can be due to inactivation or removal from the process stream. During the purification, manufacturers of monoclonal antibodies (mAbs) must demonstrate reduction of 10³ to 10⁵ or more virus particles than is estimated in a single dose equivalent of the unprocessed bulk. Estimates of the number of virus particles in a single dose equivalent could be as high as 10¹⁰ to 10¹⁵ retrovirus-like particles. Today unit operations such as viral filtration are frequently used to achieve virus clearance. These operations are validated to remove a wide range of potential adventitious viruses, with the small non-enveloped parvoviruses posing the toughest challenge.

Viral filtration is a size exclusion-based virus clearance method and is conducted industrially in dead-end mode. Membrane performance is shown to be affected by the feed pH, ionic strength and feed buffer components. Since the size of a small virus (18-22 nm) is only slightly larger than some of the larger mAbs or fusion proteins, conditions that could affect protein association or aggregation, that could promote interactions among virus, protein and membrane material are likely to affect viral filtration performances. In this work, minute virus of mice (MVM), a FDA recommended virus, was spiked to evaluate the filtration performance of a Fc-fusion protein using commercially available virus filters. The effects of feed conditions including buffer, pH and ionic strength on membrane performance and viral clearance were elucidated. Moreover, the interactions and possible associations among virus particles, proteins and membrane materials modulated by the feed conditions were investigated using dynamic light scattering technique.